AbstractID: 8281 Title: Volumetric Subtraction Angiography: Volume Registration
Our goal is to improve the visualization of the intracranial vasculature during interventional procedures where radiographically dense
objects would normally hinder clinical assessment. We describe our technique of Volumetric Subtraction Angiography (VSA), which removes
bone, metal objects, and associated artifacts from the 3-D contrast-enhanced image of the patient’s vasculature. This work utilizes a prototype
cone-beam computed tomography (CT) system, which acquires 2-D projections with a C-arm mounted x-ray image intensifier. We acquire an
anatomical mask and a contrast-enhanced cone-beam CT (during a 6-s contrast injection into the common carotid artery). Each data set is
reconstructed using a modified cone-beam CT algorithm, producing 3-D images with a 400 micron isotropic voxel spacing. The anatomical mask
is volumetrically subtracted (voxel-by-voxel) from the intra-arterial, contrast-enhanced image, producing a 3-D volumetrically subtracted
angiogram (VSA).
The VSAs of patients who are not anaesthetized may suffer from mis-registration artifacts due to patient motion. 3-D angiograms are
typically displayed using maximum intensity projections, which enhances the artifacts from even a sub-voxel mis-alignment of radiographically
dense metal. Fortunately, these artifacts may be reduced or eliminated by registration using mutual information. A rigid-body transform (3
rotations and 3 translations) and tricubic interpolation is used to align the volumes, with a sub-voxel precision, prior to subtraction.
The resulting VSAs have produced unrivaled images of the patient’s vasculature near radiographically dense objects, providing
superior visualization of the parent vessel and residual aneurysm near clips and coils. Correspondingly, we illustrate the potential of our
technique, in both surgical and endovascular image-guided procedures.