EXPERIMENTAL-STUDY OF THE EFFECTS OF FRACTIONAL GATING ON FLOW MEASUREMENTS

Velocity encoded phase imaging is subject to errors from phase and amp litude variations of the k-space data caused by beat-to-beat variation s of the flow. Fractional cardiac gating is defined as asynchronous ga ting with each phase encode step occupying a fixed fraction of the RR interval. The gating fraction is the inverse of the number of phase en code steps taken per RR interval. Studies in normal subjects show that deviations and standard errors of ascending and descending aorta flow measurements are significantly greater with decreased gating fraction . Significant errors occur when gating does not separate systolic and diastolic data. The studies establish a graded trade-off between flow measurement accuracy and precision with imaging time, and show that st andard nongated phase contrast measurements of strongly pulsatile flow are unreliable.