[A test object for quality control of the instrument for doppler (duplex) ultrasonography, based on the Draft IEC 61685 Standard]

PURPOSE

The authors, forming part of a multicenter project funded by the European Community, summarize the validation of a tissue-mimicking flow Doppler test object and of procedures for testing medical diagnostic Doppler equipment. The results of the project are expected to contribute to a future international IEC Standard concerning flow Doppler test objects (Draft IEC 61685 Standard) and for the European Medical Device Directive (MD 93/42/EEC).

METHODS

Within this project a test protocol was developed that includes a set of different procedures, suitable for checking Spectral and Colour Doppler systems. The performance parameters for describing the image quality as well as the accuracy and the correct functioning of a system are in accordance with the definitions made in the Draft IEC 61685 Standard.

RESULTS

A survey of the design and materials used for this Doppler test object will be presented with a special emphasis on the suitability of the procedures for routine measurement of performance parameters in hospitals.

CONCLUSION

The test object satisfies the requirements of the Draft IEC 61685 Standard. The test procedures in combination with this test object can be used for checking different transducer models with nominal frequencies between 2.5-10.0 MHz.

Development of an example flow test object and comparison of five of these test objects, constructed in various laboratories

Doppler test objects are used to characterise Doppler systems, both stand-alone systems and the Doppler part of so-called duplex scanners. The aim of the project partially presented here is the development and validation of an example of a Doppler test object fulfilling the requirements of the IEC 1685. The project has been carried out by nine partners of five European countries and has been funded by the European Commission. The flow Doppler test object is composed of: tissue mimicking material (TMM), blood mimicking fluid (BMF), tube (embedded in the TMM and carrying the BMF), tank flow system, including a pump and a flow meter. In the normative part of the IEC 1685, requirements are given for the values of acoustical parameters of TMM and BMF such as sound velocity, attenuation and backscattering. For BMF, requirements are given also for values of density and viscosity. In an informative (but not compulsory) annex, a description is given of a flow test object meeting these requirements as an example. 'example test object' developed during the project is composed of TMM based on agar and including SiC- and Al2O3-powders, BMF based on nylon particles suspended in water and glycerine, and a tube of c-flex, a silicon copolymer. Two tube sizes are used: 4.0 mm ID and 8.0 mm ID. During the project, very precise recipes have been developed for the composition and preparation of both TMM and BMF. Based on these recipes and a description of the construction in a design five flow test objects have been constructed in the laboratories of five participants. The test objects have been compared by measurements of the physical parameters and by Doppler measurements of the five test objects with the Doppler system. The measurements have been carried out by five observers. Inter-test object and inter-observer variabilities are determined, yielding information about usefulness of the parameters.