The accuracy of digital radiography in orthopaedic applications

Abstract

Background: Recent advances in technology and the use of image archiving and communication systems (PACS) has led some institutions to abandon conventional plain film radiography and rely solely on digital computed radiography. The level of accuracy of digital radiography in measuring distances for orthopaedic applications is unclear.

Questions/purposes: Is it possible to accurately measure small distances using digital radiographs and PACS software?

Materials and methods: A model for measuring articular step-off was created using a commercially produced radiographic phantom with predetermined markings at known distances. Radiographs were taken using both indirect and direct computed radiography systems, then uploaded to a PACS system. Eighteen observers measured the distance between standardized, preselected points on the radiographic phantom. The measured values were compared with the known values for each measurement.

Results: The mean measured values differed by 0 and 0.1 mm (SD, 0.5 mm) for indirect and direct radiographs, respectively, when measuring short distances and 1.4 mm and 2.6 mm (SD, 1.0 mm) for indirect and direct radiographs, respectively, when measuring longer distances. The intraclass correlation coefficient (ICC) for interobserver reliability was 0.82 for indirect and 0.75 for direct digital radiography. The ICC for intraobserver reliability was 0.94 for indirect and 0.90 for direct digital radiography.

Conclusion: Although the mean measured values were very accurate (within 0.1 mm for a known distance of 3.2 mm), the SD of measurements (0.5 mm) could affect the interpretation of data, especially in clinical situations such as evaluating the quality of fracture reduction.

Fig. 1

The radiographic phantom used in our study is shown. It is composed of a plastic background imprinted with radiopaque lines at fixed, known intervals.

Fig. 2

The distances measured for the indirect digital radiographs are shown.