Consistent depiction of the acidic ischemic lesion with APT MRI-Dual RF power evaluation of pH-sensitive image in acute stroke.

Purpose: Amide proton transfer-weighted (APTw) MRI provides a non-invasive pH-sensitive image, complementing perfusion and diffusion imaging for refined stratification of ischemic tissue. Although the commonly used magnetization transfer (MT) asymmetry (MTR _asym ) calculation reasonably corrects the direct RF saturation effect, it is susceptible to the concomitant semisolid macromolecular MT contribution. Therefore, this study aimed to compare the performance of MTR _asym and magnetization transfer and relaxation-normalized APT (MRAPT) analyses under 2 representative experimental conditions.
Methods: Multiparametric MRI scans were performed in a rodent model of acute stroke, including relaxation, diffusion, and Z spectral images under 2 representative RF levels of 0.75 and 1.5 µT. Both MTR _asym and MRAPT values in the ischemic diffusion lesion and the contralateral normal areas were compared using correlation and Bland-Altman tests. In addition, the acidic lesion volumes were compared.
Results: MRAPT measurements from the diffusion lesion under the 2 conditions were highly correlated (R ² = 0.97) versus MTR _asym measures (R ² = 0.58). The pH lesion sizes determined from MRAPT analysis were in good agreement (178 ± 43 mm ³ vs. 186 ± 55 mm ³ for B ₁ of 0.75 and 1.5 µT, respectively).
Conclusions: The study demonstrated that MRAPT analysis could be generalized to moderately different RF amplitudes, providing a more consistent depiction of acidic lesions than the MTR _asym analysis.
(© 2021 International Society for Magnetic Resonance in Medicine.)