From the Guidelines
A repeat MRI of the brain after stroke should be considered urgently when a patient's condition deteriorates, as stated in the Australian clinical guidelines for acute stroke management 2007 1. When to repeat an MRI of the brain after a stroke depends on several factors, including the patient's clinical status, stroke severity, and treatment received.
- The American Heart Association/American Stroke Association guideline from 2021 notes that follow-up brain imaging with MRI within 1 to 2 days can provide valuable diagnostic information, and about one-quarter of acute stroke cases with an initially negative head CT will have an MRI with evidence of acute/subacute infarction 1.
- Additional scans may be needed sooner if there is clinical deterioration, new neurological symptoms, or to monitor complications like hemorrhagic transformation or cerebral edema.
- For patients receiving thrombolytic therapy, a repeat MRI within 24 hours is often performed to assess for bleeding complications.
- The timing of follow-up imaging should be individualized based on the patient's clinical status, stroke severity, treatment received, and specific clinical questions that need answering.
- MRI is preferred over CT for follow-up due to its superior ability to detect small infarcts and differentiate between acute, subacute, and chronic changes in brain tissue, as highlighted in the 2021 guideline 1. Key considerations for repeating an MRI include:
- Clinical deterioration
- New neurological symptoms
- Monitoring complications
- Evaluating reperfusion success and identifying complications after mechanical thrombectomy
- Assessing for bleeding complications after thrombolytic therapy
- Evaluating chronic changes and recovery at 3 months post-stroke.
From the Research
Timing of Repeat MRI After Stroke
The decision to repeat an MRI of the brain after a stroke depends on various factors, including the patient's clinical condition, the initial MRI findings, and the purpose of the repeat scan.
- Early Repeat MRI: A study published in 2001 2 found that early recanalization after stroke can save tissue at risk of ischemic infarction and result in significantly smaller infarcts and better clinical outcomes. This suggests that repeat MRI may be useful in the early stages after stroke to assess the effectiveness of treatment and monitor for recanalization.
- Serial MRI: Another study from 1998 3 demonstrated the dynamic nature of progressive ischemic injury in acute stroke patients, with serial MRI showing changes in lesion volume and apparent diffusion coefficient ratio over time. This suggests that repeat MRI may be useful in monitoring the progression of stroke and guiding treatment decisions.
- Utility of Repeat Imaging: However, a study from 1996 4 found that repeat brain imaging in patients with stroke rarely results in changes in the initial diagnosis or therapeutic plan, and indications for repeat imaging are frequently not clearly stated. This suggests that repeat MRI may not always be necessary or useful in the management of stroke patients.
- Negative MRI Findings: A study from 2020 5 found that absence of an infarct on MRI is not uncommon after a clinical diagnosis of ischemic stroke, particularly in patients with lower stroke severity and better functional status. This highlights the importance of considering clinical factors when interpreting MRI findings after stroke.
- Rapid MRI Protocols: A study from 2014 6 demonstrated the feasibility of a 6-minute multimodal MRI protocol for the evaluation of patients with acute ischemic stroke, which can result in significant reduction in scan time and rival the speed of multimodal computed tomographic protocols.
Factors Influencing Repeat MRI
The decision to repeat an MRI after stroke should be based on individual patient factors, including:
- Clinical condition and severity of stroke
- Initial MRI findings and presence of infarct
- Purpose of the repeat scan (e.g. monitoring treatment effectiveness, assessing recanalization)
- Time since stroke onset and potential for changes in lesion volume or apparent diffusion coefficient ratio
- Presence of other diagnostic or therapeutic considerations (e.g. need for angiography or perfusion imaging)