Inter-laboratory comparison of HITU power measurement methods and capabilities

Abstract

High Intensity Therapeutic Ultrasound (HITU) is gaining in importance among the spectrum of therapeutic options to combat cancer. HITU has already been approved and is in clinical use for the treatment of organs like the prostate, the liver and the uterus. Nevertheless, the metrology of the applied high power ultrasound fields, and in consequence, reliable treatment planning and monitoring, is still a challenge. As part of a European Metrology Research Programme project, the four National Metrology Institutes from the UK, Germany, Italy and Turkey conducted an inter-laboratory comparison of their power measurement capabilities at power levels of 5, 25, 75 and 150 W each at frequencies of 1.1, 1.5 and 3.3 MHz. The task was to measure the total, time-averaged ultrasonic output power, emitted by the circulated transducers under specified electrical excitation conditions into an anechoic water load, and the actual rms transducer input voltage. The output value to be reported was the electro-acoustic radiation conductance including the associated standard and expanded uncertainties. Several different measurement techniques were applied to gain further insight into HITU power measurement. The deviations from the calculated comparison reference value found for the different techniques are discussed and conclusions for the further improvement of measuring procedures are drawn.