Technical Report : KUL / ESAT / PSI / 0105 Retrospective correction of the heel effect in hand radiographs July 2001

A method for retrospective correction of intensity inhomogeneities induced by the heel effect in digital radiographs is presented. The method is based on a theoretical model for the heel effect which is derived from the acquisition geometry. Because the heel effect is directly measurable in the direct exposure area only, the image is partitioned first to exclude collimation and diagnostic areas. The parameters of the model are determined by fitting the model to the direct exposure area and the correction is then applied to the whole image. The method iterates between background segmentation and heel effect correction until convergence. We evaluate the suitability of the method on flat field and phantom images and demonstrate its robustness on a database of 137 diagnostic hand radiographs.