Quantification of NAD+ proton cross-relaxation with water using downfield 1H MRS in the human brain at 7 T

Motivation: NAD+ plays a pivotal role in metabolism and its cross-relaxation with water has the potential to be a biomarker of health and disease. Goal(s): Our goal was to determine the rate of NAD+ cross-relaxation in the human brain in vivo at 7T. Approach: We utilized spectrally-selective downfield spectroscopy in paired saturation recovery experiments and fit two models of longitudinal recovery. Results: We measured an average 7.6-fold increase in apparent T1 relaxation when utilizing a broadband saturation pulse compared to a selective saturation pulse and a cross-relaxation rate of 3.9±1.5 Hz for the H2 and H6 protons of NAD+. Impact: NAD+ cross-relaxation in human brain can be exploited to increase sensitivity through T1-shortening, and its quantification may provide insights into metabolite binding in vivo.