Imaging Techniques in Large Animals
Imaging techniques in large animals bridges the gap between preclinical and clinical research. The same scanners can be used for large laboratory animals and for human beings and, with few modifications, the same scanning protocols can also be used. Therefore, knowledge obtained from imaging techniques in animal research can readily be used in humans. Similarly, medical hypotheses and problems from clinical experience with humans can often be tested and studied in large animals. Imaging techniques create either anatomical images (Computerized Tomography, CT or Magnetic Resonance Imaging, MRI) or functional images of the body (Positron Emission Tomography, PET). While X-ray radiation is used to get a cross-sectional CT image of the body, MRI involves the use of a magnetic field that forces the hydrogen cellular nuclei to align in different positions. PET utilizes radiation emitted from the animal after injection of radioactive tracers. The most commonly used large animals in imaging research are dogs, sheep, goats, pigs and nonhuman primates. These laboratory animals have large organs and blood volumes that allow repeated blood sampling, which is needed in most PET studies, while blood sampling is unnecessary for CT and MRI imaging. Large animals are outbreed, and so many animals are typically needed in each study, due to marked individual variation. That situation is unfavourable, because imaging studies of large animals are expensive and time consuming. Except for nonhuman primates, large animals must be anaesthetised for scanning procedures, and this may influence the experiments.