Optimization of Saturation Power for pH-enhanced MRI in Stroke Rodents

The sensitivity of CEST to pH makes it a potential modality for the assessment of intracellular pH alterations under pathologic conditions. We previously introduced a method for pH-enhanced MRI using amide and guanidyl protons. In this study, we determine saturation powers for imaging both exchangeable protons to optimize either contrast or contrast-to-variation ratio (CVR) between healthy and infarcted tissue in stroke rats. The contrast across parameters remained steady at ~2-3%, while CVR was dominated by variation across ROIs due to residual non-specific contrast. Optimizing CVR minimizes contrast within the lesion and contralesional tissue while preserving contrast between the two tissues.