HONOLULU—In addition to cutting them out, zapping them with radiation and poisoning them with toxic chemicals, physicians may one day be able to cook cancer cells to death using high-intensity focused ultrasound. Research under way at the University of Michigan College of Engineering could help bring this promising new technology out of the research lab and into clinical practice by giving physicians the ability to control and precisely focus ultrasound’s ability to heat and destroy tissue.

In a presentation at the Acoustical Society of America meeting Dec. 3, U-M graduate student Youssry Botros described a computational model he developed with co-researchers John L. Volakis and Emad S. Ebbini, which can direct high-intensity ultrasound around solid objects and focus the field’s intensity on small areas one to 15 centimeters deep within tissue.

” Our goal was to demonstrate the efficacy of high-intensity focused ultrasound for use in hard-to-reach areas, such as the liver,” Botros said. ” It is relatively easy to focus ultrasound’s energy on small, deep areas of tissue, but not when the tumor is located beneath solid objects, such as the ribs, which is often the case in liver cancer.”

Similar to microwave radiation, high-intensity ultrasound in the frequency range of 500 kHz to 10 MHz produces heat as it passes through tissue. Researchers at the U-M and other institutions have used ultrasound to heat tissue above the minimum temperature/time threshold required to kill cells. When heating is focused on a small area of soft tissue, effects on the patient are minimal. Ultrasound heating in bone, however, creates intense pain making treatment extremely uncomfortable.

Recent advances in ultrasound technology have produced phased arrays, which use many individual transmitters to produce an intense field of energy at specified locations, according to Volakis, U-M professor of electrical engineering and computer science.

” Phased arrays have many therapeutic advantages, but require optimum placement, operating frequency and level of intensity for each element in the array,” Volakis said. ” Our computational model is used to design the array and guide the ultrasound field through the intercostal spacings between ribs before focusing maximum intensity on a specified area of tissue beneath the ribs.”

To validate their computational model, Botros and Volakis worked with Ebbini, a U-M assistant professor of electrical engineering and computer science, and Philip VanBaren, a U-M graduate student, to develop an experimental test.

Using wooden bars to approximate a rib cage enclosing a hypothetical tumor, the U-M research team used their model to calculate optimum placement and intensity levels using a two- dimensional, 64-element ultrasound array. ” Experimental results were in excellent agreement with the heating pattern generated by the computational model,” Botros said. ” Ultrasound cooked the three-millimeter ‘tumor’ in just a few seconds without damaging surrounding tissue.”

While use of high-intensity focused ultrasound on actual patients is still at least five to 10 years away, Volakis believes the technology could one day be the basis for a new non- surgical treatment for cancer, especially in hard-to-treat areas like the liver.

” Using digitized data from a patient’s MRI scan, physicians could use the computational model to conduct a real-time simulation on the computer. Before the patient even arrives for the procedure, the physician can know the precise location of the ribs, exactly how much energy will be required and where it should be targeted. Because targeted ultrasound is so safe, the actual procedure could be done on an outpatient basis without sedation or post-surgical complications.”

Funding to develop the computational model for ultrasound phased array heating was provided by the U-M Office of the Vice President for Research and the National Institutes of Health.

Acoustical Society of AmericaEmad S. Ebbini