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Determination of position and radius of ball joints

For successful ball-joint replacement surgery, it is important to maintain the joint's geometric center. Pre-operative detection of this center is achieved by detecting the sphere that fits onto the articular surfaces in CT or MRI images. We have developed a novel technique to automatically determine the sub-voxel position and size of a sphere in unsegmented 3D images. The method is invariant to size and robust to noise. It only needs one fourth of a sphere to detect the center. Isotropically as well as anisotropically sampled images can be used. As no segmentation is required, it can be applied directly to clinical images.