The value of iterative metal artifact reduction algorithms during antenna positioning for CT-guided microwave ablation

Abstract

Objectives: To compare image quality between filtered back projection (FBP) and iterative reconstruction algorithm and dedicated metal artifact reduction (iMAR) algorithms during antenna positioning for computed tomography-guided microwave ablation (MWA). Materials and methods: An MWA antenna was positioned in the liver of five pigs under CT guidance. Different exposure settings (120kV p /200mAs-120kV p /50mAs) and image reconstruction techniques (FBP, iterative reconstruction with and without iMAR) were applied. Quantitative image analysis included density measurements in six positions (e.g., liver in extension of the antenna [ANTENNA] and liver >3 cm away from the antenna [LIVER-1]). Qualitative image analysis included assessment of overall quality, image noise, artifacts at the antenna tip, artifacts in liver parenchyma bordering antenna tip and newly generated artifacts. Two independent observers performed the analyses twice and interreader agreement was compared with Bland-Altman analysis. Results: For all exposure and reconstruction settings, density measurements for ANTENNA were significantly higher for the I30-1 iMAR compared with FBP and I30-1 (e.g., 8.3À17.2HU vs. À104.5 to 155.1HU; p 0.01, respectively). In contrast, for all exposure settings, density measurements for LIVER-1 were comparable between FBP and I30-1 iMAR (e.g., 49.4À50.4HU vs. 50.1À52.5U, respectively). For all exposure and reconstruction settings, subjective image quality for LIVER-1 was better for the I30-1 iMAR algorithm compared with FBP and I30-1. Bland-Altman interobserver agreement was from À0.2 to 0.2 for FBP and iMAR, and Cohen's kappa was 0.74. Conclusion: Iterative algorithms I30-1 with iMAR algorithm improves image quality during antenna positioning and placement for CT-guided MWA and is applicable over a range of exposure settings.

Low-dose CT with tin filter combined with iterative metal artefact reduction for guiding lung biopsy

“…Detailed analysis revealed that using iMAR with tin filtration led to slight artefact reduction in comparison to using a tin filter protocol without iMAR, and that using iMAR with a routine-dose protocol resulted in strong artefact reduction in comparison to a routine-dose protocol without iMAR. Previous studies (13,15,(19)(20)(21) have reported a reduction in metal artefacts from metal needles in CT-guided microwave ablation, metallic thoracic implants, hip prostheses, dental hardware, and spinal implants when iMAR is used, which is consistent with our results for metal needles in lung biopsy.…”

“…During a CT-guided biopsy, iMAR reconstruction can improve the display of lesions when metal artefacts significantly limit their visibility (15). Our results indicated that images obtained with the iMAR algorithm showed a significant decrease in the degree of artefacts compared to images without iMAR.…”

“…Recently, a new dedicated metal artefact reduction postprocessing algorithm-iterative metal artefact reduction (iMAR)-was developed to further reduce metal artefacts, thus improving the visualisation of the biopsy target. iMAR is an efficient technique that can be used in many situations, including for patients with hip prostheses (13), spinal instrumentation (14), and CT-guided microwave ablation (15).…”

Evaluation of the thermal sensitivity of porcine liver in CT‐guided cryoablation: an initial study

“…In further studies this effect is to be evaluated using algorithms for metal artifact reduction. 30,31 This also includes the dual-energy CT monitoring of cryoablation, whose application in a first study showed a better visualization of the cryoablation zone. 15 To achieve a better contrast-to-noise ratio, the energies should be optimized for the respective application.…”

“…The effects of the metal can be one of the reasons for the high standard deviation in the Bland‐Altman analysis. In further studies this effect is to be evaluated using algorithms for metal artifact reduction 30,31 . This also includes the dual‐energy CT monitoring of cryoablation, whose application in a first study showed a better visualization of the cryoablation zone 15 .…”