Attenuation correction in single-photon (SPET) and positron emission (PET) tomography is now accepted as a vital component for the production of artefact-free, quantitative data. The most accurate attenuation correction methods are based on measured transmission scans acquired before, during, or after the emission scan. Alternative methods use segmented images, assumed attenuation coefficients or consistency criteria to compensate for photon attenuation in reconstructed images. This review examines the methods of acquiring transmission scans in both SPET and PET and the manner in which these data are used. While attenuation correction gives an exact correction in PET, as opposed to an approximate one in SPET, the magnitude of the correction factors required in PET is far greater than in SPET. Transmission scans also have a number of other potential applications in emission tomography apart from attenuation correction, such as scatter correction, inter-study spatial co-registration and alignment, and motion detection and correction. The ability to acquire high-quality transmission data in a practical clinical protocol is now an essential part of the practice of nuclear medicine.

Transmission scanning in emission tomography

Twenty-four patients with persistent epithelial ovarian cancer after chemotherapy with or without external beam irradiation, were treated with intraperitoneally administered 131I-labeled monoclonal antibodies HMFG1, HMFG2, AUA1, H17E2, directed against tumor-associated antigens. Acute side effects were mild abdominal pain, pyrexia, diarrhea, and moderate reversible pancytopenia. One patient developed a subphrenic abscess requiring surgical drainage. Eight patients with large volume disease, ie, greater than 2 cm tumor diameter, did not respond to antibody-guided irradiation and died of progressive disease within 9 months of treatment. Sixteen patients had small-volume (less than 2 cm) disease at the time of treatment with radiolabeled antibody. Seven patients failed to respond, and of nine initial responders, four patients remain alive and free from disease 6 months to 3 years from treatment. Analysis of the data on relapse indicated that doses greater than 140 mCi were more effective than lower doses. We...

Antibody-guided irradiation of advanced ovarian cancer with intraperitoneally administered radiolabeled monoclonal antibodies.

Abnormal processing of immune complexes (IC) may be important in the pathogenesis of systemic lupus erythematosus (SLE) The clearance of large soluble IC (comprising hepatitis B surface antigen (HBsAg)/anti-HBsAg) radiolabeled with 123I was examined in 12 normal subjects and 10 patients with SLE IC localization was analyzed by static and dynamic gamma-scintigraphy Initial IC clearance from blood was more rapid in patients (median t1/2 = 215 min) than normals (median t1/2 = 515 min) due to more rapid uptake in the liver However, in the SLE group, up to 12% of complexes were released from the liver after 30-50 min Splenic uptake of immune complexes was reduced in the patients and there was reduced ability to retain IC in this organ Plasma complement levels and erythrocyte complement receptor type 1 numbers were reduced in the patients, resulting in defective opsonization of IC and reduced red cell binding in vivo These observations support the hypothesis that IC handling is abnormal in SLE

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Immune complex processing in patients with systemic lupus erythematosus. In vivo imaging and clearance studies.

Twenty-seven patients with brain glioma were scanned using {sup 123}I-labeled monoclonal antibodies against epidermal growth factor receptor (EGFR1) or placental alkaline phosphatase (H17E2). Successful localization was achieved in 18 out of 27 patients. Eleven out of 27 patients were also studied using a nonspecific control antibody (11.4.1) of the same immunoglobulin subclass and observable tumor localization was also achieved in five patients. The specificity of targeting was assessed by comparing images obtained with specific and nonspecific antibodies and by examining tumor and normal tissue biopsies after dual antibody administration. Ten patients with recurrent grade III or IV glioma who showed good localization of radiolabeled antibody were treated with 40-140 mCi of {sup 131}I-labeled antibody delivered to the tumor area intravenously (n = 5) or by infusion into the internal carotid artery (n = 5). Six patients showed clinical improvement lasting from 6 mo to 3 yr. One patient continues in remission (3 yr after therapy), but the other five who responded initially relapsed 6-9 mo after therapy and died. No major toxicity was attributable to antibody-guided irradiation. Targeted irradiation by monoclonal antibody may be clinically useful and should be explored further in the treatment of brain gliomas resistant to conventionalmore » forms of treatment.« less

https://jnm.snmjournals.org/content/jnumed/30/10/1636.full.pdf

Antibody guided diagnosis and therapy of brain gliomas using radiolabeled monoclonal antibodies against epidermal growth factor receptor and placental alkaline phosphatase.

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(96)04451-0.pdf

Therapeutic delivery of proteins to macrophages: implications for treatment of Gaucher's disease

A simplified method of absolute quantitation of activity in any region of the body is presented utilizing a series of views acquired with a scintillation camera linked to a computer. An accuracy of ±6% may be achieved. No additional programming needs to be added to the standard nuclear medicine computer software and a knowledge of the attenuation coefficients involved and the shape or position of the organs examined is not presupposed or estimated. Attenuation correction is performed using a transmission image as one of the sequence of camera views. The phantom measurements used to evaluate the technique are decsribed and some clinical results presented.

J. P. Lavender

Papers

A simplified method of quantitating organ uptake using a gamma camera