Striatal ¹⁸F-DOPA metabolism with PET-CT in patients with and without Parkinson’s disease

Objectives FDOPA kinetics are used for diagnosing Parkinson’s disease (PD). The dynamic PET limits clinical applicability. For standardization of tracer administration, a pump was used at a fixed rate, 5 mL/min for 3 min. PET-CT images were analyzed with Patlak analysis and by calculating uptake-ratios. A database was defined for patients without motor disturbances, and compared to patients without PD.

Methods 10 patients with treated brain tumor, stable (Negative Controls, negC) and 20 patients with tremors, age 31-76, were preloaded with 200 mg Carbidopa, and received 5-10 mCi ¹⁸F-DOPA 1 hr later. CT was for attenuation correction. PET acquisition was 90 min (from injection) for negC and 30 min (starting at 1 hr) for others. As input function (IF) a cerebellar or occipital cortex curve was used. A ‘standard IF’ was obtained by averaging TACs of negC normalized to the area-under-the-curve. Individual IF was derived by scaling standard IF to cerebellar or occipital uptake. VOIs of the striata were defined manually or by thresholding. Patlak analysis was done over 30 min starting at 1 hr. No corrections were applied for partial volume or metabolites. Uptake ratios relative to the cerebellar and occipital cortex were calculated.

Results Normal influx rate (Ki) with PET-CT was different (p<0.05) from historical data with PET-only. Of 20 tremor patients 10 were diagnosed with PD, 3 MSA, and 7 negative (noPD). The noPD patients are similar to negC. Striatal-to-Occipital Ratio (SOR) is as efficient as Ki for PD. The ‘standard IF’ shortens data acquisition by 1 hr and yields similar Ki. Correlation coefficients are higher with an Occipital IF than Cerebellar IF: 0.96 vs 0.88 for the caudate, and 0.96 vs 0.91 for the putamen. The anterior-posterior gradient of the putamen was most sensitive to diagnose PD.

Conclusions A database of Ki & SOR was established for FDOPA metabolism with PET-CT, using tracer delivery via pump, ‘standard IF’ scaled by actual uptake, and Patlak plot or SOR. This procedure permits differentiation of clinical Parkinsonism