Assessing Thermal Damage During Transcranial Ultrasound: A Simulation Study

Background: For therapeutic applications, it is important to develop a deep understanding of tissue heating and the corresponding tissue thermal response. The present work is concerned with the numerical investigation of the thermal response of tissues in head of rat subjected to ultrasound with aim of opening blood brain barrier. Materials and Methods: Simulations have been performed with finite element software COMSOL Multiphysics v۶.۲. A real rat head structure and biological tissue properties of the head region was considered. Pressure distribution has been calculated by solving the homogeneous Helmholtz equation. The solution of the pressure wave equation has been coupled with Pennes bioheat transfer equation to measure the temperature within the two-dimensional tissue model. Fraction of damage due to temperature increase and fraction of necrotic tissue was measured with the help of Arrhenius equation. The safe and effective condition for opening BBB, ۱MHz frequency, ۰.۲۵ MPa initial pressure and ۶۰s radiation was considered. For validation the temperature increase, an experimental experiment was designed. Results: The maximum temperature increase occurs in the bone region about ۶ °C in result of ۶۰s radiation and the temperature increase in other domains such skin and brain was more less than this amount. Considering that the threshold for thermal necrosis in bone ranges from ۴۷ °C, no significant fraction of damage and necrotic happen. Conclusion: Considering ۴۲ °C as a safe temperature that no measurable effects are observed, tissue temperature was below the damage threshold temperature and tissue damage was measured with the help of Arrhenius equation showed nearly zero damage. So this protocol can be considered safe in terms of thermal damage.

کلیدواژه ها:

Bio-heat Transfer ، COMSOL ، Thermal damage ، Ultrasound