> One of the> problems with diagnosing just what deficits traumatic> brain injury > (TBI) can cause is the inability to image> the injury(s); what is believed to cause > some of these > deficits is "shearing damage" to individual nerve > axons and/or dendrites. IOW, the > acceleration/deceleration of the brain inside the > confines of the hard skull can cause not only bruising > of brain tissue (which can show up on CT or MRI as > altered tissue density), but also tearing of > individual nerve fibers, which does not register on > CT/MRI as the resolution is not sufficient.
Shearing or diffuse axonal injury is difficult to detect with except in severe cases but MR does a much better job. Shear injuries often produce focal vascular damage as well as axonal injuries. A specific MR sequence (gradient echo imaging) is incredibly sensitive to even small amounts of blood and therefore moderate and severe axonal imjuries are detected. The axons are the long components of neurons that extend away from the cell body and carry excitation to synapses which then communicate with adjacent neurons. These long fibers are particularly prone to tearing when the brain is subjected to deceleration injuries in association with rotation. The most exciting new MR technique that is yielding promising data is Diffusion Tensor Imaging. Diffusion of water molecules within the brain can be easily be measured and imaged. The first imaging finding of stroke is reduction of diffusion in the damaged brains as the intracellular tissue becomes viscous as it dies. In our recent paper we showed that diffusion was increased in Boxers (the paper is at ajnr.org. It is in the January 2003 issue). But there is another aspect to diffusion. In gray matter water diffuses symmetrically in all directions (it is isotropic) but white matter is more organized with axons travelling together in tracts (the corpus callosum that connects the two hemispheres is such a tract). Water molecules much more rapidly along (parallel) rather than across (perpendicular) to the tracts. Thus diffusion is anisotropic (highly directional). Diffusion Tensor imaging can detect this anisotropy. A tensor is a measurement in at least 3 directions. Scalar measurement (e.g temperature) can be graphed in a single direction with a single coordinate. Vectors are two dimentional and have two coordinates like a graph. Diffusion Tensor Imaging (DTI)takes 5-10 minutes to acquire as opposed to 40 seconds for a routine diffusion image. You can get two kinds of data depending on how you analyse the information. You can obtain maps of relative anisotropy. Gray matter is zero and white matter is usually around .8. You can also generate maps of fiber tracts by using algorythims that connect the tensors in individual pixels. The tractograms are truly amazing. You can literally trace a single fiber anywhere in the brain. It is truly amazing. With this technique one can directly detect any disease of white matter such as multiple sclerosis. Shear injuries can therefore be directly visualized. This is truly the most amazing thing I have seen in all of my years. I have seen CT evolve and have been involved with MR since its earliest time. will add that bleeding from head > trauma usually is seen on initial CT or MRI, unless it > is a tiny amount or is delayed; which is why doctors > may order a repeat head scan even if the first was > 'normal,' if the person's condition warrants it.) > > [Aside: Bob Z., could you post a link to your group's > work on imaging of head injuries? TIA] > > One of the things we are learning is that brain/spinal > cord injuries, once thought essentially permanent, are > not absolutely so. While we have known that > re-training of uninjured tissue to 'take over' for the > damaged part is frequently possible, especially in > young children, it now appears that actual regrowth > and healing can also take place, albeit very slowly. > (FREX, somebody posted Christopher Reeve's recent > improvements WRT breathing and sensation, as well as > some arm movement, IIRC.) > > For both re-training and healing, it currently appears > that repetition, stimulation and self-will or > perseverence are required; in the future there will be > drugs or recombinant nerve growth factors that greatly > speed this process (research is ongoing). As with > ADD/ADHD, education is really important; > unfortunately, from reading others' posts and my own > experience, much if not most of that has to be > self-taught (although support groups are a great > resource!). > > WRT ADD/ADHD, I think that - just as for dyslexia, > autism and many other brain 'dysfunctions' like > depression or bipolar disorder - there is a huge > spectrum from the glaringly obvious to the nearly > invisible. Right now, choosing which drug to use is > at best a guesstimate, and one may have to try many > before finding the one/combination that works. Some > will not need any medication, and some will not > benefit from any of the ones we currently use. Some > of these kids just need parental attention (which, > sadly, they seem unlikely to get). If we would > research which children require different teaching > techniques (classroom vs. 'real-world,' auditory vs. > visual, thought-experiments vs. hands-on work, etc.) > for their particular brain structure/chemistry, I > think there would be less need for drugs. But there > are very definitely those who *do* improve > tremendously with medication. > > Physical modalities like exercise, nutrition, and > meditation/focusing work (I count things like tai chi > and yoga in this category), which others have written > about, are also essential; in quite a few cases, they > are sufficient therapy. > > Debbi > There Is No Gift Without Its Price Maru `:} > > __________________________________________________ > Do you Yahoo!? > Yahoo! Tax Center - forms, calculators, tips, more > http://taxes.yahoo.com/ > _______________________________________________ > http://www.mccmedia.com/mailman/listinfo/brin-l
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