From the Guidelines
To rule out stroke or TIA, I recommend ordering a diffusion-weighted imaging (DWI) MRI with apparent diffusion coefficient (ADC) mapping, along with T2-weighted and FLAIR sequences, as soon as possible after symptom onset, ideally within 24 hours for TIA evaluation. This combination provides the most sensitive and specific imaging for acute ischemic changes, which can be detected within minutes of symptom onset 1. The standard protocol should also include gradient echo or susceptibility-weighted imaging (SWI) sequences to detect hemorrhage.
Key Considerations
- DWI has a high sensitivity (88% to 100%) and specificity (95% to 100%) for detecting infarcted regions, even at very early time points, within minutes of symptom onset 1.
- If there is concern about large vessel occlusion or stenosis, adding MR angiography (MRA) of the head and neck is valuable, as it can help identify culprit intracranial lesions in the setting of suspected TIA 1.
- In cases where MRI is contraindicated or unavailable, a CT perfusion study with CT angiography would be the alternative, though it is less sensitive for small or posterior fossa infarcts 1.
Additional Recommendations
- The American Heart Association/American Stroke Association guidelines recommend MRI, including DWI, as the preferred brain diagnostic imaging modality for patients with transient ischemic neurological symptoms, with imaging to be performed within 24 hours of symptom onset or as soon as possible in patients with delayed presentations 1.
- Noncontrast MRA of the neck tends to overestimate the degree of carotid stenosis when compared with contrast-enhanced MRA, particularly in cases of high-grade stenosis, and typically, noncontrast TOF MRA technique is sufficiently sensitive to screen for culprit intracranial lesions in the setting of suspected TIA 1.
From the Research
MRI Options for Ruling Out Stroke or TIA
To rule out stroke or Transient Ischemic Attack (TIA), the following MRI options can be considered:
- Diffusion-weighted magnetic resonance imaging (DWI) is an advanced imaging technique that allows non-invasive evaluation of water diffusibility in brain tissue 2
- Magnetic resonance angiography (MRA) can be used in combination with DWI to detect artery lesions and evaluate cranial and cervical arteries 3, 4
Key Findings
Key findings from studies on the use of MRI in stroke and TIA diagnosis include:
- DWI lesions are detected in approximately 1 in 6 to 2 in 3 TIA patients, with symptom duration, speech or motor symptoms, and aetiology correlating with the rate of DWI positivity 2
- The combined interpretation of DWI images and apparent diffusion coefficient (ADC) maps enables the distinction of infarcts ≤5 days old from infarcts >10 days old 2
- DWI lesion size is a prognostic marker of stroke outcome, but cannot replace clinical outcome scores in a mixed stroke population 2
- MRA and DWI can be used to detect large-artery lesions in patients with a classical lacunar syndrome 5
Clinical Applications
Clinical applications of MRI in stroke and TIA diagnosis include:
- Early diagnosis and treatment of ischemic stroke, with DWI/MRA improving the accuracy of diagnosis and guiding therapy 3
- Detection of clinically silent ischemic lesions after carotid interventions, with DWI detecting new lesions in 37% of carotid stenting patients compared to 10% of carotid endarterectomy patients 2
- Evaluation of cranial and cervical arteries and brain tissue in TIA patients, with MRA and DWI detecting significant differences in vessel characteristics and lesion signals 4