[Characterization of the volume data of three-dimensional CT and MR angiograms for the delineation of cerebral aneurysms].

Three-dimensional CT angiography and MR angiography with perspective volume rendering were used to investigate two patients with cerebral aneurysms. Compared with the intraoperative photographs, volume data from CT angiogram and MR angiogram were characterized on simulated virtual 3D images with virtual neuro-endoscopic and transluminal imaging techniques. In a case of an unruptured double internal carotid (C2) blister aneurysm, CT angiogram showed a configuration of the distal aneurysm similar to that in the intraoperative photograph, but failed to show the margin of the proximal aneurysm adjacent to the anterior clinoid process bone due to a partial volume effect. The MR angiogram represented both aneurysms and the parent artery, including the C3-C2 internal carotid artery. The whole shape of the aneurysm, however, differed from that in the intraoperative photograph, showing instead an elongation of the aneurysmal dome. In a case of a ruptured tiny middle cerebral artery aneurysm, CT angiogram failed to show the subtle bulging of the aneurysm. In contrast, MR angiogram clearly demonstrated the bulging of the walls at the beginning of the ascending and descending branches of the M2, which is consistent with the aneurysmal convolution observed in the intraoperative photograph. In both cases, transluminal images of the 3D-CT and MR angiograms represented the intraluminal contour of the vessel and aneurysmal walls as a series of rings, and allowed a transluminal view from outside the vessel lumen through the spaces between the rings of the vessel wall. The orifices of the aneurysm and parent arteries were shown through the vessel and aneurysmal walls, providing an extensive perspective view of the angio-architecture of the aneurysm. Morphological configuration of the inner space of the vessel and aneurysm was well visualized on CT angiogram, which was consistent with the operative view. Due to a partial volume effect, the surrounding bony and venous structures overlapped with the aneurysm made them indistinguishable from each other. In contrast, the MR angiogram provided the flow-related volume information, so that dynamics of the flow in the vessel lumen visualized the elongation of the aneurysmal dome and subtle bulging of the tiny aneurysm.