The role of MRI in the early evaluation of lung microwave ablation.

PURPOSE: To retrospectively investigate the role of a contrast enhanced MRI (ceMRI) performed 24 h after a microwave ablation (MWA) of the lung, in predicting local tumour progression (LTP) and detecting complications compared to an unenhanced CT.

MATERIAL AND METHODS: Forty-nine patients who underwent MWA of 77 lung metastases between 2008 and 2015 were included. All patients received an unenhanced chest CT and a ceMRI (including T2 and ceT1) 24 h after MWA. The conspicuities of the peripheral rim and the ablated tumour were scored using 1-3 scales and compared between examinations. The safety margin was measured directly (both scores ≥2) and indirectly using a subtraction method. The ability of each imaging modality to predict LTP based on safety margin width was analysed using receiver operating characteristic curves. The MRI ability to detect a pneumothorax was compared to CT.

RESULTS: The peripheral rim was best visualised on T2 followed by T1 and CT. The tumour was best visualised on CT, followed by T1 and T2. Direct safety margin measurement was possible on CT, ceT1 and T2 in 68.8%, 64.9% and 27.3% of cases, respectively. Direct CT (AUC = 0.77) and ceT1 (AUC = 0.76) measurements had better diagnostic performance than indirect CT (AUC = 0.72), ceT1 (AUC = 0.70) and T2 (AUC = 0.69) measurements. The MRI sensitivity and specificity for pneumothorax were 60.8% and 87.0%, respectively. Only one pneumothorax >1 cm was missed.

CONCLUSIONS: A ceMRI performed 24 h after MWA of lung tumours has a similar ability to predict LTP and detect important complications as a CT has.