Mechanisms of flow-induced signal loss in MR angiography.

Mechanisms of signal loss in magnetic resonance angiography were studied with a stenotic flow phantom. The results indicate that while signal loss induced by mean fluid motions is localized about the stenosis, the fluctuating component of fluid motion induces signal loss over a much larger region, primarily distal to the stenosis. For both motion components, use of gradient moment nulling (GMN) above first order was found to be an ineffective means of reducing signal loss. In contrast, shortened gradient durations were found to reduce signal loss substantially. However, though a zeroth-order gradient is generally of the shortest duration, use of a slightly longer, first-order gradient was found to be the most robust means of reducing signal loss.