Performance Evaluation of a Digital Readout Hyperthermia Range Ultrasonic Wattmeter

Abstract

Abstmct-The accurate measurement of the high levels of radiated power from ultrasound hyperthermia equipment is necessary in order to monitor and compare the performance of such equipment. The fiist such instrument designed to accomplish this has recently been developed, which employs the radiation force principle. In this design the displacement of a 45" angled airbacked target, measured using a linear variable differential transformer (LVDT), provides a direct analog of the radiated ultrasonic power. The power measurement range covers levels from 0.25 W to 50 W with a digital readout resolution of 0.1 W. The instrument calibration was verified using National Bureau of Standards (NBS) traceable transfer standards, and the measurement agreement was within *IO percent. The instrument is a portable sealed system, weighs less than 30 lbs, and can accommodate applicators with entrance beam diameters of less than 10 cm. The general design criteria and measurement features of the device are described; an extensive evaluation is provided of the wattmeter's measurement capability; and some experimental test results performed on two clinical hyperthermia transducers are presented.