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Clinical utilization of the multiwire gamma camera (MWGC) requires low-energy radionuclides. The short-lived (9.3 min) tantalum-178 (178Ta) is ideally suited for the MWGC and can be produced from long-lived (21.7 day) tungsten-178 (178W) by a previously reported 178W/178Ta generator. This generator, however, is limited by sharp increase in breakthrough after elution of only 30-60 column-volumes. To optimize the 178W/178Ta generator for clinical use, varying eluant acid concentrations were evaluated. A reduced (from 0.1 to 0.03N) HCI concentration in the eluant, coupled with low operating temperatures (3 to 5 degrees C) allowed high (40 to 60%) 178Ta yield. Minimal 178W breakthrough (less than .01%) resulted, even after elution of more than 200 column-volumes. Each of six tested generators provided sterile, high activity (up to 100 mCi) 178Ta elutions for more than 30 days. Radiation dosimetry was estimated utilizing both human and animal biodistribution data. The whole body (critical organ) dose in adults and neonates were 1/20 (1/21) and 1/19 (1/50) respectively relative to that of technetium-99m (99mTc) as sodium pertechnetate. The optimized 178W/178Ta generator provides a commercially practical, safe source of low-energy radioisotope for the MWGC with substantial dosimetry advantages over 99mTc.

Measurements of dose rate and penetration in water have been made for neutron beams produced by 30--75 MeV protons on beryllium. The effects of Polythene filters added on the target side of the collimator have also been studied. A neutron beam comparable with a photon beam from a 4--8 MeV linear accelerator can be produced with p/Be neutrons plus 5 cm Polythene filtrations, with protons in the range 50--75 MeV. This is a more economical method than use of the d/Be reaction.

There are many radionuclides with a wide range of energies and half-lives available for use as non-sealed radiotherapeutic agents. To date, no single radionuclide has emerged as being clearly superior to all others, in the way that 99mTc predominates in diagnostic imaging. It is unlikely that one will emerge. Instead, if a particular application demands certain decay properties, the radionuclide which will be used will be the one for which appropriate chemistry can be developed and which can be produced and distributed most economically.

Positron emission tomography (PET) can probe biochemical pathways in vivo and can provide quantitative data; for that purpose, tracers labeled with positron-emitting radioisotopes are essential. This report describes the tracers that are being used or that may have future use, their production by cyclotrons, and other needed resources for PET imaging. Current routine and automated methods for convenient production of labeled compounds, coupled with simple computer-controlled accelerators, can support the creation of clinical PET centers in any large medical institution, obviating the need for in-depth research teams. An alternate approach involves the development of regional centers that provide in-house service and that supply fluorine 18- and carbon 11-labeled compounds to nearby hospitals with PET machines.

Wider application of positron emission tomography would be facilitated by the availability of positron-emitting radiopharmaceuticals labeled with nuclides, like 62Cu, that are available from parent/daughter generator systems. Using a longer-lived copper isotope (67Cu) we have examined three derivatives of copper(II) pyruvaldehyde bis(thiosemicarbazone) as potential tracers for evaluation of cerebral and myocardial blood flow: Cu(PTS), Cu(PTSM), and Cu(PTSM2) (where PTS = pyruvaldehyde bis(thiosemicarbazone), PTSM = pyruvaldehyde bis(N4-methylthiosemicarbazone), and PTSM2 = pyruvaldehyde bis(N4-dimethylthiosemicarbazone). All three lipophilic radiocopper complexes were obtained in high yield via a procedure that could be adapted to a "kit" formulation. In animal model systems Cu(PTSM) and Cu(PTSM2) show excellent uptake in the brain and heart following i.v. injection. These tracers differ in that Cu(PTSM) exhibits microsphere-like retention in the brain and heart, whereas Cu(PTSM2) substantially clears from these organs. The relative cerebral pharmacokinetics of [67Cu]Cu(PTSM) and [67Cu]Cu(PTSM2) are consistent with their known reactivity towards intracellular sulfhydryl groups.

A new osmium-191/iridium-191m (191Os/191mIr) radionuclide generator has been developed that offers high 191mIr yield (greater than 20%/ml) and low 191Os breakthrough (less than 5 X 10(-4)%/ml) when eluted with a solution of 0.001 M oxalic acid and 0.9% (normal) saline. This is the first 191Os/191mIr generator that combines the advantages of high 191mIr yield, extremely low 191Os breakthrough, and an eluate that does not require buffering prior to injection. These improvements in performance were accomplished through use of the chelate transdioxobisoxalatoosmate(VI) as the parent complex on the generator. The clinical result of the combination of higher yield and lower breakthrough is a 100-fold decrease in the estimated patient radiation dose compared with the same study performed with technetium-99m (99mTc), and the injectable eluate makes the generator easier to use. Acute and subacute toxicity studies performed on this generator eluate have shown no adverse effects attributable to the eluate.