Fast contrast‐enhanced imaging with projection reconstruction

Abstract

The use of contrast agents has lead to great advances in magnetic resonance angiography (MRA). Here we present the first application of projection reconstruction (PR) to contrast‐enhanced MRA. In this research the limited angle projection reconstruction trajectory is implemented to acquire higher resolution images per unit time than with conventional Fourier transform (FT) imaging. It is well known that as the field of view (FOV) is reduced in conventional FT imaging, higher resolution per unit time can be obtained, but aliasing may appear as a replication of outside material within the FOV. The limited angle PR acquisition also produces aliasing artifacts. This method produced artifacts that were unacceptable in x‐ray CT but that appear to be tolerable in MR angiography. Resolution throughout the FOV is determined by the projection readout resolution and not by the number of projections. As the number of projections is reduced, the resolution is unchanged, but low‐intensity artifacts appear. This thesis presents the outcome of using limited angle PR for contrast‐enhanced angiography. 3‐D volume images of the renal arteries, carotic arteries and pulmonary vessels were obtained with 512 readout resolution, about 128 projections and 32 slice encodings. This provided in‐plane resolution of 0.5×0.5 mm in a 24 s scan for the carotic arteries; resolution of 0.8×0.8 mm in a 17 s breath‐hold for the pulmonary vessels; and resolution of 0.8×0.8 mm in a 24 s breath‐hold for the renal arteries. These images have about four times greater resolution than conventional FT images acquired in equal scan time.