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

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Abstract
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. Reproduclbility 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 mllliliters 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 < 0.001), 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 < 0.001). 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.