We aimed to study tracer kinetics in radioisotope (RI) cisternography. For this purpose, we analyzed the RI images of 36 individuals in whom absence of cerebrospinal fluid (CSF) leakage was confirmed. For the semiquantitative assessment of tracer clearance, the geometric mean of the RI count in the anterior and posterior images was obtained for the entire head as well as for the whole spinal axis. After correcting for the radioactive decay of the tracer, tracer clearance was expressed as a ratio of the count in the range of the whole CSF space at different time points to that at the time of tracer delivery. Tracer clearance from the CSF space was not related to the degree of cranial transport of the tracer in 1 hour, but was significantly related with the age of the patients. At 24 hours after the injection, tracer clearance was significantly faster in the younger patients (Group I: age < 40 years) than in the older patients (Group II: age > or = 40 years). The cranial transport of the tracer appeared to be rapid in group I; however, the difference between these 2 groups was not significant. These results indicate that age should be taken in account while establishing the reference values for tracer kinetics in normal individuals.
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