Effect of foil material on the apparent yield of the 124Xe(p, x)123I reaction.

The effect of the foil material on the recovery of Xe-123 from the irradiation cell used for the measurement of the production of I-123 from the proton reaction on xenon-124 has been studied. The metal used for the foil can have a significant effect on the amount of Xe-123 which can be cryogenically pumped out of the irradiation cell at 30 min after the end of irradiation. Foils made from several metals and alloys were tested. Of these, the effect is most pronounced with "Havar" alloy foil where only 58% of the theoretically available activity was recovered. This effect should be considered and tested in the measurement of reaction cross-sections in irradiation cells and targets which have metal foils.

An improved synthesis of the inert, diffusible blood-flow tracer, [18F]fluoromethane.

An improved procedure for producing [18F]fluoromethane ([18F]FM) in batches of several hundred mCi is reported. 18F prepared by the 18O (p, n) 18F reaction in a H2(18)O target is trapped on a small column of Dowex 1 (x 10) resin to allow recovery of H2(18)O. One new feature is elution of 18F- from the column with 3 mL of CH3CN containing 67 microL 1.5 M aqueous (Bu)4N+ OH-, after residual H2(18)O has been removed with dry CH3CN. This 18F- solution reacts with CH3I in the presence of Ag2O directly to give [18F]FM, which is swept out of the reaction vessel with a stream of air, from which CH3I and other vapors are removed with a C18 SEP-PAK at room temperature. Another new technique is trapping of [18F]FM on a second SEP-PAK cooled in ethanol/dry ice. After warming the SEP-PAK to room temperature, the trapped [18F]FM can be recovered with either H2O or air. The improvements speed the preparation and minimize hands-on operations. The product has no detectable radiochemical impurities, and a specific activity of greater than 1 Ci/mumol. Non-radioactive CH3CN, CH3I and CH3OH are present at less than 0.2 mumol per batch.

MR-PET image coregistration for quantitation of striatal dopamine D2 receptors.

PURPOSE: Our goal was to assess the utility of MR-PET image coregistration to quantify dopamine D2 receptors in striatum. METHOD: Twenty-nine normal subjects were investigated with PET and [11C]raclopride and with MRI. D2 receptors were quantified using the ratio of the distribution volume in striatum to that in cerebellum. Measures obtained using regions selected directly from the PET images were compared with those obtained from MR images and then projected to coregistered PET images. RESULTS: There were no differences between measures selected from the PET images (3.9 +/- 0.5) and those from the MR images (3.9 +/- 0.65). The values for these two measures were significantly correlated and corresponded to r = 0.9, p < 0.0001. CONCLUSION: Regions of interest selected directly from PET images, where there is a large contrast between the region of interest and background, as for the case of dopamine D2 ligands, are almost identical to those obtained from coregistered MR images.