Influence of image-capturing parameters on digital X-ray radiogrammetry

The purpose of this study was to evaluate the importance of different image-capturing conditions, which might influence the characteristics of radiographs and, consequently, impact calculations of bone mineral density (BMD) and Metacarpal Index (MCI) using digital X-ray radiogrammetry (DXR). Radiographs of the left hand of deceased males were acquired three times using systematically varied parameters: 4-8 miliamp seconds (mA); 40-52 kV; film-focus distance (FFD); 90-130 cm; film sensitivity, 200/400; and different image modalities (conventional vs original digital radiographs as well as digital printouts). Furthermore, the interradiograph reproducibility using both conventional equipment and printouts vs originals of digital images and the intraradiograph reproducibility (either conventional or digital printouts) were evaluated. All BMD and MCI measurements were obtained with the DXR technology. The interradiograph reproducibility of DXR-BMD using conventional images under standardized conditions (6 mAs; 42 kV; I m FFD; film sensitivity of 200) was calculated to be coefficient of variation (CV) = 0.49% for Agfa Curix film and CV = 0.33% for Kodak T-MAT-Plus film, whereas reproducibility error using digital images ranged from CV = 0.57% (digital printouts; Philips) to CV = 1.50% (original digital images; Siemens). The intraradiograph reproducibility error was observed to be CV = 0.13% (conventional; Kodak film) vs CV = 0.27% (digital printouts; Philips). The BMD calculation was not noticeably affected by changes of FFD, exposure level, or film sensitivity/film brand, but was influenced by tube voltage (CV = 0.99% for Kodak film to CV = 2.05% for Siemens digital printouts). No significant differences were observed between the BMD and MCI data. DXR provides measurements of MCI and BMD with high precision and reproducibility. The measurements are unaffected by all tested image-capturing conditions, with the exception of tube voltage. In addition, different digital image devices clearly have an effect on DXR reproducibility.