Thermomechanical Assessment of Breast Tumor Subjected to Focused Ultrasound and Interstitial Laser Heating

During laser and ultrasound thermotherapy it is always desirable to have a precise necrosis of deeply seated tumor preserving the adjoining healthy tissue with minimum thermally induced nociceptive pain sensation to the patient. The aim of the present study is to determine the effects of nanoparticle mixed tissues under pulsed and continuous heating during high intensity focused ultrasound (HIFU) and laser interstitial thermal therapy (LITT). The present problem incorporating the tissue thermal relaxation times ( ) was solved in a 3-dimensional multilayered vasculature breast tumor model signifying the complex inhomogeneous tissue structure. The coupled Radiative transfer, Helmontz, momentum, dual phase lag (DPL) and equilibrium equations for optic, acoustic, fluid, temperature and mechanical fields respectively were solved simultaneously using COMSOL Multiphysics (Bangalore, India) software. An in-vitro study on agar based tissue phantom was also performed to validate the present numerical results of focused ultrasound heating. The thermal relaxation times of tissue causes significant changes of thermal and damage history under focused ultrasound heating compared to unfocused laser heating. With limited rise in tissue temperature, the pulsed mode of heating for longer period with lower duty cycle (16.6%) shows a target specific necrotic damage with reduced nociceptive pain in contrast to continuous mode of heating. Further, the presence of nanoparticles and multilevel artery and vein affect both the thermal and mechanical response under external heating. Thus, the present findings could help to understand the role of different external heating modes and sources on tumor necrosis during clinical practice of thermo-therapy.