Undersampled projection reconstruction applied to MR angiography.

Undersampled projection reconstruction (PR) is investigated as an alternative method for MRA (MR angiography). In conventional 3D Fourier transform (FT) MRA, resolution in the phase-encoding direction is proportional to acquisition time. Since the PR resolution in all directions is determined by the readout resolution, independent of the number of projections (Np), high resolution can be generated rapidly. However, artifacts increase for reduced Np. In X-ray CT, undersampling artifacts from bright objects like bone can dominate other tissue. In MRA, where bright, contrast-filled vessels dominate, artifacts are often acceptable and the greater resolution per unit time provided by undersampled PR can be realized. The resolution increase is limited by SNR reduction associated with reduced voxel size. The hybrid 3D sequence acquires fractional echo projections in the k(x)-k(y) plane and phase encodings in k(z). PR resolution and artifact characteristics are demonstrated in a phantom and in contrast-enhanced volunteer studies.