Results: The variance of the number of decays estimated using the Poisson distribution is significantly
different than the true variance for a 5-minute observation time of 11C, 15O, 13N, and 82Rb.
Conclusions: Durations of nuclear medicine studies often are relatively long; they may be even a few times
longer than the half-lives of some short-lived radiotracers. Our study shows that in such situations the
Poisson statistics is unsuitable and should not be applied to describe the statistics of the number of decays
in radioactive samples. However, the above statement does not directly apply to counting statistics at
the level of event detection. Low sensitivities of detectors which are used in imaging studies make the
Poisson approximation near perfect