Cerebral MR angiography with multiple overlapping thin slab acquisition. Part I. Quantitative analysis of vessel visibility.

Multiple overlapping thin slab acquisition (MOTSA) is a novel time-of-flight magnetic resonance (MR) angiography technique that combines many of the advantages of multiple-section two-dimensional and direct three-dimensional volume methods. To rigorously evaluate the vascular detail that can be obtained with MOTSA MR angiography, the authors have quantified the frequency of visibility of intracranial arterial segments and have correlated their visibility with vessel size as measured at cut-film angiography and with the position and orientation of the arterial segment. Intracranial arterial segments at least 0.9 mm in diameter (the voxel dimension used in the current application) are consistently visualized with the MOTSA technique. The fraction of small vessels visualized is improved when voxel dimensions are reduced. Visibility is noticeably better in the primary images compared with the maximum-intensity-projection (MIP) images. Top-of-slab saturation and resulting decreased vessel intensity occurred infrequently and did not result in marked image degradation in the axial images.