Cartesian Acquisition with PR-Like Sampling (CAPR)

Purpose: To combine 2D acceleration from SENSE and homodyne with view sharing to enable time-resolved 3D CE-MRA with isotropic spatial resolution and crisp temporal dynamics for characterization of transient signals. For this a CArtesian Projection-Reconstruction-like (CAPR) acquisition is used. CAPR differs from other accelerated imaging sequences because of the high level of centricity, the temporal compactness of the center of k-space, and the short temporal footprint. It is the goal of this work to describe the technique and show high diagnostic quality images from CAPR sequences adapted to peripheral vascular territories.

Materials and Methods: The CAPR k_Y-k_Z sampling pattern consists of a fully collected central region and an outer annulus of vane-like groups of views with full radial and azimuthal coverage. At each image update the center and a set of vanes is updated. The acquisition between regions is contiguous in time while no individual vane is updated preferentially to others in the set. The parameters of a CAPR N4 sequence were tailored for imaging of the calves with acquired 1mm³ isotropic spatial resolution over a 40×32×13.2cm³ FOV and 4.9s image updates with 19.6s temporal footprint. Additionally, parameters of the sequence were tailored for bilateral imaging of the feet with acquired 0.75×0.75×0.9mm³ voxels with 6.8s image updates and 27.2s temporal footprint over a 30×24×19.8cm³ FOV. All studies were performed at 3.0T following the intra-venous injection of 20ml of gadolinium contrast agent.

Results: Images of the calves attained with CAPR clearly visualize small branching vessels and show high spatial fidelity. In cases which the volunteer exhibited asymmetric L/R flow at the level of the calf, clear arterial frames for both leg were visualized with high image quality and demonstrate the temporal fidelity possible with CAPR. In dynamic series of the feet CAPR allowed characterization of arterial to venous transit of contrast as progressive filling of the major pedal vessel including the plantar arch were visualized over many frames.

Conclusion: CAPR view ordering is readily adaptable to all vascular regions studied thus far and has demonstrated both high temporal and spatial resolution while maintaining the high diagnostic quality often only associated with single phase imaging.