Measuring Iron in the basal ganglia and thalamus using Susceptibility Weighted Imaging (SWI): A presence of iron not only in lesions, but now more importantly in the basal ganglia and thalamus has been shown in IPD patients. The latter shows iron build up at the confluence of the draining veins in these areas. SWI can be run to show iron deposition in several areas of interest within the brain. SWI has very high spatial resolution and is an optimal method to study the small internal cerebral venous system. The ability to measure the amount of non-heme iron in the brain will facilitate a better understanding of the disease progression and may help in predicting the treatment outcome. Iron deposition will be evaluated from the SWI images. To measure iron content in grey matter, investigators will look at iron in the following eight regions: caudate nucleus, globus pallidus, putamen, thalamus, pulvinar thalamus (as it appears to be affected much before the rest of the thalamus), substantia nigra, red nucleus and dentate nucleus. For each deep gray matter structure, two major regions of interest will be analyzed: the entire object drawn manually and the region-of-interest that has much higher iron content. The investigators will provide the following information for these regions: iron content in the abnormal part of the structure (the investigators refer to this as the high iron content region); the area of this region; the average iron per pixel in this region; and also the investigators will quote the same three values for the total iron in these structures.