Recently an alternative method to visualise the alterations in the cerebral dopaminergic pathways of PD patients has been proposed: TCD of the substantia nigra in the brainstem. This technique has high inter-observer reliability. Becker discovered in 1994 that patients with PD had bilateral hyperechogenicity of the substantia nigra. Neuropathological studies confirm the increased echogenicity is because of iron deposition. However the reason of the increased level of iron is unknown.