  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.
