Isotropic High Spatial Resolution Magnetic Resonance Angiography of the Supra-Aortic Arteries Using Two-Dimensional Parallel Imaging (iPAT2) at 3 Tesla

Abstract

We sought to assess the feasibility of isotropic 3-dimensional contrast-enhanced magnetic resonance angiography (MRA) covering the supra-aortic and intracranial arteries with a MR sequence using parallel-imaging in phase- and slice-encoding directions. Six volunteers and 5 patients with suspected cerebrovascular disease were examined at 3.0 T using a 16-element head-neck array. Contrast-enhanced 3-dimensional MRA (repetition time 3.2 milliseconds, echo time 1.2 milliseconds, flip angle 30 degrees , bandwidth 390 Hz/pixel) was acquired with integrated generalized autocalibrating partially parallel acquisition (GRAPPA), in both phase- and slice-encoding direction. Images were evaluated independently by 2 radiologists. Signal-to-noise ratio was calculated from phantom measurements. Signal-to-ratio levels of 8.7 +/- 2.2/48.7 +/- 10.2 with and without parallel-imaging (GRAPPA x 6) were measured, respectively. Scoring of image quality by observer 1/observer 2 on a 4-point-scale (range 0-3) yielded 2.5 +/- 1.0/2.4 +/- 1.0 and 2.1 +/- 1.0/2.0 +/- 1.1 for extracranial and intracranial vessel segments in volunteers and 2.8 +/- 0.6/2.7 +/- 0.7 and 2.0 +/- 1.2/2.1 +/- 1.1 in patients, respectively. The interobserver agreement was excellent (k = 0.82). This study shows that contrast-enhanced MRA, applying parallel-imaging in both phase- and slice-encoding direction (iPAT), is feasible at 3.0 T. Coverage of the carotid and vertebro-basilar circulation was achieved.