FREQUENCY-RESPONSE OF PROSPECTIVELY GATED PHASE-CONTRAST MR VELOCITY-MEASUREMENTS

The authors developed and experimentally verified expressions that des cribe the frequency response of prospectively gated phase-contrast mag netic resonance velocity measurements, Both interleaved and noninterle aved phase-contrast techniques were evaluated, The primary determinant s of the frequency response were (a) the number of interleaved acquisi tions (N), (b) the time between acquisitions (Delta T), and (c) the de gree of balance between the first moments of the velocity-encoding gra dients. To quantify the last factor, an imbalance parameter (U) was de fined, Depending on the chosen implementation and U, deviations from t he ideal frequency responses were predicted and observed, The expressi ons also revealed an advantage of interleaved acquisitions that use a one-sided gradient configuration: no changes in the frequency response . The effects of concurrently encoding orthogonal velocity components with a Hadamard four-point scheme were examined.