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Reproducibility of ¹⁸F-FDG microPET Studies in Mouse Tumor Xenografts

¹ Department of Radiology and the Bio-X Program, Stanford University School of Medicine, Stanford, California; and ² Department of Bioengineering, Stanford University, Stanford, California

Correspondence: For correspondence contact: Sanjiv S. Gambhir, MD, PhD, The James H. Clark Center, 318 Campus Dr., East Wing, 1st Floor, Stanford, CA 94305-5427. E-mail: sgambhir{at}stanford.edu

¹⁸F-FDG has been used to image mouse xenograft models with small-animal PET for therapy response. However, the reproducibility of serial scans has not been determined. The purpose of this study was to determine the reproducibility of ¹⁸F-FDG small-animal PET studies. Methods: Mouse tumor xenografts were formed with B16F10 murine melanoma cells. A 7-min small-animal PET scan was performed 1 h after a 3.7- to 7.4-MBq ¹⁸F-FDG injection via the tail vein. A second small-animal PET scan was performed 6 h later after reinjection of ¹⁸F-FDG. Twenty-five sets of studies were performed. Mean injected dose per gram (%ID/g) values were calculated from tumor regions of interest. The coefficient of variation (COV) from studies performed on the same day was calculated to determine the reproducibility. Activity from the second scans performed after 6 h were adjusted by subtracting the estimated residual activity from the first ¹⁸F-FDG injection. For 7 datasets, an additional scan immediately before the second injection was performed, and residual activity from this additional delayed scan was subtracted from the activity of the second injection. COVs of both subtraction methods were compared. Blood glucose values were measured at the time of injection and used to correct the %ID/g values. Results: The COV for the mean %ID/g between ¹⁸F-FDG small-animal PET scans performed on the same day 6 h apart was 15.4% ± 12.6%. The delayed scan subtraction method did not produce any significant change in the COV. Blood glucose correction increased the COV. The injected dose, tumor size, and body weight did not appear to contribute to the variability of the scans. Conclusion: ¹⁸F-FDG small-animal PET mouse xenograft studies were reproducible with moderately low variability. Therefore, serial small-animal PET studies may be performed with reasonable accuracy to measure tumor response to therapy.

Key Words: ¹⁸F-FDG • small-animal PET • reproducibility • tumor xenograft • drug development

^* Contributed equally to this work.

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