Felis ISSN 2398-2950

Magnetic resonance imaging: basic principles

Synonym(s): MRI

Contributor(s): Ruth Dennis


  • MRI stands for magnetic resonance imaging, a method of diagnostic imaging.
  • Developed from nuclear magnetic resonance (NMR, spectroscopy), a method of chemical analysis.
  • With the extension of NMR into medical imaging the emotive word 'nuclear' in favor of a term which underlined the imaging aspects of the modality.
  • It has revolutionized medical and veterinary imaging, and has further potential:
    • Yields images of exceptional detail and resolution.
    • Advanced MR techniques can even provide information about tissue function.
  • More referral centers, and even general practices, now have access to MRI facilities, and the pet-owning public expects more sophisticated methods of diagnosis.
  • As MRI technology becomes cheaper and more accessible, it will become a firmly-established part of veterinary practice world-wide.
  • MR scanning is a complex procedure and requires specially-trained radiographers for acquisition and interpretation of images.

Clinical uses

Image construction

  • Images are cross-sectional 'slices' of the area under investigation.
  • Imaging is versatile and increased 3-D information can be obtained by varying:
    • The number and thickness of the slices.
    • The interslice gap.
    • The orientation of the slices relative to the body part.
  • Many different types of scan can be performed, altering the relative gray-scale of the tissues and emphasizing different tissue characteristics.

Advanced MR

  • Contrast MR:
    • Intravenous contrast medium can be used to check the integrity of the blood-brain barrier and to demonstrate the vascularity of a lesion.
  • 3-D MR:
    • With some systems 3-D imaging can be performed, which can be viewed in any plane controlled by the operator.
  • Real time MR:
    • While conventional MR scanning takes several minutes to obtain a set of slice images, faster scanning techniques are being developed.
    • These allow imaging almost in real time, and avoid artifacts created by moving tissues.
    • In people, such short scans can be performed as 'breath-hold' techniques.

MRI physics

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MRI hardware

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Further Reading


Refereed papers