Spiral CT has greater accuracy and specificity than V-P scanning in patients with an unresolved diagnosis and may be useful as the primary screening technique for PE.
Imaging of tumors by using radiolabeled monoclonal antibodies (MoAs) is hindered by the presence of background activity. To reduce this problem, the authors investigated the process of removing labeled MoAs from plasma at selected times by means of extracorporeal immunoadsorption. In seven patients with either lung or breast carcinoma, an indium-111-labeled murine antibody was intravenously administered. Six to 24 hours later, immunoadsorption was performed by passing the patients' plasma through a goat anti-mouse antibody column connected to a plasma separator. Whole-body computer images were obtained before and after the treatment. Blood pool activity in the images was reduced by an average of 59%, while tumor activity dropped by only 10%. Tumor-to-blood activity ratios therefore more than doubled, improving by an average of 121% between the pre- and posttreatment image sets. Eight of 12 areas of known disease and three areas of unknown but later documented disease were detected after the immunoadsorption process, while the three areas of unknown disease and three of the areas of known disease were not detected in the preclearance images. Thus, the feasibility of using extracorporeal immunoadsorption to improve MoA imaging of tumors was demonstrated.
Total-body, lumbar spine, and hip bone mineral density (BMD) scans were obtained in postmenopausal women to examine regional variations in mineralization of trabecular bone. One hundred ninety-nine patients were studied with dual-energy photon absorptiometry (DPA) and/or dual x-ray absorptiometry (DXA). Comparison of BMD at the different sites showed statistically significant correlations (P < .001) among all the sites; however, variations between sites were observed in many patients. Total-body measurements were within normal limits as defined by the system software in 90% of patients with substantial bone mineral loss in the spine or hip. Lumbar spine measurements calculated from the total-body scan differed from the direct measurements by an average of 10% (DPA) and 12% (DXA). These results suggest that site-specific measurements are required to assess regional osteopenia. While total-body scans may be precise and offer the advantage of total-body composition determination, BMD values derived from total-body scans cannot currently replace direct measurements.
Bone marrow is most often the dose-limiting organ in radiation immunotherapy. Controversy exists over optimal methods of estimating radiation dose to bone marrow. The authors compared findings in serial blood samples to findings in bone marrow biopsy samples as measures of bone marrow activity from which to calculate bone marrow dose. Peripheral blood samples and bone marrow biopsy samples were obtained from 11 female patients at 48 and 168 hours after infusion of iodine-131-labeled Mc5 antibody. Bone marrow biopsy data demonstrated markedly decreased specific activity compared with that measured in the peripheral blood. Activities at 48 hours after infusion ranged from 3% to 22% of the peripheral blood activity. These results indicate that activity concentration in the bone marrow is not equivalent to activity concentration in the blood for the Mc5 antibody. These results imply that a dose three to four times that indicated from serial blood samples could be tolerated by patients, provided the antibody-radioisotope does not bind to the marrow.
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