Digitizing of radiographs with a flatbed scanner

Flatbed scanners with the transparency scanning option can be used to digitize radiographs. The physical performance of this type of scanner was studied with regard to the digitizing of radiographs, including the dynamic range, the reproducibility and the homogeneity.

An Artix ArtiScan (Artix Technologies Inc., Milpitas, CA, USA) flatbed scanner with imaging editing software Aldus PhotoStyler (Aldus Corporation, Seattle, WA, USA) was used to digitize a stepped exposure image on Kodak T-MAT G films (Kodak, Rochester, NY, USA). The stepped exposure image was scanned at various locations and with different scanning settings. The pixel values of the resulting digital images were analysed. The stepped exposure image was also scanned by a laser densitometer to measure the optical densities of the steps on the film for comparison.

Using the default scanning settings, the digitized images had pixel values distributed in a narrower range than that of the optical density values of the films. The range of the pixel values was widened by increasing the scanning time. Even then, the resulting pixel value profile was not identical to the optical density profile measured on film. The characteristic curve of this digitizing system was steeper than that of the film. Different pixel value distributions were obtained when the stepped exposure image was scanned at different positions on the scanning field, and when scans were obtained at different times. Reproducible results could be acquired when the images were scanned in the same area of the scanning field without changing the scanning settings and after the power had been on for a few minutes.

In order to obtain digitized radiographs of any reliability from flatbed scanners, these should be carefully calibrated at the operating conditions.