Practical aspects of the use of urethane test objects for ultrasound quality control

Abstract

It has been previously demonstrated that the speed of sound (SoS) and attenuation of urethane test objects decreases with increasing temperature. Our aims were to assess the implications of these findings in routine practice. A urethane test object was cooled to 4°C, and multiple scans obtained during warming to measure the SoS, resolution and low contrast penetration. Images were captured and analysed as the object warmed until the SoS reached that specified by the manufacturer. Biannual performance measurements made in summer and winter were retrospectively compared for 13 scanners to determine the impact of temperature on quality control measurements in routine practice. Images were also captured with the urethane test object at room temperature, using spatial compound imaging to look for blurring. Experimentally, the SoS decreased and low contrast penetration increased as the test object warmed, confirming the temperature dependence of these variables. In the retrospective study, SoS measurements were generally lower in summer than winter, but resolution measurements were unaffected; where data were available, low contrast penetration was greater in summer than winter where a significant difference in SoS had been found. We advise that urethane test objects are stored and used in a temperature-controlled environment and stabilized before use. Even when used at the recommended temperature, differences between the SoS in the test object and that assumed by the scanner causes targets to be blurred when using spatial compound imaging. The clinical efficacy of spatial compounding, therefore, cannot be assessed using a urethane test object.