From the Guidelines
For diagnosing acute ischemic stroke, the recommended MRI protocol includes both non-contrast and contrast-enhanced sequences, with a core protocol consisting of diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC) maps, fluid-attenuated inversion recovery (FLAIR), gradient echo or susceptibility-weighted imaging (SWI), and MR angiography (MRA) of the head and neck, as supported by the most recent guidelines 1.
The choice of MRI protocol is crucial in the diagnosis of acute ischemic stroke, as it helps to determine the extent of ischemic changes, identify potential stroke mimics, and guide treatment decisions regarding thrombolysis or thrombectomy.
- The core protocol should include DWI, ADC maps, FLAIR, SWI, and MRA of the head and neck.
- Contrast administration using gadolinium-based agents (0.1 mmol/kg) is not routinely necessary for initial diagnosis but may be valuable in specific situations such as evaluating for vessel patency, identifying arterial dissection, or ruling out stroke mimics like tumors or infections 1.
- The timing of MRI is crucial, with imaging ideally performed within the first 24 hours of symptom onset when DWI is most sensitive for detecting acute infarcts 1.
- DWI shows restricted diffusion in ischemic tissue within minutes of stroke onset, appearing as hyperintense signals, while ADC maps confirm true restriction by showing corresponding hypointensity.
- FLAIR sequences help determine stroke timing (becoming positive after 3-6 hours) and identify subacute or chronic infarcts.
- SWI or gradient echo sequences are essential to exclude hemorrhagic transformation.
The most recent guidelines from 2015 support the use of MRI in the diagnosis of acute ischemic stroke, although they also emphasize the importance of non-contrast brain CT imaging and vascular imaging with CTA in guiding hyperacute care 1.
- The guidelines recommend that additional imaging, such as brain MRI or MRA, may be considered but should not delay decision and treatment with tPA thrombolysis or endovascular therapy.
- The use of advanced CT imaging, including CTP and multiphase or dynamic CTA, should also be considered as part of initial imaging, although this must not substantially delay treatment.
From the Research
MRI Protocol for Diagnosing Acute Ischemic Stroke
The recommended MRI protocol for diagnosing acute ischemic stroke involves the use of various sequences to provide a comprehensive evaluation of the brain.
- Diffusion-weighted imaging (DWI) is a crucial sequence for identifying acute ischemic stroke, as it is highly sensitive for detecting early signs of ischemia 2.
- Fluid-attenuated inversion recovery (FLAIR) imaging is also important, as it can help identify areas of infarction and detect signs of hemorrhagic transformation 3.
- Other sequences, such as T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), and apparent diffusion coefficient (ADC) mapping, can provide additional information about infarct location, volume, and age 3.
Use of Contrast in MRI Protocol
The use of contrast in MRI protocol for acute ischemic stroke is not always necessary.
- Non-contrast MRI sequences, such as DWI, FLAIR, and T2WI, can provide sufficient information for diagnosing acute ischemic stroke 3.
- However, contrast-enhanced MRI sequences, such as magnetic resonance angiography (MRA), can be useful for evaluating vascular occlusions and stenosis 4.
- A 6-minute multimodal MRI protocol that includes both non-contrast and contrast-enhanced sequences can provide a comprehensive evaluation of acute ischemic stroke and can result in significant reduction in scan time 4.
Diagnostic Accuracy of MRI Protocol
The diagnostic accuracy of MRI protocol for acute ischemic stroke is high.
- A study found that a standardized MRI stroke protocol can identify acute ischemic stroke with high sensitivity and specificity, and can also detect signs of hemorrhagic transformation 5.
- Another study found that DWI-FLAIR mismatch can be used to identify patients with acute ischemic stroke within 4.5 hours of symptom onset, which is the recommended time window for thrombolysis 6.
- The use of MRI protocol can also help reduce the need for additional CT scans, which can save time and costs 5.