What is the first line imaging modality to rule out stroke?

First-Line Imaging for Ruling Out Stroke

Non-contrast CT (NCCT) of the head is the first-line imaging modality to rule out stroke due to its speed, widespread availability, and excellent sensitivity for detecting intracranial hemorrhage. 1

Imaging Algorithm for Suspected Stroke

Initial Evaluation

• Non-contrast CT (NCCT) of the head should be performed immediately to:
  • Differentiate between hemorrhagic and ischemic stroke
  • Exclude intracranial hemorrhage before thrombolytic therapy
  • Assess the extent of early ischemic changes
  • Complete imaging within 45 minutes of emergency department arrival 1

Secondary Imaging (Based on Initial Findings and Treatment Options)

• For patients eligible for IV thrombolysis (0-4.5 hour window):

  • NCCT is sufficient to initiate treatment without waiting for further imaging 1
  • IV tPA can be administered immediately after NCCT confirms no hemorrhage

• For patients being considered for endovascular therapy:

  • NCCT followed by vascular imaging (CTA head and neck) 1
  • Alternatively, MRI with MRA can be used if rapidly available 1

• For patients outside thrombolysis window (>4.5 hours) or with TIA:

  • MRI with diffusion-weighted imaging (DWI) is preferred if available 1
  • NCCT should only be performed if MRI is not available 1

Advantages of Different Modalities

Non-contrast CT

• Rapid acquisition (critical for time-sensitive treatment decisions)
• Widely available in emergency settings
• Excellent sensitivity for detecting hemorrhage
• Sufficient to determine eligibility for IV thrombolysis 1, 2
• Can be completed within minutes of arrival

MRI with DWI

• Superior sensitivity for detecting early ischemic changes
• Can detect ischemic lesions in approximately 40% of TIA patients 1
• Better visualization of posterior fossa structures
• Provides information about stroke etiology through lesion distribution patterns 1
• No radiation exposure

CT Angiography (CTA)

• Rapidly identifies large vessel occlusions
• Evaluates cervical carotid or vertebral artery disease
• Helps determine stroke mechanism and guide treatment decisions 1, 3
• Essential for endovascular therapy planning

Common Pitfalls to Avoid

• Delaying thrombolysis for additional imaging when NCCT is sufficient to initiate treatment
• Overlooking subtle early ischemic changes on NCCT (use appropriate window settings)
• Failing to obtain vascular imaging in patients with acute stroke, which is essential for determining stroke mechanism and future stroke risk 1, 3
• Relying solely on NCCT for TIA evaluation when MRI with DWI is preferred if available 1

Special Considerations

• For patients with contraindications to MRI, NCCT with CTA is an appropriate alternative 1
• In facilities where MRI is available 24/7 with rapid acquisition times, an MRI-first approach may be considered 4
• For suspected intracranial hemorrhage, follow-up CTA may be needed to evaluate for underlying vascular malformations or aneurysms 1

By following this imaging algorithm, clinicians can rapidly differentiate between hemorrhagic and ischemic stroke, determine appropriate treatment options, and assess stroke mechanism to guide secondary prevention strategies.