Magnetic resonance imaging evaluation after radiofrequency ablation for malignant lung tumors

Objective: The objective of this study was to investigate magnetic resonance imaging (MRI) assessment of the therapeutic response in small lung malignancies (<3 cm) immediately after radiofrequency ablation (RFA). Materials and Methods: This is a retrospective analysis of MRI performance in 24 cases of small lung tumors (16 primary, 8 metastatic; 20 patients) immediately, post-RFA, and at follow-up. Variables measured included maximum diameters of tumors on pre-RFA MRI, central areas of low signal intensity (SI) on post-RFA T2-weighted images (T2WIs), and central areas of high SI on post-RFA T1WIs. Additional post-RFA measurements included the maximum diameters for areas of ground-glass opacities (GGOs) on computed tomography (CT), high SI on T2WIs, and isointense SI on T1WIs. Mean values were used for statistical analysis. Results: Before RFA, 16 primary and seven metastatic lung tumors showed isointense signals on T1WIs and hyperintense signals on T2WIs. Immediately after RFA, the ablated lesions showed central low signals and peripheral high annular signals on T2WIs and central high signals and peripheral annular isointense signals on T1WIs, with reduced SI on diffusion-weighted images. Significant differences were found between the preoperative MRI maximum tumor diameter and post-RFA diameters of central low SI areas on T2WIs and central high SI areas on T1WIs. Furthermore, there were significant differences between the post-RFA maximum diameter of circumferential high signals on T2WIs and the post-RFA maximum diameters of both GGOs on CT and circumferential isointense signals on T1WIs. There were three cases of local recurrence (two pulmonary metastases and one primary) during follow-up. Conclusions: MRI evaluation of the therapeutic response of RFA for small malignant lung tumors (<3 cm) was precise and reliable.