Motion artifacts from head motion are one of the major hurdles in brain PET. Dynamic brain PET studies can last more than one hour; voluntary and involuntary head motions are almost inevitable. This is particularly true in the elderly, or patients with dementia or movement disorders. Head restraints are often used to reduce head motion during the acquisition, but they cause discomfort for patients, and head movements still cannot be completely eliminated. Furthermore, perturbation of neurochemical processes can be introduced by the stress caused by restraint in animal studies. Anesthesia is also often used to keep animals still during acquisition; studies showed that anesthesia can also perturb the neurological process under study