Parkinson´s disease (PD) diagnosis is based upon clinical examination. Although imaging has helped doctors to identify many diseases, it still does not add too much information for the diagnosis of Parkinson´s disease. The investigators are going to perform a large sample study including PD patients, essential tremor and healthy volunteers in order to evaluate if MRI can help in the diagnosis. Our hypothesis is that fractional anisotropy (FA) in the caudal portion of substantia nigra is decreased in PD patients.

The diagnosis of Parkinson's disease (PD) is based on a set of clinical assessments that do not provide great accuracy. Although magnetic resonance imaging (MRI) and transcranial sonography (TCS) have provided important advances in the diagnosis of a number of neurological diseases, few biomarkers of PD have been described in order to support its clinical diagnosis.

Recently, one single study showed that high field MRI using diffusion tensor imaging (DTI) was able discriminate PD from healthy volunteers. This study had a small sample size (14 patients and 14 controls) and did not include the main differential diagnosis of PD.

The main objective of this study is to confirm previous findings, with a larger sample size, describe possible changes of DTI parameters in patients with essential tremor (one of the main differential diagnosis of PD), and compare DTI MRI with TCS. Our primary outcome will be the fractional anisotropy (FA) in the caudal portion of substantia nigra. As a consequence, new algorithm to discriminate PD, essential tremor and healthy volunteers will be proposed. This has a pivotal importance in order to provide support to clinical diagnosis of PD and increase its accuracy.

Inclusion Criteria:

• Parkinson´s disease patients according to UK Parkinson´s Disease Brain Bank Criteria
• Essential Tremor Patients according to Movement Disorder´s diagnosis consensus criteria.
• Healthy Volunteers: paired with PD patients by age and gender.

Exclusion Criteria:

• Contraindication to MRI
• Claustrophobia.
• Serious structural brain anomalies.
• Condition or situation in which, in the opinion of the investigator put the patient at significant risk, which can confound the results, or substantially interfere with the individual's participation in the study.

50 Parkinson´s Disease Patients 50 Essential Tremor Patients 50 Healthy Volunteers