Further in vivo characterization of [ 11 C]‐(+)‐PHNO uptake into a retina‐like region of interest in humans

The neurotransmitter dopamine is present in the retina and is involved in several modulatory functions. Unlike in rodents, dopamine D 3 receptors are expressed in the retina of humans. Recently, uptake of the D 3 receptor‐preferring radiotracer [ 11 C]‐(+)‐PHNO has been observed in a retina‐like region of interest (ROI) in humans. Here, we attempted to quantify [ 11 C]‐(+)‐PHNO uptake into this ROI using an independent sample, employing an extended scan acquisition time (120 min) and arterial kinetic modeling. Data from 14 healthy controls were analyzed (Mean Age: 38.41 ± 9.55, 3 female), 8 of which provided arterial line input function data (Mean Age: 41.07 ± 7.82, 3 female). Using Ichise's multilinear analysis (MA1) method, it was possible to quantify the volume of distribution ( V T ) of [ 11 C]‐(+)‐PHNO in this retina‐like region (Mean V T  = 13.56 ± 3.52; Mean χ 2  = 2.08 ± 2.20). Notably, the shape of the time activity curve resembled closely that of the globus pallidus. Moreover, the V T values in the retina correlated well with binding potential ( BP ND ) values calculated using the simplified reference tissue model (Mean BP ND  = 2.11 ± .94; Mean χ 2  = 5.76 ± 2.56), employing the cerebellum as the reference region ( r  = .76, r 2  = .58). In summary, we provide evidence that the in vivo uptake of [ 11 C]‐(+)‐PHNO into a retina‐like ROI in humans can be quantified using both arterial blood sampling ( V T ) and simplified reference tissue methods ( BP ND ).