What type of MRI (Magnetic Resonance Imaging) study is recommended to assess for ischemic stroke?

Optimal MRI Protocol for Ischemic Stroke Assessment

The optimal MRI protocol for assessing ischemic stroke should include diffusion-weighted imaging (DWI), fluid-attenuated inversion recovery (FLAIR), gradient-recalled echo (GRE) or susceptibility-weighted imaging (SWI), and MR angiography (MRA) sequences. 1

Core MRI Sequences for Ischemic Stroke

Essential Sequences

• Diffusion-Weighted Imaging (DWI): Most sensitive and specific technique for detecting acute infarction within minutes of onset 1
• Fluid-Attenuated Inversion Recovery (FLAIR): Best method for showing abnormal fluid accumulations and subacute infarcts 1
• Gradient-Recalled Echo (GRE) or Susceptibility-Weighted Imaging (SWI): For excluding intracerebral hemorrhage 1, 2
• MR Angiography (MRA): To demonstrate vascular occlusion 1

Additional Valuable Sequences

• Perfusion-Weighted Imaging (PWI): When combined with DWI, helps differentiate viable from non-viable hypoperfused tissue 1
• Apparent Diffusion Coefficient (ADC) maps: Helps confirm true diffusion restriction 2

Clinical Decision Algorithm

1. For patients within 3 hours of symptom onset (IV tPA candidates):

   • Either non-contrast CT or MRI is acceptable to exclude hemorrhage 1
   • If using MRI, ensure it doesn't delay IV tPA administration 1
   • Include DWI, FLAIR, GRE/SWI, and MRA if time permits 1

2. For patients beyond 3 hours from symptom onset:

   • MR-DWI is strongly recommended (Class I, Level A evidence) 1
   • Add vascular imaging (MRA) and perfusion studies 1
   • Include DWI-PWI mismatch assessment to identify salvageable tissue 1

3. For patients being considered for endovascular therapy:

   • Vascular imaging is strongly recommended (Class I, Level A) 1
   • Complete multimodal MRI including DWI, PWI, MRA, GRE/SWI, and FLAIR 1

Benefits of MRI Over CT for Stroke Assessment

• DWI is superior to CT for detecting small infarcts and posterior fossa lesions 1, 3
• DWI-FLAIR mismatch helps determine stroke onset time when unknown 2
• MRI significantly improves stroke subtype diagnosis accuracy (from 48% to 94% with DWI+MRA) 4
• Adding DWI to conventional MRI increases detection of acute lesions from 71-80% to 94% 3

Practical Implementation

• A comprehensive stroke MRI protocol can be performed in as little as 6-10 minutes using modern techniques 1, 5
• Rapid multimodal MRI protocols with good diagnostic quality are feasible and can rival CT in acquisition speed 5
• For institutions with limited MRI availability, prioritize DWI and GRE/SWI sequences 1

Important Caveats

• Do not delay IV thrombolysis for extensive MRI if the patient is within the treatment window 1
• MRI contraindications (pacemakers, metal implants, severe claustrophobia) may necessitate CT instead
• Patient cooperation is required for high-quality MRI; sedation may compromise neurological assessment
• Availability of MRI may be limited in some centers, particularly during off-hours

By implementing this MRI protocol for ischemic stroke assessment, clinicians can obtain crucial information about infarct location, size, age, vascular status, and potentially salvageable tissue, which guides appropriate treatment decisions and improves patient outcomes.