Evidence of muscle BOLD effect revealed by simultaneous interleaved gradient-echo NMRI and myoglobin NMRS during leg ischemia.

The purpose of this work was to investigate the temporal relationship between intensity changes in T2*-weighted NMR images and tissue oxygen content, measured by myoglobin proton NMR spectroscopy, in the skeletal muscle. During an ischemic stress test, the calf muscles of five healthy volunteers were studied at 3 Tesla. An interleaved NMRI-NMRS sequence was used, which made it possible to record T2*-weighted images and myoglobin spectra simultaneously. During ischemia, rapid changes in muscle signal intensity were observed on T2*-weighted images, which immediately preceded myoglobin desaturation. Bearing in mind the respective P50 of hemoglobin and myoglobin, this observation clearly favored the hypothesis that hemoglobin desaturation was responsible for the changes in T2*. This interpretation was further supported by the temporal coincidence between the experimental NMR data and a model of hemoglobin desaturation solely derived from physiological considerations.