Reduction of variance of observations on pelvic structures in CBCT images using novel mean-shift and mutual information based image registration?

In this paper, Cone-Beam Computed Tomography(CBCT) image data of colorectal cancer patients are considered for registering standard reference locations of bony structures in pelvic region. A solution is provided in this paper to automatically compute and resolve irregularities involved in locating bony structures in the pelvic region. A new algorithm is proposed to automatically locate the lowest 3D coordinates of the Pubic Symphysis (pb) and the Coccyx on a daily basis. The irregularities involved are reduced to minimum by registering CBCT images. The conventional three dimensional mutual information (MI) based registration and a novel mean shift based mutual information techniques are compared. The variations in the position of pelvic region are also compared for unregistered and registered CBCT images. The proposed algorithm, tested on CBCT image data of 25 patients, each taken over a span of 27 days consecutively, provide promising results. The variations in the locations of coccyx, pb, and the distance between them were found to be reduced due to registration of 3D CBCT images.