Evaluation of ultrafast phase-contrast imaging in the thoracic aorta

Purpose: Two ultrafast phase-contrast (PC) data acquisition strategies, multishot echo-planar imaging (EPI)-PC and segmentedk-space fast gradient-echo PC (FASTCARD-PC) were evaluated with regard to their measurement accuracy. Materials and Method: Flow measurements of the ascending and descending aorta were acquired in 10 healthy volunteers with an electrocardiogram (ECG)-triggered eight-shot EPI-PC sequence (TR/TE/flip 16/7.4/45°, 32-ms flow-phase interval, 2×2 mm in plane resolution), and FASTCARD-PC (six it-lines per band, TR/TE/flip 11/6.1/45°, 32-ms flow-phase interval, 2 × 1 mm in plane resolution). These were compared to flow-volume data acquired with conventional cine-PC (TR/TE/flip 24/7/45°, 48-ms flow-phase interval, 2 × 1 mm in plane resolution). Using cine-PC as a gold standard, the measurement accuracy of FASTCARD-PC and EPI-PC were determined. Results: Both EPI-PC and FASTCARD-PC significantly reduced data acquisition times compared to cine PC. EPI-PC flow measurements correlated well with aortic cine-PC flow-volume determinations (r=0.98). Reflecting poorer temporal resolution, FASTCARD-PC measurements were less accurate (p<0.05), evidenced by poor correlation with cine-PC data (r=0.62). Conclusion: Ultrafast PC measurements are possible. In contrast to the segmentedk-space PC technique, which is limited in temporal resolution, multishot EPI-PC provides high measurement accuracy in pulsatile vessels while keeping the image acquisition interval short enough for a comfortable breath-hold.