Fig. (3) The couples of N20 and 1/vMCA interhemispheric ratio values detected in each patient with CT/MRI scan unilateral structural ischemic or hemorrhagic alterations in the MCA supplied area, gathered in table 6, are displayed in the graph in descending order of N20 ratio values . The two ratios show divergent courses, since the value of N20 on the compromised hemisphere is < 0.65 with respect to the contralateral, whereas the 1/vMCA value reverts to ratio >0.65. The two ratios no longer correlate in this group ( p = 0.88, r = -0.05, 95% C.I.= - 0.66 to 0.59).