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Spectrally-selective measurements of reversible and irreversible transverse relaxation rates from single spin-echo PRESS acquisitions in muscle.
NMR in Biomedicine ( IF 2.9 ) Pub Date : 2020-03-13 , DOI: 10.1002/nbm.4290
Robert V Mulkern 1, 2 , Reyhaneh Nosrati 1, 2 , Mukund Balasubramanian 1, 2
Affiliation  

The goal of this study was to test a new formalism for extracting reversible and irreversible transverse relaxation rates from resonances within typical proton muscle spectra using only a single spin echo as acquired with routine single-voxel, point-resolved echo spectroscopy (PRESS) acquisitions. Single-voxel, non-water-suppressed PRESS acquisitions within the calf muscles of four healthy subjects were performed at 1.5 T using six echo times ranging from 30 to 576 ms. Novel transverse relaxation analyses of water, choline, creatine, and lipid resonances were performed based upon the disparate relaxation sensitivities of the left versus the right sides of spectroscopically sampled spin echoes. Irreversible and reversible transverse relaxation rates R2 and R2 ' were extracted for water, metabolites, and lipids using echo times of 288 ms and longer. The R2 values so obtained were compared with more conventional "gold standard" Hahn values, R2Hahn , evaluated from the echo-time dependence of spectral peak areas generated from right-side sampling alone. Water resonances displayed biexponential Hahn signal decays, consistent with observations of decreasing R2 values with increasing echo time via the new approach. Choline and creatine resonances displayed monoexponential echo-time decays, with R2Hahn values in reasonable agreement with R2 values obtained from the single-echo analyses at the longer echo times. Lipid methylene and methyl R2 values extracted from the new approach were also in reasonable accord with R2Hahn values. Further validation of the technique was provided through PRESS acquisitions on a water phantom to which various levels of gadolinium were added in order to manipulate transverse relaxation rates, yielding excellent agreement between water-resonance R2Hahn and single-echo R2 values. In summary, this work demonstrates the feasibility of measuring reversible and irreversible transverse relaxation rates for individual spectral peaks from single-echo PRESS acquisitions, enabling a reduction in overall scan time relative to the use of multiple acquisitions with varying echo time.

中文翻译:

从肌肉中单次自旋回波PRESS采集中可逆和不可逆横向松弛率的光谱选择性测量。

这项研究的目的是测试一种新的形式主义,该常规形式仅使用通过常规单体素点分辨回波光谱(PRESS)采集获得的单个自旋回波从典型质子肌肉光谱中的共振中提取可逆和不可逆的横向弛豫率。在1.5 T下,使用30至576 ms范围内的六个回波时间,在1.5 T下对四名健康受试者的小腿肌肉进行单体素,非水抑制PRESS采集。水,胆碱,肌酸和脂质共振的新型横向弛豫分析是基于光谱采样的自旋回波左右两侧的不同弛豫敏感性进行的。提取了不可逆和可逆的横向弛豫率R2和R2',用于水,代谢物,和脂质使用288毫秒或更长的回波时间。将如此获得的R2值与更常规的“金标准”哈恩值R2Hahn进行比较,后者根据仅从右侧采样生成的频谱峰面积的回波时间依赖性进行评估。水共振显示双指数哈恩信号衰减,这与通过新方法使R2值随着回波时间增加而减小有关。胆碱和肌酸共振表现出单指数回声时间衰减,R2Hahn值与在较长回声时间下从单回声分析获得的R2值合理一致。从新方法中提取的脂质亚甲基和甲基R2值也与R2Hahn值合理一致。通过在水幻影上进行PRESS采集,对该技术进行了进一步验证,水幻影中添加了各种含量的g,以控制横向弛豫速率,从而在水共振R2Hahn和单回波R2值之间产生了出色的一致性。总而言之,这项工作证明了测量单回波PRESS采集中各个光谱峰的可逆和不可逆横向弛豫率的可行性,相对于使用具有不同回波时间的多次采集,可以减少总体扫描时间。
更新日期:2020-03-13
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