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  • Denoising arterial spin labeling perfusion MRI with deep machine learning
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2020-01-15
    Danfeng Xie; Yiran Li; Hanlu Yang; Li Bai; Tianyao Wang; Fuqing Zhou; Lei Zhang; Ze Wang

    Purpose Arterial spin labeling (ASL) perfusion MRI is a noninvasive technique for measuring cerebral blood flow (CBF) in a quantitative manner. A technical challenge in ASL MRI is data processing because of the inherently low signal-to-noise-ratio (SNR). Deep learning (DL) is an emerging machine learning technique that can learn a nonlinear transform from acquired data without using any explicit hypothesis. Such a high flexibility may be particularly beneficial for ASL denoising. In this paper, we proposed and validated a DL-based ASL MRI denoising algorithm (DL-ASL). Methods The DL-ASL network was constructed using convolutional neural networks (CNNs) with dilated convolution and wide activation residual blocks to explicitly take the inter-voxel correlations into account, and preserve spatial resolution of input image during model learning. Results DL-ASL substantially improved the quality of ASL CBF in terms of SNR. Based on retrospective analyses, DL-ASL showed a high potential of reducing 75% of the original acquisition time without sacrificing CBF measurement quality. Conclusion DL-ASL achieved improved denoising performance for ASL MRI as compared with current routine methods in terms of higher PSNR, SSIM and Radiologic scores. With the help of DL-ASL, much fewer repetitions may be prescribed in ASL MRI, resulting in a great reduction of the total acquisition time.

    更新日期:2020-01-15
  • A high-resolution MRI brain template for adult Beagle
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2020-01-13
    Xueru Liu; Rui Tian; Zhentao Zuo; Hui Zhao; Liang Wu; Yan Zhuo; Yong Q. Zhang; Lin Chen

    Canines, which exhibit similar emotional and social processing to humans, are becoming one of the preferred animal models for neuroscience research. Beagles are the most common laboratory canine, thanks to their moderate size, docile nature, and strong immunity. However, there is currently no MRI brain template for the purebred Beagle, which hinders their use in studies involving neuroimaging. Here, we present the Beagle Brain Template (BBT), which consists of high-resolution in vivo T1-weighted and T2-weighted templates, as well as a myelin template, generated from purebred Beagles. We also present a normalized pipeline for mapping individual structure images onto the BBT space. The BBT shows low variation in the tissue probability map and provides descriptive statistics with smaller variability of brain tissue volumes and brain sizes than that of existing templates. This high-resolution purebred canine brain template lays the foundation for future studies aimed at in vivo analyses of the brain structure and function of the Beagle dogs.

    更新日期:2020-01-14
  • Improved detection of molecularly targeted iron oxide particles in mouse brain using B0 field stabilised high resolution MRI
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2020-01-11
    Stuart Gilchrist; Paul Kinchesh; Niloufar Zarghami; Alexandre A. Khrapitchev; Nicola R. Sibson; Veerle Kersemans; Sean C. Smart

    Purpose High resolution multi-gradient echo (MGE) scanning is typically used for detection of molecularly targeted iron oxide particles. The images of individual echoes are often combined to generate a composite image with improved SNR from the early echoes and boosted contrast from later echoes. In 3D implementations prolonged scanning at high gradient duty cycles induces a B0 shift that predominantly affects image alignment in the slow phase encoding dimension of 3D MGE images. The effect corrupts the composite echo image and limits the image resolution that is realised. A real-time adaptive B0 stabilisation during respiration gated 3D MGE scanning is shown to reduce image misalignment and improve detection of molecularly targeted iron oxide particles in composite images of the mouse brain. Methods An optional B0 measurement block consisting of a 16 μs hard pulse with FA 1°, an acquisition delay of 3.2 ms, followed by gradient spoiling in all three axes was added to a respiration gated 3D MGE scan. During the acquisition delay of each B0 measurement block the NMR signal was routed to a custom built B0 stabilisation unit which mixed the signal to an audio frequency nominally centred around 1000 Hz to enable an Arduino based single channel receiver to measure frequency shifts. The frequency shift was used to effect correction to the main magnetic field via the B0 coil. The efficacy of B0 stabilisation and respiration gating was validated in vivo and used to improve detection of molecularly targeted microparticles of iron oxide (MPIO) in a mouse model of acute neuroinflammation. Results Without B0 stabilisation 3D MGE image data exhibit varying mixtures of translation, scaling and blurring, which compromise the fidelity of the composite image. The real-time adaptive B0 stabilisation minimises corruption of the composite image as the images from the different echoes are properly aligned. The improved detection of molecularly targeted MPIO easily compensates for the scan time penalty of 14% incurred by the B0 stabilisation method employed. Respiration gating of the B0 measurement and the MRI scan was required to preserve high resolution detail, especially towards the back of the brain. Conclusions High resolution imaging for the detection of molecularly targeted iron oxide particles in the mouse brain requires good stabilisation of the main B0 field, and can benefit from a respiration gated image acquisition strategy.

    更新日期:2020-01-13
  • Water proton density in human cortical bone obtained from ultrashort echo time (UTE) MRI predicts bone microstructural properties
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2020-01-10
    Saeed Jerban; Yajun Ma; Hyungseok Jang; Behnam Namiranian; Nicole Le; Hoda Shirazian; Mark E. Murphy; Jiang Du; Eric Y. Chang

    Purpose To investigate the correlations between cortical bone microstructural properties and total water proton density (TWPD) obtained from three-dimensional ultrashort echo time Cones (3D-UTE-Cones) magnetic resonance imaging techniques. Materials and methods 135 cortical bone samples were harvested from human tibial and femoral midshafts of 37 donors (61 ± 24 years old). Samples were scanned using 3D-UTE-Cones sequences on a clinical 3T MRI and on a high-resolution micro-computed tomography (μCT) scanner. TWPD was measured using 3D-UTE-Cones MR images. Average bone porosity, pore size, and bone mineral density (BMD) were measured from μCT images at 9 μm voxel size. Pearson's correlation coefficients between TWPD and μCT-based measures were calculated. Results TWPD showed significant moderate correlation with both average bone porosity (R = 0.66, p < 0.01) and pore size (R = 0.58, p < 0.01). TWPD also showed significant strong correction with BMD (R = 0.71, p < 0.01). Conclusions The presented 3D-UTE-Cones imaging technique allows assessment of TWPD in human cortical bone. This quick UTE-MRI-based technique was capable of predicting bone microstructure differences with significant correlations. Such correlations highlight the potential of UTE-MRI-based measurement of bone water proton density to assess bone microstructure.

    更新日期:2020-01-10
  • A mixed waveform protocol for reduction of the cardiac motion artifact in black-blood diffusion-weighted imaging of the liver
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2020-01-07
    Susanne S. Rauh; Andreas J. Riexinger; Sabine Ohlmeyer; Matthias Hammon; Marc Saake; Alto Stemmer; Michael Uder; Bernhard Hensel; Frederik B. Laun

    Objective Diffusion-weighted imaging (DWI) in the liver suffers from signal loss due to the cardiac motion artifact, especially in the left liver lobe. The purpose of this work was to improve the image quality of liver DWI in terms of cardiac motion artifact reduction and achievement of black-blood images in low b-value images. Material and methods Ten healthy volunteers (age 20–31 years) underwent MRI examinations at 1.5 T with a prototype DWI sequence provided by the vendor. Two diffusion encodings (i.e. waveforms), monopolar and flow-compensated, and the b-values 0, 20, 50, 100, 150, 600 and 800 s/mm2 were used. Two Likert scales describing the severity of the pulsation artifact and the quality of the black-blood state were defined and evaluated by two experienced radiologists. Regions of interest (ROIs) were manually drawn in the right and left liver lobe in each slice and combined to a volume of interest (VOI). The mean and coefficient of variation were calculated for each normalized VOI-averaged signal to assess the severity of the cardiac motion artifact. The ADC was calculated using two b-values once for the monopolar data and once with mixed data, using the monopolar data for the small and the flow-compensated data for the high b-value. A Wilcoxon rank sum test was used to compare the Likert scores obtained for monopolar and flow-compensated data. Results At b-values from 20 to 150 s/mm2, unlike the flow-compensated diffusion encoding, the monopolar encoding yielded black blood in all images with a negligible signal loss due to the cardiac motion artifact. At the b-values 600 and 800 s/mm2, the flow-compensated encoding resulted in a significantly reduced cardiac motion artifact, especially in the left liver lobe, and in a black-blood state. The ADC calculated with monopolar data was significantly higher in the left than in the right liver lobe. Conclusion It is recommendable to use the following mixed waveform protocol: Monopolar diffusion encodings at small b-values and flow-compensated diffusion encodings at high b-values.

    更新日期:2020-01-07
  • BRAHMA: Population specific T1, T2, and FLAIR weighted brain templates and their impact in structural and functional imaging studies
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2020-01-07
    Praful P. Pai; Pravat K. Mandal; Khushboo Punjabi; Deepika Shukla; Anshika Goel; Shallu Joon; Saurav Roy; Kanika Sandal; Ritwick Mishra; Ritu Lahoti

    Differences in brain morphology across population groups necessitate creation of population-specific Magnetic Resonance Imaging (MRI) brain templates for interpretation of neuroimaging data. Variations in the neuroanatomy in a genetically heterogeneous population make the development of a population-specific brain template for the Indian subcontinent imperative. A dataset of high-resolution 3D T1, T2, and FLAIR images acquired from a group of 113 volunteers (M/F - 56/57, mean age 28.96 ± 7.80 years) are used to construct T1, T2, and FLAIR templates, collectively referred to as Indian Brain Template, “BRAHMA”. A processing pipeline is developed and implemented in a MATLAB based toolbox for template construction and generation of tissue probability maps and segmentation atlases, with additional labels for deep brain regions such as the Substantia Nigra generated from the T2 and FLAIR templates. The use of BRAHMA template for analysis of structural and functional neuroimaging data from Indian participants provides improved accuracy with statistically significant results over that obtained using the ICBM-152 (International Consortium for Brain Mapping) template. Our results indicate that segmentations generated on structural images are closer in volume to those obtained from registration to the BRAHMA template than to the ICBM-152. Furthermore, functional MRI data obtained for Working Memory and Finger Tapping paradigms processed using the BRAHMA template shows a significantly higher percentage of the activation area than ICBM-152 in relevant brain regions, i.e. the left middle frontal gyrus, and the left and right precentral gyri, respectively. The availability of different image contrasts, tissue maps, and segmentation atlases makes the BRAHMA template a comprehensive tool for multi-modal image analysis in laboratory and clinical settings.

    更新日期:2020-01-07
  • A novel in silico platform for a fully automatic personalized brain tumor growth
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2020-01-03
    Mojtaba Hajishamsaei; Ahmadreza Pishevar; Omid Bavi; Majid Soltani

    Glioblastoma Multiforme is the most common and most aggressive type of brain tumors grade four astrocytoma. Although accurate prediction of Glioblastoma borders and shape is absolutely essential for neurosurgeons, there are not many in silico platforms that can make such predictions. In the current study, an automatic patient-specific simulation of Glioblastoma growth is described. A finite element approach is used to analyze the magnetic resonance images from patients in the early stages of their tumors. For segmentation of the tumor, support vector machine method, which is an automatic segmentation algorithm, is used. Using in situ and in vivo data, the main parameters of tumor prediction and growth are estimated with high precision in proliferation-invasion partial differential equation, using genetic algorithm optimization method. The results show that for a C57BL mouse, the differences between the surface and perimeter of in vivo test and simulation prediction data, as objective function, are 3.7% and 17.4%, respectively.

    更新日期:2020-01-04
  • Detecting sub-voxel microvasculature with USPIO-enhanced susceptibility-weighted MRI at 7 T
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2020-01-03
    Yimin Shen; Jiani Hu; Khalid Eteer; Yongsheng Chen; Sagar Buch; Hani Alhourani; Kamran Shah; Quan Jiang; Yulin Ge; E. Mark Haacke

    Background Susceptibility weighted imaging (SWI) combines phase with magnitude information to better image sub-voxel veins. Recently, it has been extended to image very small sub-voxel arteries and veins by injecting intravenously the ultra-small superparamagnetic iron oxide, Ferumoxytol. Objective To determine practical experimental imaging parameters for sub-voxel cerebral vessels at 7 T. Methods Six Wistar-Kyoto rats aged 7–13 weeks were imaged. For a given spatial resolution, SWI was acquired pre- and post- Ferumoxytol with doses of 2, 4, 6 and 8 mg/kg and echo times (TEs) of 5, 10 and 15 ms at each dose. The spatial resolutions of 62.5 × 125 × 250 μm3 (acquisition time of 7.5 min) and 62.5 × 62.5 × 125 μm3 (30 min) were used. Both SWI and quantitative susceptibility mapping (QSM) data were analyzed. Contrast-to-noise ratio (CNR) was measured and used to determine the optimal practical imaging parameters for detection of small cortical penetrating arteries. Results For a given spatial resolution with an aspect ratio (frequency: phase: slice) of 2:4:8 relative to the vessel size, we found the TE-dose index (TE x dose) must be at least 40 ms·mg/kg for both SWI and QSM to reveal the most vessels. The higher the TE-dose index, the better the image quality for both SWI and QSM up to 60 ms·mg/kg. Conclusions There is an optimal TE-dose index for improved visualization of sub-voxel vessels. Choosing the smallest TE and the largest allowed dose made it possible to run the sequence efficiently. In practice, the aspect ratio of 2:4:8 and the TE-dose index ranging from 40 to 60 ms·mg/kg provided the optimal and most practical solution.

    更新日期:2020-01-04
  • DWI and PRECISE criteria in men on active surveillance for prostate cancer: A multicentre preliminary experience of different ADC calculations
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-12-30
    Francesco Giganti; Martina Pecoraro; Davide Fierro; Riccardo Campa; Francesco Del Giudice; Shonit Punwani; Alex Kirkham; Clare Allen; Mark Emberton; Carlo Catalano; Caroline M. Moore; Valeria Panebianco

    Purpose The PRECISE score estimates the likelihood of radiological progression in patients on active surveillance (AS) for prostate cancer (PCa) with serial multiparametric magnetic resonance imaging (mpMRI). A PRECISE score of 1 or 2 denotes radiological regression, PRECISE 3 indicates stability and PRECISE 4 or 5 implies progression. We evaluated the inter-reader reproducibility of different apparent diffusion coefficient (ADC) calculations and their relationship to the PRECISE score. Material and methods Baseline and follow-up scans (on the same MR systems) of 30 patients with visible lesions from two different institutions were analysed by two radiologists. The PRECISE score was initially assessed in consensus. At least six weeks later, to reduce the likelihood of being influenced by the consensus PRECISE reading, each radiologist independently calculated ADC for the following: lesion, non-cancerous tissue and urine in the bladder. Normalised ADC ratios were calculated with respect to normal prostatic tissue (npADC) and urine. Spearman's correlation (ρ), intraclass correlation coefficients (ICC), differences in ADC and ROC curves were computed. Results Interobserver reproducibility was very good (ρ > 0.8; ICC > 0.90). Lesion ADC (0.91 vs 0.73 × 10−3 mm2/s; p=0.025) and npADC ratio (0.68 vs 0.53; p=0.012) at follow-up mpMRI were different between patients with radiological regression or stability vs progression. Cut-offs of 0.77 × 10−3 mm2/s (lesion ADC) and 0.59 (npADC ratio) could differentiate the two groups (area under the curve: 0.74 and 0.77, respectively). Conclusion The ADC, npADC ratio and the PRECISE score should be recorded for MRI-based AS.

    更新日期:2019-12-30
  • Perfusion and diffusion in meningioma tumors: a preliminary multiparametric analysis with Dynamic Susceptibility Contrast and IntraVoxel Incoherent Motion MRI
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-12-28
    Marco Andrea Zampini; Giulia Buizza; Chiara Paganelli; Giulia Fontana; Emma D’Ippolito; Francesca Valvo; Lorenzo Preda; Guido Baroni

    Multiparametric MRI is a remarkable imaging method for the assessment of patho-physiological processes. In particular, brain tumor characterization has taken advantage of the development of advanced techniques such as diffusion- (DWI) and perfusion- (PWI) weighted imaging, but a thorough analysis of meningiomas is still lacking despite the variety of computational methods proposed. We compute perfusion and diffusion parametric maps relying on a well-defined methodological workflow, investigating possible correlations between pure and diffusion-based perfusion parameters in a cohort of 26 patients before proton therapy. A preliminary investigation of meningioma staging biomarkers based on IntraVoxel Incoherent Motion and Dynamic Susceptibility Contrast is also reported. We observed significant differences between the gross target volume and the normal appearing white matter for every investigated parameter, confirming the higher vascularization of the neoplastic tissue. DWI and PWI parameters appeared to be weakly correlated and we found that diffusion parameters – the perfusion fraction in particular – could be promising biomarkers for tumor staging.

    更新日期:2019-12-29
  • Field-map correction in read-out segmented echo planar imaging for reduced spatial distortion in prostate DWI for MRI-guided radiotherapy applications
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-12-13
    Robert V. Bergen; Lawrence Ryner; Marco Essig

    Diffusion-weighted echo planar imaging (DW-EPI) suffers from geometric distortion due to low phase-encoding bandwidth. Read-out segmented echo planar imaging (RS-EPI) reduces distortion but residual distortion remains in extreme cases. Additional corrections need to be applied, especially for radiotherapy applications where a high degree of accuracy is needed. In this study the use of magnetic field map corrections are assessed in DW-EPI and RS-EPI, to reduce geometric uncertainty for MRI-guided radiotherapy applications. Magnetic field maps were calculated from gradient echo images and distortion corrections were applied to RS-EPI images. Distortions were assessed in a prostate phantom by comparing to the known geometry, and in vivo using a modified Hausdorff distance metric using a T2-weighted spin echo as ground truth. Across 10 patients, field map-corrected RS-EPI reduced maximum distortion by 5 mm on average compared to DW-EPI (σ = 1.9 mm). Geometric distortions were also reduced significantly using field mapping with RS-EPI, compared to RS-EPI alone (p ≤ 0.05). The increased geometric accuracy of these techniques can potentially allow diffusion-weighted images to be fused with other MR or CT images for radiotherapy treatment purposes.

    更新日期:2019-12-13
  • Machine learning based quantification of ejection and filling parameters by fully automated dynamic measurement of left ventricular volumes from cardiac magnetic resonance images
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-12-12
    Neha Goyal; Victor Mor-Avi; Valentina Volpato; Akhil Narang; Shuo Wang; Michael Salerno; Roberto M. Lang; Amit R. Patel

    Background Although analysis of cardiac magnetic resonance (CMR) images provides accurate and reproducible measurements of left ventricular (LV) volumes, these measurements are usually not performed throughout the cardiac cycle because of lack of tools that would allow such analysis within a reasonable timeframe. A fully-automated machine-learning (ML) algorithm was recently developed to automatically generate LV volume-time curves. Our aim was to validate ejection and filling parameters calculated from these curves using conventional analysis as a reference. Methods We studied 21 patients undergoing clinical CMR examinations. LV volume-time curves were obtained using the ML-based algorithm (Neosoft), and independently using slice-by-slice, frame-by-frame manual tracing of the endocardial boundaries. Ejection and filling parameters derived from these curves were compared between the two techniques. For each parameter, Bland-Altman bias and limits of agreement (LOA) were expressed in percent of the mean measured value. Results Time-volume curves were generated using the automated ML analysis within 2.5 ± 0.5 min, considerably faster than the manual analysis (43 ± 14 min per patient, including ~10 slices with 25–32 frames per slice). Time-volume curves were similar between the two techniques in magnitude and shape. Size and function parameters extracted from these curves showed no significant inter-technique differences, reflected by high correlations, small biases (<10%) and mostly reasonably narrow LOA. Conclusion ML software for dynamic LV volume measurement allows fast and accurate, fully automated analysis of ejection and filling parameters, compared to manual tracing based analysis. The ability to quickly evaluate time-volume curves is important for a more comprehensive evaluation of the patient's cardiac function.

    更新日期:2019-12-13
  • Influence of water based embedding media composition on the relaxation properties of fixed tissue
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-12-07
    Ivan Vučković, Tarek Nayfeh, Prasanna K. Mishra, Sigapriya Periyanan, Caroline R. Sussman, Timothy L. Kline, Slobodan Macura

    Background In MRI of formalin-fixed tissue one of the problems is the dependence of tissue relaxation properties on formalin composition and composition of embedding medium (EM) used for scanning. In this study, we investigated molecular mechanisms by which the EM composition affects T2 relaxation directly and T1 relaxation indirectly. Objective To identify principal components of formaldehyde based EM and the mechanism by which they affect relaxation properties of fixed tissue. Methods We recorded high resolution 1H NMR spectra of common formalin fixatives at temperatures in the range of 5 °C to 45 °C. We also measured T1 and T2 relaxation times of various organs of formalin fixed (FF) zebrafish at 7 T at 21 °C and 31 °C in several EM with and without fixative or gadolinium contrast agents. Results We showed that the major source of T2 variability is chemical exchange between protons from EM hydroxyls and water, mediated by the presence of phosphate ions. The exchange rate increases with temperature, formaldehyde concentration in EM and phosphate concentration in EM. Depending on which side of the coalescence the system resides, the temperature increase can lead to either shortening or prolongation of T2, or to no noticeable change at all when very close to the coalescence. Chemical exchange can be minimized by washing out from EM the fixative, the phosphate or both. Conclusion The dependence of T2 in fixed tissue on the fixative origin and composition described in prior literature could be attributed to the phosphate buffer accelerated chemical exchange among the fixative hydroxyls and the tissue water. More consistent results in the relaxation measurements could be obtained by stricter control of the fixative composition or by scanning fixed tissue in PBS without fixative.

    更新日期:2019-12-07
  • Improved acceleration of phase-contrast flow imaging with magnitude difference regularization
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-12-02
    Taehoon Shin, Wanyong Shin

    Purpose To develop a regularized image reconstruction algorithm for improved scan acceleration of phase-contrast (PC) flow MRI. Methods Based on the magnitude similarity between bipolar-encoded k-space data, magnitude-difference regularization was incorporated into the conventional compressed sensing (CS) reconstruction. The gradient of the magnitude regularization was derived so the reconstruction problem can be solved using non-linear conjugate gradient with backtracking line search. Phase contrast flow data obtained in the peripheral arteries of healthy and patient subjects were retrospectively undersampled for testing the proposed reconstruction method. Three-dimensional velocity-encoded PC flow MRI was performed with prospective 4-fold undersampling for measuring arotic flow velocity in a healthy volunteer. Results In the femoral arteries of healthy volunteers, the root-mean-square (RMS) errors of mean velocities were 0.56 ± 0.09 cm/s with CS-only reconstruction and 0.46 ± 0.08 cm/s with addition of magnitude regularization for three-fold acceleration; 1.34 ± 0.17 cm/s (CS only) and 1.08 ± 0.15 cm/s (magnitude regularized) for four-fold acceleration. In the iliac arteries of the patient, the RMS errors of mean velocities were 0.72 ± 0.12 cm/s and 0.56 ± 0.10 for three-fold acceleration, and 1.75 ± 0.21 and 1.24 ± 0.19 cm/s for four-fold acceleration (in the order of CS-only and magnitude regularized reconstructions). In the popliteal arteries, the RMS errors were 0.61 ± 0.10 cm/s and 0.42 ± 0.11 for three-fold acceleration, and 1.41 ± 0.19 and 1.12 ± 0.17 cm/s for four-fold acceleration. The maximum through-plane mean flow velocities were measured as 63.2 cm/s and 84.5 cm/s in ascending and descending aortas, respectively. Conclusion The addition of magnitude-difference regularization into conventional CS reconstruction improves the accuracy of image reconstruction using highly undersampled phase-contrast flow MR data.

    更新日期:2019-12-03
  • Triple-negative breast cancer: Pretreatment magnetic resonance imaging features and clinicopathological factors associated with recurrence
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-28
    Youn Joo Lee, In Kyung Youn, Sung Hun Kim, Bong Joo Kang, Woo-chan Park, Ahwon Lee

    Purpose We aimed to investigate the magnetic resonance imaging (MRI) features and clinicopathologic factors with recurrence of triple-negative breast cancer (TNBC). Patients and methods We identified 281 patients with 288 surgically confirmed TNBC lesions who underwent pretreatment MRI between 2009 and 2015. The presence of intratumoral high signal on T2-weighted images, high-signal rim on diffusion-weighted images (DWI), and rim enhancement on the dynamic contrast-enhanced MRI and clinicopathological data were collected. Cox proportional analysis was performed. Results Of the 288 lesions, 36 (12.5%) recurred after a median follow-up of 18 months (range, 3.6–68.3 months). Rim enhancement (hazard ratio [HR] = 3.15; 95% confidence interval [CI] = 1.01, 9.88; p = .048), and lymphovascular invasion (HR = 2.73, 95% CI = 1.20, 6.23; p = .016) were independently associated with disease recurrence. While fibroglandular volume, background parenchymal enhancement, intratumoral T2 high signal, and high-signal rim on DWI, were not found to be risk factors for recurrence. Conclusion Pretreatment MRI features may help predict a high risk of recurrence in patients with TNBC.

    更新日期:2019-11-28
  • Rapid four-ring birdcage coil analysis: Design optimization for high efficiency, low interference, and improved body loading tolerance
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-22
    Kellsie Shan, Yunsuo Duan

    The Design accuracy of MRI system with dual-tuned four-ring birdcage coils remains challenging due to inter-coil interference that tends to deteriorate signal-to-noise ratio and thus image quality. In this study, we develop an accurate and efficient FEM modeling strategy by optimizing model geometries, meshing density, and boundary conditions in accord with the correlated measurements on test vehicles. By taking full advantages of simulation accuracy and efficiency, we are able to proceed with sensitivity analysis on critical RF characteristics such as resonance pattern, quality factor, coil coupling, and body loading effects, etc., which may further serve as guidelines for coil design optimization.

    更新日期:2019-11-22
  • Coil-Combined Split Slice-GRAPPA for Simultaneous Multi-Slice Diffusion MRI
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-18
    SK. HashemizadehKolowri, Rong-Rong Chen, Ganesh Adluru, Leslie Ying, Edward VR. DiBella

    Objective: To develop a kernel optimization method called coil-combined split slice-GRAPPA (CC-SSG) to improve the accuracy of the reconstructed coil-combined images for simultaneous multi-slice (SMS) diffusion weighted imaging (DWI) data. Methods: The CC-SSG method optimizes the tuning parameters in the k-space SSG kernels to achieve an optimal trade-off between the intra-slice artifact and inter-slice leakage after the root-sum-of-squares (rSOS) coil combining of the de-aliased SMS DWI data. A detailed analysis is conducted to evaluate the contributions of the intra-slice artifact and inter-slice leakage to the total reconstruction error after coil combining. Results: Comparisons of the proposed CC-SSG method with the slice-GRAPPA (SG) and split slice-GRAPPA (SSG) methods are provided using two in-vivo readout-segmented (RS) EPI datasets collected from stroke patients. The CC-SSG method demonstrates improved accuracy of the reconstructed coil-combined images and the estimated diffusion tensor imaging (DTI) maps. Conclusion: CC-SSG strikes a good balance between the intra-slice artifact and inter-slice leakage for rSOS coil combining, and so can yield better reconstruction performance compared to SG and SSG for rSOS reconstruction. The optimal trade-off between the two artifacts is robust to the contrast of SMS data and the choice of the coil combining method.

    更新日期:2019-11-18
  • Accelerated dynamic contrast enhanced MRI based on region of interest compressed sensing
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-18
    Amaresha Shridhar Konar, Nithin N. Vajuvalli, Rashmi Rao, Divya Jain, D.R. Ramesh Babu, Sairam Geethanath

    Magnetic Resonance Imaging (MRI) provides excellent soft tissue contrast with one significant limitation of slow data acquisition. Dynamic Contrast Enhanced MRI (DCE-MRI) is one of the widely employed techniques to estimate tumor tissue physiological parameters using contrast agents. DCE-MRI data acquisition and reconstruction requires high spatiotemporal resolution, especially during the post-contrast phase. The region of Interest Compressed Sensing (ROICS) is based on Compressed Sensing (CS) framework and works on the hypothesis that limiting CS to an ROI can achieve superior CS performance. In this work, ROICS has been demonstrated on breast DCE-MRI data at chosen acceleration factors and the results are compared with conventional CS implementation. Normalized Root Mean Square Error (NRMSE) was calculated to compare ROICS with CS quantitatively. CS and ROICS reconstructed images were used to compare Ktrans and ve values derived using standard Tofts Model (TM). This also validated the superior performance of ROICS over conventional CS. ROICS generated Concentration Time Curves (CTC's) at chosen acceleration factors follow similar trend as the ground truth data as compared to CS. Both qualitative and quantitative analyses show that ROICS outperforms CS particularly at acceleration factors of 5× and above.

    更新日期:2019-11-18
  • Constraints in estimating the proton density fat fraction
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-15
    Mark Bydder, Vahid G. Kouzehkonan, Yu Gao, Matthew D. Robson, Yingli Yang, Peng Hu

    The study evaluates four physically motivated constraints in the estimation of the proton density fat fraction (PDFF). Least squares approaches were developed for constraining the parameters in PDFF quantification based on the physics of magnetic resonance imaging. These were smooth fieldmap, smooth initial phase, nonnegative proton density and moderate R2∗ values. The constraints were evaluated in terms of their influence on the bias and standard deviation of the estimated parameters using numerical simulations and in vivo data acquired at 0.35 T. Results show that unconstrained least squares estimation is noisy and biased and that constraints are effective at reducing both the standard deviation and the bias in PDFF.

    更新日期:2019-11-18
  • In-situ observation for natural gas hydrate in porous medium: Water performance and formation characteristic
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-14
    Lunxiang Zhang, Mingrui Sun, Lingjie Sun, Tao Yu, Yongchen Song, Jiafei Zhao, Lei Yang, Hongsheng Dong

    Extensive efforts have been made regarding gas hydrate sample reconstruction in the laboratory for a better understanding and development of natural gas resources. Magnetic resonance imaging (MRI) is a useful method for directly observing the reconstruction of methane hydrate, yet relevant studies remain limited. In this study, a 9.4-T 400-MHz MRI instrument was employed to investigate CH4 hydrate formation in porous media involving various initial water saturation levels and sand diameters. Pressure histories and MRI signal variations were monitored to discuss the process of CH4 hydrate growth, and the three main formation stages of induction, rapid growth, and slow formation were determined. Furthermore, the liquid water performance in MRI micro-images was analyzed to predict the characteristics of CH4 hydrate formation. The results indicated that CH4 hydrate formed in a spatially and temporally random manner and that pore plugging occurred owing to the residual water encased in grown hydrate. Additionally, phase saturations, water conversion percentages, and formation rates were defined to evaluate the effect of sand diameter and initial water saturation on CH4 hydrate formation. With the reduction in the diameter of quartz glass beads from 400 μm to 100 μm, the average hydrate formation rate increased from 0.0010 min−1 to 0.0034 min−1, respectively. When the initial water saturation decreased to the optimized value (0.22 in this study), the water conversion percentage and hydrate saturation increased.

    更新日期:2019-11-15
  • snapMRF: GPU-Accelerated Magnetic Resonance Fingerprinting Dictionary Generation and Matching using Extended Phase Graphs
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-15
    Dong Wang, Jason Ostenson, David S. Smith

    Purpose: Magnetic resonance fingerprinting (MRF) is a state-of-the-art quantitative MRI technique with a computationally demanding reconstruction process, the accuracy of which depends on the accuracy of the signal model employed. Having a fast, validated, open-source MRF reconstruction would improve the dependability and accuracy of clinical applications of MRF. Methods: We parallelized both dictionary generation and signal matching on the GPU by splitting the simulation and matching of dictionary atoms across threads. Signal generation was modeled using both Bloch equation simulation and the extended phase graph (EPG) formalism. Unit tests were implemented to ensure correctness. The new package, snapMRF, was tested with a calibration phantom and an in vivo brain. Results: Compared with other online open-source packages, dictionary generation was accelerated by 10–1000× and signal matching by 10–100×. On a calibration phantom, T1 and T2 values were measured with relative errors that were nearly identical to those from existing packages when using the same sequence and dictionary configuration, but errors were much lower when using variable sequences that snapMRF supports but that competitors do not. Conclusion: Our open-source package snapMRF was significantly faster and retrieved accurate parameters, possibly enabling real-time parameter map generation for small dictionaries. Further refinements to the acquisition scheme and dictionary setup could improve quantitative accuracy.

    更新日期:2019-11-15
  • Linear signal combination T2 spectroscopy
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-14
    Marshall S. Sussman

    A technique is presented for performing T2 spectroscopy in magnetic resonance imaging (MRI). It is based on a weighted linear combination of T2 decay data. The data is combined in a manner that acts like a filter on the T2 spectrum. The choice of weighting coefficients determines the filter specifications (e.g. passband/stopband locations, stopband suppression factors). To perform spectroscopy, a series of filters are designed with narrow passbands centered about consecutive regions of the T2 spectrum. This provides an estimate of every region of the spectrum. Taken together, an initial estimate of the full T2 spectrum is thus obtained. However, the filtering process causes a distortion of the estimate relative to the true spectrum. To reduce this distortion, deconvolution is performed. The characteristics of the technique are first evaluated through simulation. The technique is then applied to experimental MRI data to demonstrate practical feasibility. T2 spectroscopy falls into a class of problems requiring inverse transformation with a set of exponential basis functions (i.e. the Laplace Transform). It is demonstrated how the present technique may be applied to problems involving non-exponential basis functions as well.

    更新日期:2019-11-14
  • Single-subject manual independent component analysis and resting state fMRI connectivity outcomes in patients with juvenile absence epilepsy
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-14
    Nicholas Parsons, Stephen Bowden, Simon Vogrin, Wendyl D'Souza

    The quality of fMRI data impacts functional connectivity measures and consequently, the decisions that clinicians and researchers make regarding functional connectivity interpretation. The present study used resting state fMRI to investigate resting state network connectivity in a sample of patients with Juvenile Absence Epilepsy. Single-subject manual independent component analysis was used in two levels, whereby all noise components were removed, and cerebrospinal fluid pulsation components only were isolated and removed. Improved temporal signal to noise ratios and functional connectivity metrics were observed in each of the cleaning levels for both epilepsy and control cohorts. Results showed full, single-subject manual independent component analysis reduced the number of functional connectivity correlations and increased the strength of these correlations. Similar effects were also observed for the cerebrospinal fluid pulsation only cleaned data relative to the uncleaned, and fully cleaned data. Single-subject manual independent component analysis coupled with short TR multiband acquisition can significantly improve the validity of findings derived from fMRI data sets.

    更新日期:2019-11-14
  • Analysis of dynamic texture and spatial spectral descriptors of dynamic contrast-enhanced brain magnetic resonance images for studying small vessel disease
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-13
    Jose Bernal, Maria del C. Valdés-Hernández, Javier Escudero, Linda Viksne, Anna K. Heye, Paul A. Armitage, Stephen Makin, Rhian M. Touyz, Joanna M. Wardlaw

    Cerebral small vessel disease (SVD) comprises various pathological processes affecting small brain vessels and damaging white and grey matter. In this paper, we propose a framework comprising region of interest sampling, dynamic spectral and texture description, functional principal component analysis, and statistical analysis to study exogenous contrast agent distribution over time in various brain regions in patients with recent mild stroke and SVD features.We compared our results against current semi-quantitative surrogates of dysfunction such as signal enhancement area and slope. Biological sex, stroke lesion type and overall burden of white matter hyperintensities (WMH) were significant predictors of intensity, spectral, and texture features extracted from the ventricular region (p-value < 0.05), explaining between a fifth and a fourth of the data variance (0.20 ≤Adj.R2 ≤ 0.25). We observed that spectral feature reflected more the dysfunction compared to other descriptors since the overall WMH burden explained consistently the power spectra variability in blood vessels, cerebrospinal fluid, deep grey matter and white matter. Our preliminary results show the potential of the framework for the analysis of dynamic contrast-enhanced brain magnetic resonance imaging acquisitions in SVD since significant variation in our metrics was related to the burden of SVD features. Therefore, our proposal may increase sensitivity to detect subtle features of small vessel dysfunction. A public version of the code will be released on our research website.

    更新日期:2019-11-13
  • Velocity encoding and velocity compensation for multi-spoke RF excitation
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-13
    Simon Schmidt, Sebastian Flassbeck, Peter Bachert, Mark E. Ladd, Sebastian Schmitter

    Purpose To investigate velocity encoded and velocity compensated variants of multi-spoke RF pulses that can be used for flip-angle homogenization at ultra-high fields (UHF). Attention is paid to the velocity encoding for each individual spoke pulse and to displacement artifacts that arise in Fourier transform imaging in the presence of flow. Theory and methods A gradient waveform design for multi-spoke excitation providing an algorithm for minimal TE was proposed that allows two different encodings. Such schemes were compared to an encoding approach that applies an established scheme to multi-spoke excitations. The impact on image quality and quantitative velocity maps was evaluated in phantoms using single- and two-spoke excitations. Additional validation measurements were obtained in-vivo at 7 T. Results Phantom experiments showed that keeping the first gradient moment constant for all k-space lines eliminates any displacements in phase-encoding and slice-selection direction for all spoke pulses but leads to artifacts for non-zero velocity components along readout direction. Introducing variable but well-defined first gradient moments in the phase-encoding direction creates displacements along the velocity vector and thus minimizes velocity-induced geometrical distortions. Phase-resolved mean volume flow in the ascending and descending aorta obtained from two-spoke excitation showed excellent agreement with single-spoke excitation over the cardiac cycle (mean difference 0.8 ± 16.2 ml/s). Conclusions The use of single- and multi-spoke RF pulses for flow quantification at 7 T with controlled displacement artifacts has been successfully demonstrated. The presented techniques form the basis for correct velocity quantification and compensation not only for conventional but also for multi-spoke RF pulses allowing in-plane B1+ homogenization using parallel transmission at UHF.

    更新日期:2019-11-13
  • Four-angle method for practical ultra-high-resolution magnetic resonance mapping of brain longitudinal relaxation time and apparent proton density
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-12
    Mustapha Bouhrara, Abinand C. Rejimon, Luis E. Cortina, Nikkita Khattar, Richard G. Spencer

    Changes in longitudinal relaxation time (T1) and proton density (PD) are sensitive indicators of microstructural alterations associated with various central nervous system diseases as well as brain maturation and aging. In this work, we introduce a new approach for rapid and accurate high-resolution (HR) or ultra HR (UHR) mapping of T1 and apparent PD (APD) of the brain with correction of radiofrequency field, B1, inhomogeneities. The four-angle method (FAM) uses four spoiled-gradient recalled-echo (SPGR) images acquired at different flip angles (FA) and short repetition times (TRs). The first two SPGR images are acquired at low-spatial resolution and used to accurately map the active B1+ field with the recently introduced steady-state double angle method (SS-DAM). The estimated B1+ map is used in conjunction with the two other SPGR images, acquired at HR or UHR, to map T1 and APD. The method is evaluated with numerical, phantom, and in-vivo imaging measurements. Furthermore, we investigated imaging acceleration methods to further shorten the acquisition time. Our results indicate that FAM provides an accurate method for simultaneous HR or UHR mapping of T1 and APD in human brain in clinical high-field MRI. Derived parameter maps without B1+correction suffer from large inaccuracies, but that this issue is well-corrected through use of the SS-DAM. Furthermore, the use of the SPGR imaging, with short TR and phased-array coil acquisition permits substantial imaging acceleration and enables robust HR or UHR T1 and APD mapping in a clinically acceptable time frame with whole brain coverage obtained in less than 2 min or 5 min. The method exhibits high reproducibility and benefits from the use of the conventional SPGR sequence, available in all preclinical and clinical MRI machines, and very simple modeling addressing a critical outstanding issue in neuroimaging.

    更新日期:2019-11-13
  • Pressure drop mapping using 4D flow MRI in patients with bicuspid aortic valve disease: A novel marker of valvular obstruction
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-11
    Ali Fatehi Hassanabad, Fiona Burns, Michael S. Bristow, Carmen Lydell, Andrew G. Howarth, Bobak Heydari, Xuexin Gao, Paul W.M. Fedak, James A. White, Julio Garcia

    Background The influence of complex bicuspid aortic valve (BAV) flow patterns on net intraluminal aortic pressure, both among patients with and without significant aortic stenosis, is unknown. Pressure drop (PD), as estimated by 4D Flow MRI, can quantify pre- vs post-valvular pressure at multiple levels simultaneously. Methods In this prospective clinical study, 32 patients with BAV with varying degrees of aortic stenosis and regurgitation and 11 healthy subjects were enrolled. 4D flow MRI was processed and analyzed at 9 pre-defined thoracic aortic levels. PD was calculated at each plane relative to a reference located within the left ventricular outflow tract. Conventional 2D phase-contrast imaging was used as reference of hemodynamic obstruction. PD was compared between healthy subjects versus BAV patients using Kruskal-Wallis H test and Mann-Whitney U. Correlation studies were conducted using Spearman's rank-order correlation. Results Both BAV patients and healthy subjects showed progressive elevation in PD from the aortic root to the distal descending thoracic aorta. However, BAV patients showed higher PD than healthy subjects (p ≤ 0.01) at all analysis planes. Patients with moderate-severe aortic stenosis (n = 5) by 2D phase-contrast (peak PG > 40 mm Hg) showed higher PD than those without in the descending aortic segments (p ≤ 0.005). A correlation (r = 0.88, p < 0.05) was observed between PD at the distal descending thoracic aorta and peak trans-valvular velocity measured by 2D phase-contrast MRI. Conclusion We demonstrated that PD with 4D flow MRI is clinically feasible in BAV patients and provides an additional physiologic description of valve-related hemodynamic obstruction.

    更新日期:2019-11-13
  • Tsallis-Entropy Segmentation through MRF and Alzheimer anatomic reference for Brain Magnetic Resonance Parcellation
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-11
    Mehran Azimbagirad, Fabrício H. Simozo, Antonio C.S. Senra Filho, Luiz O. Murta Junior
    更新日期:2019-11-13
  • MRF-ZOOM for the unbalanced steady-state free precession (ubSSFP) magnetic resonance fingerprinting
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-11
    Ze Wang, Di Cui, Jian Zhang, Ed.X. Wu, Edward S. Hui

    In magnetic resonance fingerprinting (MRF), tissue parameters are determined by finding the best-match to the acquired MR signal from a predefined signal dictionary. This dictionary searching (DS) process is generally performed in an exhaustive manner, which requires a large predefined dictionary and long searching time. A fast MRF DS algorithm, MRF-ZOOM, was recently proposed based on DS objective function optimization. As a proof-of-concept study, MRF-ZOOM was only tested with one of the earliest MRF sequences but not with the recently more popular unbalanced steady state free precession MRF sequence (MRF-ubSSFP, or MRF-FISP). Meanwhile noise effects on MRF and MRF-ZOOM have not been examined. The purpose of this study was to address these open questions and to verify whether MRF-ZOOM can be combined with a dictionary-compression based method to gain further speed. Numerical simulations were performed to evaluate the DS objective function properties, noise effects on MRF, and to compare MRF-ZOOM with other methods in terms of speed and accuracy. In-vivo experiments were performed as well. Evaluation results showed that premises of MRF-ZOOM held for MRF-FISP; noise did not affect MRF-ZOOM more than the conventional MRF method; when SNR ≥ 1, MRF quantification yielded accurate results. Dictionary compression introduced quantification errors more to T2 quantification. MRF-ZOOM was thousands of times faster than the conventional MRF method. Combining MRF-ZOOM with dictionary compression showed no benefit in terms of fitting speed. In conclusion, MRF-ZOOM is valid for MRF- FISP, and can remarkably save MRF dictionary generation and searching time without sacrificing matching accuracy.

    更新日期:2019-11-13
  • Quantitative susceptibility mapping of prostate with separate calculations for water and fat regions for reducing shading artifacts
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-09
    Ryota Sato, Toru Shirai, Yoshihisa Soutome, Yoshitaka Bito, Hisaaki Ochi

    We propose a novel processing method for reducing shading artifacts in quantitative susceptibility mapping (QSM) for prostate imaging. In the conventional method, calculation errors in the boundary regions between water and fat cause shading artifacts that degrade the image quality for QSM. In the proposed method, water and fat regions are separated, and susceptibilities in these two regions are calculated separately and then combined. Susceptibility in the water regions is calculated by using the fat regions as a background susceptibility source to remove shading artifacts. Susceptibility in the fat regions is calculated by using the constraint that shading artifacts in the water regions are suppressed to improve accuracy. In quantitative evaluation of the method with a numerical simulation, calculation errors for the water and fat regions were reduced by 62% and 85%, respectively, compared with the conventional method. In visual evaluation using human prostate imaging, the proposed method also reduced the shading artifacts unlike the conventional method. The proposed method is expected to improve the performance of QSM in diagnosing such diseases as prostate cancer.

    更新日期:2019-11-11
  • Non-contrast enhanced diagnosis of acute myocarditis based on the 17-segment heart model using 2D-feature tracking magnetic resonance imaging
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-09
    Mona Salehi Ravesh, Matthias Eden, Patrick Langguth, Tim-Christian Piesch, Johanna Karolin Lehmann, Annett Lebenatus, David Hauttemann, Joachim Graessner, Norbert Frey, Olav Jansen, Marcus Both

    Purpose The aim of this study was to investigate the diagnostic value of myocardial deformation analysis based on the 17-segment heart model using non-contrast enhanced (CE) 2D tissue feature tracking (2D-FT) technique. Material and methods Seventy patients with suspected myocarditis underwent a cardiovascular magnetic resonance (CMR) examination at 1.5 Tesla. A contrast-agent-free part of this CMR protocol was additionally performed in forty healthy volunteers (HV). Besides standard CMR data sets, 2D-FT derived segmental and global longitudinal, radial, and circumferential deformation parameters were analyzed. The 2D-FT results were compared to the combined findings from CMR imaging and endomyocardial biopsy (EMB). Results Patients were assigned to three groups depending on their ejection fraction (EF) (<40%, 40–55%, ≥55%). Compared to HV, impaired EF (<55%) was significantly correlated to reduced segmental and global strain and strain rate values. The circumferential deformation analysis was more sensitive to myocardial changes than longitudinal and radial analysis. The segmental strain/strain rate had an accuracy of 84.3%/70.0% for the diagnosis of an acute myocarditis, stated by EMB and CMR in 42 of 70 patients. In patients with preserved EF, acute myocarditis could be ruled out using only segmental strain analysis with a negative predictive value of 87.5%. Conclusion In patients with suspected myocarditis, the deformation analysis based on the 17-segment heart model provides valuable information about functional myocardial inhomogeneity. This quantitative approach could be used in addition to the clinical standard CMR protocol and represents a promising tool in the framework of a prospective automatized multiparametric CMR imaging analysis.

    更新日期:2019-11-11
  • An evaluation of the reproducibility of 1H-MRS GABA and GSH levels acquired in healthy volunteers with J-difference editing sequences at varying echo times
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-07
    James J. Prisciandaro, Mark Mikkelsen, Muhammad G. Saleh, Richard A.E. Edden

    Recent advances in J-difference-edited proton magnetic resonance spectroscopy (1H MRS) data acquisition and processing have led to the development of Hadamard Encoding and Reconstruction of MEGA-Edited Spectroscopy (HERMES) techniques, which enable the simultaneous measurement of ɣ-aminobutyric acid (GABA), the primary inhibitory amino acid neurotransmitter in the central nervous system, and of glutathione (GSH), the most abundant antioxidant in living tissue, at the commonly available magnetic field strength of 3 T. However, the reproducibility of brain levels of GABA and GSH measured across multiple scans in human subjects using HERMES remains to be established. In the present study, twelve healthy volunteers completed two consecutive HERMES scans of the dorsal anterior cingulate cortex (dACC) to assess the test-retest reproducibility of the technique for GABA and GSH measurements at TE = 80 ms. Eleven of the twelve participants additionally completed two consecutive MEGA-PRESS scans at TE = 120 ms, with editing pulses configured for GSH acquisition, to compare the reliability of GSH in the same voxel measured using the standard MEGA-PRESS at TE = 120 ms. The primary findings of study were that, 1) the coefficient of variation (CV) of measuring GABA with HERMES was 16.7%, which is in agreement with the reliability we previously reported for measuring GABA using MEGA-PRESS; and 2) the reliability of measuring GSH with MEGA-PRESS at TE = 120 ms was more than twice as high as that for measuring the antioxidant with HERMES at TE = 80 ms (CV = 7.3% vs. 19.0% respectively). These findings suggest that HERMES and MEGA-PRESS offer similar reliabilities for measuring GABA, while MEGA-PRESS at TE = 120 ms is more reliable for measuring GSH relative to HERMES at TE = 80 ms.

    更新日期:2019-11-08
  • A unified framework for mapping individual interregional high-order morphological connectivity based on regional cortical features from anatomical MRI
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-05
    Xun-Heng Wang, Yun Jiao, Lihua Li

    Building individual brain networks form the single volume of anatomical MRI is a challenging task. Furthermore, the high-order connectivity of morphological networks remains unexplored. This paper aimed to investigate the individual high-order morphological connectivity from anatomical MRI. Towards this goal, a unified framework based on six feature distances (euclidean, seuclidean, mahalanobis, cityblock, minkowski, and chebychev) was proposed to derive high-order interregional morphological features. The test-retest datasets and the healthy aging datasets were applied to analyze the reliability and the inter-subject variability of the novel features. In addition, the predictive models based on these novel features were established for age estimation. The proposed six neuroanatomical features exhibited significant high-to-excellent reliability. Certain connections were significantly correlated to biological age based on the six novel metrics (p < .05, FDR corrected). Moreover, the predicted age were significantly correlated to the original age in each regression task (r > 0.5, p < 10−6). The results suggested that the novel high-order metrics were reliable and could reflect individual differences, which could be beneficial for current methods of individual brain connectomes.

    更新日期:2019-11-05
  • Correlation between spinal cord diffusion tensor imaging and postural response latencies in persons with multiple sclerosis: A pilot study
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-05
    Chu-Yu Lee, Jessie M. Huisinga, In-Young Choi, Sharon G. Lynch, Phil Lee

    Purpose Longer latency of postural response in multiple sclerosis (MS) may be linked to imbalance and increased likelihood of falls. It may be caused by the compromised microstructural integrity in the spinal cord, as evidenced by slowed somatosensory conduction in the spinal cord. Thus, the purpose of this study is to investigate the correlation between latency of postural responses and microstructural integrity of the cervical spinal cord, the region particularly related to the disease severity in MS, using diffusion tensor imaging (DTI) metrics. Methods Seventeen persons with MS with mild-to-moderate disease severity were enrolled in this study. Postural response latencies of each patient were measured using electromyography of the tibialis anterior muscle (TA) and gastrocnemius muscle (GN) in response to surface perturbations. Cervical spinal cord DTI images were obtained from each patient. DTI mean, radial, axial diffusivity, and fractional anisotropy (FA) were measured between segments C4 and C6. Correlations of DTI metrics with postural response latencies, expanded disability status scale (EDSS) scores, and 25-ft walk (T25FW) were assessed using the Spearman's rank correlation coefficient at α = 0.05. Results Lower FA was significantly correlated with longer latencies measured on right TA in response to forward postural perturbations (r = −0.51, p = .04). DTI metrics showed no significant correlations with EDSS scores (r = −0.06–0.09, p = .73–0.95) or T25FW (r = −0.1–0.14, p = .6–0.94). DTI metrics showed no significant differences between subjects with and without spinal cord lesions (p = .2–0.7). Conclusions Our results showed a significant correlation between lower FA in the cervical spinal cord and longer latencies measured on right TA in response to forward postural perturbations in persons with MS, suggesting that impaired cervical spinal cord microstructure assessed by DTI may be associated with the delayed postural responses.

    更新日期:2019-11-05
  • MRI safety and imaging artifacts evaluated for a cannulated screw used for guided growth surgery
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-11-05
    Rachel Mednick Thompson, Eileen Fowler, Bozena Culo, Frank G. Shellock

    Objective Percutaneously-placed cannulated screws are the implant of choice for treatment of skeletal deformity associated with growing children that have spastic cerebral palsy (CP). These patients often require MRI examinations throughout their childhood to evaluate associated comorbidities and frequently for research protocols. There are concerns related to the use of MRI when metallic implants are present. Therefore, this study characterized MRI safety and imaging artifacts for a cannulated screw commonly used for guided growth. Methods Standardized and well-accepted in vitro techniques were used to evaluate a cannulated screw (4.5 mm diameter x 50 mm length, 316 L stainless steel) for MRI issues. Static magnetic field interactions (i.e., translational attraction and torque) and artifacts were tested at 3-Tesla. Radiofrequency-related heating was assessed at 1.5-Tesla/64-MHz and 3-Tesla/128-MHz using relatively high levels of RF energy (whole-body averaged specific absorption rates of 2.7 W/kg and 2.9-W/kg, respectively). Artifacts were determined using T1-weighted, spin echo and gradient echo pulse sequences. Results The cannulated screw exhibited minor magnetic field interactions (14° deflection angle, no torque). The highest temperature changes at 1.5-Tesla/64-MHz and 3-Tesla/128-MHz MRI were 2.1 °C and 2.4 °C, respectively. The maximum artifact size on a gradient echo sequence extended 20 mm relative to the dimensions of the implant. Conclusions The in vitro tests performed on the cannulated screw indicated that there were no substantial concerns with respect to the use of 1.5- and 3-Tesla MRI. Therefore, a patient with this cannulated screw can safely undergo MRI by following specific conditions to ensure safety.

    更新日期:2019-11-05
  • Inherent spatial structure in myelin water fraction maps
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-10-31
    Tobias R. Baumeister, Shannon H. Kolind, Alex L. MacKay, Martin J. McKeown
    更新日期:2019-11-01
  • Exploring the sensitivity of magnetic resonance fingerprinting to motion.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-09-09
    Zidan Yu,Tiejun Zhao,Jakob Assländer,Riccardo Lattanzi,Daniel K Sodickson,Martijn A Cloos

    PURPOSE To explore the motion sensitivity of magnetic resonance fingerprinting (MRF), we performed experiments with different types of motion at various time intervals during multiple scans. Additionally, we investigated the possibility to correct the motion artifacts based on redundancy in MRF data. METHODS A radial version of the FISP-MRF sequence was used to acquire one transverse slice through the brain. Three subjects were instructed to move in different patterns (in-plane rotation, through-plane wiggle, complex movements, adjust head position, and pretend itch) during different time intervals. The potential to correct motion artifacts in MRF by removing motion-corrupted data points from the fingerprints and dictionary was evaluated. RESULTS Morphological structures were well preserved in multi-parametric maps despite subject motion. Although the bulk T1 values were not significantly affected by motion, fine structures were blurred when in-plane motion was present during the first part of the scan. On the other hand, T2 values showed a considerable deviation from the motion-free results, especially when through-plane motion was present in the middle of the scan (-44% on average). Explicitly removing the motion-corrupted data from the scan partially restored the T2 values (-10% on average). CONCLUSION Our experimental results showed that different kinds of motion have distinct effects on the precision and effective resolution of the parametric maps measured with MRF. Although MRF-based acquisitions can be relatively robust to motion effects occurring at the beginning or end of the sequence, relying on redundancy in the data alone is not sufficient to assure the accuracy of the multi-parametric maps in all cases.

    更新日期:2019-11-01
  • Minimal number of gradient directions for robust measurement of spherical mean diffusion weighted signal.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-09-02
    Hua Li,Ho Ming Chow,Diane C Chugani,Harry T Chugani

    PURPOSE Determination of the minimum number of gradient directions (Nmin) for robust measurement of spherical mean diffusion weighted signal (S¯). METHODS Computer simulations were employed to characterize the relative standard deviation (RSD) of the measured spherical mean signal as a function of the number of gradient directions (N). The effects of diffusion weighting b-value and signal-to-noise ratio (SNR) were investigated. Multi-shell high angular resolution Human Connectome Project diffusion data were analyzed to support the simulation results. RESULTS RSD decreases with increasing N, and the minimum number of N needed for RSD ≤ 5% is referred to as Nmin. At high SNRs, Nmin increases with increasing b-value to achieve sufficient sampling. Simulations showed that Nmin is linearly dependent on the b-value. At low SNRs, Nmin increases with increasing b-value to reduce the noise. RSD can be estimated as σS¯N, where σ = 1/SNR is the noise level. The experimental results were in good agreement with the simulation results. The spherical mean signal can be measured accurately with a subset of gradient directions. CONCLUSION As Nmin is affected by b-value and SNR, we recommend using 10 × b / b1 (b1 = 1 ms/μm2) uniformly distributed gradient directions for typical human diffusion studies with SNR ~ 20 for robust spherical mean signal measurement.

    更新日期:2019-11-01
  • Typical readout durations in spiral cine DENSE yield blurred images and underestimate cardiac strains at both 3.0 T and 1.5 T.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-08-14
    Gregory J Wehner,Jonathan D Suever,Samuel W Fielden,David K Powell,Sean M Hamlet,Moriel H Vandsburger,Christopher M Haggerty,Xiaodong Zhong,Brandon K Fornwalt

    INTRODUCTION Displacement encoding with stimulated echoes (DENSE) is a phase contrast technique that encodes tissue displacement into phase images, which are typically processed into measures of cardiac function such as strains. For improved signal to noise ratio and spatiotemporal resolution, DENSE is often acquired with a spiral readout using an 11.1 ms readout duration. However, long spiral readout durations are prone to blurring due to common phenomena such as off-resonance and T2* decay, which may alter the resulting quantifications of strain. We hypothesized that longer readout durations would reduce image quality and underestimate cardiac strains at both 3.0 T and 1.5 T and that using short readout durations could overcome these limitations. MATERIAL AND METHODS Computational simulations were performed to investigate the relationship between off-resonance and T2* decay, the spiral cine DENSE readout duration, and measured radial and circumferential strain. Five healthy participants subsequently underwent 2D spiral cine DENSE at both 3.0 T and 1.5 T with several different readout durations 11.1 ms and shorter. Pearson correlations were used to assess the relationship between cardiac strains and the spiral readout duration. RESULTS Simulations demonstrated that long readout durations combined with off-resonance and T2* decay yield blurred images and underestimate strains. With the typical 11.1 ms DENSE readout, blurring was present in the anterior and lateral left ventricular segments of participants and was markedly improved with shorter readout durations. Radial and circumferential strains from those segments were significantly correlated with the readout duration. Compared to the 1.9 ms readout, the 11.1 ms readout underestimated radial and circumferential strains in those segments at both field strengths by up to 19.6% and 1.5% (absolute), or 42% and 7% (relative), respectively. CONCLUSIONS Blurring is present in spiral cine DENSE images acquired at both 3.0 T and 1.5 T using the typical 11.1 ms readout duration, which yielded substantially reduced radial strains and mildly reduced circumferential strains. Clinical studies using spiral cine DENSE should consider these limitations, while future technical advances may need to leverage accelerated techniques to improve the robustness and accuracy of the DENSE acquisition rather than focusing solely on reduced acquisition time.

    更新日期:2019-11-01
  • Subcortical brain iron deposition and cognitive performance in older women with breast cancer receiving adjuvant chemotherapy: A pilot MRI study.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-08-05
    Bihong T Chen,Kiarash Ghassaban,Taihao Jin,Sunita K Patel,Ningrong Ye,Can-Lan Sun,Heeyoung Kim,Russell C Rockne,E Mark Haacke,James C Root,Andrew J Saykin,Tim A Ahles,Andrei I Holodny,Neal Prakash,Joanne Mortimer,James Waisman,Yuan Yuan,George Somlo,Daneng Li,Richard Yang,Heidi Tan,Vani Katheria,Rachel Morrison,Arti Hurria

    As the number of older adults in the U.S. increases, so too will the incidence of cancer and cancer-related cognitive impairment (CRCI). However, the exact underlying biological mechanism for CRCI is not yet well understood. We utilized susceptibility-weighted imaging with quantitative susceptibility mapping, a non-invasive MRI-based technique, to assess longitudinal iron deposition in subcortical gray matter structures and evaluate its association with cognitive performance in women age 60+ with breast cancer receiving adjuvant chemotherapy and age-matched women without breast cancer as controls. Brain MRI scans and neurocognitive scores from the NIH Toolbox for Cognition were obtained before chemotherapy (time point 1) and within one month after the last infusion of chemotherapy for the patients and at matched intervals for the controls (time point 2). There were 14 patients age 60+ with breast cancer (mean age 66.3 ± 5.3 years) and 13 controls (mean age 68.2 ± 6.1 years) included in this study. Brain iron increased as age increased. There were no significant between- or within- group differences in neurocognitive scores or iron deposition at time point 1 or between time points 1 and 2 (p > 0.01). However, there was a negative correlation between iron in the globus pallidus and the fluid cognition composite scores in the control group at time point 1 (r = -0.71; p < 0.01), but not in the chemotherapy group. Baseline iron in the putamen was negatively associated with changes in the oral reading recognition scores in the control group (r = 0.74, p < 0.01), but not in the chemotherapy group. Brain iron assessment did not indicate cancer or chemotherapy related short-term differences, yet some associations with cognition were observed. Studies with larger samples and longer follow-up intervals are warranted.

    更新日期:2019-11-01
  • Regional cardiac function analysis from tagged MRI images. Comparison of techniques: Harmonic-Phase (HARP) versus Sinusoidal-Modeling (SinMod) analysis.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-05-20
    El-Sayed H Ibrahim,Jadranka Stojanovska,Azza Hassanein,Claire Duvernoy,Pierre Croisille,Rodica Pop-Busui,Scott D Swanson

    Cardiac MRI tagging is a valuable technique for evaluating regional heart function. Currently, there are a number of different techniques for analyzing the tagged images. Specifically, k-space-based analysis techniques showed to be much faster than image-based techniques, where harmonic-phase (HARP) and sine-wave modeling (SinMod) stand as two famous techniques of the former group, which are frequently used in clinical studies. In this study, we compared HARP and SinMod and studied inter-observer variability between the two techniques for evaluating myocardial strain and apical-to-base torsion in numerical phantom, nine healthy controls, and thirty diabetic patients. Based on the ground-truth numerical phantom measurements (strain = -20% and rotation angle = -4.4°), HARP and SinMod resulted in overestimation (in absolute value terms) of strain by 1% and 5% (strain values), and of rotation angle by 0.4° and 2.0°, respectively. For the in-vivo results, global strain and torsion ranges were -10.6% to -35.3% and 1.8°/cm to 12.7°/cm in patients, and -17.8% to -32.7% and 1.8°/cm to 12.3°/cm in volunteers. On average, SinMod overestimated strain measurements by 5.7% and 5.9% (strain values) in the patients and volunteers, respectively, compared to HARP, and overestimated torsion measurements by 2.9°/cm and 2.5°/cm in the patients and volunteers, respectively, compared to HARP. Location-wise, the ranges for basal, mid-ventricular, and apical strain in patients (volunteers) were -8.4% to -31.5% (-11.6% to -33.3%), -6.3% to -37.2% (-17.8% to -33.3%), and -5.2% to -38.4% (-20.0% to -33.2%), respectively. SinMod overestimated strain in the basal, mid-ventricular, and apical slices by 4.7% (5.7%), 5.9% (5.5%), and 8.9% (6.8%), respectively, compared to HARP in the patients (volunteers). Nevertheless, there existed good correlation between the HARP and SinMod measurements. Finally, there were no significant strain or torsion measurement differences between patients and volunteers. There existed good inter-observer agreement, as all measurement differences lied within the Bland-Altman ± 2 standard-deviation (SD) difference limits. In conclusion, despite the consistency of the results by either HARP or SinMod and acceptable agreement of the generated strain and torsion patterns by both techniques, SinMod systematically overestimated the measurements compared to HARP. Under current operating conditions, the measurements from HARP and SinMod cannot be used interchangeably.

    更新日期:2019-11-01
  • AI in MRI: A case for grassroots deep learning.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-07-10
    Kurt G Schilling,Bennett A Landman

    更新日期:2019-11-01
  • Multivariate MR biomarkers better predict cognitive dysfunction in mouse models of Alzheimer's disease.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-04-04
    Alexandra Badea,Natalie A Delpratt,R J Anderson,Russell Dibb,Yi Qi,Hongjiang Wei,Chunlei Liu,William C Wetsel,Brian B Avants,Carol Colton

    To understand multifactorial conditions such as Alzheimer's disease (AD) we need brain signatures that predict the impact of multiple pathologies and their interactions. To help uncover the relationships between pathology affected brain circuits and cognitive markers we have used mouse models that represent, at least in part, the complex interactions altered in AD, while being raised in uniform environments and with known genotype alterations. In particular, we aimed to understand the relationship between vulnerable brain circuits and memory deficits measured in the Morris water maze, and we tested several predictive modeling approaches. We used in vivo manganese enhanced MRI traditional voxel based analyses to reveal regional differences in volume (morphometry), signal intensity (activity), and magnetic susceptibility (iron deposition, demyelination). These regions included hippocampus, olfactory areas, entorhinal cortex and cerebellum, as well as the frontal association area. The properties of these regions, extracted from each of the imaging markers, were used to predict spatial memory. We next used eigenanatomy, which reduces dimensionality to produce sets of regions that explain the variance in the data. For each imaging marker, eigenanatomy revealed networks underpinning a range of cognitive functions including memory, motor function, and associative learning, allowing the detection of associations between context, location, and responses. Finally, the integration of multivariate markers in a supervised sparse canonical correlation approach outperformed single predictor models and had significant correlates to spatial memory. Among a priori selected regions, expected to play a role in memory dysfunction, the fornix also provided good predictors, raising the possibility of investigating how disease propagation within brain networks leads to cognitive deterioration. Our cross-sectional results support that modeling approaches integrating multivariate imaging markers provide sensitive predictors of AD-like behaviors. Such strategies for mapping brain circuits responsible for behaviors may help in the future predict disease progression, or response to interventions.

    更新日期:2019-11-01
  • 更新日期:2019-11-01
  • Anatomical accuracy of standard-practice tractography algorithms in the motor system - A histological validation in the squirrel monkey brain.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-09-15
    Kurt G Schilling,Yurui Gao,Iwona Stepniewska,Vaibhav Janve,Bennett A Landman,Adam W Anderson

    For two decades diffusion fiber tractography has been used to probe both the spatial extent of white matter pathways and the region to region connectivity of the brain. In both cases, anatomical accuracy of tractography is critical for sound scientific conclusions. Here we assess and validate the algorithms and tractography implementations that have been most widely used - often because of ease of use, algorithm simplicity, or availability offered in open source software. Comparing forty tractography results to a ground truth defined by histological tracers in the primary motor cortex on the same squirrel monkey brains, we assess tract fidelity on the scale of voxels as well as over larger spatial domains or regional connectivity. No algorithms are successful in all metrics, and, in fact, some implementations fail to reconstruct large portions of pathways or identify major points of connectivity. The accuracy is most dependent on reconstruction method and tracking algorithm, as well as the seed region and how this region is utilized. We also note a tremendous variability in the results, even though the same MR images act as inputs to all algorithms. In addition, anatomical accuracy is significantly decreased at increased distances from the seed. An analysis of the spatial errors in tractography reveals that many techniques have trouble properly leaving the gray matter, and many only reveal connectivity to adjacent regions of interest. These results show that the most commonly implemented algorithms have several shortcomings and limitations, and choices in implementations lead to very different results. This study should provide guidance for algorithm choices based on study requirements for sensitivity, specificity, or the need to identify particular connections, and should serve as a heuristic for future developments in tractography.

    更新日期:2019-11-01
  • Reconstruction of randomly under-sampled spectra for in vivo13C magnetic resonance spectroscopy.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2016-12-13
    Ningzhi Li,Shizhe Li,Jun Shen

    PURPOSE Over the past decade, many techniques have been developed to reduce radiofrequency (RF) power deposition associated with proton decoupling in in vivo Carbon-13 (13C) magnetic resonance spectroscopy (MRS). In this work we propose a new strategy that uses data under-sampling to achieve reduction in RF power deposition. MATERIALS AND METHODS Essentially, proton decoupling is required only during randomly selected segments of data acquisition. By taking advantage of the sparse spectral pattern of the carboxylic/amide region of in vivo13C spectra of brain, we developed an iterative algorithm to reconstruct spectra from randomly under-sampled data. Fully sampled data were used as references. Reconstructed spectra were compared with the fully sampled references and evaluated using residuals and relative signal intensity errors. RESULTS Numerical simulations and in vivo experiments at 7Tesla demonstrated that this novel decoupling and data processing strategy can effectively reduce decoupling power deposition by greater than 30%. CONCLUSION This study proposes and evaluates a novel approach to acquire 13C data with reduced proton decoupling power deposition and reconstruct in vivo13C spectra of carboxylic/amide metabolite signals using randomly under-sampled data. Because proton decoupling is not needed over a significant portion of data acquisition, this novel approach can effectively reduce the required decoupling power and thus SAR. It opens the possibility of performing in vivo13C experiments of human brain at very high magnetic fields.

    更新日期:2019-11-01
  • Quantitative analysis of peri-tumor fat in different molecular subtypes of breast cancer.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-07-04
    Jeon-Hor Chen,Yang Zhang,Siwa Chan,Ruey-Feng Chang,Min-Ying Su

    BACKGROUND AND PURPOSES The aim of this study was to develop morphological analytic methods to analyze the tumor-fat interface and in different peritumoral shells away from the tumor, and to compare the results among three molecular subtypes of breast cancer. MATERIALS AND METHODS A total of 102 women (mean age 48.5 y/o) with solitary well-defined breast cancers were analyzed, including 46 human epidermal growth factor receptor 2 (HER2) (+), 46 HER2(-) hormonal receptor (HR) (+), and 10 triple negative (TN) breast cancers. The tumor lesion, the breast, the fibroglandular and fatty tissue were segmented using well-established methods. The whole breast fat percentage and the peri-tumor interface fat percentage were measured. Three shells (SH1, SH2, SH3) surrounding the convex hall of the three dimensional (3D) tumor were defined and in each shell the volumetric percentage of fat was calculated. The peri-tumor interface fat percentage and the volumetric percentage of fat in the three peri-tumoral shells were compared among different subtypes. RESULTS In the TN group, the fat percentage on the tumor boundary was 43 ± 20% and 78 ± 12% for two dimensional (2D) and 3D measurement, respectively, which were the highest among the three subtypes but not significantly different. The fat percentage in SH2 and SH3 in the TN group was 82 ± 7% and 85 ± 7%, which was significantly higher compared to the two other two subtypes. The results remained after controlling for the whole breast fat percentage. CONCLUSIONS This study provided a feasible method for quantitative analysis of peri-tumoral tissue characteristics. Because of small patient number, the finding that TN tumors had the highest peri-tumor fat content among the three subtypes needs to be further verified with a large cohort study.

    更新日期:2019-11-01
  • A deep learning approach to estimation of subject-level bias and variance in high angular resolution diffusion imaging.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-03-31
    Allison E Hainline,Vishwesh Nath,Prasanna Parvathaneni,Kurt G Schilling,Justin A Blaber,Adam W Anderson,Hakmook Kang,Bennett A Landman

    The ability to evaluate empirical diffusion MRI acquisitions for quality and to correct the resulting imaging metrics allows for improved inference and increased replicability. Previous work has shown promise for estimation of bias and variance of generalized fractional anisotropy (GFA) but comes at the price of computational complexity. This paper aims to provide methods for estimating GFA, bias of GFA and standard deviation of GFA quickly and accurately. In order to provide a method for bias and variance estimation that can return results faster than the previously studied statistical techniques, three deep, fully-connected neural networks are developed for GFA, bias of GFA, and standard deviation of GFA. The results of these networks are compared to the observed values of the metrics as well as those fit from the statistical techniques (i.e. Simulation Extrapolation (SIMEX) for bias estimation and wild bootstrap for variance estimation). Our GFA network provides predictions that are closer to the true GFA values than a Q-ball fit of the observed data (root-mean-square error (RMSE) 0.0077 vs 0.0082, p < .001). The bias network also shows statistically significant improvement in comparison to the SIMEX-estimated error of GFA (RMSE 0.0071 vs. 0.01, p < .001).

    更新日期:2019-11-01
  • Scan-rescan repeatability and cross-scanner comparability of DTI metrics in healthy subjects in the SPRINT-MS multicenter trial.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-07-27
    Xiaopeng Zhou,Ken E Sakaie,Josef P Debbins,Sridar Narayanan,Robert J Fox,Mark J Lowe

    PURPOSE To assess intrascanner repeatability and cross-scanner comparability for diffusion tensor imaging (DTI) metrics in a multicenter clinical trial. METHODS DTI metrics (including longitudinal diffusivity [LD], fractional anisotropy [FA], mean diffusivity [MD], and transverse diffusivity [TD]) from pyramidal tracts for healthy controls were calculated from images acquired on twenty-seven 3T MR scanners (Siemens and GE) with 6 different scanner models and 7 different software versions as part of the NN102/SPRINT-MS clinical trial. Each volunteer underwent two scanning sessions on the same scanner. Signal-to-noise ratio (SNR) and signal-to-noise floor ratio (SNFR) were also assessed. RESULTS DTI metrics showed good scan-rescan repeatability. There were no significant differences between scans and rescans in LD, FA, MD, or TD values. Although the cross-scanner coefficient of variation (CV) values for all DTI metrics were <5.7%, significant differences were observed for LD (p < 3.3e-5) and FA (p < 0.0024) when GE scanners were compared with Siemens scanners. Significant differences were also observed for SNR when comparing GE scanners and Siemens Skyra scanners (p < 1.4e-7) and when comparing Siemens Skyra scanners and TIM Trio scanners (p < 1.0e-10). Analysis of background signal also demonstrated differences between GE and Siemens scanners in terms of signal statistics. The measured signal intensity from a background noise region of interest was significantly higher for GE scanners than for Siemens scanners (p < 1.2e-12). Significant differences were also observed for SNFR when comparing GE scanners and Siemens Skyra scanners (p < 2.5e-11), GE scanners and Siemens Trio scanners (p < 7.5e-11), and Siemens Skyra scanners and TIM Trio scanners (p < 2.5e-9). CONCLUSIONS The good repeatability of the DTI metrics among the 27 scanners used in this study confirms the feasibility of combining DTI data from multiple centers using high angular resolution sequences. Our observations support the feasibility of longitudinal multicenter clinical trials using DTI outcome measures. The noise floor level and SNFR are important parameters that must be assessed when comparing studies that used different scanner models.

    更新日期:2019-11-01
  • Rapid B1 field mapping at 3 T using the 180° signal null method with extended flip angle.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-07-01
    Abinand C Rejimon,Diana Y Lee,Christopher M Bergeron,You Zhuo,Wenshu Qian,Richard G Spencer,Mustapha Bouhrara

    PURPOSE To extend the null signal method (NSM) for B1 mapping to 3 T magnetic resonance imaging (MRI). BACKGROUND The NSM operates in the steady state regime and exploits the linearity of the spoiled gradient recalled echo (SPGR) signal around the 180° flip angle (FA). Using linear regression, B1 maps are derived from three SPGR images acquired at different FAs with a short repetition time. While the conventional NSM allows accurate mapping of B1 for moderate B1 variation, we observed that this method fails for the larger B1 variations typical of high-field MRI. METHODS We analyzed the effect of the FA range of the acquired SPGR images on B1 determination using the NSM for 3 T MRI through extensive numerical and in vivo analyses. B1 maps derived from the extended angle-range NSM (EA-NSM) were calculated and compared to those derived from the conventional, more restricted angle range, NSM, and to those derived from the reference, but much more time-consuming, double angle method (DAM). Furthermore, we investigated the compatibility of EA-NSM B1 mapping and the half-scan and SENSE reconstruction methods for accelerating acquisition time. RESULTS Our results show that the use of the conventional FA range leads to substantial inaccuracies in B1 determination. Both numerical and in vivo analyses demonstrate that expanding the FA range of the acquired SPGR images substantially improves the accuracy of B1 maps. Furthermore, B1 maps derived from EA-NSM were demonstrated to be quantitatively comparable to those derived from the lengthy DAM protocol. We also found that B1 maps derived from SPGR images using the EA-NSM and imaging acceleration methods were comparable to those derived from images acquired without acceleration. Finally, the use of half scanning combined with SENSE reconstruction permits whole-brain B1 mapping in ~1 min. CONCLUSIONS The EA-NSM permits accurate, fast, and practical B1 mapping in a 3 T clinical setting.

    更新日期:2019-11-01
  • Water mobility spectral imaging of the spinal cord: Parametrization of model-free Laplace MRI.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-12-26
    Dan Benjamini,Peter J Basser

    Diffusion magnetic resonance imaging (dMRI) of biological systems most often results in non-monoexponential signal, due to their complexity and heterogeneity. One approach to interpreting dMRI data without imposing tissue microstructural models is to fit the signal to a multiexponential function, which is sometimes referred to as an inverse Laplace transformation, and to display the coefficients as a distribution of the diffusivities, or water mobility spectra. Until recently, this method has not been used in a voxelwise manner, mainly because of heavy data requirements. With recent advancements in processing and experimental design, voxelwise Laplace MRI approaches are becoming feasible and attractive. The rich spectral information, combined with a three-dimensional image, presents a challenge because it tremendously increases the dimensionality of the data and requires a robust method for interpretation and analysis. In this work, we suggest parameterizing the empirically measured water mobility spectra using a bimodal lognormal function. This approach allows for a compact representation of the spectrum, and it also resolves overlapping spectral peaks, which allows for a robust extraction of their signal fraction. We apply the method on a fixed spinal cord sample and use it to generate robust intensity images of slow- and fast-diffusion components. Using the parametric variables, we create novel image contrasts, among them the information entropy of the water mobility spectrum, which pack unique features of the individual diffusion regimes in the investigated system.

    更新日期:2019-11-01
  • Transverse relaxation of cerebrospinal fluid depends on glucose concentration.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2017-08-08
    A Daoust,S Dodd,G Nair,N Bouraoud,S Jacobson,S Walbridge,D S Reich,A Koretsky

    PURPOSE To evaluate the biophysical processes that generate specific T2 values and their relationship to specific cerebrospinal fluid (CSF) content. MATERIALS AND METHODS CSF T2s were measured ex vivo (14.1T) from isolated CSF collected from human, rat and non-human primate. CSF T2s were also measured in vivo at different field strength in human (3 and 7T) and rodent (1, 4.7, 9,4 and 11.7T) using different pulse sequences. Then, relaxivities of CSF constituents were measured, in vitro, to determine the major molecule responsible for shortening CSF T2 (2s) compared to saline T2 (3s). The impact of this major molecule on CSF T2 was then validated in rodent, in vivo, by the simultaneous measurement of the major molecule concentration and CSF T2. RESULTS Ex vivo CSF T2 was about 2.0s at 14.1T for all species. In vivo human CSF T2 approached ex vivo values at 3T (2.0s) but was significantly shorter at 7T (0.9s). In vivo rodent CSF T2 decreased with increasing magnetic field and T2 values similar to the in vitro ones were reached at 1T (1.6s). Glucose had the largest contribution of shortening CSF T2in vitro. This result was validated in rodent in vivo, showing that an acute change in CSF glucose by infusion of glucose into the blood, can be monitored via changes in CSF T2 values. CONCLUSION This study opens the possibility of monitoring glucose regulation of CSF at the resolution of MRI by quantitating T2.

    更新日期:2019-11-01
  • MRI of myocardial function: motion tracking techniques.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 1996-01-01
    E R McVeigh

    Methods for the noninvasive measurement of three-dimensional myocardial motion with MRI have recently been developed using presaturation tagging and velocity-encoded phase maps. The quality of clinical cardiac MRI studies has also recently improved with the advent of breath-hold scanning. The combination of breath-hold imaging with tagging and velocity-encoding sequences has made the measurement of myocardial wall motion in patients a simple and reproducible exam. These methods make it possible to quantify the severity and extent of regional heart wall motion abnormalities both at rest and during stress. This article reviews the MRI techniques developed for these applications.

    更新日期:2019-11-01
  • Shape-appearance constrained segmentation and separation of vein and artery in pulsatile tinnitus patients based on MR angiography and flow MRI.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-06-05
    Yan Wang,Evan Kao,Yue Zhang,Bing Tian,Jingshan Gong,Farshid Faraji,Henrik Haraldsson,Matthew R Amans,David Saloner,Jing Liu

    This study reports on the development and evaluation of a novel segmentation method for extracting the internal jugular vein and the adjacent carotid artery from magnetic resonance (MR) images of patients with pulsatile tinnitus. A narrow band level set method with combined shape and appearance constraints was developed and applied to high-resolution MR images from 17 pulsatile tinnitus patients (age 52 ± 23 years, 10 females). The proposed method was validated by comparing with the manual segmentation as well as by identifying the jugular vein and carotid artery based on 4D flow MRI in which the two types of vessels have opposing flow. Our study showed that the vein and artery are in contact with each other on 30.2% of all the slices. Dice value, Peak signal-to-noise ratio (PSNR), Hausdorff distance and mean sum of square distance (MSSD) between automatic and manual segmentation were 89.13 ± 2.84%, 27.36 ± 2.39%, 17.2 ± 6.9 mm, 7.4 ± 5.5 mm, demonstrating good segmentation accuracy. The average Dice similarity coefficient and the coefficient of variation compared with 4D flow MRI was 91.42 ± 1.63% and 89.28 ± 4.54% for the internal jugular vein and the carotid artery. The present pipeline for automatic internal jugular vein quantification holds promise for efficient image interpretation in large-scale cohort studies.

    更新日期:2019-11-01
  • Registration-based image enhancement improves multi-atlas segmentation of the thalamic nuclei and hippocampal subfields.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-03-19
    Shunxing Bao,Camilo Bermudez,Yuankai Huo,Prasanna Parvathaneni,William Rodriguez,Susan M Resnick,Pierre-François D'Haese,Maureen McHugo,Stephan Heckers,Benoit M Dawant,Ilwoo Lyu,Bennett A Landman

    Magnetic resonance imaging (MRI) is an important tool for analysis of deep brain grey matter structures. However, analysis of these structures is limited due to low intensity contrast typically found in whole brain imaging protocols. Herein, we propose a big data registration-enhancement (BDRE) technique to augment the contrast of deep brain structures using an efficient large-scale non-rigid registration strategy. Direct validation is problematic given a lack of ground truth data. Rather, we validate the usefulness and impact of BDRE for multi-atlas (MA) segmentation on two sets of structures of clinical interest: the thalamic nuclei and hippocampal subfields. The experimental design compares algorithms using T1-weighted 3 T MRI for both structures (and additional 7 T MRI for the thalamic nuclei) with an algorithm using BDRE. As baseline comparisons, a recent denoising (DN) technique and a super-resolution (SR) method are used to preprocess the original 3 T MRI. The performance of each MA segmentation is evaluated by the Dice similarity coefficient (DSC). BDRE significantly improves mean segmentation accuracy over all methods tested for both thalamic nuclei (3 T imaging: 9.1%; 7 T imaging: 15.6%; DN: 6.9%; SR: 16.2%) and hippocampal subfields (3 T T1 only: 8.7%; DN: 8.4%; SR: 8.6%). We also present DSC performance for each thalamic nucleus and hippocampal subfield and show that BDRE can help MA segmentation for individual thalamic nuclei and hippocampal subfields. This work will enable large-scale analysis of clinically relevant deep brain structures from commonly acquired T1 images.

    更新日期:2019-11-01
  • Effect of labelling plane angulation and position on labelling efficiency and cerebral blood flow quantification in pseudo-continuous arterial spin labelling.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2019-02-26
    Magdalena Sokolska,Alan Bainbridge,Alvaro Rojas-Villabona,Xavier Golay,David L Thomas

    Pseudo-continuous arterial spin labelling (pCASL) is the MRI method of choice for non-invasive perfusion measurement in research and clinical practice. Knowledge of the labelling efficiency, α, is essential for accurate quantification of cerebral blood flow (CBF). Typically, a theoretical α value is used, based on an idealistic model and an assumption of spins flowing perpendicularly to the labelling plane. The aim of this work was to investigate the effect of violating this assumption, and to characterize the influence of labelling plane angulation with respect to the vessel direction on labelling efficiency and measured CBF. The effect of labelling plane angulation on labelling efficiency was demonstrated using a numerical simulation of spins at different velocities. Acquisitions from healthy volunteers were used to test the effect of a range of angulation offsets. Additional sub-optimal positions of the labelling plane with respect to the vertebral arteries, at locations where the direction of flow changes significantly from the head-foot direction, were also considered. No significant change in the measured CBF was seen when the labelling plane was angled up to 60° to the labelled vessel or when it was placed in sub-optimal positions. This study shows that in adult subjects, the efficiency of pCASL is robust to the angulation and positioning of the labelling plane beyond the range of potential operator error.

    更新日期:2019-11-01
  • A simple and fast adaptive nonlocal multispectral filtering algorithm for efficient noise reduction in magnetic resonance imaging.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-08-28
    Mustapha Bouhrara,Michael C Maring,Richard G Spencer

    PURPOSE We recently introduced a multispectral (MS) nonlocal (NL) filter based on maximum likelihood estimation (MLE) of voxel intensities, termed MS-NLML. While MS-NLML provides excellent noise reduction and improved image feature preservation as compared to other NL or MS filters, it requires considerable processing time, limiting its application in routine analyses. In this work, we introduced a fast, simple, and robust filter, termed nonlocal estimation of multispectral magnitudes (NESMA), for noise reduction in multispectral (MS) magnetic resonance imaging (MRI). METHODS Through extensive simulation and in-vivo analyses, we compared the performance of NESMA and MS-NLML in terms of noise reduction and processing efficiency. Further, we introduce two simple adaptive methods that permit spatial variation of similar voxels, R, used in the filtering. The first method is semi-adaptive and permits variation of R across the image by using a relative Euclidean distance (RED) similarity threshold. The second method is fully adaptive and filters the raw data with several RED similarity thresholds to spatially determine the optimal threshold value using an unbiased criterion. RESULTS NESMA shows very similar filtering performance as compared to MS-NLML, however, with much simple implementation and very fast processing time. Further, for both filters, the adaptive methods were shown to further reduce noise in comparison with the conventional non-adaptive method in which R is set to a constant value throughout the image. CONCLUSIONS NESMA is fast, robust, and straightforward to implement filter. These features render it suitable for routine clinical use and analysis of large MRI datasets.

    更新日期:2019-11-01
  • Measurement of fat fraction in the human thymus by localized NMR and three-point Dixon MRI techniques.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2018-04-02
    Kenneth W Fishbein,Sokratis K Makrogiannis,Vanessa A Lukas,Marilyn Okine,Ramona Ramachandran,Luigi Ferrucci,Josephine M Egan,Chee W Chia,Richard G Spencer

    PURPOSE To develop a protocol to non-invasively measure and map fat fraction, fat/(fat+water), as a function of age in the adult thymus for future studies monitoring the effects of interventions aimed at promoting thymic rejuvenation and preservation of immunity in older adults. MATERIALS AND METHODS Three-dimensional spoiled gradient echo 3T MRI with 3-point Dixon fat-water separation was performed at full inspiration for thymus conspicuity in 36 volunteers 19 to 56 years old. Reproducible breath-holding was facilitated by real-time pressure recording external to the console. The MRI method was validated against localized spectroscopy in vivo, with ECG triggering to compensate for stretching during the cardiac cycle. Fat fractions were corrected for T1 and T2 bias using relaxation times measured using inversion recovery-prepared PRESS with incremented echo time. RESULTS In thymus at 3 T, T1water = 978 ± 75 ms, T1fat = 323 ± 37 ms, T2water = 43.4 ± 9.7 ms and T2fat = 52.1 ± 7.6 ms were measured. Mean T1-corrected MRI fat fractions varied from 0.2 to 0.8 and were positively correlated with age, weight and body mass index (BMI). In subjects with matching MRI and MRS fat fraction measurements, the difference between these measurements exhibited a mean of -0.008 with a 95% confidence interval of (0.123, -0.138). CONCLUSIONS 3-point Dixon MRI of the thymus with T1 bias correction produces quantitative fat fraction maps that correlate with T2-corrected MRS measurements and show age trends consistent with thymic involution.

    更新日期:2019-11-01
  • Lesion magnetic susceptibility response to hyperoxic challenge: A biomarker for malignant brain tumor microenvironment?
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2017-12-10
    Pinar Senay Özbay,Sonja Stieb,Cristina Rossi,Oliver Riesterer,Andreas Boss,Tobias Weiss,Felix Pierre Kuhn,Klaas Paul Pruessmann,Daniel Nanz

    BACKGROUND AND PURPOSE Quantitative susceptibility mapping has been previously used to differentiate lesions in patients with brain tumors. The aim of this work was to characterize the response of magnetic susceptibility differences in malignant brain tumors and surrounding edema to hyperoxic and hypercapnic respiratory challenges. METHODS Images of malignant brain tumor patients (2 glioblastoma multiforme, 2 anaplastic astrocytoma, 1 brain metastasis) with clinical MRI exams (contrast-enhanced T1w) were acquired at 3T. 3D multi-gradient-echo data sets were acquired while the patients inhaled medical-air (21% O2), oxygen (100% O2), and carbogen (95% O2, 5% CO2). Susceptibility maps were generated from real and imaginary data. Regions of interest were analyzed with respect to respiration-gas-induced susceptibility changes. RESULTS Contrast-enhancing tumor regions with high baseline magnetic susceptibility exhibited a marked susceptibility reduction under hyperoxic challenges, with a stronger effect (-0.040 to -0.100ppm) under hypercapnia compared to hyperoxia (-0.010 to -0.067ppm). In contrast, regions attributed to necrotic tissue and to edema showed smaller changes of opposite sign, i.e. paramagnetic shift. There was a correlation between malignant tumor tissue magnetic susceptibility at baseline under normoxia and the corresponding susceptibility reduction under hypercapnia and - to a lesser degree - under hyperoxia. CONCLUSION In this small cohort of analysis, quantification of susceptibility changes in response to respiratory challenges allowed a complementary, functional differentiation of tumorous sub-regions. Those changes, together with the correlations observed between baseline susceptibility under normoxia and susceptibility reduction with challenges, could prove helpful for a non-invasive characterization of local tumor microenvironment.

    更新日期:2019-11-01
  • Reduced distortion artifact whole brain CBF mapping using blip-reversed non-segmented 3D echo planar imaging with pseudo-continuous arterial spin labeling.
    Magn. Reson. Imaging (IF 2.112) Pub Date : 2017-09-05
    Neville D Gai,Yi Yu Chou,Dzung Pham,John A Butman

    PURPOSE To implement and evaluate interleaved blip-up, blip-down, non-segmented 3D echo planar imaging (EPI) with pseudo-continuous arterial spin labeling (pCASL) and post-processing for reduced susceptibility artifact cerebral blood flow (CBF) maps. MATERIALS AND METHODS 3D EPI non-segmented acquisition with a pCASL labeling sequence was modified to include alternating k-space coverage along phase encoding direction (referred to as "blip-reversed") for alternating dynamic acquisitions of control and label pairs. Eight volunteers were imaged on a 3T scanner. Images were corrected for distortion using spatial shifting transformation of the underlying field map. CBF maps were calculated and compared with maps obtained without blip reversal using matching gray matter (GM) images from a high resolution 3D scan. Additional benefit of using the correction for alternating blip-up and blip-down acquisitions was assessed by comparing to corrected blip-up only and corrected blip-down only CBF maps. Matched Student t-test of overlapping voxels for the eight volunteers was done to ascertain statistical improvement in distortion. RESULTS Mean CBF value in GM for the eight volunteers from distortion corrected CBF maps was 50.8±9.9ml/min/100 gm tissue. Corrected CBF maps had 6.3% and 4.1% more voxels in GM when compared with uncorrected blip up (BU) and blip down (BD) images, respectively. Student t-test showed significant reduction in distortion when compared with blip-up images and blip-down images (p<0.001). When compared with corrected BU and corrected BD only CBF maps, BU and BD corrected maps had 2.3% and 1% more voxels (p=0.006 and 0.04, respectively). CONCLUSION Pseudo-continuous arterial spin labeling with non-segmented 3D EPI acquisition using alternating blip-reversed k-space traversal and distortion correction provided significantly better matching GM CBF maps. In addition, employing alternating blip-reversed acquisitions during pCASL acquisition resulted in statistically significant improvement over corrected blip-up and blip-down CBF maps.

    更新日期:2019-11-01
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