DIGITAL SUPERIMPOSITION OF CT AND POSITIVE SPECT TUMOR IMAGES - PHANTOM STUDY AND CLINICAL-APPLICATIONS

Digital superimposition of SPECT and CT data was evaluated in a phanto m and then applied to patient data. Seven patients were studied. Six p atients had pheochromocytomas as evidenced by I-131 or I-123 MIBG loca lization and one had ovarian cancer imaged by In-ill OC125 MoAb. Anato mic or skin landmarks identified the level of each SPECT transaxial sl ice. Both SPECT and CT image data sets were transferred to a minicompu ter connected to an image processor. Afterwards, a scaled, rotated, an d translated realignment was performed. Data for each modality were co ded in different primary colors and then superimposed. Superimposition of phantom data was checked for the absence of distortion of pinpoint and large structures. For suspected tumor sites, superimposition of t he patients' slices were allowed to check for matching SPECT and CT ab normalities to localize a SPECT abnormality without a corresponding CT lesion or to distinguish SPECT abnormalities from those seen on CT. I n one case, the technique failed because of very low I-131 MIBG-tumor uptake. The superimposition decreases false positives in SPECT and bot h false negatives or false positives in CT.