Deformation estimated using a multiresolution wavelet representation for adaptive radiation therapy

Registration of planning CT (PCT) images with daily cone beam CT (CBCT) images is an important task for adaptive radiation therapy (ART). Considering that both global and local deformation are existing in image pairs to be registered, estimation of deformation in a coarse-to-fine strategy with the optimization process can prevent convergence into local minima traps. In this paper, deformation is estimated using a multiresolution wavelet representation for medical image registration. The wavelet, being an inherently hierarchical representation of a signal, is naturally suitable for such progressive optimization starting from the low resolution approximation of the signal which represents the global deformation, through the details in its different orientations and ending with the finest details of the signal which represent the local deformation. The experiments on PCT and CBCT images show accuracy and robustness when compared to traditional B-spline based free form deformation (FFD) methods.