Stanford University

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NEWS RELEASE

10/30/01

Dawn Levy, News Service (650) 725-1944; e-mail: dawnlevy@stanford.edu

Scott awarded Whitaker grant to improve a minimally invasive treatment for breast cancer

Women facing breast cancer often choose treatments aimed at conserving the breast. But minimally invasive treatments such as those using freezing, lasers and ultrasound may result in high rates of tumor recurrence or inadequate treatment of large tumors. Greig C. Scott, Ph.D., a research associate in electrical engineering, has been awarded a $228,001 grant from the Whitaker Foundation to improve another minimally invasive treatment radio frequency (RF) ablation, or tumor reduction using radio waves.

"RF ablation is well established in cardiac treatments as safe and effective," says Scott, one of 38 investigators receiving a total of $8.6 million in grants from the Whitaker Foundation, a private nonprofit dedicated to improving health care though biomedical engineering. "To use this therapy on other organs, doctors need better tools to guide the intervention and visualize the therapy. I want to create these imaging tools with MRI [magnetic resonance imaging]."

The grant will support Scott's work, begun more than 10 years ago while a graduate student at the University of Toronto, to develop a next-generation scanner that employs MRI to improve RF ablation. RF ablation uses electrodes in the form of needles stuck into tumors and pads placed on the skin of a patient's back to pass RF current between electrodes and through tumors targeted for destruction. The technique can directly image these currents and likely will allow doctors to treat larger tumors than they now can with minimally invasive methods.

Breast tissue, with its lobes and ducts and muscle and more, is highly heterogeneous. Electrical current will encounter different levels of resistance (impedance) as it travels through tissues with different densities, including tumors. When current flows through dense tissue, increased resistance causes the tissue to heat up, Scott explains.

"The ablation process will be highly dependent on the electrical impedance of these tissues," Scott says. "We want to ensure that the current is concentrated in the tumor without forming hot spots in healthy tissue in alternate pathways."

The radio frequencies used are in the range of an AM radio channel, so patients do not experience any sensation from the electrical current. Therapeutic RF signals are more than a million times stronger than those received in AM radios.

RF currents, magnetic fields and electromagnetic waves are linked, and Scott's next-generation scanner will make use of those connections.

In MRI, which can image the body in real time, a person is placed in a static magnetic field, and hydrogen nuclei in the body emit radiowave frequencies that are proportional to that magnetic field. In RF ablation, frequencies are set to the same frequencies as hydrogen.

"It turns out that MRI can directly image RF magnetic fields that are tuned to the MRI system," Scott says.

With Senior Research Associate Steven Conolly and engineering and radiology Professor Emeritus Albert Macovski, Scott is developing a new "prepolarized" MRI system in which two inexpensive electromagnets are alternatively pulsed on a high-field magnet boosts the signal, and a low-field magnet reads out the signal. This work is funded by the National Institutes of Health and the National Cancer Institute, and in the past has been funded by California's Tobacco-Related Disease Research Program, the Defense Advanced Research Projects Agency and the Whitaker Foundation.

Cell membranes and structures change the electrical resistance of a tumor hand-in-hand with the frequency transmitted by the ablation electrodes. The prepolarized MRI system can match this frequency by changing its readout field.

MRI will allow direct detection of tumors in a new way that is completely different from today's indirect method of impedance tomography, in which current repeatedly passes through pairs of electrodes and mathematics reconstructs what the resistance values must have been and therefore, where the tumor must be.

MRI already allows pinpoint targeting of tumors. With impedance tomography, resolution, on the order of centimeters, gets worse toward the center of an imaged tumor slice. With MRI, resolution is uniform throughout an image, and doctors can target sites 10 times smaller.

With radiology Assistant Professor Bruce Daniel, Scott is also adding RF transmitter and control electronics to a next-generation interventional scanner. He then will study ways to improve the contrast of images obtained with this system for RF ablation. Scott predicts that it will take at least five years for the technology to be available in clinics.

"We expect these advances to significantly improve the efficacy of RF ablation as a minimally invasive therapy for breast cancer," Scott says. Benefits may include improved design of ablation electrodes and the ability to pre-plan RF pathways for strategic ablation.

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By Dawn Levy

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