Improvements in MR angiography using phase-corrected data sets.

The objective of this work is refinement of an MR angiography technique via postprocessing removal of phase errors which inhibit static signal subtraction. Projective views of the object are obtained using interleaved flow-compensated and noncompensated gradient waveforms. Complex subtraction of data sets is required since a projection dephase pulse is used for static signal suppression. This renders the difference image susceptible to systematic phase errors which are modeled as a smoothly varying multiplicative phase function. The error function is estimated by comparison of heavily spatial filtered renditions of the object acquired without projection dephasing in order to minimize influence of flow. The phase correction is then applied to high-resolution data sets collected with projection dephasing to enhance flow sensitivity. The technique is demonstrated by improvement of MR angiograms of rats acquired on a 2-T, 31-cm-bore system.