Techniques for performing quantitative measurements of high intensity focused ultrasound intensity distributions noninvasively.

Abstract

Estimation of the HIFU intensity field at clinically relevant power levels can be difficult due to the possibility of hydrophone damage or of sensor interference with the focused beam. To address this issue, we have developed two non‐invasive methods for determining the intensity in free field and in tissue‐mimicking material. In the first method, streaming field generated by the absorption of acoustic energy in liquid is measured using particle image velocimetry. The intensity distribution giving rise to the velocity field is computed by performing the operations of the Navier–Stokes equations upon the experimentally measured streaming field. The second technique (IR thermography) involves the use of an infrared camera to measure the temperature within a tissue‐phantom. An air interface is required at the phantom boundary in order for the IR camera to observe the temperature rise. Quantitative determination of the intensity can be difficult due to the presence of the air interface (at which the intensity is zero), heat conduction within the phantom, and convection currents arising in the air. Mathematical relations that address these complications and allow for intensity measurements have been derived. Intensity fields obtained using both methods will be shown, along with comparisons with hydrophone measurements.