The Effects of Radiometry on the Accuracy of Intensity Based Registration

Besides several other factors, radiometric differences between a reference and a floating image greatly influence the achievable accuracy of image registration. In this work we derive the magnitude of registration inaccuracy coming from changes in radiometric properties. This is done for the example of medical X-ray image registration. We therefore estimate the change of image intensity with respect to object shape, X-ray attenuation of the object material and the initial X-ray energy by modeling a simplified image formation process. The change in intensity is then used to determine a closed form estimation of the resulting registration error, independent from a specific registration algorithm. Finally the theoretical calculations are compared to the accuracy of intensity based registration performed on X-ray images with different radiometric properties. Results show that the herewith derived accuracy estimation is well suited to predict the achievable accuracy of a registration for images with radiometric differences.