Effects of tissue microstructure on ultrasonic heating with interstitial applicator

Calculated heating rates achieved with an interstitial ultrasonic applicator have been observed to differ significantly with the rates observed in porcine brain. One of the reasons for the discrepancy could have been treatment of the tissue as a homogenous medium, neglecting a microstructure of the tissue. The role of the microstructure is discussed in this presentation. The applicator consisting of a piezoelectric transducer driven in cw mode at about 1.0 MHz attached to a waveguide in the form of G18 spinal needle supplied ultrasound energy into about 288 cm³ samples of normal in vitro and emulsified porcine brain. Hyperthermia of 9-15 K observed in the two types of samples resulted In significantly different heating rates and plateau of temperature. Results of measurements compared with theoretical estimates gave better agreement for emulsified tissue