A revisit to quantitative PET with ¹⁸F-FDOPA of high specific activity using a high-resolution condition in view of...

With the advent of regenerative/cell therapy for Parkinson's disease (PD), ¹⁸F-FDOPA has drawn new attention as a biomarker of the therapeutic that cannot be evaluated with radiopharmaceuticals for dopamine transporter. Since most previous ¹⁸F-FDOPA PET studies were carried out many years ago with a PET scanner of lower resolution and with ¹⁸F-FDOPA of low specific activity synthesized from ¹⁸F-F₂, we used a newer PET/CT scanner with a high-resolution condition and ¹⁸F-FDOPA synthesized from ¹⁸F-F^- to re-evaluate this technique on normal subjects and patients with PD, together with D₂ receptor imaging with ¹¹C-raclopride (RAC).

PET scans were carried out with ¹⁸F-FDOPA for 120 min and with ¹¹C-RAC for 60 min on 10 patients clinically diagnosed with PD and on 10 normal control subjects. Image reconstruction parameters were optimized with phantom experiments. Graphical analysis and the ratio method for the late-phase images were performed to quantify the striatal uptakes.

The specific activity of ¹⁸F-FDOPA was as high as 4000 MBq/nmol. We empirically determined appropriate reconstruction parameters to obtain high-resolution PET images with enough quantitative accuracy. Both ¹⁸F-FDOPA and ¹¹C-RAC PET showed higher uptake values on normal subjects than those of the previous studies probably due to high-resolution. Quantified ratio values strongly correlated with the graphical values for both tracers. Furthermore, ¹⁸F-FDOPA uptake in the substantia nigra was clearly visualized in most subjects.

Quantitative ¹⁸F-FDOPA and ¹¹C-RAC PET scans using a high-resolution condition are considered to provide essential information for regenerative dopaminergic therapy. Furthermore, the ratio analysis for the late-phase PET scans with ¹⁸F-FDOPA and ¹¹C-RAC enhances the clinical utility of these dopaminergic PET as imaging biomarkers of PD.