MRI brain (summary)

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 characterise strokes and space-occupying lesions.

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  • indications
  • important pathology
  • benefits
    • multiplanar assessment of the brain
    • exceptionally detailed images of the brain
    • different sequences allow assessment of different pathology
    • no ionising 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 centre 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

Different pulses and different signals provide the 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 oedema 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 tumours
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rID: 38277
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  • MRI head (summary)

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Cases and figures

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    Normal midline
    Figure 1: normal midline brain
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    Figure 2: axial T2 brain
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    Fig 3: sagittal T1 - Chiari I malformation
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    Fig 4: sagittal FLAIR - MS plaques
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    Fig 5: DWI in left parietal acute stroke
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