Canis ISSN: 2398-2942

Magnetic resonance imaging: basic principles

Synonym(s): MRI

Contributor(s): Ruth Dennis

Introduction

  • 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 revolutionised 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 worldwide.
  • MR scanning is a complex procedure and requires specially-trained radiographers for acquisition and interpretation of images.
    Print off the owner factsheet Scanning - the inside picture to give to your client.

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 emphasising 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.
  • 3D 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 artefacts 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

Publications

Refereed papers

  • Recent references from VetMedResource and PubMed.
  • Tidwell A S et al (1999) Advanced imaging concepts - a pictorial glossary of CT and MRI technology. Clin Tech Small Anim Pract 14(2), 65-111.
  • Mattoon J S et al (1998) MRI case presented as part of the 1997 ACVR oral certification examination - computed tomography/magnetic resonance imaging elective. Vet Radiol Ultrasound 39(2), 154-155.
  • Widmer W R et al (1997) Artifacts and technical errors presented as part of the 1996 ACVR oral certification examination. Vet Radiol Ultrasound 38(2), 156-158.
  • Shores A (1993) New and future advanced imaging techniques. Vet Clin North Am Small Anim Pract 23(2), 461-469.
  • Shores A (1993) Magnetic resonance imaging. Vet Clin North Am Small Anim Pract 23(2), 437-459.
  • Sande R D (1992) Radiography, myelography, computed tomography, and magnetic resonance imaging of the spne. Vet Clin North Am Small Anim Pract 22(4), 811-831.


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