Numerical analysis of heat transfer and hemodynamics in inhibition of stent restenosis by high intensity focused ultrasound hyperthermia.

Objective: High Intensity Focused Ultrasound (HIFU) hyperthermia has the potential to inhibit stent restenosis due to its high efficiency, safety and non-invasiveness. It is crucial to have a good understanding of the characteristics of hemodynamic response and heat transfer in treated tissues for future clinical HIFU hyperthermia.

Methods: An acoustics-thermal-fluid-force coupling model considering acoustic streaming effect and fluid-solid interaction is established to investigate the effects of operating parameters on the hemodynamic characteristics and the temperature distribution in the target region.

Results: Within an appropriate range, a decrease in curvature radius of transducer and increases in both sonication angle and vibration amplitude can increase the hyperthermia temperature effectively. However, the time-averaged wall shear stress near the stent struts in the blood vessel is reduced, which may increase the risk of thrombosis. The ultrasound-induced heat generation reaches maximum at the angle of 90° with the ultrasound beam perpendicular to the stented vessel. The maximum increase in amplitude raises the vessel temperature by 27.49 K. However, this also causes a maximal decrease in time-averaged wall shear stress near the stent struts by 11.76 %, 11.70 % and 18.64 %, respectively. In addition, increasing curvature radius is preferable to achieve a more uniform temperature distribution across the vessel wall, but the lower energy density caused by it may prevent the outer vessel wall from reaching the desired therapeutic temperature.

Conclusions: It is advisable to combine larger curvature radius with increased sonication angles or vibration amplitudes to optimize energy and temperature distribution while minimizing hemodynamic risks.