3D pulmonary CT image registration with a standard lung atlas

A 3D anatomic atlas can be used to analyze pulmonary structures in CT images. To use an atlas to guide segmentation processing, the image being analyzed must be aligned and registered with the atlas. We have developed a 3D surface-based registration technique to register pulmonary CT volumes. To demonstrate the method, we have constructed an atlas from a CT image volume of a normal human male. The atlas is registered to new images in two steps: 1) a global transformation, and 2) a local elastic transformation. In the local transformation, the image and atlas volumes are divided into small subimages called cubes. The similarity between cubes in the image and atlas is measured to find the best match displacement vectors. These displacement vectors are processed using Burr's dynamic model to give a smoothed deformation vector for each voxel in the image. This method has been tested by three intra-subject registrations and three inter-subject registrations from four different normal human subjects. The results show that lung surface-based registration can register the internal lobar fissures from the atlas to the image within about 2.73 +/- 2.05 mm for intra-subject registration, and 5.96 +/- 4.99 mm for inter-subject registration. This registration can be used as an initialization for additional segmentation processing.