Quantification of aromatase binding in the female human brain using [¹¹ C]cetrozole positron emission tomography

Aromatase, the enzyme that in the brain converts testosterone and androstenedione to estradiol and estrone, respectively, is a putative key factor in psychoneuroendocrinology. In vivo assessment of aromatase was performed to evaluate tracer kinetic models and optimal scan duration, for quantitative analysis of the aromatase positron emission tomography (PET) ligand [¹¹ C]cetrozole. Anatomical magnetic resonance and 90-min dynamic [¹¹ C]cetrozole PET-CT scans were performed on healthy women. Volume of interest (VOI)-based analyses with a plasma-input function were performed using the single-tissue and two-tissue (2TCM) reversible compartment models and plasma-input Logan analysis. Additionally, the simplified reference tissue model (SRTM), Logan reference tissue model (LRTM), and standardized uptake volume ratio model, with cerebellum as reference region, were evaluated. Parametric images were generated and regionally averaged voxel values were compared with VOI-based analyses of the reference tissue models. The optimal reference model was used for evaluation of a decreased scan duration. Differences between the plasma-input- and reference tissue-based methods and comparisons between scan durations were assessed by linear regression. The [¹¹ C]cetrozole time-activity curves were best described by the 2TCM. SRTM nondisplaceable binding potential (BP_ND ), with cerebellum as reference region, can be used to estimate [¹¹ C]cetrozole binding and generated robust and quantitatively accurate results for a reduced scan duration of 60 min. Receptor parametric mapping, a basis function implementation of SRTM, as well as LRTM, produced quantitatively accurate parametric images, showing BP_ND at the voxel level. As PET tracer, [¹¹ C]cetrozole can be employed for relatively short brain scans to measure aromatase binding using a reference tissue-based approach.