In preclinical Positron Emission Tomography (PET) imaging, several research groups have recently proposed different experimental set ups allowing multiple animals to be simultaneously imaged in a scanner in order to reduce the costs and increase the throughput. Simultaneous scanning of several animals also ensures injections with the same specific activity, which may be otherwise subject to significant variations when animals are injected at different time and possibly with tracers from different productions. In addition, it is well known that the performance of a PET system, in terms of spatial resolution and sensitivity, is optimal at the center of the field of view (FOV) and degrades quickly with increasing distance from the center. In previous studies, the technical feasibility has been demonstrated and the signal degradation caused by additional mice in the FOV characterized, however, the impact of the signal degradation on the outcome of a PET study has not yet been studied.
In a project collaborated by the ANSTO/University of Sydney node of the National Imaging Facility, the collaborators thoroughly investigated, using Monte Carlo simulated [18F]FDG and [11C]Raclopride PET studies, different experimental designs for whole-body and brain acquisitions of two mice and assessed the actual impact on the detection of biological variations as compared to a single mouse setting.
First, the validation of the PET-SORTEO Monte Carlo simulation platform for the simultaneous simulation of two animals was extended. Then, [18F]FDG and [11C]Raclopride input mouse models for the simulation of realistic whole-body and brain PET studies were designed. Simulated studies allowed the scientists to accurately estimate the differences in detection between single- and dual-mode acquisition settings that are purely the result of having two animals in the FOV. Validation results showed that PET-SORTEO accurately reproduced the spatial resolution and noise degradations that were observed with actual dual phantom experiments. The simulated [18F]FDG whole-body study showed that the resolution loss due to the off-center positioning of the mice was the biggest contributing factor in signal degradation at the pixel level and a minimal interanimal distance as well as the use of reconstruction methods with resolution modeling should be preferred. Dual mode acquisition did not have a major impact on ROI-based analysis except in situations where uptake values in organs from the same subject were compared. The simulated [11C]Raclopride study however showed that dual-mice imaging strongly reduced the sensitivity to variations when mice were positioned side-by-side while no sensitivity reduction was observed when they were facing each other.
This is the first study showing the impact of different experimental designs for whole-body and brain acquisitions of two mice on the quality of the results using Monte Carlo simulated [18F]FDG and [11C]Raclopride PET studies. This study validates unique experimental capabilities, which enable researchers to make the most of the radiotracers production and scanners availability.
1 Australian Nuclear Science and Technology Organization (ANSTO), Kirrawee DC, Australia
2 Brain & Mind Centre, National Imaging Facility (NIF), University of Sydney/ANSTO Node, Sydney, Australia
3 CERMEP – Imagerie du vivant, Lyon, France
4 Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Strasbourg, France
5 CNRS, UMR7178, 67037 Strasbourg, France
Reilhac, Anthonin, et al. “Simultaneous scanning of two mice in a small-animal PET scanner: a simulation-based assessment of the signal degradation.” Physics in Medicine and Biology 61.3 (2016): 1371.