THEORETICAL DESIGN OF A FIXED-FOCUS TRANSDUCER FOR THE ULTRASOUND THERMOTHERPY OF BRAIN

Purpose: Brain tumors are the most difficult ones to treat. The margin between destruction of a tumor and irreversible damage to surrounding tissue is narrow in the brain. Ultrasound could be an effective treatment because of its ability to propagate deep in tissue and generate a temperature rise throughout the tumor while leaving the surrounding normal tissue intact. This study investigates whether cytotoxic temperature could be generated throughout a brain tumor without any undesired overheating at the other sites of the brain.

Methods and Materials: An appropriate fixed focus transducer was designed considering the effective parameters and limitations which are dominant in the case of brain. A real 2 dimensional brain model was constructed from a MR image. A piece of the skull bone has been removed to allow ultrasound to propagate in to the brain. The resultant acoustic pressure was calculated using rayleigh integral. Then the generated temperature elevation was calculated using bioheat equation applying finite element method on the model.

Results: Results demonstrates that a peak temperature of up to 60 degrees centigrade could be obtained in the center of the tumor in 3 seconds of sonication. Also the generated temperature at the post target bone is negligible.

Conclusions: The cytotoxic temperature could be obtained throughout the tumor around 3 seconds without overheating the post target bone. The short treatment time of the procedure could decrease the effect of high blood perfusion. Also because of the sharp focal plane this procedure has the ability to destroy small tumors at primary stages and sharply demarcate the normal tissue from the destroyed tumor cells.