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

Abstract

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.