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

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.