Introduction
The adenosine A1 and A2A receptors in the human brain can be visualized by PET with [11C]MPDX 1 and [11C]TMSX 2 , respectively. Previously we proposed a method for extracting a plasma time-activity curve (pTAC) using independent component analysis (EPICA) from dynamic PET images 3 to omit serial arterial blood sampling in kinetic analysis. EPICA is a pTAC extraction method assuming that spatial distributions of the brain tissue and the blood vessels are statistically independent. In this study, EPICA was applied to dynamic PET images with two adenosine receptor ligands, and parametric images on distribution volumes (DVs) and binding potentials (BPs) were estimated by Logan plot using the estimated pTAC.
Methods
Dynamic PET scans were performed on 18 subjects (including 11 normal volunteers and 7 patients with epilepsy or other disorders) with [11C]MPDX, and 5 normal volunteers with [11C]TMSX. The DVs were calculated in each voxel by Logan plot using the EPICA-estimated pTAC. The candidate for reference region was manually drawn on the cerebellum. Voxels beyond 80 percentile of DV image were excluded to refine the reference region. BP maps were calculated using the DV images and the reference regions. Several ROIs ([11C]MPDX: 7, [11C]TMSX: 2) were placed on each subject's image, and nonlinear least square method was applied for ROI-based comparison.
Results
The examples of the estimated BP maps were shown in Fig. 1. BP maps of [11C]MPDX show relatively high values across the brain, while BP maps of [11C]TMSX show extremely high values in striatum and thalamus, as compared with other areas. ROI-based comparison was shown in Fig. 2. There was close agreement between both calculated results.
Estimated BPs
ROI-based comparison of the estimated BPs
Conclusion
We conclude that EPICA allows BP parametric imaging of adenosine A1 and A2A receptors without arterial blood sampling.