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Magnetic resonance imaging (MRI) is a complex computerized imaging technique, which has been a clinical diagnostic tool since 1980. MRI is used to create images with extraordinary detail of the body or brain by applying nuclear magnetic resonance phenomena. The distribution of hydrogen nuclei (protons), found in cellular water, depends on the tissue type and whether or not the tissue is healthy or diseased.

The MRI technique utilizes a strong magnetic field, pulsed electromagnetic fields known as gradients, and radio waves to stimulate the protons and produce the image in the region of interest. The image is produced then displayed on a gray scale from black to bright white. These densities are only representations of specific signal intensities as described in MRI. The image brightness is a complex function of the hydrogen concentration or intensity. Contrast, described as the difference between signal intensities, provides the optimum difference between light and dark regions of the tissue or organ to help the veterinarian detect lesions, such as a tumor. Although MRI is normally a noninvasive technique, contrast agents can be administered to a subject to enhance a region of interest. How is MRI used? Soft tissue, such as internal organs, are relatively transparent to X-rays, limiting the practical application of other imaging modalities such as computed tomography (CT). MRI, however, has exceptional sensitivity for these tissues with 100% increase in soft tissue resolution compared to it's closest competitor CT. MRI has the added plus of not using ionizing radiation.

The magnetic resonance phenomenon has been steadily gaining in vitro application in the fields of chemistry, biochemistry, and the medical life sciences since its inception in 1946. The technique was first extended to a live animal by Jasper Jackson in 1967, and the first two-dimensional MR image was generated in 1972 by Paul Lauterbur. Since initial reports of the identification of central nervous system (CNS) abnormalities by magnetic resonance imaging during the 1980's, the progression of MR as a diagnostic modality for CNS disease has been rapid. Magnetic Resonance Imaging became routine in human medicine during the 1980s


Caring for your pet after an MRI
 
Thames Valley Veterinary Services
London, Ontario
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