Determination of receptor density and binding affinity quantitatively, using PET/MRI technique in mice, rats, monkeys etc., is frequently used for the research of Parkinson’s, Alzheimer’s, schizophrenia, drug detoxification, drug addiction and dependence. Simultaneously, according to the targets of drugs against neuropsychiatric disorders, we can use PET imaging technique to evaluate in-vivo candidate drugs’ receptor occupancy, receptor affinity and assess drugs’ pharmacodynamics and mechanisms.