MR Imaging–guided Focused US Ablation of Breast Cancer: Histopathologic Assessment of Effectiveness—Initial Experience

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Abstract
To evaluate the effectiveness of noninvasive magnetic resonance (MR) imaging-guided focused ultrasonographic (US) ablation of breast carcinomas. Before undergoing tumor resection, 12 patients with invasive breast carcinomas were treated with MR imaging-guided focused US ablation consisting of multiple sonications of targeted points that were monitored with temperature-sensitive MR imaging. The patients were treated with either one of two focused US systems. The effectiveness of the treatment was determined at histopathologic analysis of the resected mass that was performed to determine the volumes of necrosed and residual tumor. Complications resulting from the procedure were assessed by means of questionnaires, medical examinations, and MR image analysis. US ablation was well tolerated by the patients, and with the exception of minor skin burns in two patients, no complications occurred. Histopathologic analysis of resected tumor sections enabled quantification of the amount of necrosed and residual tumor and visualization of the surrounding hemorrhage. In three patients treated with one of the US systems, a mean of 46.7% of the tumor was within the targeted zone and a mean of 43.3% of the cancer tissue was necrosed. In nine patients treated with the other US system, a mean of 95.6% of the tumor was within the targeted zone and a mean of 88.3% of the cancer tissue was necrosed. Residual tumor was identified predominantly at the periphery of the tumor mass; this indicated the need to increase the total targeted area (ie, with an increased number of sonications). Thermal coagulation of small breast tumors by means of MR imaging-guided focused US appears to be a promising noninvasive ablation procedure.