EXPERIMENTAL CONFIRMATION OF PHASE-ENCODING OF INSTANTANEOUS DERIVATIVES OF POSITION

Previous theoretical reports described the dependence of interpretatio n of the observed phase of the NMR signal on the time origin(s) of mom ent calculations and position's Taylor series expansion. This work pro vides experimental confirmation of predictions derived from that theor y. For accelerative motion, experimental phase-encoded velocity measur ements give instantaneous values at a time corresponding to the origin used for waveform moment calculations. For laminar flow,experimental intensity profiles agree well with theoretical simulations; new findin gs extend amplitude and spatial distributions of oblique flow profiles beyond previous descriptions. Experiments using sequences with contro lled position of the time origins for phase and read axes show that di splacement and motion artifacts are reduced when they're coincident (p ulsed flow, nongated acquisitions), and virtually eliminated when comb ined with gating. Potentially significant clinical consequences of coi ncident and noncoincident time origins are demonstrated in human head MIP MRA images. These results have fundamental implications in wavefor m design.