Abstract
To evaluate the effects of metal artifact reduction (MAR) on cryoprobe-induced artifact for improvement of therapeutic ice ball visualization in CT-guided cryoablation of musculoskeletal (MSK) metastases. An iterative MAR algorithm (Siemens, Germany) was retrospectively applied to 12 cases of CT-guided MSK cryoablation in 11 patients from November 2016 to August 2017. The final cryoablation CT image with greatest metal artifact caused by the cryoprobe was compared before and after application of MAR. Three experienced interventional radiologists performed a blinded, qualitative evaluation of side-by-side images with and without MAR using a modified 4-point scale (0-3; 0 denotes no artifact, 3 severe artifact). The metal artifact beyond and adjacent to the probe, metallic artifact compromising the ice ball margins, and visualization of critical structures within 1 cm of the margins was scored. Quantitative measurements of CT attenuation (Hounsfield Unit) and standard deviation (noise) were made in four locations: beyond the probe, directly overlying the probe tip, and within and outside of the ice ball margins. Wilcoxon signed-ranks test was used to compare variables. Qualitative analysis showed image quality improvement in MAR images beyond the probe tip (mean score 1.6/0.9, without MAR vs with MAR, p = 0.002), adjacent to the probe (0.8/0.4, p = 0.011), and ice ball conspicuity (1.1/0.5, p = 0.007). There was a trend towards improved visualization of critical structures within 1 cm of ice ball margins (0.8/0.4, p = 0.07). Quantitative analysis confirmed a noise decrease for MAR images beyond the probe (HU 90.5 ± 57.6, 64.8 ± 48.5, without MAR vs with MAR; p = 0.002) and within the ice ball (25.1 ± 8.7, 20.6 ± 7.0; p = 0.008). Noise overlying the probe tip and at critical structures was not significantly improved. MAR provides both qualitative and quantitative improvements for the visualization of the therapeutic ice ball during CT-guided cryoablation of musculoskeletal metastases.
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