Is MRI with or without contrast recommended for a patient suspected of having a stroke?

MRI Without Contrast is Recommended for Suspected Stroke

MRI without IV contrast is the preferred initial imaging modality for patients with suspected stroke due to its high sensitivity for detecting acute ischemic changes without requiring contrast administration. 1

Imaging Options for Stroke Evaluation

MRI Without IV Contrast

• MRI of the head is highly effective in evaluating the extent of completed ischemic infarct in patients with suspected stroke
• Diffusion-weighted imaging (DWI) and T2-weighted sequences are particularly sensitive for detecting acute ischemic changes 1, 2
• Does not require IV contrast, making it safer for patients with renal impairment or contrast allergies 2
• Provides superior detection of acute ischemia compared to CT (83% vs 26% sensitivity) 3

When to Add MRA Without IV Contrast

• Should be performed in conjunction with MRI head without contrast to evaluate for:
  • Intracranial steno-occlusive disease
  • Large vessel occlusions
  • Vascular abnormalities 1
• Non-contrast MRA using time-of-flight (TOF) technique can identify arterial occlusions without contrast 2

Special Considerations

Timing Considerations

• For patients presenting within 6 hours of symptom onset (hyperacute phase):
  • CT is often performed first due to speed and availability for determining eligibility for thrombolysis 4
  • However, MRI can better identify early ischemic changes and is superior for wake-up strokes 1

Contrast Use Scenarios

• MRI without and with contrast is primarily indicated when:
  • Brain tumors or other stroke mimics are suspected 1
  • Secondary workup is needed after initial non-contrast imaging 1

Perfusion Imaging

• Contrast-enhanced MRI perfusion or arterial spin labeling (ASL, non-contrast) may be considered to:
  • Detect at-risk brain regions beyond the 24-hour period
  • Evaluate hemodynamic effects in patients with carotid occlusion 1, 2
  • Identify salvageable tissue 2

Clinical Algorithm for Stroke Imaging

1. Initial presentation with suspected stroke:

   • MRI head without contrast with DWI sequence is preferred 1, 2, 3
   • Add MRA head without contrast for vascular evaluation 1

2. If MRI is contraindicated or unavailable:

   • CT head without contrast followed by CT angiography 5

3. For patients beyond 24 hours from symptom onset:

   • MRI without contrast remains the preferred modality 1
   • Consider adding carotid Doppler ultrasound to evaluate for carotid stenosis 1

4. When to consider contrast:

   • Only when stroke mimics (tumors, infections) are suspected 1
   • For evaluation of certain vascular abnormalities when non-contrast studies are inconclusive 1

Pitfalls to Avoid

• Relying solely on CT for stroke diagnosis, as it has significantly lower sensitivity (10%) compared to MRI (46%) for detecting acute ischemic stroke 3
• Delaying treatment for endovascular therapy candidates by performing unnecessary contrast studies 1
• Using contrast routinely when non-contrast MRI provides sufficient diagnostic information in most cases 2
• Overlooking the need for vascular imaging (MRA) which provides complementary information to parenchymal imaging 1

MRI without contrast provides the optimal balance of diagnostic accuracy and patient safety for stroke evaluation, with the addition of non-contrast MRA providing valuable complementary vascular information without exposing patients to the risks associated with contrast agents.