Acclerated Dual Venc Phase Contrast VIPR in Healthy Volunteers

Introduction: Rapid imaging techniques now allow for the acquisition of volumetric, time-resolved, phase contrast (PC) images with three directional velocity encoding. Covering large vascular territories with a single 4D PC MRI makes choosing the proper velocity encoding (Venc) challenging. If the Venc is too low for a vessel of interest, velocity aliasing occurs. If chosen too high, the velocity-to-noise ratio (VNR) suffers as VNR ~ 1/Venc. 5-pt velocity encoding has been proposed to address this issue, but the gains in the dynamic Venc range are modest [1]. Previous work demonstrated the benefits of accelerated dual Venc PC VIPR in phantom studies [5] when larger gains in dynamic range are desired, i.e. when imaging flow jets or when measuring velocity fields for peak flow and wall shear stress calculations. It was the aim of this in-vivo study to compare flow measurements derived from different dual venc settings to those obtained with (1) a 4-point balanced and a (2) 5-point velocity encoded PC VIPR acquisition as well as (3) a targeted standard Cartesian 2D phase contrast (2D PC) acquisition. Background: Dual Venc acquisitions can improve the VNR while maintaining dynamic range utilizing (1) a low Venc data set to provide a good VNR and (2) a high Venc data set to identify and correct for velocity aliasing [2, 3]. However, in 4D velocity mapping, this approach significantly lengthens the already long scan duration. For undersampled acquisitions, such as PC VIPR [4], accelerated dual Venc images can be obtained utilizing additional undersampling to capture the high Venc acquisition. Since the high Venc image is only utilized for unwrapping the low Venc small errors from additional undersampling will not influence the final image.