B-spline interpolation for bend intra-oral radiographs

Digital subtraction radiography (DSR) has been demonstrated to improve the detection of minute bone changes during the diagnosis of Periodontal diseases. However, during a dental X-ray session, it is not possible to control the bending of the X-ray film when installed in a patient's mouth. This leads to errors in the subsequent analysis. Error compensation can be done by a warping transformation, in conjunction with a reference wire grid attached to the X-ray film. However, the wire grid has to be attached to the film manually. The grid itself is a source of error in that it obscures the image and causes information loss. In this paper we propose a compensation method without the use of a reference grid. It is a simple algorithm based on B-spline interpolation and image scaling. No prior information about the bending is required. When compared with warping transformation, the method induces less disturbance to the pixel values during the compensation process. As a result, the proposed method produces more accurate image data for subsequent analysis.