Development of the ultrasound power meter for therapeutic applications

The total output power from a medical ultrasound transducer has to be measured due to various reasons but in general they are related to patient safety and assessment of performance. The objective of this work was to develop an ultrasound power meter to measure a total output power from therapeutic ultrasound devices. The implementation of this work utilizes a radiation force balance technique based on the method recommended in the International Electrotechnical Commission (IEC 61161). Ultrasound therapy unit and its transducer were used as an ultrasonic source. To verify the performance of the developed system, the ultrasonic power measurement results from our developed ultrasound power meter were compared with those from the commercial ultrasound power meter (UPM) at 5 nominal intensity values (0.5 W/cm 2 , 1 W/cm 2 , 1.5 W/cm 2 , 2 W/cm 2 , 3 W/cm 2 ) with three frequencies, 0.86 MHz, 2 MHz and 3 MHz, and four different output pulse modes; continuous wave (100% duty cycle), 1:2 (50% duty cycle), 1:5 (20% duty cycle) and 1:10 (10% duty cycle). The results show that the developed system is currently able to determine the ultrasonic output power in the frequency range from about 1 MHz to 3 MHz, and in the power range from 100 mW to approximately 15 W. Current efforts are being made to focus on testing the performance of the developed ultrasound power meter by comparing the results from the developed system with those from the standard system at the National Institute of Metrology, Thailand (NIMT) and developing a three axis positioning system with computer control for the alignment of the ultrasonic transducer.