Validation of [18F]FES for Imaging of Brain Estrogen Receptors

Estrogens are the primary female sex hormones that play a major role in the development and maintenance of secondary sexual functions. In addition, estrogens play an important role in cardiovascular, musculoskeletal, immunological, bone development and central nervous system processes. Actions of estrogens are mediated by a group of specialized receptors, known as estrogen receptors. Estrogens were found to be neuroprotective and may thus protect against development of neurodegenerative disorders like Alzheimer's disease, Parkinson's disease and multiple sclerosis. In addition, estrogens may also play an important role in psychiatric disorders, like depression. To improve our understanding of the action of estrogens in the brain, it is important to study the expression of estrogen receptors in the brain. Positron emission tomography (PET) is the most suitable technique for non-invasive imaging of brain receptors. \[18F\]FES is a PET tracer that is regularly used in the UMCG to image the estrogen receptor expression in breast cancer patients, but has never been used for quantitative imaging of brain estrogen receptors. Quantification of the expression of brain receptors by PET usually requires arterial blood sampling to obtain the plasma input function of the tracer. Arterial blood sampling causes discomfort to the patient and therefore can be an obstacle especially in longitudinal studies. The aim of this study is therefore to investigate whether \[18F\]FES PET imaging for quantification of estrogen receptors in the human brain is feasible without arterial blood sampling, using a reference tissue model (SRTM) or an image derived input function (IDIF), so the discomfort associated with arterial blood sampling can be avoided.