The procedure utilizes a focused ultrasound transducer built into a standard MRI apparatus. The patient lies prone on the table with the breast to be treated immersed in a water bath that houses the ultrasound apparatus. MRI is used both to guide the ultrasound apparatus and to assess the extent of the area affected by heating. The amount of tissue affected per impulse depends both on power and on time. At 100 W of power, a 12-sec pulse will destroy a volume of tissue about 4 mm in diameter.
Treatment is done on an outpatient basis under mild conscious sedation.
In addition to standard radiological follow-up, including scans for appearance of metastases, the tumor area is biopsied at six months. Any patients found to have residual tumor are then retreated. Twenty-two patients have been treated with this technique to date. Sixteen of these were considered poor surgical candidates, mainly due to advanced age, while six had refused surgery. The tumors ranged in size from 6 mm to 25 mm.