Objectives: [11C]PK11195 is a peripheral-benzodiazepine-receptor radioligand used for detection of microglial inflammation. Normal uptake by means of semiquantification was measured in order to establish reference data. The applicability of this semiquantitative approach was tested in three multiple sclerosis patients.
Materials and methods: Seven controls and three patients underwent MR and PET scanning. Coregistered static scans 40 minutes postinjection of [11C]PK11195 were used for assessment of relative ligand uptake by comparison to whole-brain uptake.
Results: For static scans acquired in near steady-state, the relative ligand uptake was significantly higher in gray matter structures as compared to the whole brain (ratio: 1.041 +/- 0.06, p = 0.036) whereas it was comparable in white matter (1.010 +/- 0.035). Intersubject reproducibility was 11.4% and 12.9% for white and grey matter. Intrasubject reproducibility was of the same order: 14.0% and 14.5% respectively. In two clinically active patients with Gadolinium-positive T1-weighted lesions on MRI the focal ligand uptake was significantly increased (1.36 and 1.14, p = 0.001). In one clinically stable patient, the uptake value corresponding with a T2-weighted MR lesion was not different from normal brain measurements.
Conclusion: The current investigations show that normal brain uptake of [11C]PK11195 is very low and shows the feasibility of a semiquantitative method which can be applied to larger cohorts of patients subgroups.