Fig. 1

Three imaging slices used to calculate the gray matter attenuation to white matter attenuation ratio. Left, high convexity level (a). Middle, centrum semiovale level (b). Right, basal ganglia level (c). In each slice, the Hounsfield units (HU) were measured within circle 1 on the gray matter and within circle 2 on the white matter. Then, each HU value was then calculated based on the average of the values for the right and left brains. The slice thickness was 5 mm, and the circle size was 10 mm2