Imaging Technologies

Imaging

Many traditional methods of investigating disease in animal models involve invasive handling and restraint of the animal, followed by sampling and measurement of body fluids and tissues. At some point, the animal may be sacrificed for further analysis. However, non-invasive and minimally-invasive imaging techniques that provide images of body systems (e.g., organs, tumours and molecular pathways) are becoming increasingly available to use as alternatives, even for small animals such as rodents.

Use of imaging can make important contributions to Replacement, Reduction and Refinement alternatives. In some cases, imaging of humans can replace the need to conduct investigations with animals (Replacement alternative). In the area of Reduction alternatives, 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. In addition, 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 smaller numbers of animals and there is no need for invasive surgery and/or serial sacrifice. For Refinement alternatives, imaging techniques can allow the use of earlier humane endpoints and fewer invasive procedures.

Imaging Techniques

Some of the available techniques include:

  • Bioluminescence involves light produced by a chemical reaction inside an organism. It can occur naturally (e.g., bacteria, algae and jellyfish), or be engineered (e.g., mammalian cells.) It is currently used to monitor carcinogenesis, tumour growth and the course of bacterial and viral infections.
  • Fluorescent Markers are animal cells which have been  genetically altered to express a fluorescent protein. A blue light is used to capture the image in freely moving animals. Fluorescent markers are currently used to monitor tumour growth and bacterial infections.
  • Magnetic Resonance Imaging (MRI) uses the absorption and emission of energy by hydrogen atoms in water, fat, protein and carbohydrate to provide high resolution anatomical information and measurements of physiology, metabolism, pathology and pharmacology. MRI techniques can be used to monitor cancer development, assess the effect of therapeutic interventions, and replace histological techniques in phenotype screens.
  • Positron Emission Technology (PET) detects picomolar concentrations of radioisotopes in vivo. Miniaturized PET equipment, called micro PET, allows for use of this technique on small animals. Currently, it is used for early detection of cancer, measurements of blood radioactivity without the need for blood sampling, and imaging of in vivo gene expression.
  • Quantum Dots are nano-crystals of semi-conducting material that can be chemically conjugated to biological molecules. When they are excited by a light pulse, they emit distinct colours. This is a novel technique and possible toxicity to the animal from the semi-conducting material is not fully known.

This section has been adapted from the National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs) website and Hudson (2005).

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