Automated transducer testing and calibration with a dynamic phantom

Variation in transducer array performance for biomedical imaging and non-destructive testing (NDT) is inherent in manufacturing, and performance degradation also occurs when the devices are in service. It is already straightforward to determine basic device functionality through transmit and receive sensitivity measurements and from electrical impedance. However, this requires special equipment and procedures likely to be inaccessible to end users. Nevertheless, validation of transducer performance is of increasing importance as the use of array systems grows for NDT and for medical diagnosis and treatment management by non-specialist users. Our objective here was to produce an automated system for array validation through calculation of the resolution integral (RI). The dynamic phantom that has been developed is based on imaging two filamentary targets positioned in a tank of liquid tissue-mimicking material under computer control. The mechanism for this is reliable and inexpensive, with the filaments coupled magnetically through the tank wall. Images are captured and analysed to assess targets resolution in an automated feedback loop. The new phantom has been tested on a total of 18 imaging systems in clinical use. Results were repeatable and consistent when compared with those produced with more conventional techniques. Furthermore, RI calculation successfully differentiated recent, high quality scanners from others and also differentiated linear flat and convex probes and phased arrays. The dynamic phantom thus offers assessment of ultrasound imaging systems quantitatively for purchasing decisions, delivery acceptance and on-going quality assessment. With further work, it will be developed to test systems rigorously and to benchmark them for comparison and prior to introduction to service.