Subtraction 3D CT angiography with the orbital synchronized helical scan technique for the evaluation of postoperative cerebral aneurysms treated with cobalt-alloy clips

Abstract

Background and purpose: CT angiography (CTA) has been used for the evaluation of intracranial aneurysms and recently has been applied to assess postoperative aneurysms treated with titanium-alloy clips. We investigated the clinical usefulness of subtraction CTA by using the orbital synchronized helical scan technique (OSHST) for evaluating intracranial aneurysms surgically treated with cobalt-alloy clips.

Materials and methods: We scanned an agar gel phantom with a cobalt-alloy clip mounted in the center by using subtraction CT with and without OSHST. Eighteen patients (20 aneurysms) who underwent surgery with cobalt-alloy clips were postoperatively evaluated with subtraction CTA with OSHST, and the results were compared with those from digital subtraction angiography. Two neuroradiologists independently evaluated the 3D CTA images and source images with and without subtraction for the presence of residual flow in the aneurysm and stenotic change in parent or neighboring arteries.

Results: For the phantom study, significantly fewer artifacts from clips were noted on images obtained by using subtraction CT with OSHST than on those obtained without OSHST. For the clinical study, subtraction CTA with OSHST also showed fewer clip artifacts than did conventional CTA. Image quality was poor, and we were unable to diagnose residual neck for 5% (1/20) with subtraction CTA with OSHST and 75% (15/20) with conventional CTA. For evaluation of adjacent vessels, image quality was poor for none (0/20) with subtraction CTA with OSHST and for 55% (11/20) with conventional CTA. For subtraction CTA with OSHST, sensitivity in detecting residual neck was 1.0, and specificity was 0.94. For conventional CTA, sensitivity and specificity were both 0.25.

Conclusions: OSHST is a useful technique for subtracting cobalt-alloy clips, and subtraction CTA with OSHST is available for evaluating aneurysms after clipping with cobalt-alloy clips.

Fig 1.

A cobalt-alloy clip scanned with and without OSHST. A, Control image. B, Second image with OSHST. C, Second image without OSHST. D, Subtraction image (B − A). E, Subtraction image (C − A). The streak artifact generated by the clip is in the same direction as that with OSHST (A and B), and the subtraction image (D) eliminates the artifacts. Subtraction image without OSHST (E) removes the clip itself, but the artifact around the clip remains.

Fig 2.

One-year follow-up of a 46-year-old man who underwent clipping of an aneurysm of the right middle cerebral artery with 2 cobalt-alloy clips. A, Subtraction CTA. B, Conventional CTA. C, 3D DSA with clips. D, 3D DSA without clips. Subtraction CTA (A) and 3D DSA (C and D) represent re-expansion of the aneurysm (arrows). Visualizing the aneurysm on conventional CTA (B) is complicated by a large artifact arising from the clips.

Fig 3.

Two-month follow-up of a 38-year-old man who underwent clipping of a left middle cerebral artery aneurysm with a cobalt-alloy clip. A, Subtraction CTA. B, Conventional CTA. C, DSA of the left internal carotid artery. Conventional CTA (B) represents the pseudostenosis (arrow) at proximal M2 near the clipping site.