MRI brain (summary)

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This is a basic article for medical students and other non-radiologists

MRI brain is a specialist investigation that is used for the assessment of a number of neurological conditions. It is the main method to investigate conditions such as multiple sclerosis and headaches, and used to characterize strokes and space-occupying lesions.

Reference article

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Summary

  • indications
    • confirmation of stroke
    • assessment of intracranial tumor
    • chronic headache
    • seizure disorder
  • important pathology
  • benefits
    • multiplanar assessment of the brain
    • exceptionally detailed images of the brain
    • different sequences allow assessment of different pathology
    • no ionizing radiation (especially important in children)
  • limitations
    • much longer investigation (20-40 minutes)
    • less available (longer waiting list)
    • patients may be claustrophobic
    • contraindicated in patients with some metallic implants
      • most pacemakers are not MRI-compatible
  • procedure
    • patient positioned on the MRI couch
    • head coil positioned over their head
    • patient moved into the center of the magnet
    • sequences acquired
  • similar tests
    • CT head
      • first-line investigation in most acute situations
    • CT head with contrast
      • initial assessment of intracranial lesions

About MRI

Different pulses and different signals provide a variety of sequences and images that we use. Unlike CT where we describe "density", images are described by signal intensity ("hyper-" bright, "hypo-" dark).

  • T1
    • provides the most anatomically-relevant images
    • fluid (in CSF and orbits) is dark
    • grey matter is darker than the white matter
  • T2
    • standard sequence
    • fluid is bright
    • white matter is darker than grey
  • FLAIR (fluid attenuation inversion recovery)
    • commonly used sequence
    • similar to T2, but the fluid is darker or "suppressed"
    • useful for areas of edema or inflammation
    • used to identify plaques in multiple sclerosis (especially periventricular)
  • DWI and ADC (diffusion-weighted imaging and apparent diffusion coefficient)
    • these "blocky" images show how easily water moves around
    • restricted diffusion occurs in stroke, abscesses and cellular tumors
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