Using a complex variety of sequences, MR can provide data concerning both structural and physiological derangements. MR technology continues to develop and is becoming generally available. PET imaging provides unparalleled insights into cerebral physiology and pathophysiology, but is not widely available and is primarily a research tool. Perfusion imaging based on CT techniques (xenon CT and CT perfusion) can be implemented easily in most hospital centres, and provide quantitative perfusion data in addition to structural images. Physiological imaging techniques can only provide ‘snap shots’ of physiology within the injured brain, but they can be repeated, and such data can be used to assess the impact of therapeutic interventions. Although MRI provides greater spatial resolution, particularly within the posterior fossa and deep white matter, a complete assessment of the burden of injury requires imaging of cerebral physiology. CT allows rapid assessment of brain pathology which ensures patients who require urgent surgical intervention receive appropriate care. This review will discuss the role of structural imaging using computed tomography (CT) and magnetic resonance imaging (MRI) and physiological imaging using CT perfusion, 131Xe CT, MRI and spectroscopy (MRS), single photon emission computed tomography, and positron emission tomography (PET) in the assessment, management, and prediction of outcome after head injury. So, an automobile accident, for example, where you move forward and stop, the brain is rotating inside of the skull.Head injury remains an important cause of death and disability in young adults. That can happen front to back as well when the head moves in this direction. So you can imagine with an acceleration-deceleration injury, like being hit by a boxer and being hit on the jaw, the head turning, eventually the head stops, but the brain keeps turning inside of the skull so you get this rotational-type injury. A rotational injury is one where the brain turns inside of the skull. If you were hit directly in the nose with a punch, that would move the head back in one plane, and the brain would go from front to back and might, in fact, bounce off of the skull. The linear injury is one that is best described as sort of a piston action, and that would be if-let's say we're talking about boxing. And that can involve either a linear injury or rotational injury. Also as part of this injury, there are various dynamics going on with this shaking injury that we talked about, or the acceleration-deceleration injury. So all of a sudden it stops working toward repairing those cells, and so you slow down in that process, and that can take anywhere from a few hours to 5 or 10 days to get back to normal physiological function at those brain cell levels. Unfortunately, you begin to run out of glucose, and after a mild head injury, your brain is slightly swollen and doesn't allow as much blood to get into the brain and bring you that energy source. That requires energy, which is essentially in the form of glucose, and you have glucose in the brain, and it uses that glucose to make this change. So your brain-when it is injured, those cells try to get back to normal, and they try to bring the sodium and potassium back into the cell and expel the calcium. And it can cause death of the brain cell, which is referred to as apoptosis. When a brain cell is shaken, it discharges its sodium and potassium, and that is replaced by calcium, which is actually very good for your bones but not very good for your brain. But the kind of injuries we're discussing are mild head injuries, or concussions, and they usually just involve that shaking of the brain, where there is a bioelectrical discharge of energy and there is a physiological process that involves the use of glucose in the brain and things happening, actually, at the cellular level of the brain. If it's shaken violently, it can hit areas of the skull and create swelling and bleeding in the brain. And what happens there is the brain is shaken. Most of the injuries you see in sports and that sort of thing are the acceleration variety. The dynamics of a closed head injury, which is what we are talking about today, is that the brain is either subjected to a direct insult, which is called a blunt injury, or is a shaking or what we refer to as an acceleration-deceleration injury.
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