Cerebral blood flow measurement during embolization of the rat brain using the xenon injection method

The purpose of this study was to investigate if cerebral blood flow (CBF) was influenced by the volume of the bolus using the intracarotid 133Xenon method in anesthetized rats, and to evaluate the effect of intracarotid embolization on hemispheric CBF. In 18 male Sprague-Dawley rats hemispheric CBF was calculated from recorded clearance of an intracarotid injected 50 microliters bolus of 133Xenon. A second clearance recording was done after the injection of a 200 microliter bolus of 133Xenon. Then the 18 animals were divided in 3 subsets each of 6 animals. In the first subset of 6 animals a bolus of 200 microliters 133Xenon was given, clearance was recorded before and after the injection of a suspension of microemboli. In all the above experiments within 90 sec after the initial bolus of 133Xenon, 20 microliters 133Xenon remaining in the carotid catheter was flushed into the brain by saline or the suspension of emboli. In the second subset of 6 rats the distribution of 133Xenon in various parts of the brain and head was examined after killing the animals 35 sec after injection of a 200 microliter bolus of 133Xenon. The third subset of 6 rats was treated as the second subset, except for the size of the bolus which was 50 microliters of 133Xenon. The calculated CBF values were independent of the volume of the bolus. At the post-mortem examination 76% of the radioactivity was located in the right hemisphere and majority of the remainder in the head outside the brain. The clearance curve was not monoexponential, but flattened out within the initial 30 sec when clearance from areas with CBF dominated the initial 15-second period, then clearance form areas with lower CBF values were more prominent in the following 15-second period. Embolization significantly reduced right hemispheric CBF to 0.26 (0.09-0.50) of the value immediately before embolization. The findings demonstrate applicability of CBF measurements using the intra-arterial 133Xenon injection method during embolization of the rat brain, provided a second bolus of 133Xenon is given before the embolization.