MR-guided ultrasound attracts new vendors to clinical space

Much has happened in the year since the FDA approved the first MR-guided ultrasound device for the treatment of uterine fibroids. The pioneers of this new product area, InSightec and its imaging partner GE Healthcare, have launched initiatives to find other clinical applications. One is a pivotal trial of ExAblate 2000 for the treatment of breast fibroadenomas. Another combines two feasibility studies of the safety and efficacy of the device for ablating breast cancers and eliminating brain tumors through an intact skull.

Philips Medical Systems has begun clinical trials of its own MR-guided ultrasound device, one aimed at uterine fibroids, the other at breast lesions. Siemens Medical Solutions has also entered this technology segment, hoping to develop a product in partnership with a Chinese company, Haifu Technology of Chongqing, experienced in focused ultrasound.

The three approaches are similar yet distinct. All capitalize on the strengths of the two technologies involved. Ultrasound is used to focus intense beams of sound energy to destroy lesions, providing a noninvasive alternative to surgery. MR identifies treatment targets by constructing volumetric and cross-sectional images, then quantifies the extent of tissue ablation by calculating thermal maps.

The InSightec/GE and fledgling Haifu/Siemens systems concentrate ultrasound on single points. The devices heat small targets of tissue within a lesion. The Haifu technology, which has been used extensively in China to destroy a range of lesions, focuses energy on a 3 x 1-mm point. The InSightec system focuses on a point about 1 x 3 cm.

In contrast, Philips' technology heats a volume of tissue, such as a lesion. The heating begins in the center and moves outward in a spiral pattern. This approach may decrease treatment time from the current two to three hours to 10 or 20 minutes, according to Dr. Joop J. van Vaals, Philips' director of new business, cardiac and interventional MR.

InSightec hopes to reduce treatment time by expanding the focal point of each ultrasonic blast and reducing the interval between blasts, according to Robert W. Newman, vice president and North American pole manager.

InSightec was the first company to bring MR-guided focused ultrasound to market. With data from clinical trials of more than 1100 women treated for uterine fibroids and a reimbursement code for the procedure, the company has installed ExAblate 2000 in 10 sites and should place another 10 units by the end of the year, Newman said.

The ExAblate 2000 uses the same transducer with 200 phased-array elements for treating uterine fibroids and breast lesions. A similar approach may be used to address pathologies elsewhere in the body. A prototype focused ultrasound unit, using a transducer with about 1000 elements, uses the surface of a patient's head as an acoustic window to create "hot spots" in the brain. The prototype is being tested in an initial safety study of 10 patients with brain tumors at Brigham and Women's Hospital in Boston, Newman said.

The Philips system has 256 phased-array elements for ablating uterine fibroids. Like the InSightec system, it is embedded in the table of an MR scanner. Philips is also developing an arc-shaped breast probe that can be positioned on the side of the breast. Rather than shooting through the breast or along the nipple area toward the breast, the probe would focus radiofrequency waves only at lesions in different areas of the breast, not toward the chest, van Vaals said.

In the last several weeks, Siemens signed an agreement with Haifu Technology to integrate its Model JC Haifu Focused Ultrasound tumor therapeutic system into Siemens MR scanners. Siemens chose Haifu because of its extensive experience with high-energy therapeutic ultrasound. Haifu has tested its focused ultrasound tumor treatment system in about 4500 cases, according to Nealie Hartman, Siemens clinical marketing manager.

Specifications for the Siemens integrated focused ultrasound product and the initial applications to pursue FDA approval have yet to be determined. The overall plan is to integrate the focused ultrasound system in new 1.5T scanners and offer an upgradable unit for existing owners of Siemens MR systems, Hartman said.

In addition to high-energy therapeutic ultrasound units for 1.5T MR scanners, Philips and InSightec are working on devices that can be incorporated into 3T scanners. Philips also is making its ultrasound unit compatible with a 1T open MRI system. All focused ultrasound devices will be upgradable to compatible installed systems, van Vaals said.

All three companies see wider use of MR-focused high-energy ultrasound ahead. Philips wants to broaden clinical applications to the prostate, liver, and brain, possibly targeting the release of drugs or gene expression in molecular imaging. Siemens expects focused ultrasound to be used in the breast and prostate as well as for uterine fibroids, Hartman said.

InSightec is looking at the possibility of expanding current labeling, which allows ExAblate 2000 to be used only in women no longer planning for childbirth. The company would like to apply the device to women who are infertile because of uterine fibroids. The company also seeks to create unique transducers for treating peripheral bone tumors and targeting prostate tumors transrectally.

"Once imaging and localization techniques got better, we started doing lumpectomies of the breast rather than mastectomies to take out only the diseased part of breast tissue and leave everything else. Our vision is that we're going to do same with the prostate," Newman said. "We will have the guidance technology with MR to show the way and a very precise, very localized ability to treat just the cancer and leave the rest of the organ intact."