Threshold behavior of droplet release in automated fluorine-18 fluorodeoxyglucose quality control

This study aimed to investigate the variability in optimal dispensing volume required for reliable droplet release in automated fluorine-18 fluorodeoxyglucose ([18F]FDG) quality control and to identify factors affecting reproducibility. Dispensing behavior was evaluated using an automated quality control system across multiple sessions. Droplet formation and release were assessed at different dispensing volumes under routine operating conditions. Particular attention was given to small-volume dispensing used for semi-quantitative pH paper testing, thin-layer chromatography-based residual Kryptofix testing, and aluminum ion testing. Droplet release reliability was found to be highly sensitive to small differences in dispensing volume. At volumes around 0.011 ml, droplets frequently adhered to the needle tip and failed to reach the target surface. Increasing the volume to approximately 0.013 ml resulted in consistent droplet release. Borderline behavior was observed at intermediate volumes (0.012 ml), with variability depending on syringe and needle characteristics. The optimal dispensing volume exhibited time-dependent shifts, likely associated with changes in syringe condition and surface properties. Reliable droplet release in automated [18F]FDG quality control is strongly influenced by small variations in dispensing volume and system-dependent factors. Careful adjustment and periodic verification of dispensing parameters are essential to ensure reproducibility in routine clinical operations.