Clinical significance of 3D reconstruction of arteriovenous malformation using digital subtraction angiography and its modification with CT information in stereotactic radiosurgery.

PURPOSE: A three-dimensional (3D) reconstruction method of arteriovenous malformation (AVM) nidus from digital subtraction angiography (DSA) in combination with CT and/or MRI was developed, and its usefulness was evaluated in this study.
MATERIALS AND METHODS: The contour of the AVM nidus was delineated on two orthogonal projected DSA images. First, the volume and center of the AVM nidus were calculated in a classic DSA plan using three maximal lengths of the nidus in three perpendicular directions, assuming that the nidus had a prolate ellipsoid shape. Second, in the 3D-DSA plan, the contours of the AVM nidus on the two orthogonal projected DSA images were segmented to be compatible with the slice thickness of the CT image. Assuming that each segment of the nidus has an ellipsoid pillar shape, the volume and center of each segment were calculated. The volume and 3D shape of the nidus were calculated by 3D reconstruction in the 3D-DSA plan. Third, in the CT-DSA plan, the contour based on the segmented DSA was superimposed on the corresponding transaxial CT image slice by slice. The cylindrical shape of the nidus in the transaxial image was modified using the enhanced CT images in the CT-DSA plan. These three planning methods were compared using dose-volume statistics from real patients' data. Eighteen patients with intracranial AVMs in different brain locations who had been treated by radiosurgery were the subjects of this study. To examine the visibility (validity) of the nidus on the CT image, the "nidus" was delineated on an enhanced CT image without DSA superposition in the CT plan and compared with the CT-DSA plan.
RESULTS: The variance in the distance between coordinates determined by the CT plan and those determined by the classic DSA plan was significantly larger than the variance in the CT-DSA plan (p < 0.0001 for lateral, AP, and craniocaudal directions). The difference in the variance was not reduced by the addition of MRI (p < 0.0001 for each direction). The mean volume +/- SD of the nidus calculated was 5.9 +/- 8.0 cm(3) in the classic DSA plan, 4.0 +/- 5.6 cm(3) in the 3D-DSA plan, and 3.6 +/- 5.2 cm(3) in the CT-DSA plan. The 3D-DSA plan significantly reduced the mean nidus volume 31.8% +/- 12.7% from the classic DSA plan (p = 0.0054). The CT-DSA plan further significantly reduced the volume 9.8% +/- 8.8% from the 3D-DSA plan (p = 0.0021). The mean overlapping volume of the nidus between the CT plan and CT-DSA plan was 2.6 +/- 4.3 cm(3) (range 0.17-18.9), corresponding to 63.7% +/- 19.2% (range 11.4-85.3%) of the volume in the CT-DSA plan.
CONCLUSIONS: The superposition of the segmented DSA information on CT was shown to be an important tool to determine the precise shape of the nidus and is suggested to be useful to reduce partial occlusion of the AVM or radiation complications in radiosurgery.