MicroPET FDG mouse imaging: Evaluation of 50 consecutive tail vein injections

Objectives Intravenous (IV) injection of FDG in mice via the lateral tail vein is the most commonly used method of administration and can be technically challenging. Evaluation of the quality of FDG injection is necessary to determine if the PET scan is quantitatively accurate. The aim of this study was to evaluate 50 consecutive FDG injections in mice both qualitatively and quantitatively.

Methods During injection, qualitative evaluation was performed and classified according to specific criteria as good, intermediate, or poor. After 60 min, a 10 min body microPET scan and 2 min scan of the tail were acquired. Injection sites were quantitatively evaluated by determining mean and maximum percentage of the injected dose per gram (%ID/g). Validation of tail imaging in-vivo FDG compared to ex-vivo was performed on 7 extra mice by sacrificing them after scans, removing and re-scanning their tails, then measuring tail FDG ex-vivo in a gamma-counter. To assess baseline amounts of FDG in the tail without a tail injection, 3 more mice were injected by intraperitoneal (IP) method, imaged and quantitatively evaluated in the same way.

Results Validation of imaging to ex-vivo data yielded an excellent correlation with r-squared value of 0.95. Correlation of qualitative to quantitative methods yielded 42 matching good (mean 2.4, max 9.0 %ID/g), 2 intermediate and 1 poor IV injections. The %ID/g of good injections were confirmed by IP results mean 3.0, max 11.8 %ID/g. There were 5 cases of mismatching results, 1 false-negative, 4 false-positive for interstitial injections between the 2 methods, however using qualitative evaluation accuracy was true 90% (45/50) of the time. The overall success rate of good IV injections was 92% (46/50) using quantitative evaluation.

Conclusions A qualitative evaluation is all that is necessary if the IV injection is classified as good using our specific criteria. In uncertain, intermediate, or poor classifications, a scan and quantitative evaluation of the tail should be performed to aid in determining if the body PET scan is quantitatively accurate