Abstract
Mild traumatic brain injury (mTBI) is a significant public health care burden in the United States. However, we lack a detailed understanding of the pathophysiology following mTBI and its relation to symptoms and recovery. With advanced magnetic resonance imaging (MRI), we can investigate brain perfusion and oxygenation in regions known to be implicated in symptoms, including cortical gray matter and subcortical structures. In this study, we assessed 14 mTBI patients and 18 controls with susceptibility weighted imaging and mapping (SWIM) for blood oxygenation quantification. In addition to SWIM, 7 patients and 12 controls had cerebral perfusion measured with arterial spin labeling (ASL). We found increases in regional cerebral blood flow (CBF) in the left striatum, and in frontal and occipital lobes in patients as compared to controls (p = 0.01, 0.03, 0.03 respectively). We also found decreases in venous susceptibility, indicating increases in venous oxygenation, in the left thalamostriate vein and right basal vein of Rosenthal (p = 0.04 in both). mTBI patients had significantly lower delayed recall scores on the standardized assessment of concussion, but neither susceptibility nor CBF measures were found to correlate with symptoms as assessed by neuropsychological testing. The increased CBF combined with increased venous oxygenation suggests an increase in cerebral blood flow that exceeds the oxygen demand of the tissue, in contrast to the regional hypoxia seen in more severe TBI. This may represent a neuroprotective response following mTBI, which warrants further investigation.
Highlights
Over 1.7 million Americans suffer a traumatic brain injury (TBI) each year, most of which are classified as mild TBI, called concussion [1]
Based on the previously described procedure [40,49], the following steps were taken for susceptibility weighted imaging and mapping (SWIM) processing: a) skull stripping to remove the artifacts caused by skull and brain tissue interface by using the software package MRIcro (MRIcro, Version 1.40) with the Brain Extraction Tool (BET) [50]; b) phase unwrapping to extract susceptibility weighted imaging (SWI) phase signal; c) background field removal to correct the background field inhomogeneity according to the method by Pandian et al in 2008 [51]; d) inverse filtering to extract susceptibility signal; and e) iterative reconstruction to remove remnant ringing of potential microhemorrahges
As a result of concussion, the brain has increased relative CBF (rCBF) and higher venous oxygenation. This finding is in opposition to our original hypothesis that the brain may have decreased rCBF and decreased venous oxygenation
Summary
Over 1.7 million Americans suffer a traumatic brain injury (TBI) each year, most of which are classified as mild TBI (mTBI), called concussion [1]. Decreases in perfusion or venous oxygenation in the brain could indicate either a potentially at-risk area with unmet energy demands or a change in energy demands (a result of a change in function), which represent two entirely different injury responses with different implications for outcome. These hypoperfused areas can be identified by decreased CBF and oxygenation [11]; in patients with moderate to severe TBI ischemic volume has been shown to correlate with negative outcomes [12]. We administered a short neurocognitive assessment, the standardized assessment of concussion (SAC) [43], to examine the correlation between the cognitive deficits and the imaging abnormalities
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