Contrast-enhanced MR angiography of supraaortic vessels: the effect of voxel size on image quality.

BACKGROUND AND PURPOSE Several acquisition strategies may be used for imaging supraaortic vessels by using contrast-enhanced MR angiography. The purpose of this study was to assess the effect of voxel size on image quality of MR angiograms. METHODS Fourty-four patients underwent 3D MR angiography in the coronal plane. Patients were randomly assigned into two groups according to the voxel size of MR angiograms: group 1 referred to a 1.3 x 1.29 x 1.25-mm voxel size and group 2 to a 0.95 x 0.76 x 0.82 mm voxel size. Signal-to-noise ratios (SNRs) were measured and image artifacts were analyzed by consensus between observers. The delineation of the arterial lumen was independently ranked on a four-point scale (1 = not assessable; 2 = poor delineation; 3 = fair delineation; 4 = optimal delineation). RESULTS The overall interobserver agreement for the delineation of the arterial lumen was good (K = .84, P < .0001), with a rank significantly higher in group 2 (68% of arteries graded as 4) compared with group 1 (76% graded as 3). SNRs were significantly higher by using the conventional resolution technique, with a negative correlation between SNRs and artery delineation (P < .0001). Image artifacts, however, were more frequent with the high-resolution technique, including wrap-around artifacts and signal fall-off at the origin of the great vessels. CONCLUSION MR angiograms with a decreased voxel size improve the delineation of cervical carotid and vertebral arteries, despite reduced SNRs and additional artifacts.