From the Guidelines
For new-onset stroke, a non-contrast CT scan should be requested as the initial imaging study, as it is the preferred first-line imaging test for suspected acute stroke, according to the most recent evidence from 1.
Reasons for Preference
- It's faster and more widely available than MRI
- It can quickly rule out hemorrhagic stroke
- It's sufficient to guide initial treatment decisions, especially regarding thrombolysis The National Institutes of Health Stroke Scale (NIHSS) is a scoring system that should be used to assess stroke severity, evaluating 15 items including level of consciousness, gaze, visual fields, facial palsy, motor function, sensory function, language, and attention, with scores ranging from 0 (no stroke symptoms) to 42 (severe stroke), as noted in 1 and 1.
Additional Considerations
If time allows and MRI is readily available, it can provide more detailed information about the extent and location of ischemia, as discussed in 1. However, MRI should not delay treatment if CT is more immediately accessible.
Key Principle
Remember, "time is brain" in acute stroke care, and rapid assessment and imaging are crucial to determine eligibility for time-sensitive treatments like thrombolysis or thrombectomy, emphasizing the importance of prompt action based on the initial CT scan, as highlighted in 1 and 1.
From the Research
Imaging Modalities for New-Onset Stroke
- Computed Tomography (CT) scan is the most commonly used initial imaging tool to evaluate stroke, due to its sensitivity for hemorrhage, rapid acquisition, and widespread availability 2.
- Noncontrast head CT remains the ideal first study for stroke evaluation, with CT angiography (CTA) being the most common follow-up study to identify intracranial large vessel occlusions and cervical carotid or vertebral artery disease 2.
- Magnetic Resonance Imaging (MRI) and Magnetic Resonance Angiography (MRA) can provide valuable insights for outcomes prognostication as well as stroke etiology, but are not typically used as the initial imaging modality 2.
Comparison of CT and MRI
- A study comparing the sensitivity of neuroimaging techniques in ischemic stroke found that MRI was significantly more sensitive than CT in detection of ischemic lesion, particularly in patients with lacunar infarcts 3.
- However, CT is reliable for detection of considerable number of cortical ischemic strokes of the anterior cerebral circulation within the first 12 hours after stroke onset 3.
- After 48 hours from stroke onset, CT, MRI, and Diffusion-Weighted Imaging (DWI) show high sensitivity in detection of ischemic lesion of all clinical stroke subtypes 3.
Automated Imaging Techniques
- Automated ASPECTS scoring using machine learning has been shown to be effective in determining ASPECTS on noncontrast CT images in patients with acute ischemic stroke 4.
- The use of automated imaging techniques can improve the accuracy and efficiency of stroke diagnosis and treatment 4.
Clinical Practice
- Non-contrast CT is predominantly used in clinical practice for acute stroke imaging, but MRI can also be used to exclude contraindications to thrombolysis treatment 5.
- Advanced stroke imaging techniques such as CT and MR angiography and perfusion imaging are increasingly being used in acute stroke settings 5.