Acute Stroke MRI Protocol Recommendations

Core Imaging Sequences

Diffusion‑Weighted Imaging (DWI) is the most sensitive and specific modality for detecting acute cerebral ischemia within minutes of symptom onset, outperforming CT and other MRI sequences. American Heart Association/American Stroke Association (AHA/ASA) recommendation based on high‑quality evidence. 2
Fluid‑Attenuated Inversion Recovery (FLAIR) identifies subacute ischemia, helps exclude stroke mimics, and can reveal subarachnoid hemorrhage. American College of Radiology (ACR) guideline. 1
Gradient‑Recalled Echo (GRE) or Susceptibility‑Weighted Imaging (SWI) reliably excludes intracranial hemorrhage with sensitivity equal to or better than CT and detects microbleeds and intravascular thrombus. ACR recommendation. 3

Time‑of‑flight or contrast‑enhanced MR Angiography (MRA) of both intracranial and cervical arteries should be obtained during the initial evaluation to identify large‑vessel occlusion, arterial stenosis, and to clarify stroke mechanism; it is essential when endovascular therapy is being considered. ACR guideline. 5

Perfusion imaging (MR perfusion or arterial spin labeling) added for patients presenting 6–24 h after last known well or with wake‑up stroke to delineate salvageable tissue via core‑perfusion mismatch. AHA/ASA Class I recommendation. 6
DWI‑FLAIR mismatch can be used to select patients who may benefit from intravenous thrombolysis beyond the conventional 4.5‑hour window. AHA/ASA recommendation. 6

A standard multimodal MRI protocol (DWI, FLAIR, GRE/SWI, MRA, and perfusion) can be completed in approximately 10 minutes. ACR guideline. 2
Imaging acquisition must not delay intravenous thrombolysis when patients are within the therapeutic window; rapid protocols are therefore mandatory. AHA/ASA recommendation. 3

Minimum required sequences: DWI, FLAIR, GRE/SWI to exclude hemorrhage and assess ischemic extent. ACR guideline. 1
MRA should be added if endovascular therapy is available and it does not postpone treatment. AHA/ASA recommendation. 2

A complete protocol including head and neck MRA is strongly recommended during the initial assessment. ACR guideline. 5
Perfusion imaging is advised when presentation is beyond 6 hours from onset to identify viable penumbra. AHA/ASA recommendation. 6

Multimodal MRI is preferred over CT, focusing on DWI (positive in ~40 % of TIAs), vascular imaging (MRA or CTA), and determination of stroke mechanism. ACR guideline. 7

Acute ischemia detection: DWI sensitivity approaches 100 %, compared with <60 % for early CT. AHA/ASA evidence. 2
Superior visualization of small infarcts and posterior‑fossa lesions. AHA/ASA evidence. 2
Better identification of stroke mimics. ACR evidence. 4
Enhanced detection of microhemorrhages and chronic vascular disease. AHA/ASA evidence. 3
GRE/SWI provides hemorrhage detection equal to or better than CT. AHA/ASA evidence. 3

MRI should be employed only when it does not delay treatment and the facility can achieve acquisition speeds comparable to CT‑based pathways. AHA/ASA recommendation. 2
The presence of fewer than five microbleeds on GRE is not a contraindication to intravenous thrombolysis; the risk associated with more than five microbleeds remains uncertain. AHA/ASA guidance. 2
24/7 availability of rapid‑acquisition MRI is essential for routine acute‑stroke imaging. ACR recommendation. 8
All required imaging should be completed within 30 minutes of hospital arrival to maintain treatment timelines. AHA/ASA guideline. 6