Quantitative measurement of periodontal bone changes by digital subtraction

The use of an aluminium reference object in radiographical studies permits quantification of periodontal bone changes. A digital subtraction techninque was developed for this purpose. To obtain optimal performance, two corrections have to be applied on the image: one to correct for systematic inhomogeneities such as the Heel‐effect and one to correct for film and development inhomogeneities. With an image processing system these and other necessary manipulations can be carried out easily and quickly. The method was tested on a series of radiographs of phantoms with inserted aluminium cylinders. The determined volumes corresponded well with the actual volumes within the system error. This error was found to be proportional to the surface of the inspected area (0.054 mm1/mm2) . Hence, in longitudinal studies, the method promises to be an accurate and quantitative tool, and it may be able to replace subjective and non‐quantitative observer studies.