Anaesthesia and physiological monitoring during in vivo imaging of laboratory rodents: considerations on experimental outcomes and animal welfare

The use of imaging technologies is increasing in biomedical research due to their great scope for non-invasively studying biochemical and biological processes in the living animal. Their application represents a major impact on the refinement of in vivo studies in animal models, in particular for allowing longitudinal monitoring of the onset and the progression of disease within the same animal, and studying the biological effects of drug candidates and their therapeutic effectiveness. They provide a very useful set of tools for a more rapid, efficacious and cost-effective use and characterisation of animal disease models, with great potential for translational research. Indeed, small animal imaging is extensively used as a preclinical experimental tool in many animal models of human diseases including cardiovascular [1], neurodegenerative [2] and musculoskeletal disorders [3] and cancer studies [4]. More recently, it has been applied for the development of stem cell-based therapies [5,6]. There have also been advances wherein researchers are increasingly using imaging for phenotyping and characterisation of transgenic disease models [7].The main challenge for in vivo imaging remains the ‘biological motion’ not only regarding the physical restrain, but also the respiratory and cardiac activities affecting the quality of the images. In contrast to human studies, imaging of small animals generally requires anaesthesia which helps to restrain the animals and their gross motion, but there is still the need to control cardiac and respiratory motion. During anaesthesia, there is an inevitable autonomic nervous system depression which induces cardiovascular and respiratory depression and induces hypothermia. In addition, other conditions such as repeated anaesthesia required for longitudinal studies, the exposure of ionising radiations and the use of contrast agents and/or imaging biomarkers will also have consequences on the physiology of the animal and therefore will nee