Utilization of 3-D elastic transformation in the registration of chest X-ray CT and whole body PET

Describes a 3-D elastic transformation which compensates for the non-rigid deformation of the chest that is seen in X-ray CT relative to PET images of the thorax. X-ray CT is widely used for detection and localization of lesions in the thorax. Whole Body PET with 18-FDG is accepted for staging and for measuring tumor response to therapy. The combination of these two modalities to locate metabolically active tumors in CT images should prove to be of significant value in lung cancer staging and treatment planning. Due to the differences in the acquisition conventions and scan duration, the subject's arms are positioned overhead for X-ray CT or at the side for PET, causing a change in the shape of the thorax, requiring non-rigid transformations to achieve proper registration. Techniques to register chest X-ray CT and Whole Body PET images were developed and evaluated. The accuracy of 3-D elastic transformation was tested by phantom study. Studies on patients with lung carcinoma were used to assess the technique for localizing 18-FDG uptake and for correlating PET transmission to X-ray CT images. Results showed that the elastic transformation provided an accurate alignment and reliable correlation of the detailed anatomy of the CT with the functional information of the PET images.