AbstractsBiology & Animal Science

The 3Rs of reduction, refinement and replacement are the guiding principles of animal research and embedded in national and international legislation regulating the use of animals in scientific procedures. Awake imaging by MRI of rodents can offer a reduction by increasing the quality of scientific data through longitudinal imaging using less animals by avoiding a serial sacrifice design and refinement through reducing the stressful effects animals are exposed to, in comparison to existing models. Before awake imaging can become an established biomarker it must be demonstrated that pathology is traceable with comparable or an improvement on results using existing biomarkers.To validate awake imaging of rodents three study types were conducted in two different rodent species: imaging of the progression of Aspergillus fumigatus infection in the mouse lung using anaesthetized animals; analysis of stress in rats during imaging and imaging restraint; imaging of the abdomen in awake rats and a prospective study into the utility of this method for imaging the progression of Candida albicans renal infection.The first study type used an established model of invasive pulmonary aspergillosis in mice to test the utility of MRI for tracking infection in the lung parenchyma. Images of collapsed parenchyma were obtained and shown to increase as the infection progressed. Further work is required to establish this as a clinically relevant biomarker.The study type used restraint, blood collection and imaging as stressors using corticosterone levels as a surrogate of stress. Analysis of levels in blood and faeces by RIA and ELISA allowed comparison of stress during anaethetised and awake imaging for the first time. There were no differences in rat corticosterone levels during anaethetised and awake imaging indicating that awake imaging was no more stressful than currently used procedures.The third study type employed restrainers and acclimatisation to MRI scanner noise to acclimatize rats for awake abdomen imaging. Both anaethetised and awake rats were imaged with FLASH and IntraGate™ sequences. These methods were utilized in an established model of disseminated candidiasis by imaging the kidney. Comparable image quality was obtained in awake animals, with the utility of the method validated by imaging differences in renal pathology between vehicle and low and high dose treated animals. In conclusion, the first steps have been taken towards establishing awake animal imaging by MRI. The imaging is no more stressful than using an anaesthetic and was a useful biomarker in the rat abdomen and capable of tracking disease development. Further work is required to make the technique fully quantitative and automated and hence become a useful tool for monitoring progression of fungal infection and other pathology.