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MR Imaging–guided Focused US Ablation of Breast Cancer: Histopathologic Assessment of Effectiveness—Initial Experience¹

¹ From the Department of Radiology, Hôpital Saint-Luc du Centre Hospitalier de l’Université de Montréal, 1058 St-Denis, Montreal, Quebec, Canada H2X 3J4. Received January 15, 2002; revision requested March 15; final revision received September 27; accepted October 21. Supported by a grant from InSightec-TxSonics, Dallas, Tex. Address correspondence to D.G. (e-mail: yvan.boulanger@umontreal.ca).

View larger version (54K): [in a new window]   Figure 1. A, Illustration of the MR imaging-guided focused US (FUS) system for ablation of breast tumors. The patient lies prone on the focused US table inside the MR imaging magnet bore. The transducer is positioned to focus the ultrasound beam inside the breast tumor. The beam produces a temperature increase and coagulation necrosis at the focal point. Multiple sonications allow treatment of the whole tumor volume plus surrounding margins. B, Illustration of the modified focused US ablation system used to treat patients 9-12. The breast is placed in a gel-filled container to improve acoustic coupling.

View larger version (64K): [in a new window]   Figure 2. Coronal T1-weighted MR images (fast spoiled gradient-echo sequence, 36/8, 45° flip angle, 256 x 128 matrix, 31-kHz bandwidth) illustrating the strategy used for MR imaging-guided focused US ablation of a breast tumor. A, MR image shows the outline (polygon in A and C) of the treatment area and the locations of the focused US focal points (circles) to which energy will be applied to coagulate a section of the tumor plus the tumor margins. B, MR image acquired immediately after the application of the focused ultrasound beam shows the location of a focal point where a temperature increase was induced. C, MR image acquired during focused US ablation. The squares indicate the locations of the points that have already been treated.

View larger version (69K): [in a new window]   Figure 3. Two macroscopic sections of a resected breast tumor specimen obtained from patient 6, 2 weeks after MR imaging-guided focused US ablation, show necrosed tissue areas (arrows) and peripheral hemorrhagic areas (red areas).

View larger version (139K): [in a new window]   Figure 4. Histopathologic breast tumor tissue specimens obtained after MR imaging-guided focused US ablation (hematoxylin-eosin stain; original magnification, x25). The cell cytoplasm is pink, the nuclei are dark blue, the fibrous connective tissue (ie, collagen) is yellow, and the red blood cells are bright red. These specimens correspond to different regions of the breast tumor tissue (invasive ductal carcinoma) excised from patient 10, 3 days after MR imaging-guided focused US ablation. A, The epithelial cells are confined to ducts within a lobule. Coagulation necrosis is evident from the shrinkage of some nuclei, the diffuse granular and foamy cytoplasmic degeneration, and the presence of larger cytoplasmic nuclei. B, Necrotic infiltrating cancer cells, endothelial cells, and ductal epithelial cells are seen. Note the obvious loss of cytoplasmic borders, the smudging of the cells, and the marked shrinkage of the nuclei in the neoplastic cells, all of which resulted from necrosis. C, An area where the fibrous stroma is markedly distorted by hemorrhage is seen. The blood vessel lumina are expanded by necrotic debris and red blood cells. In addition, some pink material, which may represent fibrin, is present, indicating local thrombosis. The central tubular structures correspond to a breast duct lined by necrotic cells. D, Some breast ducts lined by thin intact and probably viable (regenerating) myoepithelial cells are seen. All ductal lumina are filled with granular lavender-pink debris from necrotic epithelial cells. The smudged profiles in the fibrous stroma suggest the presence of necrotic invasive carcinoma cells. Infiltrates of acute inflammatory cells are scattered throughout the stroma. Blood vessels are prominent owing to the expansion of red blood cells. Because the biopsy site overlapped with the treatment site, the changes seen represent postbiopsy necrosis, inflammation, and regeneration, as well as focused US treatment effects.

View larger version (30K): [in a new window]   Figure 5. Histogram summarizing the effectiveness of the MR imaging-guided focused US treatments according to the histopathologic results for 12 patients with breast cancer. The percentages of tumor volume in the targeted zone (black bars) and the percentages of necrosed tissue in the targeted zone (white bars) are illustrated. Patients 1-3 were treated with the Mark 1 focused US system protocol, and the remaining patients were treated with the Mark 2 protocol. The numerators and denominators used to calculate the percentages are given in Table 3.