3D computerized occlusion rating of embolized experimental aneurysms using noninvasive 1.5T MR imaging

Abstract

Background and purpose: For embolized cerebral aneurysms, the initial occlusion rate is the most powerful parameter to predict aneurysm rerupture and recanalization. However, the occlusion rate is only estimated subjectively in clinical routine. To minimize subjective bias, computer occlusion-rating (COR) was successfully validated for 2D images. To minimize the remaining inaccuracy of 2D-COR, COR was applied to 1.5T 3D MR imaging.

Materials and methods: Twelve experimental rabbit aneurysms were subjected to stent-assisted coil embolization followed by 2D DSA and 3D MR imaging. Subjective occlusion-rate (SOR) was estimated. Linear parameters (aneurysm length, neck width, parent vessel diameter) were measured on 2D DSA and 3D MR imaging. The occlusion rate was measured by contrast medium-based identification of the nonoccluded 2D area/3D volume in relation to the total aneurysm 2D area/3D volume. 2D and 3D parameters were statistically compared.

Results: There were no limiting metallic artifacts by using 3D MR imaging. Linear parameters (millimeters) were nearly identical on 2D DSA and 3D MR imaging (aneurysm length: 7.5 ± 2.6 versus 7.4 ± 2.5, P = .2334; neck width: 3.8 ± 1.0 versus 3.7 ± 1.1, P = .6377; parent vessel diameter: 2.7 ± 0.6 versus 2.7 ± 0.5, P = .8438), proving the high accuracy of 3D MR imaging. COR measured on 3D MR imaging was considerably lower (61.8% ± 26.6%) compared with the following: 1) 2D-COR (65.6% ± 27.1%, P = .0537) and 2) 2D-SOR estimations (69.2% ± 27.4%, P = .002). These findings demonstrate unacceptable bias in the current clinical standard SOR estimations.

Conclusions: 3D-COR of embolized aneurysms is easily feasible. Its accuracy is superior to that of the clinical standard 2D-SOR. The difference between 3D-COR and 2D-COR approached statistical significance. 3D-COR may add objectivity to the ability to stratify the risk of rerupture in embolized cerebral aneurysms.

Fig 1.

Microsurgical aneurysm creation and 2D DSA occlusion rating of aneurysm No. 3. A, Microsurgical creation of the venous-pouch arterial-bifurcation aneurysm in the rabbit. An artificial arterial bifurcation is created between the right (1) and left (2) common carotid artery. Then a venous pouch (asterisk) is sutured into the bifurcation, mimicking the aneurysm sac. B, 2D DSA anteroposterior view of the partially embolized aneurysm shows the unoccluded part of the aneurysm (red arrow). The small white arrows indicate the longitudinal radiopaque markers of the Neuroform stent. C, The borders of the contrast medium or coil-filled aneurysm parts and the orifice plane are outlined (green). The area filled or refilled by contrast medium within the total aneurysm area is defined on the posttreatment DSA, by using an attenuation-gradient-based distinction (red area within the aneurysm total area).

Fig 2.

3D MR imaging volumetric occlusion rating of aneurysm No. 3. A, Overview: right common carotid artery (1), left common carotid artery (2), and recanalized volume of the aneurysm (red arrow). B, The aneurysm outer border can be well-delineated (red arrow). C, The aneurysm outer border is circled in red. B and C, The embolized part of the aneurysm directly borders the left common carotid artery (white arrow, 2). D, The recanalized part (red arrow) of the aneurysm can be well identified. E, The recanalized aneurysm part is false-color-labeled (red area), and the aneurysm outer border is encircled (red). F, The 3D reconstruction: right common carotid artery, (1) left common carotid artery, (2) false-color-labeled embolized aneurysm volume (yellow), and false-color-labeled recanalized aneurysm volume (green).