TSPO and Alzheimer disease: Nonetheless, the cerebellum, with little or no inflammation, particularly at early AD stages, has been used or suggested as a reference region for TSPO PET in AD.93-95 Other suggested pseudo-reference regions have included the caudate nucleus8 and Braak region VI.96 Finally, the use of a PET tracer label with the 11C isotope requires the availability of a cyclotron at the site of use, because 11C has too short a half-life to be shipped.