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We have introduced a model-based approach to assessing the accuracy of non-rigid registration, without the need for ground truth. The validation experiments, based on perturbing correspondences obtained using ground truth, show that we are able to detect increasing mis-registration using just the registered image data. The results obtained for different sizes of shuffle neighbourhood show that the use of shuffle distance rather than Euclidean distance improves the range of mis-registration over which we can detect significant changes in registration accuracy. More importantly, we should that out method lied in tight correlation with a successful assessment that uses ground-truth annotation. We have shown that all approaches are capable of detecting statistically significant differences in registration accuracy between three different (plausible) approaches to NRR.
We believe that this represents an important advance in the assessment of NRR, because it establishes an entirely objective basis for evaluating the reliability of NRR-based experiments, and for comparing the performance of different methods of NRR. The fact that no ground truth data is required means that the method can be applied routinely. Further work is needed to compare the results obtained using our new approach with those obtained using more sophisticated segmentation-based methods of evaluation. It is also worth using the method to investigate a wider variety of registration algorithms, possibly extending our method to 3D.