A NEW FIDUCIAL ALIGNMENT SYSTEM TO OVERLAY ABDOMINAL COMPUTED-TOMOGRAPHY OR MAGNETIC-RESONANCE ANATOMICAL IMAGES WITH RADIOLABELED ANTIBODYSINGLE-PHOTON EMISSION COMPUTED TOMOGRAPHIC SCANS

Background. The use of computed tomography (CT) or magnetic resonance (MR) to overlay or register uptake patterns displayed by single-photon emission computed tomography (SPECT) with specific underlying anatomy has the potential to improve image interpretation and decrease diagno stic reading errors. The authors have developed a method that will all ow the selection of a region of interest on MR or CT images that corre lates with SPECT antibody images from the same patient. This method wa s validated first in phantom studies and subsequently was used on thre e patients with suspected colorectal carcinoma. Methods. Two patients were injected with the technetium-99m-labeled 88BV59 immunoglobulin G human antibody, and the third patient was injected with the iodine-131 -labeled 16.88 immunoglobulin hi human antibody. CT or MR scans were o btained before antibody infusion, and subsequent SPECT scans were obta ined on the first or fourth day after infusion. A customized body cast with landmarks was used for each patient during the CT, MR, and SPECT scans to match slice positions for all scanning modalities. Correspon ding fiducial landmarks were identified on axial images. A computer gr aphics program was written to match and overlay corresponding landmark s for each imaging modality. The image registration accuracy was measu red by comparing fiducial marker separations (center to center) on the registered scans. This separation uncertainty was 1-2 mm for CT-MR an d 3-4 mm for CT-SPECT phantom studies. Results. For patient studies, t he fiducial alignment uncertainty was 3-4 mm for axial CT-SPECT and MR -SPECT images, and 6-8 mm for sagittal CT-SPECT and MR-SPECT images. T he accuracy of the anatomic alignment of the patient and image registr ation system was +/- 1 cm in the medial-lateral axis and +/- 2 cm in t he cranial-caudal direction. Conclusions. This type of image analysis may resolve uncertainties with the anatomic correlation of SPECT image s that otherwise may be regarded as questionable when SPECT is used al one for radioimmunodiagnosis.