Technical NoteAutomated synthesis of [11C]choline, a positron-emitting tracer for tumor imaging
Introduction
[11C]choline is a radioactive compound we have developed for tumor imaging with PET in patients. It is particularly effective in imaging tumors localized in the brain, lung, esophagus, rectum, prostate and urinary bladder (Hara et al., 1977a, Hara et al., 1977b). The localized tumor is clearly visualized in images reconstructed from data acquired at 5–15 min after injection. The shortness of the time required for acquisition of data has enabled us to perform the [11C]choline PET several times a day by utilizing one or more batches of [11C]choline; if the radioactivity is lost (half-life of 11C, 20 min), it can be supplemented by repeated synthesis. This frequent process of synthesis and PET study is possible only by using the automated 11C-choline synthetic apparatus we constructed.
The characteristics of this apparatus are; (1) easy setup (manual handling), (2) full automation during synthesis and purification, (3) high yield, (4) high purity, (5) high specific activity and (6) complete sterility and complete avoidance of pyrogenicity, theoretically and experimentally, in the final product. This report presents the constitution, operation and performance of the apparatus.
Section snippets
Principle of [11C]choline synthesis
[11C]CO2 is produced by a 14N(p, α)11C nuclear reaction in a cyclotron. When the cyclotron runs for 10 min, the synthetic apparatus is replenished by manual handling for the subsequent operation. [11C]CO2 is transported from the cyclotron to the apparatus and [11C]CH3I is produced in the first reaction vessel by the usual method (Comar et al., 1976). [11C]CH3I is transported to a second reaction vessel and dissolved in dimethylaminoethanol (0.5 ml) at −10°C. On heating the second vessel at 130°C
Performance of the [11C]choline synthetic apparatus
This [11C]choline synthetic apparatus was operated more than 200 times. The performance was always excellent.
[11C]CO2 was produced with a cyclotron, under the following condition: N2 target (99.99% N2); 20 MeV proton beam; 30 μA beam current; 10-min irradiation time. Approximately 26 GBq (700 mCi) of [11C]CO2 was collected in the first reaction vessel. Starting from this radioactivity, and after a 20-min operation of the apparatus, approximately 11 GBq (300 mCi) of [11C]choline chloride was obtained
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