The Short Answer Educational content only, not medical advice. No test described here diagnoses concussion on its own, and concussion diagnosis remains clinical. The advanced imaging methods covered in this series are research tools that detect group-level differences and are not validated to diagnose or exclude concussion in an individual person. Be cautious about clinics selling scans or brain maps as diagnostic. Discuss any assessment with a concussion-experienced clinician who can interpret it alongside your history and examination. Susceptibility-weighted imaging detects substances that distort the local magnetic field, principally blood products such as hemosiderin and deoxyhemoglobin, along with iron and calcium. This makes it far more sensitive than standard MRI sequences to tiny hemorrhages, called microbleeds, produced when shear forces tear small vessels during injury. Research has examined whether microbleeds on susceptibility-weighted MRI predict post-traumatic complaints after mild traumatic brain injury (Hageman et al., 2022). The most important practical point is that most people with concussion have no microbleeds at all, so a negative scan is the expected result and tells you very little. It detects blood products invisible on standard MRI sequences. Microbleeds mark where shear forces tore small vessels. Most concussion scans show none, so a negative result is uninformative. How the Sequence Works Certain substances are paramagnetic, meaning they distort the magnetic field around them. Deoxygenated hemoglobin and its breakdown products, particularly hemosiderin, have this property strongly. Susceptibility-weighted imaging combines magnitude and phase information from a gradient echo acquisition to amplify these local field distortions, so a tiny deposit of blood product produces a signal void much larger than the deposit itself, a phenomenon called blooming. That amplification is what makes millimeter-scale hemorrhages visible when conventional sequences show nothing. The same physics makes the sequence sensitive to veins, iron deposition, and calcification. What Microbleeds Represent During rapid acceleration and deceleration, tissues of different densities move at different rates, generating shear forces at their interfaces. These forces stretch and tear axons and also rupture small vessels running alongside them. The resulting microbleeds therefore mark locations where shear injury occurred, which is why they cluster at the gray-white matter junction, in the corpus callosum, and in the brainstem. Their distribution serves as a visible marker of diffuse axonal injury, which is otherwise inferred rather than seen. More extensive microbleeding generally indicates greater injury severity. What the Research Examines The clinically interesting question is whether microbleeds predict outcome. Research examining susceptibility-weighted MRI and microbleeds in mild traumatic brain injury has addressed whether their presence predicts post-traumatic complaints (Hageman et al., 2022). The broader pattern across trauma imaging research is that microbleed burden correlates with injury severity more reliably than it predicts symptoms in mild injury, and many people with substantial persistent symptoms have entirely normal susceptibility-weighted imaging. That mismatch reflects the fact that symptoms after concussion arise from vestibular, cervical, visual, autonomic, sleep, and mood mechanisms rather than from visible hemorrhage. Where It Is Clinically Useful The sequence has genuine clinical roles. In moderate and severe traumatic brain injury it demonstrates the extent of diffuse axonal injury and contributes to prognosis. In suspected non-accidental injury it detects hemorrhage of different ages. It also identifies other pathology relevant to differential diagnosis, including cavernous malformations and superficial siderosis. Where a person with concussion has atypical features, focal neurological signs, or an unexpectedly severe course, adding susceptibility-weighted imaging to an MRI is reasonable as part of investigating for something other than uncomplicated concussion. How to Interpret a Result A negative result is normal and expected, and it neither excludes concussion nor indicates that symptoms lack a physical basis. A positive result confirms hemorrhage occurred but does not by itself explain symptoms, predict recovery, or change most treatment decisions, and it may warrant reclassification of the injury as complicated mild traumatic brain injury, which affects monitoring. Findings also need careful reading, since normal veins, calcification, and iron deposition mimic microbleeds. In every case the scan supplements clinical assessment rather than replacing the identification of treatable symptom drivers (Silverberg et al., 2020). Assessment identifies what is driving symptoms. Cervical and vestibular contributors are among the most commonly found and the most treatable. Start your 3-day free trial for joint-specific mobility programming addressing the neck side of those findings. Supporting Mobility Routine JME 14 Chin tucks reduce the upper cervical tension driving cervicogenic headache, one of the most common findings on post-concussion assessment. Ten repetitions with 5-second holds. JME 1 Cervical rotation restores segmental mobility, which is directly relevant where assessment identifies a cervical contribution to dizziness. Ten repetitions per direction. JME 15 Cervical lateral flexion addresses side-bending restriction sustaining neck tension and headache. Ten repetitions per side. JME 16 Cervical flexion and extension restore sagittal mobility restricted by suboccipital guarding after impact. Eight slow repetitions. JME 2 Cervical retraction reinforces a neutral head position, reducing the postural strain that worsens symptoms during screen-based testing. Ten repetitions per set. JME 150 Thoracic rotation restores mid-back motion, which reduces compensatory load on the cervical spine. Eight repetitions per direction. JME 227 Overhead reach opens the thoracic spine and rib cage, supporting the breathing mechanics behind nervous system regulation. Ten repetitions with controlled tempo. JME 155 Diaphragmatic breathing lowers sympathetic drive, which reduces the symptom load that degrades performance on any cognitive assessment. Ten slow breaths, several times daily. Start your 3-day free trial for joint-specific mobility programming addressing the cervical contributors assessment identifies. Common Mistakes Reading a negative scan as evidence that symptoms are not physical Expecting microbleeds in uncomplicated concussion, where they are uncommon Assuming microbleed count predicts symptom severity or recovery Confusing normal veins, calcification, or iron with microbleeds Pursuing the sequence when clinical features are typical Treating a positive finding as changing most treatment decisions Delaying vestibular and cervical assessment while awaiting imaging Progression Standard CT first where indicated acutely, to exclude bleeding, fracture, and mass effect. Where clinical features are typical, no further imaging is needed, and assessment should move to vestibular, ocular, cervical, sleep, and mood contributors. Reserve susceptibility-weighted imaging for atypical presentations, focal neurological signs, or an unexpectedly severe course, ordered by a clinician as part of investigating alternative pathology. Interpret any finding alongside examination rather than as a standalone explanation for symptoms. What does SWI detect? Substances distorting the local magnetic field, principally blood products such as deoxyhemoglobin and hemosiderin, plus iron and calcium. This makes it far more sensitive than standard sequences to microbleeds, tiny hemorrhages produced when shear forces tear small vessels. Do most people with concussion have microbleeds? No. Microbleeds are uncommon in uncomplicated concussion, so a negative scan is the expected result. A negative result does not exclude concussion and does not indicate that symptoms lack a physical basis. Do microbleeds predict how bad symptoms will be? Not reliably in mild injury. Microbleed burden correlates better with injury severity than with symptom outcome, and many people with substantial persistent symptoms have entirely normal susceptibility-weighted imaging, because symptoms arise from mechanisms other than visible hemorrhage. When is SWI worth ordering? For atypical presentations, focal neurological signs, or an unexpectedly severe course, as part of investigating pathology other than uncomplicated concussion. It also has established roles in moderate and severe injury and in suspected non-accidental injury. Does a positive finding change treatment? Usually not directly. It confirms hemorrhage occurred and may reclassify the injury as complicated mild traumatic brain injury, which affects monitoring. Symptom management still depends on identifying vestibular, cervical, visual, sleep, and mood contributors clinically. How These Tools Fit Together Concussion diagnosis is clinical. It rests on the injury mechanism, the symptoms, and the examination, and international consensus guidance is explicit that no single test establishes or excludes the diagnosis (Patricios et al., 2023). Everything described in this series sits in a supporting role. Sideline and clinic tools such as SCAT6, VOMS, and King-Devick add structure and reproducibility to the clinical assessment. Computerized cognitive batteries quantify one specific domain. Advanced imaging methods detect group-level differences in research populations and are not validated for individual diagnosis (Maas et al., 2022). Confusing these roles is the most common error patients and clinicians make. What Assessment Is Actually For Confirming a clinical picture already suspected from history and examination Identifying which subtype is driving symptoms: vestibular, ocular, cervical, mood, sleep, or migraine Tracking change over time against the person's own earlier results Supporting return-to-play and return-to-work decisions with objective data Ruling out structural injury needing emergency treatment, which is what standard CT does Directing treatment toward the specific system involved Documenting recovery for insurance, legal, or occupational purposes Why Advanced Imaging Is Not Diagnostic Yet The barrier is not that these methods detect nothing. Diffusion imaging, functional MRI, magnetoencephalography, spectroscopy, and perfusion imaging all show reproducible group differences between concussed and control populations. The barrier is the gap between a group difference and an individual diagnosis. Concussion effects are small relative to normal human variation, findings differ in direction between studies and time points, most research lacks pre-injury baselines, acquisition and analysis methods vary between centers, and few studies report the sensitivity and specificity needed to classify one person (Lindsey et al., 2023, and Mayer et al., 2015). A test cannot be clinically diagnostic until it performs reliably on a single scan against a validated normative reference, and that threshold has not been met. Questions Worth Asking About Any Test Several questions separate useful assessment from expensive noise. Does the result change treatment, or only produce a label. Is there a baseline or normative comparison appropriate to your age, sex, and background. What are the sensitivity and specificity for individual diagnosis, and does the provider quote them. Would a concussion-experienced clinician interpret this alongside examination findings, or is it delivered as a standalone report. Is the test being sold directly to patients outside standard clinical pathways. Persistent symptoms usually reflect treatable vestibular, cervical, visual, sleep, or mood problems, and identifying those through clinical assessment changes management in a way most advanced imaging currently does not (Silverberg et al., 2020). References Patricios, J. S., Schneider, K. J., Dvorak, J., et al. (2023). Consensus statement on concussion in sport: the 6th International Conference on Concussion in Sport, Amsterdam, October 2022. British Journal of Sports Medicine, 57(11), 695-711. PubMed Echemendia, R. J., Brett, B. L., Broglio, S., et al. (2023). Sport Concussion Assessment Tool 6 (SCAT6). British Journal of Sports Medicine, 57(11), 622-631. PubMed Mucha, A., Collins, M. W., Elbin, R. J., et al. (2014). A brief Vestibular/Ocular Motor Screening (VOMS) assessment to evaluate concussions: preliminary findings. American Journal of Sports Medicine, 42(10), 2479-2486. PubMed Krause, D. A., Hollman, J. H., Breuer, L. T., et al. (2022). Validity indices of the King-Devick concussion test in hockey players. Clinical Journal of Sport Medicine, 32(3), e313-e315. PubMed Farnsworth, J. L., Dargo, L., Ragan, B. G., et al. (2017). Reliability of computerized neurocognitive tests for concussion assessment: a meta-analysis. Journal of Athletic Training, 52(9), 826-833. PubMed Wilmoth, K., Brett, B. L., Emmert, N. A., et al. (2023). Psychometric properties of computerized cognitive tools and standard neuropsychological tests used to assess sport concussion: a systematic review. Neuropsychology Review, 33(4), 675-692. PubMed Dretsch, M., Parish, R., Kelly, M., et al. (2015). Eight-day temporal stability of the Automated Neuropsychological Assessment Metric (ANAM) in a deployment environment. Applied Neuropsychology: Adult, 22(4), 304-310. PubMed Tenney, J. R., Gloss, D., Arya, R., et al. (2021). Practice guideline: use of quantitative EEG for the diagnosis of mild traumatic brain injury. Report of the Guideline Committee of the American Clinical Neurophysiology Society. Journal of Clinical Neurophysiology, 38(4), 287-292. PubMed Lindsey, H. M., Hodges, C. B., Greer, K. M., et al. (2023). Diffusion-weighted imaging in mild traumatic brain injury: a systematic review of the literature. Neuropsychology Review, 33(1), 42-121. PubMed Mayer, A. R., Bellgowan, P. S., & Hanlon, F. M. (2015). Functional magnetic resonance imaging of mild traumatic brain injury. Neuroscience and Biobehavioral Reviews, 49, 8-18. PubMed Huang, M., Lewine, J. D., & Lee, R. R. (2020). Magnetoencephalography for mild traumatic brain injury and posttraumatic stress disorder. Neuroimaging Clinics of North America, 30(2), 175-192. PubMed Hageman, G., Hof, J., Nihom, J., et al. (2022). Susceptibility-weighted MRI and microbleeds in mild traumatic brain injury: prediction of posttraumatic complaints? European Neurology, 85(3), 177-185. PubMed Eisele, A., Hill-Strathy, M., Michels, L., et al. (2020). Magnetic resonance spectroscopy following mild traumatic brain injury: a systematic review and meta-analysis on the potential to detect posttraumatic neurodegeneration. Neurodegenerative Diseases, 20(1), 2-11. PubMed Hamer, J., Churchill, N. W., Hutchison, M. G., et al. (2020). Sex differences in cerebral blood flow associated with a history of concussion. Journal of Neurotrauma, 37(10), 1197-1203. PubMed Alosco, M. L., Mariani, M. L., Adler, C. H., et al. (2021). Developing methods to detect and diagnose chronic traumatic encephalopathy during life: rationale, design, and methodology for the DIAGNOSE CTE Research Project. Alzheimer's Research and Therapy, 13(1), 136. PubMed Maas, A. I. R., Menon, D. K., Manley, G. T., et al. (2022). Traumatic brain injury: progress and challenges in prevention, clinical care, and research. Lancet Neurology, 21(11), 1004-1060. PubMed Silverberg, N. D., Iaccarino, M. A., Panenka, W. J., et al. (2020). Management of concussion and mild traumatic brain injury: a synthesis of practice guidelines. Archives of Physical Medicine and Rehabilitation, 101(2), 382-393. PubMed