Should I get an MRI (Magnetic Resonance Imaging) with or without contrast to rule out a stroke?

MRI Without Contrast is Recommended for Stroke Diagnosis

For ruling out stroke, MRI without contrast is the recommended imaging modality due to its superior sensitivity for detecting acute ischemic changes compared to CT, without requiring contrast administration.

Why MRI Without Contrast is Preferred

• MRI without contrast, particularly diffusion-weighted imaging (DWI), can detect acute ischemic changes within minutes of stroke onset, while these changes may not be visible on CT for hours 1
• DWI-MRI has significantly higher sensitivity (83%) compared to CT (26%) for diagnosing acute stroke 2
• There is no relevant literature supporting the use of contrast-enhanced MRI specifically for the initial evaluation of suspected acute stroke 1, 3
• MRI can reliably detect both acute ischemic changes and rule out hemorrhage, making it a comprehensive single imaging modality for stroke diagnosis 2, 3

When Contrast May Be Considered

• Contrast-enhanced MRI may be helpful only in secondary workup when stroke mimics such as brain tumors are suspected, but not for primary stroke diagnosis 3, 1
• MRI head without and with contrast should be reserved for cases where there is suspicion for conditions that can mimic ischemic stroke, such as tumors 3
• The American College of Radiology guidelines do not support the use of contrast-enhanced MRI as the initial imaging test for stroke evaluation 3

MRI Protocol Considerations

• A standard MRI protocol for stroke should include 3:

  • T2-weighted or fluid-attenuated inversion recovery (FLAIR) sequence
  • Diffusion-weighted sequence (DWI)
  • Susceptibility-weighted imaging (to detect blood products)

• If vascular imaging is needed, MR angiography (MRA) of the head can be performed without contrast using 3D time of flight techniques 3

• Non-contrast MRA of the head is useful for screening for intracranial steno-occlusive disease in the setting of stroke 3

Limitations and Pitfalls

• DWI-MRI can have false negatives, particularly for small ischemic strokes in the posterior fossa (approximately 50% within the first 48 hours) 1, 4
• Waiting for contrast studies when non-contrast MRI would suffice can unnecessarily delay time-sensitive treatments like thrombolysis 1
• Assuming a negative initial MRI definitively rules out stroke is a pitfall, particularly for small posterior fossa infarcts that may be missed in the first 24-48 hours 1, 4

Clinical Decision Algorithm

1. For suspected acute stroke:

   • Start with MRI brain without contrast with DWI sequence 3, 1
   • Include susceptibility-weighted imaging to detect hemorrhage 3

2. If vascular imaging is needed:

   • Add non-contrast MRA of the head 3
   • Consider contrast-enhanced MRA only if accurate quantification of carotid stenosis is required 3

3. Only consider contrast-enhanced MRI if:

   • Initial non-contrast MRI is negative but clinical suspicion remains high 1
   • There is suspicion for stroke mimics like tumors or infection 3

By following this approach, you'll receive the most accurate diagnostic information for stroke while avoiding unnecessary contrast administration and potential delays in treatment.