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

Objective: 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.

Method: 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.

Results: 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.

Conclusion: 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.