Neuroimaging in Ischemic Stroke Diagnosis

Introduction to Ischemic Stroke Imaging

The American Heart Association and the American College of Radiology recommend a comprehensive MRI protocol for diagnosing ischemic stroke, including diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI), and MR angiography (MRA) sequences, to identify the mismatch pattern characteristic of ischemic stroke and luxury perfusion 1, 2, 3

Perfusion-weighted imaging (PWI) should include contrast-enhanced dynamic susceptibility contrast (DSC) perfusion to assess cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) 2, 3
Diffusion-weighted imaging (DWI) is essential for identifying cytotoxic edema and core infarct tissue, as well as for DWI-PWI mismatch assessment, and is the most sensitive and specific technique for detecting acute infarction within minutes of onset 1, 2, 3
T2-weighted FLAIR is recommended for subacute infarct visualization and edema assessment, and is the best method for showing abnormal fluid accumulations and subacute infarcts 1, 4
T2*-weighted gradient echo (GRE) or susceptibility-weighted imaging (SWI) should be used to exclude hemorrhage, and is used for excluding intracerebral hemorrhage 1, 5
MR angiography (MRA) is necessary to evaluate vascular patency and identify occlusions, and can be performed without or with contrast, and is used to demonstrate vascular occlusion 1, 6, 5, 7
T1-weighted imaging, pre- and post-contrast, is used to assess blood-brain barrier disruption 4

Luxury perfusion is characterized by increased regional cerebral blood flow (rCBF) relative to metabolic demand, normal or elevated cerebral blood volume (CBV) in the affected area, and decreased mean transit time (MTT) 2

Contrast administration should be a single dose of gadolinium (0.1 mmol/kg) with a minimum 5-minute delay between injection and T1-weighted sequence acquisition, and acquisition parameters should include a maximum slice thickness of 3 mm and in-plane spatial resolution of 1 × 1 mm 4
Total acquisition time should be kept under 25-30 minutes, and a comprehensive stroke MRI protocol can be performed in as little as 6-10 minutes using modern techniques 1, 4

In patients with renal impairment (eGFR <30 mL/min/1.73m²), non-contrast ASL perfusion should be used instead of gadolinium-based techniques, and CT perfusion can be considered as an alternative when MRI is contraindicated 2, 3
For patients within 3 hours of symptom onset, either non-contrast CT or MRI is acceptable to exclude hemorrhage, and for patients beyond 3 hours from symptom onset, MR-DWI is strongly recommended (Class I, Level A evidence) to identify salvageable tissue 1, 6
For patients being considered for endovascular therapy, vascular imaging is strongly recommended (Class I, Level A) and a complete multimodal MRI including DWI, PWI, MRA, GRE/SWI, and FLAIR should be performed, and do not delay IV thrombolysis for extensive MRI if the patient is within the treatment window 1, 6