Motion measurements from individual MR signals using volume localization.

Abstract

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 resolution of several milliseconds. The trajectory of the excited volume is derived from the time-dependent frequency of the MR signal, which changes as the volume moves through a magnetic-field gradient. Phantom and in vivo experiments confirm that this method can monitor the trajectory of plug-like structures accurately, with T2* decay limiting the measurement period. The displacement of flowing blood in a human aorta has been measured for 65 msec from one MR 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 useful for capturing rapid motions. An interesting property of this method is that it measures motion from the reference frame of the moving anatomy.