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 characterize strokes and space-occupying lesions.

Reference article

This is a summary article; we do not have a more in-depth reference article.

Summary

• indications
  • confirmation of stroke
  • assessment of intracranial tumor
  • chronic headache
  • seizure disorder
• important pathology
  • stroke
  • intracranial tumors
  • multiple sclerosis
• 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