Reduction of Coil Mass Artifacts in High-Resolution Flat Detector Conebeam CT of Cerebral Stent-Assisted Coiling

Abstract

Background and purpose Developments in flat-panel angiographic c-arm systems have enabled visualization of both the neurovascular stents and host arteries in great detail, providing complementary spatial information in addition to conventional DSA. However, the visibility of these structures may be impeded by artifacts generated by adjacent radio-attenuating objects. We report on the use of a metal artifact reduction (MAR) algorithm for high resolution contrast-enhanced CBCT (VasoCT) for follow-up imaging of stent-assisted coil embolization. Materials and methods VasoCT data was acquired in 25 patients that underwent stent-assisted coiling. Reconstructions were generated with and without MAR and were reviewed by three experienced neuroradiologists using a 3-point scale. Results With MAR, the observers agreed that the visibility had improved by at least one point on the scoring scale in more than 40% of the cases (κ = 0.6) and that the streak artifact was not obscuring surrounding structures in 64% of all cases (κ = 0.6). MAR improved the image quality which allowed for visibility sufficient for evaluation in 65% of the cases, and was preferred over no MAR in 92% (κ = 0.9). Significantly higher scores were given with MAR (p < 0.0001). Conclusion Although MAR is not capable of fully removing artifacts caused by implants with high x-ray absorption, we have shown that the image quality of VasoCT data is improved drastically. The impact of the artifacts on the visibility varied between cases, and yet the overall visibility of the contrast-enhanced CBCT with MAR improved in the majority of the cases.

Evaluation of a Metal Artifacts Reduction Algorithm Applied to Postinterventional Flat Panel Detector CT Imaging

“…The first FDCT-adequate MAR algorithm proposed by Prell et al 2 used a nonlinear interpolation procedure to restore corrupted data and has subsequently been shown to decrease metal artifacts of FDCT images obtained for neuroendovascular procedures. 13,14 This finding correlates with the results of the current study in which we show that the MAR algorithm described above significantly lowered the amount of metal artifacts hindering visualization of the intracranial tissues. Another strategy used to successfully reduce metal artifacts in FDCT imaging is to subtract a volume reconstructed from data corrupted by artifacts from an initial uncorrected volume reconstruction without a nonlinear interpolation process to replace the corrupted data.…”

“…An effective means of reducing the metal artifacts caused by metal implants would make FDCT imaging an ideal postprocedural technique to visualize complications such as intracranial hemorrhage, residual filling of aneurysms, or thrombus within newly deployed stents. Several strategies have been proposed to reduce the metal artifacts for conventional multidetector row CT, 13 but these strate-…”

“…Also, data that are completely degraded by severe artifacts, including motion artifacts or conebeam artifacts at the skull base, for example, cannot be recovered by the MAR algorithm. 13 Despite these limitations, the MAR algorithm represents a significant improvement of the FDCT image quality, increasing the value of FDCT as a post-neurointerventional procedure imaging technique.…”

Artifact Reduction of Different Metallic Implants in Flat Detector C-Arm CT

“…Other studies, based on their own versions of a MAR algorithm, have further demonstrated the visualization usefulness of the stent strut and parent vessels in stent-assisted coiling. 9,10 However, the efficacy of the MAR algorithm, as described above in managing different metal objects, has not been reported, to our knowledge. The patients in our study did not undergo FDCT before the operation.…”

“…Further studies based on a previous MAR algorithm 8 have demonstrated the success in coiling and stentassisted coiling FDCT and CT angiography. 9,10 However, the comparison of the efficacy of artifact reduction for various sizes and types of metal objects was seldom discussed. In this study, we investigated whether a MAR prototype software could reduce artifacts stemming from different high-attenuation implants and improve the diagnostic confidence of radiologists.…”