Dual gradient-echo MRI of post-contraction changes in skeletal muscle blood volume and oxygenation

Abstract

Analysis of post-contraction MRI signal intensity (SI) transients may allow noninvasive studies of microvascular reactivity and blood oxygenation recovery. The purpose of this study was to determine the physiological basis for post-contraction changes in short-echo (6 ms) and long-echo (46 ms) gradient-echo (GRE) MRI signals (S6 and S46, respectively). Six healthy subjects were studied with the use of dual GRE MRI and near-infrared spectroscopy (NIRS). S6, S46, total hemoglobin concentration ([THb]), and oxyhemoglobin saturation (%HbO2) were measured before, during, and after 2 and 8 s dorsiflexion maximal voluntary contractions, and 5 min of proximal arterial occlusion. The changes in S 6 and [THb] after the 2-s contractions were similar to those following 8-s contractions, but changes in %HbO2 and S46 were greater following 8-s contractions than after the 2-s contractions. [THb] and S6 did not change during and following 5 min of arterial occlusion, but %HbO2 and S46 were both significantly depressed at similar occlusion durations. Also, distance measures indicated similarity between S6 and [THb] and between S46 and %HbO2. We conclude that following brief human skeletal muscle contractions, changes in S6 primarily reflect changes in blood volume and changes in S46 primarily reflect changes in blood oxygenation. © 2007 Wiley-Liss, Inc.