Parametric Binding Images of the TSPO Ligand 18F-DPA-714

¹⁸F-labeled N,N-diethyl-2-(2-[4-(2-fluoroethoxy)phenyl]-5,7-dimethylpyrazolo[1,5-α]pyrimidine-3-yl)acetamide (DPA-714) is a radioligand for the 18-kDa translocator protein. The purpose of the present study was to identify the best method for generating quantitative parametric images of ¹⁸F-DPA-714 binding.

Methods: Ninety-minute dynamic ¹⁸F-DPA-714 PET scans with full arterial sampling from 6 healthy subjects and 9 Alzheimer disease (AD) patients were used. Plasma-input-based Logan graphical analysis and spectral analysis were used to generate parametric volume of distribution (V_T) images. Five versions of Ichise, reference Logan, and 2 basis function implementations (receptor parametric mapping and simplified reference tissue model 2 [SRTM2]) of SRTM, all using gray matter cerebellum as the reference region, were applied to generate nondisplaceable binding potential (BP_ND) images.

Results: Plasma-input Logan analysis (r² = 0.99; slope, 0.88) and spectral analysis (r² = 0.99, slope, 0.93) generated estimates of V_T that correlated well with values obtained using nonlinear regression. BP_ND values generated using SRTM2 (r² = 0.83; slope, 0.95) and reference Logan analysis (r² = 0.88; slope, 1.01) correlated well with nonlinear regression-based estimates.

Conclusion: Both Logan analysis and spectral analysis can be used to obtain quantitatively accurate V_T images of ¹⁸F-DPA-714. In addition, SRTM2 and reference Logan analysis can provide accurate BP_ND images. These parametric images could be used for voxel-based comparisons.