A contrast-correction method for digital subtraction radiography

A contrast correction method for digital subtraction radiography has been developed. Optical density of radiographs was digitized into gray levels using a drum-scanning microdensitometer with high accuracy. Gray levels of one image are converted to be equal to that of the other image using the equation obtained from gray level relations of both images. The reliability of this method was tested using radiographs of a copper step wedge which was exposed and processed under different conditions. The results show that the minimal detectable difference of the optical density was 0.04 for optimal conditions and 0.05 even for the different conditions. These indicate that the digital subtraction with contrast correction using a microdensitometer may be useful for extracting radiographic changes exclusively and it holds the potential for evaluating periodontal therapy quantitatively.