Fig 2. A, Coronal MIP projection from contrast-enhanced MRA shows the supra-aortic arteries with voxel dimensions of 0.7 x 0.6 x 0.8 during 20 seconds. B, Sagittal and axial MIPs from contrast-enhanced MRA (upper row) and TOF-MRA (lower row) show a 20 x 16 mm aneurysm arising from the basilar artery tip. Note the only portion of the aneurysm sac that is visualized on the TOF-MRA study is the superior portion (inflow zone) of the dome (arrows). The loss of signal intensity and incomplete enhancement of the aneurysm sac at TOF-MRA make the full sac size and geometry difficult to perceive.