CLINICAL FUSION OF 3-DIMENSIONAL IMAGES USING BREMSSTRAHLUNG SPECT AND CT

Infusional brachytherapy for treatment of neoplasms, with colloidal P- 32 has been used to treat Various tumors in the pancreas, liver, brain , rung, and head and neck. In performing such treatments, anatomical v erification of the location of the administered P-32 from the image ob tained by Bremsstrahlung SPECT alone is not possible due to the lack o f internal landmarks, since the radionuclide is distributed only in th e tumor and does not usually accumulate in the normal organs. The purp ose of this study was to provide a practical three-dimensional approac h for image fusion between Bremsstrahlung SPECT and CT. Methods: The t umors in four cancer patients were injected directly with P-32 under C T guidance. A Bremsstrahlung SPECT study using Tc-99m backscatter sour ces to obtain the body contour was then performed. SPECT images were u sed to generate the skin contours using a threshold detection method. A three-dimensional surface was generated from these contours using a tiling program and fused with a corresponding CT surface generated fro m a CT scan in the same patient through an iterative surface-fitting a lgorithm. The three-dimensional surface of the region of high-activity , corresponding to the infused tumor, was then generated using the Bre msstrahlung SPECT data by mapping the iso-count surfaces through a com puter program. The three-dimensional image of the organ then was fused with the registered CT-SPECT datasets. Results: The accuracy of fit m easured as the mean distance between the SPECT and CT surfaces was in the range of 3-4 mm. Conclusion: The anatomical co-registration of Bre msstrahlung SPECT with CT images using the outer surface-fitting algor ithm is a reliable tool. This correlation permits direct anatomic conf irmation of the region of the P-32 activity distribution with the anat omic site selected for injection.