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Trauma Imaging Techniques

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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.

Report

Description

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Trauma

Pediatrics

Neuroradiology

MRI

Emergency

CT

Brain

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