Determining exercise‐induced blood flow reserve in lower extremities using phase contrast MRI

Abstract

To study the changes in limb blood flow during lower extremity exercise using phase contrast (PC) MRI in normal volunteers. Healthy volunteers performed plantar flexion exercise (<1 W) for four minutes. Flow velocity was measured using cardiac-gated, cine PC-MRI sequences (fast gradient recalled echo [GRE]; multishot echo planar imaging [EPI]) on a 3T scanner at the level of the superficial femoral artery (SFA): 1) preexercise; 2) immediately postexercise; 3) during three minutes recovery; and 4) postrecovery. At rest there was a triphasic flow waveform in the SFA. During exercise it changed to a monophasic pattern with an increase in total flow; there were variable changes in vessel size and flow velocity. The waveform regained the triphasic pattern during recovery. The exercise-induced flow reserve (FR) was 167 +/- 90%. PC-MRI demonstrates that the resting triphasic flow waveform transforms into a monophasic pattern with submaximal exercise and returns to baseline with recovery. This increase in the regional blood flow allows for measurement of exercise-induced FR in the SFA.