[18F] LBT-999 PET Compared to [123I]-FP/CIT SPECT to Distinguish Between Parkinson's Diseases and Essential Tremor

Inclusion Criteria: * Patients aged 35 to 80 (male or female) * Patients: * suffering from an essential tremor as defined by Elble's criteria from 2000 (excluding head tremor in decubitus and compatible with the study by the investigator) * or with Parkinson's disease as defined by the United Kingdom Parkinson's Disease Society Brain Bank (UKPDSBB) * Patients with clinical symptoms dated more than 18 months ago * Women of childbearing potential who must have effective contraception at baseline and up to 30 days after the last administration of the radiopharmaceutical (investigational medicinal product or comparator) * Patients affiliated with or receiving a social security scheme * Patients who have been fully informed about the organization of the research and who have signed their informed consent Exclusion Criteria: * Patients with atypical non-idiopathic Parkinson's syndrome (multi system atrophy, progressive supranuclear palsy, etc.) * Patients treated with deep brain stimulation * Patients with functional psychogenic movements * Patients with severe and progressive psychiatric disorders * Patients with disabling dyskinesia or essential tremor that are incompatible with imaging studies * Patients who have had an ionizing radiation examination on the brain within the last 3 months * Individuals with a contraindication to PET or SPECT imaging: * Patients with claustrophobia * Patients refusing to be informed in case of abnormalities detected during imaging tests * Patients treated with amphetamines, benzatropine, amfebutamone, cocaine, mazindol, methylphenidate, phentermine or sertraline * Individuals with a known allergy to the active substance or one of the excipients of the product under investigation or to the reference product or to or to thyroid treatment * Woman of childbearing age without effective contraception in the opinion of the investigator * Any other serious unstabilized chronic condition deemed incompatible with the study by the investigator * Patients unable to sign the informed consent * Patients participating in a protocol or in a period of exclusion from a protocol * Patients who received compensation of more than 6000 € in the last 12 months prior to enrollment in clinical studies * Patients in a period of exclusion from the national volunteer database during which they cannot participate in another clinical study * Patients not affiliated with a social security scheme * Patients refusing to participate * Individuals referred to in articles L. 1121-5 to L. 1121-8 and L1122-2 of the French Public Health Code