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