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The consortium relationship at State University of New York at Buffalo School of Medicine and Biomedical Sciences have made it possible to establish in this community a multi-institutional effort to develop positron emission tomography (PET). The type of approach used and the modalities employed to generate community, university, and federal support are presented. The development of PET technology has led to a greater understanding between the various disciplines, and joint efforts have been made to establish pilot projects in a number of research protocols in the clinical applications that are currently available today. The consortium concept has led to early consideration by third-party carriers to consider reimbursement for those established PET procedures that can be applied clinically. Hopefully, with the passage of time and the maturation of a regional PET center, the concepts proposed might be used as models for other installations throughout the country.

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Carrier free [125I]IBZP, R-(+)-8-[125I] iodo-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol), was prepared from the corresponding uniodinated compound by an oxidative iodination reaction with chloramine-T and sodium [125I]iodide. After purification by column chromatography the desired uptake was obtained with a high purity (greater than 95%). The agent showed good localization in brain after i.v. injection in rats, with an uptake of 2.7, 1.2 and 0.8% dose/organ at 2, 15 and 30 min post injection, respectively. The regional distribution in rat brain, as measured by in vivo autoradiography, displayed a high uptake in the caudate putamen, accumbens nucleus and substantia nigra, regions known to have a high concentration D-1 dopamine receptors. The uptake ratio of striatum/cerebellum increased with time; at 30 s and 2 h after injection the ratio was 1.1 and 5.3, respectively. The specific uptake in the D-1 dopamine receptor regions can be blocked by pretreatment with SCH-23390, a selective D-1 dopamine receptor antagonist (SCH-23390). The corresponding iodine-123 (t1/2 = 13 h, gamma energy 159 keV) labeled agent may be suitable for SPECT imaging of CNS D-1 dopamine receptors.

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A new CNS D-2 dopamine receptor imaging agent [125I]IBZM, (S)-3-[125I]-iodo-N-[(1-ethyl-2-pyrrolidinyl)] methyl-2-hydroxy-6-methoxybenzamide, was prepared by either an exchange reaction or by the chloramine-T method. After an i.v. injection, the agent easily passed through the blood-brain barrier and localized in the rat brain. At 2, 15, 30 and 60 min after the injection, the brain uptake was 2.9, 2.3, 1.8 and 0.7% dose/organ, respectively. Regional uptake ratio of striatum/cerebellum (target to nontarget ratio) increased from 1.4 at 30 s to 10.3 at 2 h after the i.v. injection. Digital autoradiography of rat brain sections showed high regional uptake in the caudate putamen and accumbens nucleus, areas known to have a high concentration of the D-2 dopamine receptor. The specific uptake at the D-2 dopamine receptor site was blocked by pretreatment with spiperone, a selective D-2 antagonist. When labeled with 123I (t1/2 = 13 h, 159 keV), [123I]IBZM may be useful for imaging the CNS D-2 dopamine receptor.

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In conjunction with single photon emission computed tomography (SPECT), iodine-123 (123I)-labeled N,N,N'-trimethyl-[2-hydroxy-3-methyl-5-iodobenzyl]-1,3-propanediamine (HIPDM) has been used clinically as a regional cerebral perfusion imaging agent. The [123I]HIPDM can be prepared by a simple aqueous exchange reaction in a kit form. We synthesized unlabeled HIPDM by condensation of 2-hydroxy-3-methyl-5-iodobezaldehyde and N,N,N'-trimethyl-1,3-propanediamine, followed by a sodium borohydride reduction reaction. The kinetics of the radioactive iodine exchange reaction for the preparation of [123I]HIDM is controlled by the pH, the temperature, and the presence of reductant (sodium bisulfite), and oxidant (sodium iodate). The reaction is a second order iodine-iodine exchange with an activation energy of 30.6 kcal/mole. The mechanism of this reaction probably involves the formation of an active 1+ or iodine free radical, which is sensitive to the presence of a reductant, such as sodium bisulfite.

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Bidentate monophosphates--phosphonoacetate (PAA), 2-phosphonoproprionate (PPA), 2-methyl-2-phosphonoproprionate (MPPA), and carbamyl phosphate (CAP)--which are pyrophosphate analogs, were successfully labeled with Sn(II)-reduced [99mTc] pertechnetate in high yield (greater than 95%). Biodistribution studies show that these Tc-99m-labeled monophosphates do localize in bone. At 2 hr after injection, Tc-99m CAP has average femur uptakes of 1.9% in rats and 2.9% in rabbits, which correspond to calculated total-bone uptakes of 38% and 58%, respectively. These are comparable with the femur uptakes for Tc-99m methylene diphosphonate (MDP), which are 1.8% in rats and 2.7% in rabbits. However, the blood clearance rate for Tc-99m CAP was slower than that observed for Tc-99m MDP making the former less desirable for use as a bone-scanning agent. The femur uptakes for Tc99m PAA are 0.9% in rats and 1.2% in rabbits, corresponding to 18% and 24% in total bone, respectively. The PAA derivatives PPA and MPPA have much lower bone uptake. Technetium-99m CAP also concentrates in necrotic myocardium in rats, in amounts comparable to Tc-99m pyrophosphate.

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