Rad Flashcards
(39 cards)
What color is bone on CT? Ventricular system? Blood?
Bright white; dark; white
Septum pellucidum to midline magic number for emergent sign
20mm
What does Hounsfield units measure?
Density of tissues
Pros and cons to CT
Pros: quick, better in acute emergency, less expensive than MRI, better for acute intracranial hemorrhage and skull fracture
Cons: radiation, insensitive to early non-hemorrhagic stroke, metal can degrade image, abuse, posterior fossa and issue d/t higher density (hard for cerebellum)
How does MRI work?
Hydrogen ions are like little magnets > thrown into high energy state > when the return to a low energy state, an image is obtained from the energy that’s released
T1 image
Anatomic sequence; fat bright, water dark black
T2 image
Pathologic sequence; fat dark, water bright white
FLAIR
Mix of T1 and T2; sensitive for a lot of things, mostly white matter disorders (i.e. MS)
Pros and Cons of MRI
Pros: no bone artifact, better assessment of tumors, white matter disease and early edema, ischemic injury earlier than CT, vascular flow, multi-planar, non acute or subacute neurologic deficits
Cons: no metal allowed, no pacemakers, no ferric aneurysm clips in brain, claustrophobia, expensive (pre-approval), cannot repeat limited portions of exam
Contrast used to…
Enhance tumors, inflammatory processes, enhance vasculature and vascular lesions
MRI contrast
Gadolinium (alters magnetic properties of certain materials)
CT contrast
Iodine
Major complication of gadolinium
Nephrogenic systemic sclerosis (hardening of skin/soft tissues)
MC type of head injury (found post-trauma)
Parenchymal contusion
Epidural on CT
biconvex-shaped; limited by sutures; active bleeding is lower density (darker); more common with MVA
what would make an epidural more likely operative?
If it’s temporal > pressure on brain stem
Subdural on CT
crescent-shaped; within dura itself so not limited by sutures; more common with falls (acceleration-deceleration) and older patients
CT density with SDH timeline
Acute 0-3-4 days: hyperdense
Subacute 3-20 days: isodense
Chronic >20 days: hypodense (like CSF)
Shear injuries
Rapid acceleration/deceleration, large WM tracts (corpus callosum, brainstem, deep white matter), occurs @ gray-white matter interface d/t differences in mass
Cytotoxic edema
- Etiology: infarction/ischemia
- Na/K pump defect
- Intracellular
- no/poor steroid response
- involves gray and white matter
- w/i 6 hours (MRI most sensitive)
Vasogenic edema
- Etiology: tumor, trauma, hemorrhage
- BBB defect
- extracellular edema
- steroid response
- white matter
- CT frequently (-) 12-24 hours
Best test for detecting an early ischemic stroke
MRI; BUT you would CT first to rule out hemorrhage
Plain films use
Acute trauma, chronic/acute pain w/ no trauma and no response to therapy w/ or w/o neurologic symptoms, radicular pain (may be subtle or absent)
Fracture/dislocation imaging
X-ray/CT
