Iterative Algorithms Applied to Treated Intracranial Aneurysms

Abstract

Purpose: To investigate the impact of iterative metal artifact reduction (iMAR) on artifacts related to neurosurgical clips or endovascular coils when combined to filtered back projection (FBP) or advanced modelled iterative reconstruction (ADMIRE).

Material and methods: In this study 21 unenhanced brain computed tomography (CT) examinations were reconstructed with FBP and level 2 of ADMIRE, both techniques with and without iMAR algorithm, resulting in 4 series per acquisition. Subjective assessment of artifact reduction was performed as a double-blinded evaluation with a 5-point-scale. Objective analysis was performed by comparing central tendencies and distributions of voxel densities. The central tendency was assessed as the mean voxel density in Hounsfield units. The distribution was assessed by evaluating the shape and asymmetry of the histograms of voxels densities with measures of kurtosis and skewness, respectively.

Results: Inter-reader agreement was excellent (>0.8). FBP and ADMIRE without iMAR were scored 4 and with iMAR 5. Unusual artifacts were noted in all of the series reconstructed with iMAR, especially when combined with ADMIRE. Kurtosis revealed statistical differences for all reconstruction techniques (p ≤ 0.0007) except for the association of FBP with iMAR (p = 0.2211) for the coiling population and skewness demonstrated no statistical difference in any population (p ≥ 0.0558), confirming the subjective analysis results, except for the ADMIRE algorithm with or without iMAR (p ≤ 0.0342) in the coiling population.

Conclusion: iMAR led to the reduction in artifacts due to intracranial metallic devices. However, it created a new artifact in the form of a halo of photon-starvation, especially when combined with ADMIRE. The combination of FBP and iMAR seems more suitable, combining the beneficial metal artifact reduction without the emergence of a halo of photon starvation just around the point of interest.

Keywords: Artifacts; Computed tomography (CT); Computer-assisted algorithms; Intracranial aneurysm.