Traditional methods of investigating human disease in animal models often involve invasive sampling and measurement of body fluids and tissues, requiring handling and restraint (which can be distressing for laboratory animals), after which the animals may be sacrificed for further analysis. However, technological advances are making non-invasive imaging techniques increasingly available as practical alternatives to traditional procedures. A variety of techniques can provide images of body systems (e.g. organs, tumours, molecular pathways) with varying degrees of accuracy and permit the refinement, reduction or replacement of the use of animals in experiments.
For example, imaging techniques allow serial studies on the same animal, so reducing inter-animal variation and thus the overall number of animals needed to achieve statistical significance. Because diseases and responses to exogenous substances can be monitored in a temporal and spatial manner, a greater amount of data can be obtained from small numbers of animals and there is no need for invasive surgery and/or serial sacrifice. Non-invasive imaging techniques can also enable more meaningful and humane endpoints to be used, e.g. by allowing early detection of cancerous cells.
Many of the techniques require anaesthesia to prevent motion degradation of images.
T2-weighted structural MRI scan of an anaesthetised rat (in plane resolution is 78um with a 1.5mm slice thickness; data collection time 23 minutes).
Illustration of the MRI measures of perfusion and tissue homeostasis in an experimental model of acute middle cerebral artery ischaemia. Anatomical (T2-weighted) scan appears normal (left), while cerebral blood volume (centre) shows greatly reduced perfusion to the left hemisphere, accompanied by reduction in the apparent diffusion coefficient (right).
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