Summary:No method has been reported for measuring CBF, repeatedly and noninvasively, in the rat brain. A new method is described, which is noninvasive to the brain, skull, or cervical large vessels. Two pairs of co incidence detectors were positioned, one over the rat brain and the other at the loop of a catheter inserted into the femoral artery. The coincidence head curve and ar terial curve were recorded after intravenous injection of 1-[IIC]butanol in IS rats. CBF was calculated by one compartment curve fitting (CBFo) from I-min data and with the recirculation corrected height/area method from 3-min data (CBFh . 3min) and S-min data (CBFh . Smin). CBFo agreed well with CBFh . Smin, although a slight overestimation was observed in CBFh . 3min. TheThe desirability of establishing a method by which CBF in the rat brain can be measured re peatedly and noninvasively is obvious. Determina tions of CBF in rats have been made by various methods which can be classified into two groups. The first group includes the indicator fractionation technique (Schaefer et al., 1976;Gibson and Duffy, 1981; Ginsberg et al., 1981a-d; Sage et al., 1981), direct tissue counting (Ekl6f and Siesj6, 1973; EklOf et al., 1974;Matsumoto et al., 1975; Gjedde et aI., 1980;Horton et al., 1980;Ginsberg et al., 1982), the autoradiographic technique (Sakurada et al., 1978;Lear et al., 1981), the microsphere method (Pannier Abbreviations used: CBFo, Cerebral blood flow calculated by one-compartment curve fitting; CBFh . 3min, CBF calculated by recirculation corrected height/area method from 3-min data;CBFh . 5min, CBF calculated by recirculation corrected height/ area method from 5-min data.
275normal CBFo in the normocapnic group (n = 6, Paco2 36.7 ± 2.3 mm Hg) was 1.76 ± 0.49 ml/g min (mean ± SD). A good correlation was observed between CBFo (y) and Paco2 (x), and the regression line was y = 0.0629x -0.71S (r = 0.88, p < 0.0001). We concluded that this method gives the stable blood flow values noninvasively and with a minimum loss of blood «0.28 ml per mea surement). Applications of this method include activation studies, studies on the effect of drugs and treatments, and water and oxygen extraction fraction studies using dif ferent tracers in the same rat.