High intensity focused ultrasound power measurement based on cross-spectral density technique

Abstract

The purpose of this work was to develop a dependable and safe method of measurement of HIFU fields without mechanical damage to the sensor. The metrology for the applied high ultrasonic power of HIFU has vital importance for patient safety, however it still remains a challenge. Among the measurement methods, radiation force balance and calorimetric buoyancy are frequently used; however, the heating transmission of the target and drift of the balance induce high uncertainties. In this paper, an alternative method is described. Instead of using a balance, the method relies on scanning the ultrasound field in two parallel planes using a hydrophone before the focusing area, which avoids the hydrophone being damaged by high intensities. In addition to the ultrasonic power, the instantaneous intensity can also be determined. In HIFU fields, nonlinear effects will inevitably occur and therefore hydrophone deconvolution is used to account for the pressure pulse distortion caused by its non-uniform sensitivity. The principles and theory behind the cross-spectral density technique is outlined and validation experiments are presented. The uncertainties of the technique proposed are on the order of 10% for intensity measurements. These value maybe further reduced by improving the accuracy of hydrophone sensitivity.