Systematic assessment of anaesthetic procedures for better alignment and compliance with radiotracer microPET-CT imaging in small animals

Non-invasive, functional imaging techniques such as positron emission tomography-computed tomography (PET/CT) provide the means for studying physiological and pharmacological processes in real-time, both in animals or humans (1) Positron emission tomography-computed tomography imaging has made a major footprint in preclinical research of pharmacology, molecular biology and medical sciences, facilitating innovation in neuroscience, cancer, inflammation and cardiovascular research. Rodent animal models are commonly anaesthetised with ketamine or isoflurane in order to prevent movement artefacts during image acquisitions (2) however, such anaesthesia often alters the physiological condition of the rodents. Consequently, the micro positron emission tomography/computed tomography (microPET/CT) findings obtained in anaesthetised animals may not accurately represent the physiological properties (3) This investigation aims to systematically align different anaesthetics with common radiotracers for PET/CT imaging studies to provide information that can enhance the radiotracer representation according to their targeting mechanism in rodents to advance the quality and translatability of microPET/CT-derived data. The following compatible anaesthetics were not only mainly assessed for suitability of using [18F]fluorodeoxyglucose ([18F]FDG) but also for [68Ga] Ga-DOTA-tate-, or [68Ga]Ga- PSMA-11-microPET-CT diagnostics: isoflurane, sevoflurane, pentobarbital, propofol or combination of fentanylcitratefluanisone/ diazepam and ketamine/xylazine. These anaesthetic agents were compared based on animal physiology (respiration rate, body temperature, apparent glucose metabolism and expected radiotracer biodistribution). The investigated anaesthetics caused altered respiration rate, body temperature, glucose metabolism and have effects on target organs, which affected radiotracer biodistribution. Isoflurane inhalation is the most desired anaesthetic procedure; however, both sevoflurane and isoflurane (also ketamine/xylazine administration) induced hypoglycaemia. Sevoflurane can be suggested over isoflurane for cardiac imaging. Propofol is suitable for [18F]FDG imaging but should be avoided for neuroimaging causing decreased cerebral glucose metabolism. Pentobarbital does not alter the blood glucose metabolism but has a lower safety margin for rodent anaesthesia. Fentanylcitrate-fluanisone/diazepam the preferred injectable anaesthetic option for [18F]FDG being the least interfering with glucose metabolism. Tumour imaging quality using [68Ga]Ga-DOTA-tate- or [68Ga]Ga- PSMA-11-microPET/CT was supported by isoflurane or sevoflurane; however, higher glucocorticoid levels and certain neuroendocrine abnormalities occurred (may originated by hypothermia). This investigation proved that anaesthetics used for preclinical research using microPET/CT imaging need to be carefully aligned with the radiotracer's half-life, and metabolism, to warrant an uninterrupted image acquisition of high quality. A better understanding of the interplay between radiotracers and available anaesthesia agents can allow for the best choice of anaesthesia that will improve the performance and outcome of imaging studies. Thus, radiotracers are supported to show their full research potential to become non-invasive in vivo biomarkers or sensitive drug efficacy monitoring tools. (authors)