The validity of an intravenous isotope method for cerebral blood flow measurements. An experimental study

Abstract

The intravenous isotope method has been examined. The method uses ⁹⁹Tc as the indicator with recording of the radioactivity with two gamma-detectors placed bilaterally over the skull and oriented over the bifurcation of the middle cerebral artery. 65% of the total curve obtained was found to be generated by activity passing in the ipsilateral internal carotid artery, 25% in the contralateral internal carotid artery and less than 10% by activity passing in the two external carotid arteries. The counting rate efficiency for an intracerebral location was 19.4 ± 1.8 times the count rate from the same activity placed at 1 m distance in air which in turn was 5 cps/μCi. The variability in efficiency from patient to patient was thus estimated at ± 9 %. The duration of the input bolus had a marked influence on the curve, which will be of importance since it showed a rather large variability from patient to patient. Using the peak activity as an index of the cerebral blood flow the intravenous method showed a surprisingly good correlation with the ¹³³Xe wash-out method; the correlation coefficient was 0-93 and the variability at slightly subnormal values estimated at ± 15%. It is concluded that the method can be used in the case of limited demands on the accuracy of the cerebral blood flow determinations.

Key Words:

• cerebral circulation
• indicator dilution curves
• monitored volume
• external and internal carotid contribution
• input bolus