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The use of medical imaging as a non-invasive or minimally invasive method to assess disease or treatment response continues to grow. A similar trend is observed in pre-clinical research, in general, and more specifically in macaques, enabling longitudinal assessment of disease in individual animals. Computed tomography (CT) is such an imaging technique used to obtain clinically applicable data. To acquire a chest CT using a cone beam tomography system, some kind of respiration control is needed. A commonly used technique for this is endotracheal intubation and mechanical ventilation. However, although routinely performed this can increase the risk of impact on welfare in comparison with non-invasive imaging. Therefore, we studied the option of retrospectively gated CTs: acquiring high resolution chest CTs in freely breathing macaques. For this, we compared 748 CTs obtained during free breathing with 881 CTs obtained with mechanical ventilation in combination with a breath-hold procedure predominantly on the appearance of misregistration artifacts. The scans were obtained during different stages of multiple experimentally induced respiratory diseases. The comparison shows that although there are still streaking artifacts present in the retrospective gated scans, the amount of shading artifacts is reduced to such a level that it possibly dominates underlying lesions, causing misdiagnosis. Our data reveal that the use of retrospective gating in high resolution CTs for macaques can be successfully applied. With the use of this technique, artifacts due to free breathing are reduced to a diagnostically appropriate level. Most importantly, this technique makes chest CTs with this instrumentation a non-invasive modality.

Medical imaging as method to assess the longitudinal process of a SARS-CoV-2 infection in non-human primates is commonly used in research settings. Bronchoalveolar lavage (BAL) is regularly used to determine the local virus production and immune effects of SARS-CoV-2 in the lower respiratory tract. However, the potential interference of those two diagnostic modalities is unknown in non-human primates. The current study investigated the effect and duration of BAL on computed tomography (CT) in both healthy and experimentally SARS-CoV-2-infected female rhesus macaques (Macaca mulatta). In addition, the effect of subsequent BALs was reviewed. Thorax CTs and BALs were obtained from four healthy animals and 11 experimentally SARS-CoV-2-infected animals. From all animals, CTs were obtained just before BAL, and 24 hours post-BAL. Additionally, from the healthy animals, CTs immediately after, and four hours post-BAL were obtained. Thorax CTs were evaluated for alterations in lung density, measured in Hounsfield units, and a visual semi-quantitative scoring system. An increase in the lung density was observed on the immediately post-BAL CT but resolved within 24 hours in the healthy animals. In the infected animals, a significant difference in both the lung density and CT score was still found 24 hours after BAL. Furthermore, the differences between time points in CT score were increased for the second BAL. These results indicate that the effect of BAL on infected lungs is not resolved within the first 24 hours. Therefore, it is important to acknowledge the interference between BAL and CT in rhesus macaques.

Medical imaging as method to assess the longitudinal process of a SARS-CoV-2 infection in non-human primates is commonly used in research settings. Bronchoalveolar lavage (BAL) is also regularly used to determine the local virus production and immune effects of SARS-CoV-2 in the lower respiratory tract. However, the potential interference of those two diagnostic modalities with each other is unknown in non-human primates. The current study investigated the effect and duration of BAL on computed tomography (CT) in both healthy and experimentally SARS-CoV-2-infected female rhesus macaques (Macaca mulatta). In addition, the effect of subsequent BALs was reviewed. Thorax CTs and BALs were obtained from four healthy animals and 11 experimentally SARS-CoV-2-infected animals. From all animals, CTs were obtained just before BAL, and 24 hours post-BAL. Additionally, from the healthy animals, CTs immediately after and four hours post-BAL were obtained. Thorax CTs were evaluated for alterations in lung density, measured in Hounsfield units, and a visual semi-quantitative scoring system. An increase in the lung density was observed on the immediately post-BAL CT but resolved within 24 hours in the healthy animals. In the infected animals, a significant difference in both the lung density and CT score was still found 24 hours after BAL. Furthermore, the differences between timepoints in CT score were increased for the second BAL. These results indicate that the effect of BAL on infected lungs is not completed within the first 24 hours. Therefore, it is of importance to acknowledge the interference between BAL and CT in rhesus macaques.

Introduction: The present study was designed to assess whether [18F]PK-209 (3-(2-chloro-5-(methylthio)phenyl)-1-(3-([18F]fluoromethoxy)phenyl)-1-methylguanidine) is a suitable ligand for imaging the ion-channel site of N-methyl-D-aspartate receptors (NMDArs) using positron emission tomography (PET). Methods: Dynamic PET scans were acquired from male rhesus monkeys over 120min, at baseline and after the acute administration of dizocilpine (MK-801, 0.3mg/kg; n=3/condition). Continuous and discrete arterial blood samples were manually obtained, to generate metabolite-corrected input functions. Parametric volume-of-distribution (VT) images were obtained using Logan analysis. The selectivity profile of PK-209 was assessed in vitro, on a broad screen of 79 targets. Results: PK-209 was at least 50-fold more selective for NMDArs over all other targets examined. At baseline, prolonged retention of radioactivity was observed in NMDAr-rich cortical regions relative to the cerebellum. Pretreatment with MK-801 reduced the VTof [18F]PK-209 compared with baseline in two of three subjects. The rate of radioligand metabolism was high, both at baseline and after MK-801 administration. Conclusions: PK-209 targets the intrachannel site with high selectivity. Imaging of the NMDAr is feasible with [18F]PK-209, despite its fast metabolism. Further in vivo evaluation in humans is warranted.