Using vascular structure for CT-SPECT registration in the pelvis

The authors outline a method for three-dimensional registration of pelvic CT and ¹¹¹In-labeled monoclonal antibody capromab pendetide (¹¹¹In MoAb 7E11.C5) images using ^99mTc-labeled red blood cell SPECT data. Methods: This method of CT-SPECT registration relies on the identification of major blood vessels in the CT and ^99mTc SPECT images. The vessels are segmented from the image datasets by outlining them on transverse planar slices using a mouse-based drawing tool. Stacking the transverse outlines provides a three-dimensional representation of the vascular structures. Registration is performed by matching the surfaces of the segmented volumes. Dual isotope acquisition of ¹¹¹In and ^99mTc activities provides precise SPECT-SPECT registration so that registration in three dimensions of the ¹¹¹In MoAb and CT images is achieved by applying the same transformation obtained from the ^99mTc SPECT-CT registration. Results: This method provided accurate registration of pelvic structures and significantly improved interpretation of ¹¹¹In MoAb 7E11.C5 exams. Furthermore, sites of involvement by prostate cancer suggested by the ¹¹¹In MoAb examination could be interpreted with the bony and soft tissue (nodal) anatomy seen on CT. Conclusion: This method is a general clinical tool for the registration of pelvic CT and SPECT imaging data. There are immediate applications in conformal radiation therapy treatment planning for certain prostate cancer patients.