Post‐contractile BOLD contrast in skeletal muscle at 7 T reveals inter‐individual heterogeneity in the physiological responses to muscle contraction

Muscle blood oxygenation‐level dependent (BOLD) contrast is greater in magnitude and potentially more influenced by extravascular BOLD mechanisms at 7 T than it is at lower field strengths. Muscle BOLD imaging of muscle contractions at 7 T could, therefore, provide greater or different contrast than at 3 T. The purpose of this study was to evaluate the feasibility of using BOLD imaging at 7 T to assess the physiological responses to in vivo muscle contractions. Thirteen subjects (four females) performed a series of isometric contractions of the calf muscles while being scanned in a Philips Achieva 7 T human imager. Following 2 s maximal isometric plantarflexion contractions, BOLD signal transients ranging from 0.3 to 7.0% of the pre‐contraction signal intensity were observed in the soleus muscle. We observed considerable inter‐subject variability in both the magnitude and time course of the muscle BOLD signal. A subset of subjects ( n  = 7) repeated the contraction protocol at two different repetition times ( T R : 1000 and 2500 ms) to determine the potential of T 1 ‐related inflow effects on the magnitude of the post‐contractile BOLD response. Consistent with previous reports, there was no difference in the magnitude of the responses for the two T R values (3.8 ± 0.9 versus 4.0 ± 0.6% for T R  = 1000 and 2500 ms, respectively; mean ± standard error). These results demonstrate that studies of the muscle BOLD responses to contractions are feasible at 7 T. Compared with studies at lower field strengths, post‐contractile 7 T muscle BOLD contrast may afford greater insight into microvascular function and dysfunction.