Equipment-independent reference values for dopamine transporter imaging with 123I-FP-CIT

Reliable reference values are helpful to interpret and compare the results of dopamine transporter imaging with SPECT. Since semi-quantitative reference values cannot be easily transferred between imaging equipments, this study aimed to establish equipment independent normal values for the true striatal binding of 123I-FP-CIT.

Specific striatal FP-CIT binding of 6 healthy volunteers and 26 patients with essential tremor were used to generate a reference range by applying an equipment specific resolution dependent factor to compensate for recovery effects. This factor has been determined previously by a series of standardized phantom measurements of an anthropomorphic basal ganglia phantom. Herewith, the resulting DAT binding values represent the expected true specific binding in the striatum.

On average, true specific striatal binding was 5.83 +/- 0.96 in healthy controls, 5.25 +/- 0.67 in patients with essential tremor and 5.36 +/- 0.75 in the entire study cohort.

These preliminary results may serve as a basis for the generation of a generally accepted equipment independent reference range for dopamine transporter imaging with 123I-FP-CIT. By a simple phantom measurement that can be accomplished within one day factors related to specific imaging equipment and processing can be corrected for, resulting in specific binding values which may enable a more standardized interpretation of dopamine transporter scans.