Undersampled Projection Imaging for Time-Resolved Contrast-Enhanced 3D MR Angiography (PR-TRICKS)

Contrast-enhanced MRA methods which provide temporal information, such as the 3D-TRICKS technique[1], have tradeoffs between temporal resolution and spatial resolution[2]. Acquiring data with adequate temporal resolution often limits the achievable spatial resolution. It is desirable to have high in-plane resolution along with good temporal resolution. Recently we have shown that angularly undersampled projection-reconstruction imaging can obtain high resolution images of the vascular anatomy in a short imaging time[3]. Two methods used in Ref. [3] involve hybrid acquisitions with projections acquired in the kx-ky plane and Fourier phase encoding in the kz direction. The first (ZIPR) acquires all kz phase encodes at each projection angle, potentially producing azimuthal weighting of the kspace data by the contrast agent passage. The second (PRIZE) acquires all projection angles at each kz phase encoding before moving to the next, producing weighting by the contrast agent curve along the Fourier-encoded kz direction. However, this method can be difficult to time correctly and only produces a single volume of data during the arterial phase. We have combined the undersampled projection technique with the previously described 3D-TRICKS method[1] to obtain high in-plane resolution with good temporal resolution and Fourier weighting (PR-TRICKS). Since projections are acquired in the kx-ky plane, variablerate k-space sampling[1] is constrained to the kz direction. Similar to the PRIZE technique, all projection angles are acquired sequentially at each kz phase encoding before moving to the next phase encoding.