Flow quantitation with echo-planar phase-contrast velocity mapping: in vitro and in vivo evaluation

We present a multishot echo-planar imaging (EPI) phase-contrast implementation for flow quantitation. The measurement accuracy of this technique was evaluated in vitro and in vivo. A gated eight-shot EPI phase-contrast sequence (TR/TE = 16/7.4, 45 degrees flip angle), with a flow-phase interval of 32 msec and an in-plane resolution of 2 x 2 mm was initially evaluated in a pulsatile flow phantom. Subsequently, EPI phase-contrast flow measurements of the ascending and descending aorta, obtained in 10 volunteers, were compared with flow volume data acquired with a conventional cine phase-contrast sequence (TR/TE = 24/7, 45 degrees flip angle, 48-msec flow-phase interval, 2 x 1 mm in-plane resolution). Comparisons between flow measurements were made using data obtained with the flow probe and cine phase contrast as the standard of reference for in vitro and in vivo measurements, respectively. EPI phase-contrast sequences reduced data acquisition times tenfold compared with cine phase-contrast sequences. EPI phase-contrast flow measurements correlated well with phantom flow (r = .98, slope = 1.1) as well as with aortic cine phase-contrast flow volume determinations (r = .98). A 95% confidence interval of measurement differences between echo-planar and cine phase-contrast imaging, ranging from 2.0 to -1058 mL/min was computed. Ultrafast phase-contrast flow measurements are possible. Multishot EPI phase-contrast imaging provides high measurement accuracy in pulsatile vessels while keeping the image acquisition interval short enough to be accomplished in a comfortable breath-hold.