Figure 1:

Basic sequence diagram depicting the principle underlying both electrocardiographically gated fast spin-echo (SE)-based MR angiography and flow-sensitive dephasing (FSD)-prepared steady state free precession (SSFP) MR angiography. Three-dimensional volumetric acquisitions in arterial diastole and arterial systole are obtained consecutively, with arterial signal intensity dephasing occurring during systole but not diastole. Subtraction of the systolic data set from the diastolic data set cancels out venous signal and static tissue, leaving only high arterial signal intensity. Scout phase-contrast imaging allows selection of the optimal systolic trigger delay (TD). A = artery, V = vein.