Ann Biomed Eng. 2011 Oct 13. [Epub ahead of print]
Maximum Principal Strain and Strain Rate Associated with Concussion Diagnosis Correlates with Changes in Corpus Callosum White Matter Indices.
McAllister TW, Ford JC, Ji S, Beckwith JG, Flashman LA, Paulsen K, Greenwald RM.
Department of Psychiatry, Section of Neuropsychiatry, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH, 03756, USA, firstname.lastname@example.org.
On-field monitoring of head impacts, combined with finite element (FE) biomechanical simulation, allow for predictions of regional strain associated with a diagnosed concussion. However, attempts to correlate these predictions with in vivo measures of brain injury have not been published. This article reports an approach to and preliminary results from the correlation of subject-specific FE model-predicted regions of high strain associated with diagnosed concussion and diffusion tensor imaging to assess changes in white matter integrity in the corpus callosum (CC). Ten football and ice hockey players who wore instrumented helmets to record head impacts sustained during play completed high field magnetic resonance imaging preseason and within 10 days of a diagnosed concussion. The Dartmouth Subject-Specific FE Head model was used to generate regional predictions of strain and strain rate following each impact associated with concussion. Maps of change in fractional anisotropy (FA) and median diffusivity (MD) were generated for the CC of each athlete to correlate strain with change in FA and MD. Mean and maximum strain rate correlated with change in FA (Spearman ρ = 0.77, p = 0.01; 0.70, p = 0.031), and there was a similar trend for mean and maximum strain (0.56, p = 0.10; 0.6, p = 0.07), as well as for maximum strain with change in MD (-0.63, p = 0.07). Change in MD correlated with injury-to-imaging interval (ρ = -0.80, p = 0.006) but change in FA did not (ρ = 0.18, p = 0.62). These results provide preliminary confirmation that model-predicted strain and strain rate in the CC correlate with changes in indices of white matter integrity.
These authors in the article just reported above have basically used accelerometers to capture the head motion impacts from the entire group of helmeted players in real game/practice conditions. How they have interpreted their data is very clever. They have asked themselves the question: How does these impacts affect the brain matter itself in terms of strain changes depending on how strong plus from which direction their brains were set in motion within their skulls. For once the so-called normal DIFFUSION TENSOR IMAGE (DTI) images of the players could be compared to the DTI images following a concussion since preseason MRI images were made for each player.The DTI image differences that the authors picked up after the concussion used fractional anistropy, (FA) whose definition I have enclosed from Wikipedia. In this case fiber density, axonal diameter plus myelination of the white matter. So what are all these fancy words here? What is happening? What is FA change all about?
These authors are reporting as their conclusion that the central white matter tracts that connect the two hemispheres have changed strain character, but in what way you might ask? I would argue that the white matter tract of the corpus callosum that joins the two hemispheres has experienced in the concussive motion what Penfield termed brain pull, or what I call a brain vortex event, as the two hemispheres rotate in the concussion shape change event, the white matter connecting the two hemispheres has been stretched, hence the changes in the fractional anistropy that the post concussion diffusion tensor imaging (DTI), unlike strict MRI imaging has revealed.
Essentially the authors appear to be describing shape changes within the brain particularly within the corpus callosum after the concussion reveals the strain changing from the preseason DTI image.
This is a very exciting development. These Dartmouth investigators are reporting real brain FA alterations following a concussion which is basically our premise. If such brain shape rotation is happening other fractional anistropy should be also visible in central medulla zones involving both the vagal (x) nerve together with the glossopharyngeal (IX) nerve at the medulla zone, no? There is our neurocardiac connection.
It looks like it’s just a matter of time that we too can make our point of brain rotation happening with each concussive hit. Stay tuned !
Fractional anisotropy (FA)
Fractional anisotropy (FA) is a scalar value between zero and one that describes the degree of anisotropy of a diffusion process. A value of zero means that diffusion is isotropic, i.e. it is unrestricted (or equally restricted) in all directions. A value of one means that diffusion occurs only along one axis and is fully restricted along all other directions.
with the trace
Alternatively, FA can be calculated as
- ^ Basser, P.J. & Pierpaoli, C. (1996). “Microstructural and physiological features of tissues elucidated by quantitative-diffusion-tensor MRI”. Journal of Magnetic Resonance, Series B, 111, 209-219
- The next paper from right here in Montreal at Université de Montréal confirms the same zone of the corpus callosum citing biomechanical strain, there’s that brian shape change which is tensegrity or Penfileld brain pull or excuse my enthusiasm -McHugh brain shape or cerebrovortex. Looks like a trend !
- J Neurotrauma. 2011 Oct;28(10):2049-59. Epub 2011 Oct 4.
Acute and chronic changes in diffusivity measures after sports concussion.
1 Département de Psychology, Université de Montréal , Montréal, Québec, Canada .
Abstract Despite negative neuroimaging findings in concussed athletes, studies indicate that the acceleration and deceleration of the brain after concussive impacts result in metabolic and electrophysiological alterations that may be attributable to changes in white matter resulting from biomechanical strain. In the present study we investigated the effects of sports concussion on white matter using three different diffusion tensor imaging (DTI) measures: fractional anisotropy (FA), mean diffusivity (MD), and axial diffusivity (AD). We compared a group of 10 non-concussed athletes with a group of 18 concussed athletes of the same age (mean age 22.5 years) and education (mean 16 years) using a voxel-based approach (VBA) in both the acute and chronic post-injury phases. All concussed athletes were scanned 1-6 days post-concussion and again 6 months later in a 3T Siemens Trio(™) MRI. Three 2×2 repeated-measures analyses of variance (ANOVAs) were conducted, one for each measure of DTI used in the current study. There was a main group effect of FA, which was increased in dorsal regions of both corticospinal tracts (CST) and in the corpus callosum in concussed athletes at both time points. There was a main group effect of AD in the right CST, where concussed athletes showed elevated values relative to controls at both time points. MD values were decreased in concussed athletes, in whom analyses revealed significant group differences in the CST and corpus callosum at both time points. Although the use of VBA does limit the analyses to large tracts, and it has clinical limitations with regard to individual analyses, our results nevertheless indicate that sports concussions do result in changes in diffusivity in the corpus callosum and CST that are not detected using conventional neuroimaging techniques.
- [PubMed – in process]