Research Update
Brain waves for ultrasound therapy
CMAJ 1997;157:1012
© 1997 Canadian Medical Association
Say the word "ultrasound" and many people immediately think of diagnostics or prenatal imaging, but Dr. Boguslaw Jarosz, a medical physicist at Ottawa's Carleton University, sees an image in which ultrasound thermotherapy of brain tumours is an outpatient procedure by the next millennium.
Jarosz specializes in medical ultrasound, and while he was conducting research in hyperthermia he realized that ultrasonic needle-like radiators placed in the brain can provide more precise depositing of controlled power in tissues than electromagnetic interstitial thermal therapy. The advantage is that ultrasound radiation can be accurately controlled to the perimeter of a tumour, thus limiting the radiation to the extent of the tumour and not beyond.
At the moment, interstitial methods of thermal therapy for brain tumours remain the alternative to high-risk and intricate surgical removal. But, as Jarosz explains, the true potential of ultrasound radiation is that the energy source can emanate from outside the area of treatment.
Temperature management is critical to the quality of thermotherapy and his current research continues to study the measurement and management of interstitial temperatures in the brain while under the influence of ultrasonic waves. The experiments have led to the development of a brain phantom for test purposes. This "artificial brain," made from laboratory gel, can simulate the brain because it has similar properties of density and conduction. Jarosz is confident the transmission of ultrasonic waves can be focused and contained within a specific area of tissue, but much remains to be learned. Power requirements relating to randomly vascularized tissue and blood flow, for example, are yet to be fully understood.
Another challenge relates to temperature determination for the treatment volume. In the future, a beam of focused ultrasound will be transmitted through the skull and measurements of the phase and amplitude distortions will reveal temperature distribution in specific areas. Jarosz is literally making waves that may have far-reaching benefits; eventually, the trauma of brain surgery may become a thing of the past.
His research has been published in Transactions of Biomedical Engineering (November 1996), published by the Institute of Electrical and Electronic Engineers (IEEE). His paper on "Ultrasonic heating with waveguide interstitial applicator array" was presented at the May 1997 IEEE conference on instrumentation and measurement technology, held in Ottawa. -- © Mark Sunderland
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