Topic 3 - structural imaging Flashcards
what are the advantages of structural imaging
diagnosis (if visible - not common in concussion)
in vivo anatomy
why is CT the structural imaging of choice
speed, availbility, lower cost, and limited contraindications
how does CT work
rotating xray detectors that measure the reduction in xrays and process detector data into grey scale images
what is CT sensitive to (easily see)
facial fractures
hemorrhage in all brain spaces
(layers of scans across the brain)
how many CT scans reveal an abnormality in concussion workups
~3%
<1% require neurosurgical intervention
what is the canadian CT head rule
CT only required for patients with minor head injuires that have other red flag symptom(s)
- allows for much fewer scans because they are not needed
why is MRI sometimes useful
doesn’t use ionising radiation
role in the acute setting
what are the downsides of MRI
rarely identifies a concussion
- used with more severe TBIs/soft tissue damage but even then it’s tough to differentiate
how does an MRI work
uses a strong magentic field and radiofrequency pulse to excite spinning protons in tissues to create imaging with different contrasts
why does MRI work in humans
water content (water molecules have a slight positive and slight negative)
- can detect changes in water movement based on the spin put on the molecule
what does DTI look for
expected water mvmt in the brain
- unexpected = probable damage
why does DTI work
- water molecules move in the brain
- water motion can be used to infer about neuroanatomy
- dominated by static anatomy and less influenced by physiology
what is isotropic diffusion
water that is free to move in any direction
(lake)
what is anisotropic diffusion
water that moves along one axis but not others
(river)
how is anisotropic used in the brain to estimate axonal organisation
water moves more easily along the axonal bundles rather than perpendicular to the bundles (fewer obstacles to prevent mvmt)
