Compensatory Amide Proton Transfer Ratio (CAPTOR) Imaging to Improve the Specificity of Tissue Acidosis MRI

Phillip Zhe Sun¹, A Gregory Sorensen¹

Amide proton transfer (APT) imaging has been shown sensitive to microenvironment pH and can detect ischemic tissue acidosis. However, the commonly used magnetization transfer (MT) asymmetry analysis is susceptible to concomitant RF irradiation effects (spillover, intrinsically asymmetric MT etc), and hence, may not be specific to pH-dependent APT mechanism. Here, we propose a compensatory APT ratio (CAPTOR) approach that subtracts the label scan (famide) from the mean of two compensatory images around the amide proton offset instead of a reference scan (-famide). Our data showed that CAPTOR had less heterogeneity among cerebral tissue types, and more specific to APT process.