Using vascular structure for CT-SPECT registration in the pelvis

The authors outline a method for three-dimensional registration of pelvic C T and (111)ln-labeled monoclonal antibody capromab pendetide ((111)ln MoAb 7E11.C5) images using Tc-99m-labeled red blood cell SPECT data. Methods: Th is method of CT-SPECT registration relies on the identification of major bl ood vessels in the CT and Tc-99m SPECT images. The vessels are segmented fr om the image datasets by outlining them on transverse planar slices using a mouse-based drawing tool. Stacking the transverse outlines provides a thre e-dimensional representation of the vascular structures. Registration is pe rformed by matching the surfaces of the segmented volumes. Dual isotope acq uisition of (111)ln and (TC)-T-99m activities provides precise SPECT-SPECT registration so that registration in three dimensions of the (111)ln MoAb a nd CT images is achieved by applying the same transformation obtained from the Tc-99m SPECT-CT registration. Results: This method provided accurate re gistration of pelvic structures and significantly improved interpretation o f (111)ln MoAb 7E11.C5 exams. Furthermore, sites of involvement by prostate cancer suggested by the (111)ln MoAb examination could be interpreted with the bony and soft tissue (nodal) anatomy seen on CT. Conclusion: This meth od is a general clinical tool for the registration of pelvic CT and SPECT i maging data. There are immediate applications in conformal radiation therap y treatment planning for certain prostate cancer patients.