Ultrasound micro-power meter

Abstract

Novel ultrasound imaging procedures such as harmonics imaging and power Doppler imaging have increased the amount of ultrasonic energy deposition into patient body tremendously. Two safety indices, Thermal and Mechanical Indices, have been proposed to address this concern. Accurate value of ultrasound power output is required in order to calculate the indices. Therefore, this give rises to the need for a device that is capable of measuring ultrasound output power quickly and accurately. In this paper, a micro-power meter, a dual chamber heat conduction calorimeter (HCC) is designed, built and tested for the purpose of measuring ultrasonic output power of clinical diagnostic ultrasound devices. The dual chamber heat conduction calorimeter (HCC) is composed of two identical water filled Aluminum wells housed in two separated compartments of an insulated box. The two compartments form the measuring and reference chambers of the calorimeter. The wells are sealed with plastic membranes that constitute the entrance window for the ultrasound. The bottom of each well is stuffed with a 4 cm layer of 0.5 cm thick rubber pads. These pads serve as a sonic-to-heat energy exchanger. A small resistive heater is embedded in both rubber pads for calibration purposes. Heat is measured with a series of Seebeck effect thermoelectric devices (thermopiles) sandwiched between the well and the heat sink surrounding the wells. The output voltage signal from the thermopiles is amplified, digitized, then analyzed and displayed in term of Thermal Index with a PC-based system. The performance and sensitivity of the HCC is tested and measured, initially with the embedded resistive heaters, then with an experimental transducer, and lastly with transducers from clinical ultrasound scanners.