Design and initial performance of PETbox4, a high sensitivity preclinical imaging tomograph

Objectives PETBox4, a new tomograph dedicated to preclinical imaging of mice is currently under development at the Crump Institute for Molecular Imaging. This system presents a significant improvement on sensitivity and spatial resolution compared to the first generation PETBox system. We report here on the design and initial performance characteristics of this new system.

Methods PETBox4 consists of four opposing detector heads, arranged in a box like geometry. Each detector head is made by a 24 × 50 array of 1.825 × 1.825 × 7mm BGO scintillation crystals with a crystal pitch of 1.9025 mm. The effective area of each scintillator array is 45.58 × 95.05 mm, which is coupled to two Hamamatsu H8500 photomultiplier tubes via a glass light guide. The reconstructed FOV of the system is 45 × 45 × 94 mm. Images are reconstructed with the ML-EM algorithm and a system model based on a parameterized detector response. The complete system is integrated with a real time respiratory monitoring system, and provides anatomical reference images via a combination of x-ray projection, optical images and a digital mouse atlas.

Results For the four heads, the measured crystal energy resolution ranged from 13.9% to 40.4% full width at half maximum (FWHM), with a mean of 18.0%. With an energy window of 150 - 650 keV optimized for mouse imaging, the measured peak absolute sensitivity was 14.0% at the center of the FOV, matching reasonably close the results of GATE Monte Carlo simulations. Preliminary measurements of the intrinsic detector spatial resolution yielded 1.7 mm fwhm in the transverse and 1.6 mm fwhm in the axial direction.

Conclusions In comparison to the first generation two panel PETBox system, PETBox4 achieves substantial improvements on sensitivity and spatial resolution, while it provides full 3D tomographic PET images, retaining the small overall footprint