Flashcards in Neuroimaging Deck (25):
How do important materials look on CT?
Air is VERY black
water less black
brain is grey
edema is darker grey (at least 6-8 hrs post-event)
blood, and contrast are the same housefield unit- so you need to know if you have contrast CT! Both are quite white
bone is whitest of all.
What kind of abnormalites can you see on CT?
BIG things. good for blood (stroke, head trauma) contrast helps you see massess/abscesses.
How do you describe findings on CT
in terms of density. (NOT intensity)
What are disadvantages of CT? Advantage?
LOTS of X-ray radiation
axial and coronal view only
new stuff less likely to show up.
not very sensitive
Advantage: much faster, less claustrophobic. relatively specific.
What do epidural hematomas look like?
concave white thing
What are common characteristics of epidural hematoma?
convex white thing; midline shift common
In addition to hematomas, what is another finding that can be seen on CT?
What is contrast? What can it help us see?
IV iodinated dye that highlights breakdown of blood brain barrier
helps us see tumors, abscesses, and vascular malformations
What are contraindications for CT contrast?
renal insufficiency, allergies
What are the early ischemic signs on CT?
sulcal effacement and loss of cortical ribbon (ie the color looks normal but the brain is too smooth looking)
and hyperdense arteries (acute clot)
What is CT angiography?
contrasted study with time series of images to track bolus. you can reconstruct vessels in 3D
What is CT perfusion?
contrasted study that measures tissue viability. It can measure blood volume and blood transit time (without blood volume, tissue will start to die. if there isn't a change in blood volume, but transit time is slow, you can still potentially save tissue with surgery or something similar)
What are advantages of MRI? Disadvantage?
advantage: can order axial, sagittal, or coronal cuts; magnetic- so no radiation exposure, no bone artifacts, more sensitive and more contrast btw gray and white matter
but, slow and expensive. Also arteries don't show up, because blood is flowing too much. can't do in ppl with pacemakers.
What are T1, T2, and FLAIR MRI views?
T1: white matter white, grey matter grey CSF dark
T2: white matter grey, grey matter white. CSF bright
FLAIR: white matter grey, grey matter white, CSF dark. abnormal white matter is hyperintense (but be careful about abnormalities that are too close to the ventricles)
What is MRI contrast?
gadolinium DTPA. also shows BBB breakdown (abscesses, neoplasms, subacute cerebral infarctions.
What is DWI and ADC?
useful for evaluation of acute strokes (stroke area = white on DWI and dark on ADC. Dark ADC indicates cortical white matter tract disorganization.
What is GRE>
Gradient recall echo- good for finding microhemorrhages (look like little dark holes in brain) (example showed was amyloid angiopathy
What is MRA/ MR angiography?
visualize blood vessels. much safer than CT angiography (no radiation, no arterial puncture, no contrast). overestimates stenosis and may suggest arterial occlusion in cases of high grade stenosis. good for cerebral aneurysms, arteriovenous malformations, arterial dissection, CNS vasculitis, and arterial stenosis. CT is btter for cerebral aneurysms and cartodi stenosis- slightly more sensitive.
What is SPECT>
labels metabolic substrates- good for detecting areas of altered metab like cancer or seizure
What is fMRI?
meausures brain activity by detecting associated changes in blood flow based on nearby deoxygenated Hb- not used much clinically
What types of blood abnormalities can we see on CT and MRI?
MRI: GRE shows microhemorrhages
What kinds of ischemia abnormalities can we see on CT and MRI?
CT: early ischemic changes are sucal effacement and hyperdence MCA
MRI: acute ischemic areas with DWI/ADC
What masses/abscesses can we see on CT/MRI?
CT: parenchyma changes; enhancements post contrast
MRI: T1 pre and post contrast
What demyelination lesions can we see on CT/MRI?
CT: hard to assess. white matter may be hypodense
MRI; FLAIR to assess for hyperintensities. contrast enhancement if lesions are active. Dawson's fingers seen in saggital MRI of MS in many cases.