Flow phenomenon in second section of multisection MR imaging of laminar flow

A flow phantom experiment was performed with flowing water through soft PVC tubes and a 2.0-T unit. A multisection image was obtained as nine different velocities, 0.5-43 cm/sec, were applied. As the velocity was increased, the pattern of the second section changed into ring and target shapes. In velocities above 5 cm/sec the second section has a small round shape, then it is distorted and lost. The pattern was influenced by primary influx of fully magnetized spins during a prior repetition time, secondary influx during section transition time, and the influx of partially saturated spins from the first section