Cardiac-gated MR angiography of pulsatile flow: k-space strategies.

Signal strength in time-of-flight magnetic resonance (MR) angiography of pulsatile flow is modulated by the time-varying intraluminal magnetization strength. The specific appearance of MR angiographic images therefore depends on the relationship of different phase-encoding steps to the pulsatile flow waveform. Cardiac-phase gating can be applied with phase-encoding reordering to acquire different regions of k-space during the desired phases of the cardiac cycle. The authors have developed a simulation program for evaluating the merits of different encoding strategies for pulsatile flow. The model was validated with phantom studies. High signal intensity relative to that in conventional MR angiographic studies can be attained with strategies that impose relatively small penalties in total acquisition time.