Brain Regions showing Manganese Accumulation in the Human versus the Rat Brain

3for the smelters, 0.025 mg/m 3 for the welders and <0.005 mg/m 3 for controls. None of the subjects showed neurological or motor disorder symptoms. The mean duration of exposure was 19 ± 7 years (range 10 – 26 years) for the smelters and 6.6 ± 3 years (range 3-12years) for the welders. All human MRI scans were performed on a 3T Philips Achieva whole body system using a 12-channel head coil. A 3D T1-weighted gradient echo sequence (TE/TR = 4.6ms/9.7ms, voxel size=1x1x1.25 mm 3 , 120 slices) was used to obtain high-resolution images from the whole brain. Abnormal T1 hyperintensities in the 3D images were evaluated by a radiologist. In addition, a series of T1-weighted inversion recovery images (single coronal slice through globus pallidus, slice thickness 5mm, TR/TE = 4000/15ms, IR = 3000, 1221, 534, 100ms) was used to determine the T1 relaxation time in a region of interest (ROI) in the globus pallidus. The PI was calculated based on (a) the signal ratio between a ROI within the globus pallidus (GP) and white matter in the frontal cortex (PIwm) and (b) the signal ratio between the same ROI in the GP and a ROI in the neck muscle (PImu). For the animal model of chronic Mn exposure, male Sprague-Dayley rats (220g) received ip injections of MnCl 2 (6 mg Mn/kg bodyweight, 5 d/wk) for 6 weeks. MRI images were aquired after 6 weeks on a 9.4T Varian Horizontal Bore MRI Scanner using a T1weighted sequence (TR/TE = 500/ 10 ms, 4 averages, pixel size 0.2 x 0.2 x 0.8 mm 3