Clinical study to demonstrate an at least equivalent performance of a new PET molecular Imaging radiopharmaceutical named [18F] LBT-999 in brain imaging compared to the SPECT reference method named [123I]-FP-CIT to establish the differential diagnosis between Parkinson's Disease 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