A Novel Subtraction Method to Reduce Metal Artifacts of Cerebral Aneurysm Embolism Coils

To investigate a novel subtraction method (S-MAR), combing metal artifact reduction (MAR), virtual monochromatic imaging (VMI), and subtraction CT angiography (CTA) to remove the metal artifacts of coils after endovascular embolotherapy of intracranial aneurysms.

In this retrospective study, 29 patients with 38 coils after endovascular embolotherapy of intracranial aneurysms who underwent cerebral CTA using a dual-layer detector spectral CT were included. Conventional CT images (CI), virtual non-enhanced (VNC) images and VMI ranging from 40 to 120 KeV in steps of 10 were reconstructed. These images were then postprocessed to CI_MAR, VMI_MAR and VNC_MAR with MAR software (O-MAR; Philips Healthcare, Cleveland, OH, USA). The novel subtraction method (S-MAR) was derived from subtraction imaging between VNC_MAR and the optimal VMI_MAR. Contrast-to-noise (CNR) and Noise_(Background) of CI, CI_MAR, VMI, and VMI_MAR were calculated quantitatively. Two Independent radiologists qualitatively assessed artifacts in all images using coil artifact score (CA score), a 5-point Likert scale. Besides, all coils were divided into two groups (group 1: diameter < 5.0 mm, group 2: diameter ≥ 5.0 mm). Differences between two groups were statistically analyzed.

The optimal KeV was 40 KeV. Strong correlations between diameter of coils and the CA score of CI were found (r_s = 0.652, P < 0.05). CNR, Noise and CA score were significantly improved by CI_MAR and VMI_MAR compared with CI (P < 0.05). The S‑MAR showed significantly better performance compared with CI, CI_MAR, VMI, and VMI_MAR in reducing metal coil artifacts according to the CA score (P < 0.05), especially in group 2.

The novel S‑MAR proved to be a promising method to reduce coil metal artifacts and elevate the vessel visualization adjacent to coils. It could develop to be widely used in cerebral CTA after coiled aneurysms.