Bolus-Tracked Biphasic Contrast-Enhanced CT Imaging Following Microwave Liver Ablation Improves Ablation Zone Conspicuity and Semi-automatic Segmentation Quality.

Abstract

Purpose: Contrast-enhanced CT (CECT) may be performed immediately following microwave liver ablation for assessment of ablative margins. However, practices and protocols vary among institutions. Here, we compare a standardized bolus-tracked biphasic CECT protocol and compare this with a single venous phase fixed delay protocol for ablation zone (AZ) assessment.

Methods: An institutional review board approved study performed at a specialist cancer centre. A prospective cohort of patients undergoing bolus-tracked biphasic imaging was compared with a retrospective cohort of patients who underwent fixed delay venous phase imaging. AZ conspicuity and segmentation quality were semi-quantitatively scored using Five-point Likert scales. Time between ablation and image acquisition was recorded for each AZ and was correlated to AZ conspicuity and segmentation quality.

Results: Forty patients, median age 59 years (IQR 48-66 years), 24 men, underwent microwave ablation of 68 liver tumours. AZ conspicuity was higher in the bolus-tracked (n = 33) vs. fixed delay (n = 35) cohorts, 4.5 vs. 2.5, P < 0.0001. Commensurate segmentation quality was also higher, 5.0 vs. 3.0 respectively, P < 0.0001. Ordinal regression showed that image quality scores declined by 3-4% for each minute that passes after ablation, particularly for arterial phase images, where regression coefficients were - 0.04, P = 0.007, and -0.03, P = 0.012 for conspicuity and segmentation quality, respectively.

Conclusion: Bolus-tracked biphasic contrast-enhanced CT protocols improve both conspicuity and semi-automatic segmentation quality of microwave liver ablation zones, particularly if imaged soon after ablation.

Evidence-based medicine: Level 2b; exploratory prospective cohort study.