Imaging Acute Ischemic Tissue Acidosis with Quantitative in vivo Amide Proton Transfer (APT) MRI

Phillip Zhe Sun¹, Enfeng Wang¹, Jerry S. Cheung¹

Amide proton transfer (APT) MRI is capable of imaging tissue acidosis during acute stroke. However, magnetization transfer asymmetry (MTRasym) is often calculated for pH-weighted APT contrast, which is subject to a baseline shift (MTRasym) attributable to the slightly asymmetric magnetization transfer (MT) effect. In this study, we modeled MTRasym as a superposition of pH-dependent APT contrast and a baseline shift MTRasym (i.e., MTRasym=APTR(pH) + MTRasym). We found schemic lesion pH was 6.44 0.24, significantly reduced from that of the normal tissue (7.03 0.05), which correlated with tissue perfusion and diffusion rates.