Motion measurements from individual MR signals using volume localization

A novel method is presented for measuring motion using individual magnetic resonance (MR) signals, This method uses a volume-localized excitation with reduced spatial encoding to measure displacement with a temporal resolutio n of several milliseconds. The trajectory of the excited volume is derived from the time-dependent frequency of the MR signal, which changes as the vo lume moves through a magnetic-held gradient. Phantom and in vivo experiment s confirm that this method can monitor the trajectory of plug-like structur es accurately, with T2* decay limiting the measurement period. The displace ment of flowing blood in a human aorta has been measured for 65 msec from o ne NIR signal, with a theoretical accuracy of 0.25 mm and an effective time resolution of 2 msec, The high temporal resolution of this method is usefu l for capturing rapid motions. An interesting property of this method is th at it measures motion from the reference frame of the moving anatomy. (C) 1 999 Wiley-Liss, Inc.