High-Intensity Focused Ultrasound (HIFU) Simulations in OnScale

Model Description

OnScale is commonly used for the simulation of high-intensity focused ultrasound (HIFU). With HIFU, ultrasound is focused to a point either by mechanical focusing (a bowl-shaped device) or by electrical steering (a phased array). Mechanical attenuation in the propagating medium causes energy from the ultrasound wave to be lost as heat. The large pressure at the focal region, however, results in the largest temperature rise at that location. Selectively directing the focus to regions of unwanted tissue allows it to destroy solid tumors.

Figure 4. Temperature field at end of CW thermal simulation

OnScale can model both the ultrasound wave propagation and thermal aspects of HIFU. Finite-element (FE) models require a driving force, and thermal models are no different. In the case of a thermal model, the driving force is the energy deposition across the model, as calculated from the mechanical wave propagation. Although this energy deposition and temperature rise could be calculated simultaneously, the significant difference in time scale between thermal and mechanical effects makes such an approach inefficient. Because the mechanical wave propagation occurs on a scale of microseconds and the thermal effects on a scale of seconds (a factor of 1,000,000 difference), the mechanical and thermal models may be decoupled without loss of simulation accuracy. The usual sequence is to run the mechanical ultrasound propagation model to completion and then use the results in a second, thermal model that is run at a different time step. Thus, you need two OnScale input files for this example: one for the mechanical model and another for the thermal model.

Figure 2. Steady state under CW excitation

Typical Outputs from Thermal Analysis

• Temperature rise 
• Displacement 
• Thermal stress

Runtime Statistics

Files

The following input files are required to run this model, click here to download the input files:

Download: 1-3 High-Intensity Focused Ultrasound (HIFU) - Thermal Analysis

Note: Run the acoustic simulation first