Development and evaluation of mini-EXPLORER: a long axial field-of-view PET scanner for non-human primate imaging

Abstract

Rationale: We describe a long axial field-of-view (FOV) positron emission tomography (PET) scanner for high sensitivity and total-body imaging of non-human primates, and present the physical performance and first phantom and animal imaging results. Methods: The mini-EXPLORER was built using the components of a clinical scanner (Siemens mCT) reconfigured with a detector ring diameter of 43.5 cm and axial length of 45.7 cm. NEMA NU-2 and NU-4 phantoms were used to measure sensitivity and count rate performance. Reconstructed spatial resolution was investigated by imaging a radially stepped point source and a Derenzo phantom. The effect of the wide acceptance angle was investigated by comparing performance with maximum acceptance angles between 14° – 46°. Lastly, an initial assessment of the in vivo performance of the mini-EXPLORER scanner was undertaken with a dynamic ¹⁸F-FDG non-human primate (rhesus monkey) imaging study. Results: The NU-2 total sensitivity was 5.0%, and the peak noise equivalent count rate (NECR) measured with the NU-4 monkey scatter phantom was 1,741 kcps, both obtained using the maximum acceptance angle (46°). The NU-4 scatter fraction was 16.5%, less than 1% higher than with a 14° acceptance angle. The reconstructed spatial resolution was ~3.0 mm at the center of the FOV, with a minor loss in axial spatial resolution (0.5 mm) when the acceptance angle increased from 14° to 46°. The rhesus monkey ¹⁸F-FDG study demonstrated the benefit of the mini-EXPLORER’s high sensitivity, including the ability for fast imaging (1 second early frames), excellent image quality (30 second and 5 minute frames), and the capability for late time-point imaging (18-hours post-injection), all obtained with a single bed position that captured the major organs of the rhesus monkey. Conclusion: This study demonstrated the physical performance and imaging capabilities of a long axial FOV PET scanner designed for high sensitivity imaging of non-human primates. Further, the results of this study suggest that a wide acceptance angle can be used with a long axial FOV scanner to maximize sensitivity, while introducing only minor trade-offs such as a small increase in scatter fraction and slightly degraded axial spatial resolution.