Towards quantitative small-animal imaging on hybrid PET/CT and PET/MRI systems

Abstract

Aim Over the past two decades, innovations in small-animal positron emission tomography (PET) have reached an impressive level, which has brought countless opportunities to explore the major puzzles in biomedical research. It is a given that pairing information coming from different imaging modalities renders unprecedented knowledge and provides a great insight into various facets of biological systems, such as anatomy, function, physiology, and metabolism in animal models of human diseases, which are difficult to be beaten by standalone PET scanners. The development of bimodal and tri-modal imaging platforms with advanced software solutions dedicated for quantitative studies in small-animals has spurred academic and industrial interest. However, it is undisputed that the potential success of these scanners in filling the translational gap between human and animal findings, hinges to a great extent upon optimization and standardization of relevant parameters and acquisition protocols, which is often overlooked. Methods This article reviews the trends till 2020 in the field of preclinical PET imaging with emphasize on image reconstruction and quantitative corrections implemented on state-of-the-heart hybrid systems. First, the challenges, limitations, and benefits offered by multi-modality imaging systems are described and then, the most commonly used strategies, as well as novel techniques for image reconstruction and image corrections (attenuation, scattering, normalization, motion, and partial volume effect) are presented. The advantages and disadvantages of different methods are also discussed. We also briefly touch upon the factors that should be considered for reliable kinetic modeling and absolute quantitation in preclinical small animal research. Conclusions Multi-modality imaging has attracted a lot of research, particularly in the preclinical portfolio. Nevertheless, more research is still needed to optimize the conceptual design, reach the limits of quantitative imaging and implement standardized protocols for small-animal studies. Without any doubt, exploring the potential advantages of combined imaging units providing optimal image quality and reliable tools for quantification of biological parameters through standardized imaging protocols is one of the goals of translational research.

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