Global Gray matter, white matter ROI CBF value and their ratios were plotted against age. No group difference was found in global gray matter and white matter perfusion values between the normal young and elderly subjects. The GM/WM ratio is significantly higher in young controls than the elderly subjects (p<0.009, t-test). There are weak correlations between age and global GM perfusion (CC= − 0.24, p<0.292), WM perfusion (CC= 0.17, p<0.457). Significant negative correlations was found between age and GM/WM perfusion ratio (CC = − 0.62, P<0.002).