An important issue in rodent imaging is the question whether it is possible to use both female and male animals in tracer development and evaluation, rather than animals from a single sex. For this reason, we have made repeated 18F-FDG scans of the brain of adult rats (either males, or females at different phases of the estrous cycle). Our study was aimed to answer the following questions: a. Are there differences in brain metabolism between male and female rats? b. Are there differences in the cerebral 18F-FDG uptake of female rats at different phases of the estrous cycle? and c. Is the test-retest variability of 18F-FDG PET different in males and females? Methods: Long-Evans rats (age 1 yr) were divided into three groups: 1. Males (n=8), 2. Females in metestrous (low estrogen levels, n=8), and 3. Females in proestrous (high estrogen levels, n=8). Two small animal PET scans using 18F-FDG and rapid arterial blood sampling were made at an interval of 10 days in subjects anesthetized with isoflurane in oxygen (thus, 48 scans were made in total). Body temperature, heart rate, glucose levels in plasma and blood oxygenation were monitored in all rats during the scans. A preliminary analysis was performed on data from the entire brain. Data from predefined brain regions will be analyzed in the near future, using kinetic modeling. Results: Females showed a significantly higher brain uptake of 18F-FDG than males, particularly in the initial scan (+40%, P < 0.0001). Higher estrogen levels were associated with increased brain metabolism, since the accumulation of 18F-FDG was 11.5% higher in proestrous than in metestrous or other phases of the estrous cycle (P < 0.02; in the second scan, a few animals were in diestrous or estrous rather than the desired proestrous or metestrous phase). Cerebral glucose metabolism in the test and retest condition was identical in males, but females showed a significant decline (-10.5 ± 2.6%). Conclusion: Based on the results for this particular model, the mixing of sexes or the mixing of female rats in different phases of the estrous cycle in tracer evaluation protocols will result in an impairedtest-retest stability of the PET data and a need for larger group sizes to maintain the same statistical power in group comparisons.
Original languageEnglish
Pages (from-to)S316-S317
Number of pages2
JournalEuropean Journal of Nuclear Medicine and Molecular Imaging
Issue numberSuppl.2
Publication statusPublished - 6-Oct-2017
Event30th Annual Congress of the European Association of Nuclear Medicine (EANM'17) - Vienna, Austria
Duration: 21-Oct-201725-Oct-2017
Conference number: 30th


  • Positron Emission Tomography (PET)
  • RAT
  • Small animal imaging

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