Statistical Power Analysis of in Vivo Studies in Rat Brain Using PET Radiotracers 1 1Transcripts of the BRAINPET97 discussion of this chapter can be found in Section VIII.

The objective of this study is to analyze the statistical power of in vivo rat competition studies performed in the developmental process of new radioligands for positron emission tomography (PET). These calculations are important for determining the number of animals necessary to detect a significant change of radiotracer uptake for a control versus a treated group of rats. The analysis is based on a series of studies carried out in rats with the D 1 agonist [ 11 C]SKF 82957 and the D 1 antagonist [ 11 C]SCH 23390. The average variance of the percentage injected dose of tracer per gram of brain tissue at 45 min postinjection in different brain regions was calculated for three groups of rats. The power to detect a change due to drug treatment on the radioligand uptake in each region was calculated for different numbers of rats. The average coefficient of variance for all three groups showed similar results, ranging from 8 to 23%. This study provides an empirical basis for selecting the number of rats necessary to detect a significant change in tracer uptake. Using the striatum as an example, total blocking studies may significantly (p 0.05) be determined with a small number of rats (90% change with n = 4 rats). Smaller changes require larger number of rats (25% change with n = 8 rats) to obtain the same statistical power. These results suggest that these power calculations can be used for any in vivo rat studies with PET radioligands having similar coefficients of variance.