Fig. (4) Patient No. 9 showed parallel courses of N20 and 1/vMCA interhemispheric ratios ( always > 0.65), with significant statistical correlation ( p <0.01, r = 0.94, C.I. 0.57 to 0.99). This patient never developed CT/MRI scan alteration of MCA area. He showed transient vasospasm, even bilateral, (BFV >120 < 240), normal N20 amplitude and was always asymptomatic during the survey.