FDOPA metabolism in the adult porcine brain: influence of tracer circulation time and VOI selection on estimates of striatal DOPA decarboxylation

Different methodologies for PET data analysis influence the magnitude of es timates of blood-brain transfer coefficients and rate constants for the met abolism of FDOPA in living striatum. We now test the effects on several kin etic parameters of automatic procedures for volume of interest (VOI) select ion. We also tested the sensitivity of the estimates to dynamic frame seque nce duration, and produced a standard method for minimizing the variations in physiological estimates for FDOPA kinetics in minipig brain. We used min ipigs because our previous work has shown them to provide an appropriate an imal model for study normal and pathological cerebral DOPA metabolism using PET. Time-activity curves in striatum of adult minipigs were acquired in V OIs defined manually on MR-images, or alternatively on the basis of the rad ioactivity concentration based on the most radioactive voxel in the last sc an frame. For all frame sequences, the relative decarboxylase activity (k(3 )(D)) declined significantly (P < 0.006) as the VOI threshold declined from 95 to 70% of the most radioactive voxel. Irrespective of VOI size, the mag nitude of k(3)(D) declined significantly (P < 0.001) from 0.074 +/- 0.008 t o 0.045 +/- 0.005 per min (mean +/- S.E.M.) as total sequence length increa sed from 60 to 120 min circulation. The method of VOI selection had no sign ificant effect on the striatum decarboxylation index of FDOPA calculated re lative to the radioactivity in cerebellum (k(3)(S)). (C) 2001 Elsevier Scie nce B.V. All rights reserved.