Biomedical subjects

C K Macgowan

Publications and source records attributed to C K Macgowan.

3 recordsLinked to original sources

PubMed2001

Fast measurements of the motion and velocity spectrum of blood using MR tagging.

A new method is presented for tracking the motion of blood and determining its velocity spectrum from magnetic resonance data collected within a single heartbeat. The method begins by tagging a column of blood in a vessel by combining a 1D SPAMM excitation with a 2D cylindrical excitation. A series of 1D projections of the tagging pattern is acquired from a train of gradient echoes. The influence of specific excitation profiles and velocity profiles on the motion of the tags is explored for steady flow. It is shown mathematically, and confirmed with phantom experiments, that the velocity of a tag equals the mean velocity of the excited fluid when the velocity spectrum is symmetric about its mean velocity. The velocity spectrum is derived by analyzing the interference between tags moving at different velocities. This appears to be the first use of magnitude tagging to obtain velocity spectra. Representative measurements in a human aorta are presented to assess feasibility in vivo. Magn Reson Med 45:461-469, 2001.

Aorta↗

PubMed1999

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 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.

Aorta, Thoracic↗

PubMed1996

Phase-encode reordering to minimize errors caused by motion.

A new method for suppressing the effects of motion in MR images by reordering the acquisition of k space has been developed. Existing reordering methods suffer from image blurring. The method presented here applies specifically to translation along the phase-encoding direction, in which case it reduces both ghosting and blurring. The method is conceptually similar to a linear phase shift of k space, except that it has the advantage of not corrupting stationary structures inadvertently. The method is intended for anatomic sites in which substantial translational motion occurs along the phase-encoding direction, such as the cranial-caudal motion of the liver and kidneys. The reordering method is motivated from an analysis of factors affecting the severity of motion artifacts. The theory behind the reordering method is described and validated experimentally by imaging a moving phantom.

Artifacts↗