Effect of flip angle on volume flow measurement with nontriggered phase‐contrast MR: In vivo evaluation in carotid and basilar arteries

Abstract

To evaluate the effect of flip angle on volume flow rate measurements obtained with nontriggered phase-contrast magnetic resonance imaging (MRI) in vivo. We prospectively measured volume flow rates of the bilateral internal carotid artery and the basilar artery with cine and nontriggered phase-contrast MRI. For nontriggered phase-contrast imaging, flip angles of 4, 15, 60, and 90 degrees were used for 40 volunteers and of 8, 15, and 30 degrees for 54 volunteers. Lumen boundaries were semiautomatically determined by pulsatility-based segmentation using cine phase-contrast MRI. Identical lumen boundaries were used for nontriggered phase-contrast imaging. The ratio of volume flow rate obtained with nontriggered phase-contrast imaging to that obtained with cine phase-contrast imaging significantly increases with an increase in the flip angle. The mean ratios lie within a relatively narrow range of +/-15% with a wide range of flip angles of 8-90 degrees . As the flip angle increases, ghost artifacts become prominent and signal-to-noise and contrast-to-noise ratios increase. Flip angles between 8 and 60 degrees are most appropriate for nontriggered phase-contrast MR measurements in the internal carotid and the basilar artery.