Considerations for gradient echo echo planar imaging of skeletal muscle

Adequate blood circulation to muscles is important for good health. In recent years, researchers have increasingly used magnetic resonance imaging (MRI) to study temporal skeletal muscle physiological changes using gradient echo (GRE) echo planar imaging (EPI). These studies, typically involving exercise or ischemic challenges, have differentiated healthy subjects from athletic or unhealthy populations, such as those with peripheral vascular disease. The T* 2 -weighted GRE EPI signal is sensitive to changes in bloodflow and oxygenation in muscle. Furthermore, the signal can be weighted differently by adjusting the echo time (T E ), achieving either blood volume (BV) or blood oxygenation level dependent (BOLD) imaging. This paper comprehensively reviews the muscle GRE EPI literature to date, with a particular emphasis on studies that have also used other modalities in an attempt to elucidate the GRE EPI signal characteristics. Finally, the systemic and muscle physiological factors that are thought to influence the GRE EPI signal during and after exercise are described. These include temperature, blood flow, blood oxygen saturation, myoglobin, and postural effects. The summary attempts to predict, based on the published literature, the temporal dynamics of these signal-influencing parameters in a hypothetical exercise experiment. © 2018 by Begell House, Inc.