Skeletal muscle BOLD MRI: from underlying physiological concepts to its usefulness in clinical conditions.

Blood oxygenation-level dependent (BOLD) MRI has gained particular attention in functional brain imaging studies, where it can be used to localize areas of brain activation with high temporal resolution. To a higher degree than in the brain, skeletal muscles show extensive but transient alterations of blood flow between resting and activation state. Thus, there has been interest in the application of the BOLD effect in studying the physiology of skeletal muscles (healthy and diseased) and its possible application to clinical practice. This review outlines the potential of skeletal muscle BOLD MRI as a diagnostic tool for the evaluation of physiological and pathological alterations in the peripheral limb perfusion, such as in peripheral arterial occlusive disease. Moreover, current knowledge is summarized regarding the complex mechanisms eliciting BOLD effect in skeletal muscle. We describe technical fundaments of the procedure that should be taken into account when performing skeletal muscle BOLD MRI, including the most often applied paradigms to provoke BOLD signal changes and key parameters of the resulting time courses. Possible confounding effects in muscle BOLD imaging studies, like age, muscle fiber type, training state, and drug effects are also reviewed in detail.

Blood oxygenation level-dependent (BOLD) MRI of human skeletal muscle at 1.5 and 3 T.

PURPOSE: To evaluate the dependence of skeletal muscle blood oxygenation level-dependent (BOLD) effect and time course characteristics on magnetic field strength in healthy volunteers using an ischemia/reactive hyperemia paradigm. MATERIALS AND METHODS: Two consecutive skeletal muscle BOLD magnetic resonance imaging (MRI) measurements in eight healthy volunteers were performed on 1.5 T and 3.0 T whole-body MRI scanners. For both measurements a fat-saturated multi-shot multiecho gradient-echo EPI sequence was applied. Temporary vascular occlusion was induced by suprasystolic cuff compression of the thigh. T2 time courses were obtained from two different calf muscles and characterized by typical curve parameters. Ischemia- and hyperemia-induced changes in R2 (ΔR2) were calculated for both muscles in each volunteer at the two field strengths. RESULTS: Skeletal muscle BOLD changes are dependent on magnetic field strength as the ratio ΔR2(3.0 T)/ΔR2(1.5 T) was found to range between 1.6 and 2.2. Regarding time course characteristics, significantly higher relative T2 changes were found in both muscles at 3.0 T. CONCLUSION: The present study shows an approximately linear field strength dependence of ΔR2 in the skeletal muscle in response to ischemia and reactive hyperemia. Using higher magnetic fields is advisable for future BOLD imaging studies of peripheral limb pathologies.