Abstract
Traumatic brain injury (TBI) is a common condition with many potential acute and chronic neurological consequences. Standard initial radiographic evaluation includes noncontrast head CT scanning to rapidly evaluate for pathology that might require intervention. The availability of fast, relatively inexpensive CT imaging has fundamentally changed the clinician's ability to noninvasively visualize neuroanatomy. However, in the context of TBI, limitations of head CT without contrast include poor prognostic ability, inability to analyze cerebral perfusion status, and poor visualization of underlying posttraumatic changes to brain parenchyma. Here, the authors review emerging advanced imaging for evaluation of both acute and chronic TBI and include QuickBrain MRI as an initial imaging modality. Dynamic susceptibility-weighted contrast-enhanced perfusion MRI, MR arterial spin labeling, and perfusion CT are reviewed as methods for examining cerebral blood flow following TBI. The authors evaluate MR-based diffusion tensor imaging and functional MRI for prognostication of recovery post-TBI. Finally, MR elastography, MR spectroscopy, and convolutional neural networks are examined as future tools in TBI management. Many imaging technologies are being developed and studied in TBI, and some of these may hold promise in improving the understanding and management of TBI. ABBREVIATIONS ASL = arterial spin labeling; CNN = convolutional neural network; CTP = perfusion CT; DAI = diffuse axonal injury; DMN = default mode network; DOC = disorders of consciousness; DTI = diffusion tensor imaging; FA = fractional anisotropy; fMRI = functional MRI; GCS = Glasgow Coma Scale; MD = mean diffusivity; MRE = MR elastography; MRS = MR spectroscopy; mTBI = mild TBI; NAA = N-acetylaspartate; SWI = susceptibility-weighted imaging; TBI = traumatic brain injury; UHF = ultra-high field.
Highlights
I n the United States, traumatic brain injury (TBI) accounts for more than 280,000 hospitalizations and 50,000 deaths annually.[52]
QuickBrain MRI is a rapid T2 fast spin echo sequence that requires 1–3 minutes for image acquisition; this imaging protocol has been trialed for the initial imaging of pediatric patients with Traumatic brain injury (TBI) with promising results but is not yet the standard of care.[58]
Work done by Moenninghoff et al has demonstrated that UHF susceptibility-weighted imaging (SWI) MRI reveals an average of 41% more traumatic microbleeds caused by diffuse axonal injury (DAI) than does 3T SWI, and these lesions appear larger on UHF SWI MRI.[83]
Summary
Perfusion imaging is based on the relationship between a defined tissue volume, the mean transit time through that tissue, and flow of blood through that tissue.[14]. 1B and 2C).[13,30] In a study by Soustiel et al, CTP performed within 48 hours of TBI was able to delineate cerebral contusions that required at least 7 days to become apparent on noncontrast CT.[62] A study by Metting et al demonstrated that, in patients with mild TBI and negative findings on head CT, CTP was able to predict functional outcome at 6 months, based on the presence of frontal lobe perfusion abnormalities.[42] This same group showed that postTBI amnesia was associated with frontal lobe abnormalities during the amnesic event.[41] In moderate and severe TBI, several groups have demonstrated that early CTP showing normal or hyperperfusion correlates with a favorable outcome while hypoperfusion correlates with a worsened outcome.[6,79] There are data to suggest that intermittent CTP can help guide interpretation of cerebral perfusion pressure values and possibly improve functional outcome.[76] Mean transit time from CTP may be useful in determining where an oxygen tensor monitor should be placed by targeting areas most at risk for hypoxia.[23] there has been much promising data supporting the use of CTP in TBI, there is still no rigorous clinical investigation to support its routine use or to incorporate this imaging modality as a standard of care
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