Background 18F-Fluoromethyl-choline (18F- FMCH) has recently been used in the detection of tumours with slow glucose metabolism such as cancer of the prostate. However, to get good imaging in the radiopharmaceutical product a low concentration of N, N-dimethylaminoethanol (DMAE) is important.

At the Cyclotron and Radiochemistry Laboratory of the University Hospital of Perugia, F18 is combined with methylcholine to obtain F18-Fluoromethylcholine (18FMCh), used in PET-CT patients with prostate cancer.

Purpose To reduce the final concentration of DMAE and increase the chemical yield

Materials and methods The synthesis is carried out are carried out by an automated procedure (GE Medical Systems TRACERlab FXFN). From the precursor dibromoethane (DBM), using Kriptofix (K222), substitute a Br atom with F18, to get F18-fluorobromomethane (F18-FBM), subsequently purified through 3 cartridges Sep-Pak Silica cartridge. In place of the C-18 and CM plus (Waters) indicated by Shao, an Oasis HLB Extraction Cartridge Plus LP cartridge is then used, previously loaded with DMAE, which reacts with the F18 generating FMCH. Finally, the Oasis WCX is placed in series with the Oasis HLB in order to purify the radiopharmaceutical.

To optimise the yield of the synthesis:

• flow-time of He (32 ml/min) was increased from 10 to 20 min

• the volume of acetonitrile was increased from 3 to 4.5 ml in order to reduce the free volume of the reactor

The changes facilitated the transfer of the intermediate gas present in the reactor to the chromatographic columns.

Finally, to purify the radiopharmaceutical, an Oasis WCX column was used in series with the Oasis HLB.

Results DMAE concentration decreased from 80 ppm to 1.5 ppm and synthesis yield increased from 5% to 16%

Conclusions Since DMAE is a molecule that competes with the cellular uptake of 18F-FMCH reducing its concentration in the radiopharmaceutical synthesised allows us to improve the final imaging sensitivity and quality.

No conflict of interest.