Is MRI with or without contrast (gadolinium) recommended for diagnosing stroke?

MRI Without Contrast is Recommended for Diagnosing Stroke

MRI without contrast is the preferred imaging modality for diagnosing stroke, as it provides superior diagnostic accuracy without the risks associated with gadolinium administration. 1

Rationale for Non-Contrast MRI in Stroke Diagnosis

Superior Diagnostic Capability

• MRI without contrast, particularly diffusion-weighted imaging (DWI), is highly sensitive for detecting acute ischemic changes and is superior to CT for stroke diagnosis 2
• DWI-MRI can detect acute ischemic stroke in 46% of patients within 3 hours of symptom onset, compared to only 7% with CT 2
• Non-contrast MRI has a sensitivity of 83% for diagnosing acute stroke versus only 26% for CT 2

Clinical Guidelines Support

• The American College of Radiology (ACR) states that MRI without contrast is useful for evaluating the extent of completed ischemic infarct due to its high sensitivity for acute ischemic changes 1
• Current American Heart Association (AHA) guidelines recommend either non-contrast CT or MRI before thrombolytic therapy to exclude hemorrhage and determine ischemic changes 1

When Contrast May Be Considered

Gadolinium contrast should be reserved for specific clinical scenarios:

1. Stroke Mimics: When brain tumors or other conditions that mimic stroke are suspected 1
2. Secondary Workup: For patients with stroke-like symptoms where the initial non-contrast imaging is inconclusive 1
3. Perfusion Assessment: In select cases beyond 24 hours from onset to detect additional at-risk regions not demonstrated by DWI 1
4. Cryptogenic Stroke: To identify unstable plaque or other culprit lesions 1

Risks of Gadolinium Administration

• Nephrogenic systemic fibrosis in patients with advanced renal failure (eGFR <30 mL/min/1.73m²) 1, 3
• Gadolinium reactions, though uncommon, can be dangerous 1
• Gadolinium-based contrast can reduce detection of the hyperintense vessel sign (HVS), an important marker of acute ischemic stroke 4

Algorithmic Approach to Stroke Imaging

1. Initial Imaging: Non-contrast MRI with DWI and T2-weighted sequences

   • Provides high sensitivity for acute ischemic changes
   • Can detect both acute and chronic hemorrhage 2
   • Should be interpreted within 45 minutes of patient arrival 1

2. If vascular assessment needed: Add MRA without contrast

   • For evaluation of large vessel occlusion
   • Note that non-contrast MRA may overestimate carotid stenosis 1

3. If perfusion assessment needed: Consider MR perfusion

   • Preferably using arterial spin labeling (ASL) technique which doesn't require contrast 1
   • Or contrast-enhanced perfusion if ASL unavailable and benefits outweigh risks

4. If stroke mimic suspected: Only then consider MRI with contrast

   • To evaluate for tumors or other pathologies 1

Important Caveats

• Time is critical in acute stroke management - imaging should not delay treatment with intravenous thrombolytics in appropriate patients 1
• For patients presenting within the thrombolytic window (4.5 hours), rapid imaging is essential - in some centers, CT may be preferred due to faster acquisition time
• Small posterior fossa strokes may be missed on early MRI in up to 50% of cases within the first 48 hours 1
• In patients with contraindications to MRI (pacemakers, metallic implants), CT remains the appropriate alternative 1

In conclusion, MRI without contrast should be the standard approach for diagnosing stroke when available and not contraindicated, with contrast reserved only for specific clinical scenarios where additional information is needed beyond what non-contrast imaging can provide.