Image/blood VT ratios (mean ± SD) and scores calculated for each method.

The scores are calculated by giving 2 points each time the image/arterial VT ratio comprised between ±5%, 1 point if comprised between ±5–10%, and 0 points if higher than ±10%. The most accurate results for both tracers were obtained using two blood-based methods (Chen and Mourik) and the Logan plot. When VT ratios were calculated using these two blood-based methods and an unconstrained two-tissue compartment model (2TCM), the overall results were less accurate. Please note that even if the Chen-[11C]PBR28 score is comparable between the two modeling approaches (11/38 vs. 12/38), the 2TCM yields a greater bias and a greater standard deviation of the mean VT ratio (1.10±0.17 vs. 1.15±0.20).