TSPO and neoplasm: However, [18F]FET PET is known to depict vital brain tumor tissue beyond tumor extent in MRI [50]; therefore, it would also be highly interesting to include the above-mentioned TSPO KO model in future dual tracer PET studies with [18F]GE-180 and [18F]FET, all the more when investigating TSPO expression in brain tumors under therapeutic circumstances, e.g., after radiotherapy [17].