Exercise-related changes in aortic flow measured with spiral echo-planar MR velocity mapping.

Spiral echo-planar magnetic resonance (MR) velocity mapping was used to measure exercise-related changes in flow in the descending thoracic aorta in 10 healthy volunteers. Flow was measured at rest and immediately after dynamic exercise, with a 0.5-T imager with a surface receiving coil and electrocardiographic triggering. Supine exercise was performed with a home-built pedaling apparatus. Spiral velocity mapping was performed in a transverse plane through the descending thoracic aorta with the subject at rest. The subject was then asked to perform maximum exercise, stop, and hold his breath during a four-heartbeat acquisition time. Eight cine frames with a temporal resolution of 50 msec were acquired through systole. Each image was acquired in 40 msec during spiral acquisition of k-space data, starting at the center, 6 msec after the excitation pulse. Reproducibility of the technique was established by repeating the flow measurement in four consecutive heartbeats. At rest, the heart rate (mean +/- standard deviation), mean aortic flow, peak aortic flow, and time to peak flow were 68 beats per minute +/- 6, 41 milliliters per beat +/- 8, 107 mL/sec +/- 20, and 175 msec +/- 25, respectively. After exercise, the heart rate and mean and peak aortic flow were significantly increased (P < .001), measuring 101 beats per minute +/- 12, 57 milliliters per beat +/- 11, and 158 mL/sec +/- 29, respectively, while the time to peak flow (115 msec +/- 32) was significantly reduced (P < .001). The four sets of values obtained for the first four consecutive heartbeats measured at rest were similar, as were those obtained for the first four heartbeats after exercise.