High-intensity focused ultrasound (HIFU) has been investigated as a noninvasive surgical method for the treatment of tumors located in various tissues including brain, prostate, liver, kidney and breast. When the ultrasonic beams emitted from the transducer is focused into the target tissue, the temperature in the focal region rises above 56℃ in a short time, which results in tissue necrosis without damaging overlying or surrounding tissues.
Recent efforts in HIFU research have been focused on the treatment of uterine fibroids. Uterine fibroid is benign neoplasm that occurs in approximately three out of four menopausal women. The incidence rate of this disease in pregnant women is 25%-30%. Several treatment methods currently exist for uterine fibroids but they have some serious shortages. For instance, hormone therapy is a noninvasive method to treat fibroids but if medication is discontinued, fibroids regrow. These show that HIFU therapy is better than others.
Since the most important requirement in the HIFU therapy is safety, the consequences of the therapy must be predicted before treatments of tumors. Thus, a proper model for predicting the temperature distribution by ultrasound source in a human body is needed.
Kim Sang Jin, a researcher at the Faculty of Physical Engineering, has described and simulated geometrical and mathematical models of the thermal coagulation necrosis region caused by HIFU radiation on the human uterus for different types of transducers and frequencies.
He used two models for the HIFU simulation. In one model, only the linear parts in the Westervelt equation was considered, and in the other one, thermal conduction and viscosity were included. He compared the differences in the temperature distribution for both models, varying the shape of transducer and the frequency.
The results show the shape of transducer and the frequency greatly affect the temperature field in the uterine fibroid.
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