Purpose: Xtrim-PET is a newly designed Silicon Photomultipliers (SiPMs)-based prototype PET scanner dedicated for small laboratory animal imaging. We present the performance evaluation of the Xtrim-PET scanner following NEMA NU-4 2008 standards to help optimizing scanning protocols which can be achieved through standard and reliable system performance characterization. Methods: The performance assessment was conducted according to the National Electrical Manufacturers Association (NEMA) NU-4 2008 standards in terms of spatial resolution, sensitivity, counting rate performance, scatter fraction and image quality. The in vivo imaging capability of the scanner is also showcased through scanning a normal mouse injected with 18 F-FDG. Furthermore, the performance characteristics of the developed scanner are compared with commercially available systems and current prototypes. Results: The volumetric spatial resolution at 5 mm radial offset from the central axis of the scanner is 6.81 µl, whereas a peak absolute sensitivity of 2.99% was achieved using a 250-650 keV energy window and a 10 ns timing window. The peak noise-equivalent count rate (NECR) using a mouselike phantom is 113.18 kcps at 0.34 KBq/cc with 12.5% scatter fraction, whereas the NECR peaked at 82.76 kcps for an activity concentration level of 0.048 KBq/cc with a scatter fraction of 25.8% for rat-like phantom. An excellent uniformity (3.8%) was obtained using NEMA image quality phantom. Recovery coefficients of 90%, 86%, 68%, 40% and 12% were calculated for rod diameters of 5, 4, 3, 2 and 1 mm, respectively. Spill-over ratios for air-filled and water-filled chambers were 35% and 25% without applying any correction for attenuation and Compton scattering effects. Conclusion: Our findings revealed that beyond compactness, lightweight, easy installation and good energy resolution, the Xtrim-PET prototype presents a reasonable performance making it suitable for preclinical molecular imaging-based research.

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Missing areas in PET sinograms and severe image artifacts as a consequence thereof, still gain prominence not only in sparse-ring detector configurations but also in full-ring PET scanners in case of faulty detectors. Empty bins in the projection domain, caused by inter-block gap regions or any failure in the detector blocks may lead to unacceptable image distortions and inaccuracies in quantitative analysis. Deep neural networks have recently attracted enormous attention within the imaging community and are being deployed for various applications, including handling impaired sinograms and removing the streaking artifacts generated by incomplete projection views. Despite the promising results in sparseview CT reconstruction, the utility of deep-learning-based methods in synthesizing artifact-free PET images in the sparse-crystal setting is poorly explored. Herein, we investigated the feasibility of a modified U-Net to generate artifact-free PET scans in the presence of severe dead regions between adjacent detector blocks on a dedicated highresolution preclinical PET scanner. The performance of the model was assessed in both projection and image-space. The visual inspection and quantitative analysis seem to indicate that the proposed method is well suited for application on partial-ring PET scanners.

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.

Background: Radiation-induced hematopoietic suppression and myelotoxicity can occur due to the nuclear accidents, occupational irradiation and therapeutic interventions. Bone marrow dysfunction has always been one of the most important causes of morbidity and mortality after ionizing irradiation. Objective: This study aims to investigate the protective effect of telmisartan against radiation-induced bone marrow injuries in a Balb/c mouse model. Material and Methods: In this experimental study, male Balb/c mice were divided into four groups as follow: group 1: mice received phosphate buffered saline (PBS) without irradiation, group 2: mice received a solution of telmisartan in PBS without irradiation, group 3: mice received PBS with irradiation, and group 4: mice received a solution of telmisartan in PBS with irradiation. A solution of telmisartan was prepared and administered orally at 12 mg/kg body weight for seven consecutive days prior to whole body exposing to a single sub-lethal dose of 5 Gy X-rays. Protection of bone marrow against radiation induced damage was investigated by Hematoxylin-Eosin (HE) staining assay at 3, 9, 15 and 30 days after irradiation. Results: Histopathological analysis indicated that administration of telmisartan reduced X-radiation-induced damage and improved bone marrow histology. The number of different cell types in bone marrow, including polymorphonuclear /mononuclear cells and megakaryocytes significantly increased in telmisartan treated group compared to the only irradiated group at all-time points. Conclusion: The results of the present study demonstrated an efficient radioprotective effect of telmisartan in mouse bone marrow against sub-lethal X-irradiation.