Interactive Transcript
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The technical aspects of imaging a patient who has head
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trauma are important and I want to emphasize
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with respect to the CT imaging,
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which is usually done as the primary mode of evaluation
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of the patient in the emergency room,
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that thin section images are critical.
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At our institution, we see the 0.75 millimeter or
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0.6 millimeter thin sections on all of our CT scans
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for patients who have head trauma.
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The technologist may reconstruct them in 2-3 millimeter
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thick sections in the axial, coronal or sagittal plane.
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But because sometimes the imaging findings of traumatic
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head injury are relatively subtle,
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I highly recommend that you look at the thin sections
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for this indication. Not only that,
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but I usually will make my own reconstructions in coronal
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or sagittal plane, rather than using the thicker section
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3 millimeter thick sections that the technologists provide.
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And that's because small subdural hematomas or
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epidural hematomas may be 1-2 millimeters thick,
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and therefore, the potential for partial volume
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averaging is quite high.
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In addition with traumatic brain injury,
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we usually say that you have
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to look at the brain with multiple windows.
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And by that, I mean both a brain window,
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as well as a broader window and centered image
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that will allow you to detect those subtle
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subdural collections, as well as the bone windows in
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order to see fractures. So at the very least,
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you should be looking at three separate windows,
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that is brain subdural window, and bone window,
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as well as
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multiple planes, be it axial, coronal and sagittal planes.
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With regard to MR imaging,
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at a very basic, we need our T1 and T2 weighted scans
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to be able to detect the hemorrhage
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and to be able to characterize its age.
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However,
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susceptibility weighted imaging has become a mainstay
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of imaging for head trauma because of its
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increased sensitivity to blood products,
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both deoxyhemoglobin for acute hemorrhage,
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as well as hemosiderin for the chronic effects of hemorrhage,
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as well as methemoglobin,
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which is our marker for subacute hemorrhage.
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Some facilities will do an MR technique that highlights
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the bone marrow in order to detect fractures.
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This is true in particular if you have a policy of using
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MR in pediatric cases to avoid any type
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of radiation of the patient for CT.
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So in some instances, the emergency department
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is ordering MR imaging in children
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as the first and initial evaluation of the patient
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rather than CT, in order to avoid irradiating young brains.
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As with CT, it's best to do multiplanar imaging.
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I mentioned susceptibility weighted MRI,
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and this is a technique
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which was developed by Mark Haacke.
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It's a wonderful technique for evaluation of
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blood products. It is, as he says here,
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a 3D velocity compensated gradient echo sequence that
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combines magnitude information as well as phase
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information and accentuates the visibility of susceptible
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foci such as small veins and hemorrhage.
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We usually will reconstruct this in what is called
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a minimum intensity projection, a MIP,
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which refers to not the maximum intensity projection,
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but the minimum intensity projection,
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to see all the darkest signals that represent hemorrhage.
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In this situation,
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we have a gradient echo scan on the left side
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which shows lots of little black dots of hemorrhage,
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in this case hemosiderin,
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because there's no edema around them.
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But note that on the exact same slice,
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using susceptibility weighted imaging,
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we see so many more little dots of these hemorrhage,
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these foci of hemosiderin with this technique.
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So, although gradient echo technique used to be our
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best masterpiece for looking for hemorrhage,
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we've now replaced that with susceptibility
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weighted imaging, which is far superior.
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Thank you to Mark Haacke.
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