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Technologist AbstractsTechnologist Posters |
1 College of Pharmacy, University of New Mexico, Albuquerque, New Mexico
2108
Objectives: Gamma counters are used in the evaluation of small animal biodistribution studies. In vivo radiotracer distribution is evaluated using a gamma counter then related back to the initial input function to determine the activity localized in tissues (%ID/G). The aim of this study was to develop a method for robust characterization of the input function, dose administered, in biodistribution studies.
Methods: Radioactive standards were prepared and assayed using a dose calibrator. Standards were diluted by mass to detectable activity levels, then counted as they decay through the full range of response. The theoretical activity over the decay time was calculated based on the initial dose calibrator measurements and subsequent dilutions. The theoretical activity was compared to the observed count rate to determine the linear range of response.
Results: A comparison of the theoretical activity versus the observed count rate showed correlation in the activity range of 1,000 – 300,000 dpm. The observed response within this range yielded an R2 value of 1.00. Counts observed versus theoretical disintegrations showed an average percent error of 0.86 percent. Analysis of the data showed an area outside the linear range, activities greater than 330,000 dpm, with higher percent error that continued to increase with increasing activity.
Conclusions: There are limits to the accuracy of measurements produced within the detectable range of the gamma counter. In order to accurately estimate localized tissue activity and pharmacokinetics based on count rates, it is important to accurately characterize the input function to improve the accuracy of tissue distribution measurements performed.
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