Novel proton exchange rate MRI presents unique contrast in brains of ischemic stroke patients.,Journal of Neuroscience Methods

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Novel proton exchange rate MRI presents unique contrast in brains of ischemic stroke patients.
Journal of Neuroscience Methods ( IF 2.7 ) Pub Date : 2020-09-05 , DOI: 10.1016/j.jneumeth.2020.108926
Zhenxiong Wang ₁ , Mehran Shaghaghi ₂ , Shun Zhang ₃ , Guiling Zhang ₃ , Yiran Zhou ₃ , Di Wu ₃ , Zhuoli Zhang ₄ , Wenzhen Zhu ₃ , Kejia Cai ₂

Affiliation

Background

To map and quantify the proton exchange rate ( $k_{e x}$ ) of brain tissues using improved omega plots in ischemic stroke patients and to investigate whether $k_{e x}$ can serve as a potential endogenous surrogate imaging biomarker for detecting the metabolic state and the pathologic changes due to ischemic stroke.

New Method

Three sets of Z-spectra were acquired from seventeen ischemic stroke patients using a spin echo-echo planar imaging sequence with pre-saturation chemical exchange saturation transfer (CEST) pulse at $B_{1}$ of 1.5, 2.5, and 3.5 $μ T$ , respectively. Pixel-wise $k_{e x}$ was calculated from improved omega plot of water direct saturation (DS)-removed Z-spectral signals.

Results

The derived $k_{e x}$ maps can differentiate infarcts from contralateral normal brain tissues with significantly increased signal (893 ± 52 $s^{- 1}$ vs. 739 ± 34 $s^{- 1}$ , P < 0.001).

Comparison with Existing Method(s)

The $k_{e x}$ maps were found to be different from conventional contrasts from diffusion-weighted imaging (DWI), CEST, and semi-solid magnetization transfer (MT) MRI. In brief, $k_{e x}$ MRI showed larger lesion areas than DWI with different degrees and different lesion contrast compared to CEST and MT.

Conclusions

In this preliminary translational research, the $k_{e x}$ MRI based on DS-removed omega plots has been demonstrated for in vivo imaging of clinical ischemic stroke patients. As a noninvasive and unique MRI contrast, $k_{e x}$ MRI at 3 T may serve as a potential surrogate imaging biomarker for the metabolic changes of stroke and help for monitoring the evolution and the treatment of stroke.