Time-resolved and high-resolution MRA in a rabbit model of pulmonary embolism at 7 T: preliminary results

Abstract

Evaluate feasibility of using time-resolved and high-resolution, contrast-enhanced magnetic resonance angiography (MRA) at 7 T for characterization of an animal model of pulmonary embolism. MRAs were performed in five rabbits using a 7-T MR scanner. Preceding the MR studies, each rabbit underwent a pulmonary artery catheterization with balloon placement. Two doses of gadodiamide were injected: first during a time-resolved MRA, immediately followed by a high-resolution acquisition. Balloon was then deflated, permitting reperfusion for 5 min. A second dose was then injected and another high-resolution MRA acquired. Measurements of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and vessel cross-sections down to fourth-order branches were made, among other parameters. Occlusion was detected in all rabbits. Despite a TE of 0.58 ms for the time-resolved MRA, regions of nonuniform enhancement attributed to susceptibility effects at the 7-T field were observed in perfused lung. Mean SNR=7.5+/-3.3 and 134.2+/-46.5 for the lung and aorta, respectively, and mean CNR=126.7+/-46.4 for aorta versus lung were obtained. Diameters of vessels in lung that was never occluded were not statistically different from those in reperfused lung. Results show that time-resolved and high-resolution MRA of the lung are feasible at 7 T and provide high SNR, CNR and resolution, but TEs smaller than 0.58 ms are required to avoid susceptibility artifacts in time-resolved MRAs.