The potential role of dynamic MRI in assessing the effectiveness of high-intensity focused ultrasound ablation of breast cancer

Purpose: To retrospectively evaluate magnetic resonance imaging (MRI) features of breast cancer after high-intensity focused ultrasound (HIFU) ablation. Materials and methods: Six patients with invasive ductal carcinomas underwent HIFU ablation. In all patients, dynamic MRI was performed prior to and two weeks after HIFU. Serial follow-up studies were performed. Changes in signal intensity and size of the index tumour in addition to peripheral enhancement patterns were evaluated. Histopathological results were compared with MRI findings. Results: All patients had a single index tumour with a mean size 25.6 mm (range 12 to 37 mm) at the ablation time. In three of six patients, thin rim enhancement around the ablation zone was seen on the subtraction image after first ablation, which showed no change on follow-up MRI. Complete ablation was confirmed by the histopathology (biopsy in two and surgery in one). In the remaining three patients, nodular or irregular thick enhancement was shown on the subtraction image and viable tumour was confirmed by surgery and biopsy in two patients. Conclusion: The MR characteristics of successfully ablated breast cancers included central dark signal intensities with thin rim enhancement on subtraction images. Nodular or irregular thick enhancements should raise concern of partial ablation. We propose MRI plays a critical role in assessing the effectiveness of HIFU treatment.