Novel proton exchange rate MRI presents unique contrast in brains of ischemic stroke patients.

BACKGROUND

To map and quantify the proton exchange rate (k) of brain tissues using improved omega plots in ischemic stroke patients and to investigate whether k 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 of 1.5, 2.5, and 3.5 μT, respectively. Pixel-wise k was calculated from improved omega plot of water direct saturation (DS)-removed Z-spectral signals.

RESULTS

The derived k maps can differentiate infarcts from contralateral normal brain tissues with significantly increased signal (893 ± 52 svs. 739 ± 34 s, P < 0.001).

COMPARISON WITH EXISTING METHOD(S): The k 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 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 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 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.