Thermo-mechanical assessment of nanoparticle mixed vascular tissues under pulsed ultrasound and laser heating

During the laser and ultrasound based 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 compare the thermomechanical response of vascular tissues with and without nanoparticles between (a) continuous and pulse mode heating, and (b) focused ultrasound and interstitial laser heating. A 3-D multi-layered and multi-leveled vascular breast tumor model was developed. The present bioheat model incorporates inhomogeneous tissue conditions in the form of non-Fourier time lagging characteristics and complex vascular network of tissue. The radiative transfer, linearized pressure wave, momentum, dual-phase-lag, Arrhenius, and equilibrium equations were solved for the optic, acoustic, fluid, temperature, damage and mechanical fields respectively using the 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 non-Fourier effect on temperature and damage responses of tissue has been revealed more in focused ultrasound based continuous mode heating compared to the interstitial laser based pulse mode heating. With limited tissue temperature rise, the proposed pulse mode heating scheme provides tumor specific ablation sparing the healthy tissues with minimum thermally induced nociceptive pain unlike the continuous mode heating scheme. Further, the presence of nanoparticles and multilevel artery and vein in present tumor model causes significant changes in thermal, damage, and mechanical responses under external heating. The present findings could be beneficial in understanding the role of different heat imposition techniques during the nanoparticle assisted minimally invasive thermo-therapy of cancer.