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Brain imaging can help doctors investigate particular neurologic symptoms and look for other causes, but a routine MRI or PET scan cannot currently confirm or rule out Long COVID. A normal scan does not make brain fog or other symptoms less real. Long COVID is assessed clinically, using a person’s history and examination as well as any relevant tests.
Is Long COVID diagnosed with a brain scan?
No. The CDC’s Long COVID Clinical Guidance, dated March 9, 2026, says clinicians may diagnose Long COVID from a patient’s history and physical-examination findings; no laboratory test definitively diagnoses or rules it out. The guidance also says: “Objective laboratory or imaging findings should not be used as the only measure or assessment of a patient’s well-being.”
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That distinction matters: a scan can show an abnormality, but an abnormality alone does not establish that Long COVID caused it or that it explains a particular person’s symptoms. Conversely, a scan without a visible abnormality does not exclude Long COVID.
What can a routine brain MRI show?
MRI produces structural images that can help evaluate a specific neurologic concern and identify or exclude other conditions. It is not a general-purpose test for brain fog, nor has routine MRI established a single pattern that identifies Long COVID.
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A prospective multicenter Norwegian study published in Frontiers in Neurology on November 13, 2025, followed 140 people referred for persistent neurologic symptoms after COVID-19. Its findings illustrate why results need clinical context:
- Most participants had white-matter hyperintensity scores of 0 or 1, and scores did not differ significantly from those of healthy controls.
- At six months, distinct non-contrast MRI lesions interpreted as consistent with inflammation or demyelination appeared in 4% (5 of 120 participants).
- Cerebral microbleeds appeared in 16% (21 of 131 participants), at rates the authors said aligned with population studies.
- Among participants who received contrast, cranial nerve enhancement appeared in 5% (5 of 93) at six months and was observed in 7% (7 of 94) at follow-up. Some enhancement was subclinical, and its clinical meaning was not always clear.
These figures describe a referred specialist cohort, not all people with Long COVID. The study did not establish that any of these findings is a diagnostic signature or determine how accurately a scan can diagnose Long COVID in an unselected population. White-matter changes and microbleeds are nonspecific, so their presence does not by itself identify a cause.
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Why can an MRI be normal when someone has brain fog?
A routine MRI looks for visible structural findings; it does not measure every aspect of cognition or explain every neurologic symptom. The Norwegian study found a gap between common complaints and what standard imaging showed. Clinical guidance published in 2024 recommends a detailed history and neurologic examination for cognitive symptoms, with neuropsychological testing considered where appropriate. Imaging may be warranted when focal neurologic abnormalities are present.
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When might imaging be considered?
Imaging is most useful when it addresses a clinical question—such as whether a concerning symptom or examination finding could reflect another neurologic condition. Guidance supports considering brain imaging when focal neurologic abnormalities are present; it does not recommend a scan as routine proof of Long COVID.
The 2022 ESCMID rapid guideline says the limited evidence does not support brain imaging as a general investigation of Long COVID complaints, except to rule out other causes or for research. The decision should be made with a clinician based on symptoms, examination findings and possible alternative diagnoses, rather than on the Long COVID label alone.
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Can PET or advanced imaging diagnose Long COVID?
The available guidance and study evidence do not establish PET or advanced quantitative imaging as validated routine tests for diagnosing Long COVID in an individual. These approaches should not be treated as interchangeable with routine MRI: they may answer different questions, and detecting a pattern does not by itself show that it explains symptoms or changes treatment. Advanced quantitative imaging remains unestablished in routine clinical practice, according to the 2025 Norwegian study.
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Should an MRI be repeated?
Not automatically. In the Norwegian study, MRI changes between six and twelve months were infrequent among the 88 participants scanned at both time points: 5% developed one new white-matter hyperintensity, another 5% had one fewer, and no new ischemic infarctions were identified. The study authors concluded that MRI primarily helps exclude alternative diagnoses and that repeat imaging has limited clinical benefit when there are no new symptoms. A clinician can reassess whether a new or changing symptom creates a reason for further imaging.
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