Compare Rates of Agreement Between Clinical Diagnosis and Visual Assessment of DaTscan™ Images in Non-Caucasian and Caucasian Subjects With Parkinson's Disease (PD) or Essential Tremor (ET)

Inclusion Criteria:

For Non-Caucasians:

- Non-Caucasian male and female adult participants (greater than or equal to 18 years of
age) with an initial diagnosis of suspected PD or ET who underwent DaTscan SPECT
imaging to assist with the participant's final clinical diagnosis of PD or ET.

- The participant had existing diagnostic-quality and interpretable DaTscan SPECT images
of the brain.

For Caucasians:

- Caucasian male and female adult participants (greater than or equal to 18 years of
age) with an initial diagnosis of suspected PD or ET who underwent DaTscan SPECT
imaging to assist with the participant's final clinical diagnosis of PD or ET.

- The participant had existing diagnostic-quality and interpretable DaTscan SPECT images
of the brain.

- The participant was matched by final clinical diagnosis, sex and age (±5 years) with a
non-Caucasian participant.

Exclusion Criteria:

- Known/suspected structural abnormalities of the brain (e.g., hydrocephalus; brain
tumor; stroke; etc.) that could grossly distort the DaTscan images.

- Participants whose race and ethnic information could not be determined from source
document review.