Abstract

At post mortem, the hypopigmented substantia nigra (SN) of Parkinson disease (PD) patients generally shows a decrease in neuromelanin (NM) with an increase in ferritin particularly in dopaminergic neurones. Relaxometry-based MRI methods of assessing iron content in the SN depend on the microscopic distribution of iron. Phase mapping or susceptibility weighted imaging methods are sensitive to the magnetic susceptibility and hence iron content of tissue, but both are affected by the geometrical distortion of the phase information. We hypothesise that susceptibility mapping will provide a more direct, in vivo measure of iron in the brains of PD patients. Nine PD patients and controls were recruited under local ethics approval (05/Q2402/87). High-resolution T2* weighted MRI scans were acquired using a 7-T Philips Achieva MRI scanner. The relative magnetic susceptibility was measured in the manually outlined whole SN and its medial part representing the pars compacta (PC) compared to surrounding white matter. Values were averaged over both sides all slices. Statistical analysis found a significant difference for the PC susceptibility between PD patients and normal control subjects (p=0.042) but not for the whole SN (p=0.18). This is the first demonstration of high-resolution magnetic susceptibility mapping of the SN of PD patients and shows a focal increase in magnetic susceptibility in the PC only, consistent with an increase in iron.