MRI (introduction)

Dr Jeremy Jones et al.

MRI (an abbreviation of magnetic resonance imaging) is an imaging modality that uses non-ionizing radiation to create useful diagnostic images. MRI was initially called Nuclear Magnetic Resonance Imaging after its early use for chemical analysis. The "Nuclear" was dropped off about 25 years ago because of fears that people would think there was something radioactive involved, which there is not.

NMR was discovered simultaneously by two physicists, Felix Bloch and Edward Mills Purcell, just after the end of World War II. Bloch trained in quantum mechanics and was involved with atomic energy and then radar counter-measures. At the end of the war, he returned to his earlier work in the magnetic moment of the neutron. Purcell was involved with the development of microwave radar during the War then pursued radio waves for evaluation of molecular and nuclear properties. They received the Nobel Prize in Physics in 1952 for this discovery.

MRI, the use of NMR to produce 2D images was accomplished by Paul Lauterbur, imaging water and Sir Peter Mansfield who imaged fingers of a research student, Dr Andrew Maudsley in 1976. Maudsley continues to make a significant contribution to MRI R&D. Raymond Damadian obtained human images a year later in 1977. Lauterbur and Mansfield received the Nobel Prize in Physiology or Medicine in 2003 for their development of MRI.

An MRI scanner consists of a large, powerful magnet in which the patient lies. A radio wave antenna is used to send signals to the body and then receive signals back. These returning signals are converted into images by a computer attached to the scanner. Imaging of almost any part of your body can be obtained in any plane. 

Why use MRI

Advantages

The advantages of MRI include: 

  1. the ability to image without the use of ionising radiation (x-ray) unlike CT scanning
  2. images may be acquired in multiple planes (Axial, Sagittal, Coronal, or Oblique) without repositioning the patient. CT images have only relatively recently been able to be reconstructed in multiple planes with the same spatial resolution
  3. MRI images demonstrate superior soft tissue contrast than CT scans and plain films making it the ideal examination of the brain, spine, joints and other soft tissue body parts
  4. some angiographic images can be obtained without the use of contrast material, unlike CT or conventional angiography
  5. advanced techniques such as diffusion, spectroscopy and perfusion allow for precise tissue characterisation rather than merely 'macroscopic' imaging
  6. functional MRI allows visualisation of both active parts of the brain during certain activities and understanding of the underlying networks
Disadvantages

There are many disadvantages and challenges to implementing MRI scanning. 

MRI scans are more expensive than CT scans and take longer to acquire so patient comfort is sometimes an issue. Additionally, images are subject to unique artefacts that must be recognised and abated (see MRI artefacts).

MRI scanning is not safe for patients with some metal implants and foreign bodies. Careful attention to safety measures is necessary to avoid serious injury to patients and staff, and this requires special MRI compatible equipment and stringent adherence to safety protocols (see MRI safety)

See also

MRI physics
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Article information

rID: 6317
Sections: Physics, Radiography
Synonyms or Alternate Spellings:
  • Nuclear magnetic resonance imaging
  • NMR
  • Nuclear magnetic resonance imaging (NMRI)
  • Magnetic resonance imaging (MRI)
  • Magnetic resonance imaging

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