Should an MRI (Magnetic Resonance Imaging) brain be done with or without contrast to assess for stroke?

MRI Brain Without Contrast is the Preferred Imaging Modality for Stroke Assessment

MRI brain without contrast is the recommended imaging modality for assessing stroke, providing superior diagnostic accuracy for ischemic changes without the risks associated with gadolinium administration. 1, 2

Initial Imaging Approach for Suspected Stroke

Non-Contrast MRI

• MRI without contrast offers higher sensitivity than CT for detecting both acute and chronic ischemic changes
• Includes essential sequences:
  • Diffusion-weighted imaging (DWI): Highly sensitive for early ischemic changes
  • T2-weighted sequences: Detect both acute and chronic changes
  • Susceptibility-weighted imaging: Detects hemorrhage
  • FLAIR: Shows subacute and chronic ischemic changes

Time Considerations

• If rapid treatment decisions are needed (within 4.5-hour thrombolytic window), non-contrast CT may be performed first due to faster acquisition time 1
• MRI without contrast should follow as soon as possible for definitive diagnosis
• Studies show that early MRI (within 12 hours of admission) facilitates stroke evaluation and decreases hospital length of stay 3

Vascular Assessment When Needed

For Large Vessel Occlusion (LVO) Assessment

• MRA head without contrast should be added to evaluate intracranial vasculature 1
• Time-of-flight (TOF) MRA technique is sufficiently sensitive to screen for culprit intracranial lesions 1
• In patients with renal insufficiency or contrast allergy, TOF MRA is particularly valuable 1

For Extracranial Vessel Assessment

• MRA neck without contrast can evaluate extracranial vasculature 1
• Current American Heart Association guidelines recommend noninvasive imaging of cervical carotid arteries within 48 hours of onset for TIA or minor stroke patients who are candidates for carotid endarterectomy or stenting 1

When Is Contrast Indicated?

Contrast administration is generally NOT necessary for initial stroke assessment, but may be considered in specific scenarios:

• When stroke mimics are suspected (tumors, infections, etc.) 2
• For secondary workup of patients presenting with stroke-like symptoms 1
• For perfusion assessment when benefits outweigh risks 2
• For evaluation of cerebral metastases (in patients with known intracranial tumors) 4

Common Pitfalls and Caveats

• Small posterior fossa strokes may be missed on early MRI in up to 50% of cases within the first 48 hours 2
• Non-contrast MRA of the neck tends to overestimate the degree of carotid stenosis compared to contrast-enhanced MRA, particularly in high-grade stenosis 1
• Some strokes may not be visualized on MRI, particularly very early brainstem strokes 5
• In patients with contraindications to MRI (pacemakers, metallic implants), CT remains the appropriate alternative 2
• Delay in obtaining MRI should not postpone thrombolytic therapy in appropriate candidates 1, 2

Alternative Approaches

• For patients with renal impairment or contrast allergies: Non-contrast MRI with TOF MRA is the preferred approach 1
• For hyperacute stroke evaluation (within 4.5 hours): Initial non-contrast CT followed by MRI if time permits 1
• For patients unable to undergo MRI: Non-contrast CT with CT angiography if vascular assessment is needed 1

By prioritizing MRI without contrast for stroke assessment, clinicians can achieve optimal diagnostic accuracy while avoiding unnecessary contrast administration and its associated risks.