MR-guided ultrasound offers new strategy for uterine fibroids

Patients with uterine fibroids have a new treatment option, which uses MR to guide a high-power ultrasound beam that heats and destroys fibroid tumors. The ExAblate 2000 technology was approved by the FDA in October and showcased at the 2004 RSNA meeting.

"With this therapy, women can be treated as outpatients and quickly return to normal activities. We've been able to see an improvement in symptoms and in their quality of life," said Dr. Elizabeth Stewart, clinical director of the Center for Uterine Fibroids at Brigham and Women's Hospital and co-principal investigator of the clinical study that was instrumental in securing FDA approval of the device.

Uterine fibroids lead to more than 200,000 hysterectomies each year, according to the National Institutes of Health. They are the most common noncancerous tumors among women of childbearing age. ExAblate 2000 could have a major impact on the management of these patients.

The technology might also be used to treat benign breast fibroadenomas, as well as brain, liver, and bone tumors. The ultrasound beam emitted by ExAblate 2000 can destroy diseased tissue in seconds.

"It has remote mechanical guidance that you can use to focus ultrasound energy to a pinpoint within the patient," said Dave Weber, Ph.D., manager of global high-field MR business for GE.

The technology was installed at seven sites as part of its clinical evaluation for the treatment of uterine fibroids. The sites include Brigham and Women's Hospital, the Mayo Clinic, Johns Hopkins University, and several medical institutions in Europe and Israel.

ExAblate 2000 attaches to a standard 1.5T Signa MR scanner, and MR images guide the tightly focused beam to its target. MR thermometry monitors the ablative effects in real-time by detecting phase changes in proton resonance frequency, which are associated with changes in temperature.

The ultrasound beam ablates and destroys abnormal tissue, yet it raises the temperature of surrounding healthy tissue by only a few degrees. This excess heat dissipates through normal body conduction and perfusion.

MR is first used on the morning of the procedure to obtain a full set of pelvic images that help locate the uterus and fibroid tissue. Images are also used to develop the treatment plan, which identifies the area to be heated with ultrasound.

The patient returns to the MR scanner, where she lies prone throughout the procedure. She is awake but mildly sedated as the ultrasound beam is focused repeatedly on specific points in the tumor. MR images taken during each heating cycle visualize the target tissue and quantify the degree of heating.

"The MR images provide not only target identification but real-time feedback to the physician performing the procedure on what the treatment area looks like before, during, and after the heating," said Dr. Clare Tempany, a professor of radiology and director of clinical MRI at Brigham and Women's Hospital.

Up to 100 individual pulses of ultrasound may be delivered over a three-hour treatment, Tempany said. At its conclusion, MR images are acquired with intravenous contrast material to assess the effect of the treatment.

"In our hospital, we have found the learning curve to be very short," she said. "This is really due to the fact that the images guide the physician every step of the way."

The FDA approved the new system for the noninvasive treatment of uterine fibroids in October, four months after the agency's obstetrics and gynecology devices panel recommended its approval. ExAblate 2000 was previously CE-certified in Europe.

GE owns 20% of InSightec, the Israeli company that developed the technology. Elbit Medical Imaging, an Israeli investment firm, owns

54% of the joint venture, and the employees of InSightec own the remainder.