Digital subtraction radiography (DSR) is a technique used to determine qualitative changes that occur between two images taken at different points in time. The first image is the baseline image and the second image shows the changes that have occurred since the time the first image was taken. DSR involves subtracting the pixel values from the first image from the pixel values of the second image. The result of the subtraction process is visualization of the changes only because everything unchanged has been removed. In order for images to be subtracted, they need to have the same image projection geometry, receptor placement and file size so that the subtracted image provides the desired information. Reconstruction software has become available to correct placement and image projection geometry to make DSR more feasible for use by clinicians. Also, digital images have standard file sizes and number of pixels in each image, which facilitates the operation.Subtracted images may reveal a continued disease process or demonstrate the effectiveness of a particular treatment. In 1998, Parsell et al. studied various methods to detect oral cancellous bone lesions and found that digital subtraction radiography with or without enhancement improved the likelihood of a correct cancellous defect diagnosis. In another study by Danesh et al., DSR was used to compare radiographic crestal alveolar bone mass and change in clinical periodontal attachment level following guided tissue regeneration. The investigators found strong agreement between digital subtraction radiographic assessment of crestal alveolar bone mass and clinical attachment level. These and other studies suggest that digital subtraction radiography will prove to be a useful tool in the diagnosis and treatment of dental disease.
