Imaging performance of the LabPET small-animal PET scanner

Abstract

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Objectives: LabPET is an APD-based, fully digital PET scanner designed for molecular imaging of small animals. It exists in two versions, LabPET4 and LabPET8, with 3.75 and 7.5 cm axial lengths and adaptable transaxial FOV up to 10 cm. Imaging performance was evaluated with phantoms and with rats and mice using multiple tracers under various scanning conditions.

Methods: Spatial resolution was measured with point source and hot spot phantoms to assess resolving power and recovery coefficients (RC). Sensitivity, count rate performance and scatter fraction were investigated using mouse and rat phantoms with dedicated field collimators and varying lower energy thresholds from 100 to 450 keV. Images of animals injected with Na¹⁸F, ¹⁸FDG, ¹⁸FES, ¹³NH₃ and ¹¹C-(aceto)acetate were obtained under static, WB, dynamic and gated data acquisition protocols.

Results: FBP reconstructed tangential/radial resolution is 1.3/1.4 mm FWHM (2.5/2.4 FWTM) at CFOV. Using hot spot phantoms with MLEM reconstruction, 1.35 mm spots can be clearly resolved and RC>0.6 for 2 mm rods. Improved performance is achieved with optimized lower energy threshold and field collimators adapted to animal species. Dynamic PET imaging of the rat brain and mouse heart was demonstrated with ¹⁸FDG and ¹¹C-acetoacetate. Gated ¹⁸FDG acquisition of the mouse heart clearly displays the left and much fainter right myocardium. Receptor PET imaging with ¹⁸FES enabled discrimination of tumors with different estrogen receptor status.

Conclusions: Performance of LabPET meets the requirement for state-of-the-art molecular imaging of small laboratory animals.

Research Support: NSERC, CIHR & WM Keck Foundation