Interstitial instrumentation for therapeutic ultrasonic heating: modeling the discrete blood vessels

Interstitial ultrasound instrumentation became an important technology in thermotherapy of deep seated or hard to reach by external devices tumors. The instrumentation efficacy strongly depends on focal tissue properties, especially local blood vessels. We evaluate effects of the vessels on temperature distribution elevated from basal by deposition of ultrasound energy. In the proposed model, we take into account several micron diameter blood vessels in proximity to ultrasound four-applicator array. The tissue at large distances from the array is modeled as a volume of modified effective conductivity. Our Finite Element Analysis of so defined problem indicates best agreement between simulation and experiment with the choice of fixed nodal temperature not across the vessel nor the vessel lumen but at 60% of the lumen. We evaluate requirements on the array to avoid local underheating that could lead to performance a failure of the instrumentation.