Validation and Reproducibility of Measurement of 5-HT1A Receptor Parameters with [carbonyl-11C]WAY-100635 in Humans: Comparison of Arterial and Reference Tissue Input Functions

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Abstract
Serotonin 5-HT1A receptors are implicated in the pathophysiology of neuropsychiatric conditions. The goal of this study was to evaluate methods to derive 5-HT1A receptor parameters in the human brain with positron emission tomography (PET) and [ carbonyl-11C]WAY 100635. Five healthy volunteer subjects were studied twice. Three methods of analysis were used to derive the binding potential (BP), and the specific to nonspecific equilibrium partition coefficient (k3/k4). Two methods, kinetic analysis based on a three compartment model and graphical analysis, used the arterial plasma time-activity curves as the input function to derive BP and k3/k4. A third method, the simplified reference tissue model (SRTM), derived the input function from uptake data of a region of reference, the cerebellum, and provided only k3/k4. All methods provided estimates of regional 5-HT1A receptor parameters that were highly correlated. Results were consistent with the known distribution of 5-HT1A receptors in the human brain. Compared with kinetic BP, graphical analysis slightly underestimated BP, and this phenomenon was mostly apparent in small size-high noise regions. Compared with kinetic k3/k4, the reference tissue method underestimated k3/k4 and the underestimation was apparent primarily in regions with high receptor density. Derivation of BP by both kinetic and graphical analysis was highly reliable, with an intraclass correlation coefficient (ICC) of 0.84 ± 0.14 (mean ± SD of 15 regions) and 0.84 ± 0.19, respectively. In contrast, the reliability of k3/k4 was lower, with ICC of 0.53 ± 0.28, 0.47 ± 0.28, and 0.55 ± 0.29 for kinetic, graphical, and reference tissue methods, respectively. In conclusion, derivation of BP by kinetic analysis using the arterial plasma input function appeared as the method of choice because of its higher test—retest reproducibility, lower vulnerability to experimental noise, and absence of bias.

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