N-G-NITRO-L-ARGININE METHYL-ESTER MODIFIES THE INPUT FUNCTION MEASURED BY DYNAMIC SUSCEPTIBILITY CONTRAST MAGNETIC-RESONANCE-IMAGING

In rat brain dynamic susceptibility contrast magnetic resonance (MR) i mages, vessels visible on the same scan plane as the brain tissue were used to measure the characteristics of the input function of the NIR contrast agent gadopentetate dimeglumine. MR images were acquired 30 a nd 60 minutes after intravenous injections of 3 mg/kg and 15 mg/kg N-G -Nitro-L-arginine methyl ester (L-NAME) (n = 9). The time of arrival ( TOA) and the mean transit time corrected for TOA of the input function were increased by 3 mg/kg or 15 mg/kg L-NAME. The area of the input f unction was increased by 15 mg/kg L-NAME. In two animals, similar modi fications of the input function induced by 20 mg/kg L-NAME were revers ed by infusion of sodium nitroprusside. In two other animals, MABP was increased by phenylephrine to a similar extent as in L-NAME experimen ts, but did not induce the same modifications of the input function, s howing that the action of L-NAME on the input function was not simply caused by an effect on MABP. These results show that the input functio n can be significantly altered by manipulations widely used in cerebro vascular studies. These input function changes have important implicat ions for calculation of cerebral blood flow.