Term
| basic neuroimaging techniques |
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Definition
plain radiographs (x-rays)
computed tomography (CT)
magnetic reasonance imaging (MRI)
cerebral (endovascular) angiography |
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Term
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Definition
readily available
inexpensive
show bones well |
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Term
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Definition
of relatively little value in showing pathological processes
not tomopgraphic - no slices
does not show normal or abnormal soft tissue |
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Term
| indications for plain radiographs |
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Definition
| may show subtle non-displaced fractures - important in suspected cases of child abuse |
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Term
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Definition
tomographic - can stack slices to be reformatted in any plane and help visualize better
shows majority of osseous abnormalities better than any other modality
"windows" can manipulate image to highlight different tissues based on density
detect soft tissue lesions better than xray |
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Term
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Definition
difficult to resolve some similar, normal soft tissues from one another; to delineate normal from some pathologic soft tissues; evaluate some areas of the brain that are limited by artifacts
radiation exposure
some images use contrast (may be nephrotoxic) |
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Term
CT
density and attenuation |
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Definition
density and attenuation refer to the process of absorption of the x-ray beam
increased density areas have greater attenuation of the x-ray beam
lower density areas have lower attenuation - absorb less of the x-ray beam |
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Term
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Definition
more electrons/more density --> absorb more x-ray --> WHITER
bones, iodine-based contrast material, acute blood, calcification, pathologic mineralization, some foreign bodies |
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Term
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Definition
less dense --> absorb less x-ray --> darker
fluid in ventricles, fat, gas (air), fluid |
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Definition
no ionizing radiation
better resolution than CT
multiplanar imaging
fewer artifacts
images can be generated that highlight different kinds of magnetic filed differences between tissues
best delineates soft tissues both intrinsic and immediately extrinsic to the brain
no known side effects |
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Term
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Definition
not ideal for directly visualizing dense osseous structures
interpretation of light/dark not intuitive
scans must be obtained separately |
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Term
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Definition
T1-weighted (T1w)
T2-weighted (T2w)
FLuid Attenuatied Inversion Recovery (FLAIR) |
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Term
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Definition
best for delineating anatomy
used in contrast scans
CSF over the surface of the brain and in ventricles appears black |
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Definition
exquisitely sensitive to subtle changes in water concentrations which reflect most pathologic processes (strokes, tumors, infections...)
fluid appears white
changes manifest as increased signal (more whiteness) |
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Term
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Definition
same idea as T2w, except normal fluid appears dark so better able to see pathology (still shows up white)
"super" T2w scan
normal fluid (ventricles, subarachnoid spaces) has no signal and is black, and so subtle path processes (still white) are much easier to identify |
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Term
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Definition
SUBacute subarachnoid hemorrhage best seen on FLAIR
multiple sclerosis plaques
subtle metastases from melanoma |
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Term
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Definition
| *ACUTE subarachnoid hemorrhage* |
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Term
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Definition
endovascular placement of catheter into femoral artery and passed to aortic arch up to neck/head (vertebral or carotid artery)
inject contrast into individual blood vessels, serial plain x-rays |
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Term
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Definition
best delineates intrinsic blood vessel pathology
can be used to inject drugs into specific blood vessel territories for diagnostic or therapeutic purposes
catheters can be placed directly into aneurysms, vascular malformations and recently occluded vessels for definitive therapy |
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Term
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Definition
risky, expensive
requires expensive equipment and highly trained personnel
0.1-0.5% chance of causing stroke |
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Term
| best seen on cerebral angiography |
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Definition
intrinsic blood vessel pathology:
atherosclerosis
vasculitis
aneurysms
AVMs
dural venous sinus thromboses
fistulas
blocked vessels |
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Term
| fancier CNS imaging techniques |
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Definition
CT - biopsy, pefusion, CTA
MR: MRA, diffusion/perfusion MRI, MR spectroscopy
Angiography: coils, stenting, clot lysis, clot retrieval |
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Term
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Definition
MR scanning technique that takes advantage of the fact that moving tissues (blood) generate signal while stationary tissues do not
can be used to create images of the vascular system |
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Term
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Definition
| images of moving blood within blood vessels can be created with a sufficient level of detail that in many cases, formal endovascular catheter angiography can be avoided |
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Term
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Definition
| images molecular movement of water ("Brownian" motion) |
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Term
diffusion MR
low vs. high diffusion |
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Definition
low diffusion = molecular movement is more "impeded"...intracellular water molecules are limited by cell membranes (ex: water in a cell)
high diffusion = molecules move relatively greater distance with time...extracellular water which is not limited by cell membranes (ex: water in ventricular system; water outside cell) |
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Term
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Definition
*can delineate strokes within minutes of injury*
VERY sensitive to ischemic changes in the brain
dMR looks at subtle shift of water in the cell - can pick up cytotoxic edema (increased intracellular water from osmotic gradient caused by acidosis/increased Ca in ischemic cascade) -- intracellular water has impeded diffusion, shows up as increased signal (white)
help identify ischemic penumbra...impeded diffusion usually means irreversible brain damage |
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Term
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Definition
yield hemodynamic map of brain perfusion during a bolus of contrast administration
reflects blood flow, not brain cell function
white areas reflect worse perfusion
abnormality may be reversible or irreversible |
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Term
| diffusion/perfusion MR mismatch |
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Definition
comparison of perfusion and diffusion MRs in the setting of acute cerebral ischemia
if perfusion deficit (blood flow) is more extensive than diffusion deficit (usually representative of permanent injury/infarct), possible that the area of perfusion abnormality withOUT diffusion abnormality represents viable brain
"ischemic penumbra" -- area at risk of going to permanent injury, but not yet reversibly injured; may benefit from aggressive therapy |
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Term
| diffusion/perfusion MR match |
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Definition
| in comparing dMR and perfusion MR, if the areas of deficit are identical, then the damage to the brain might be done at there is no "at risk" brain to salvage - aggressive therapy not warranted |
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Term
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Definition
used to evaluate brain tissue metabolites
standard MR hardware does chemical imaging |
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Term
| common MR spec metabolites |
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Definition
N-acetyl-aspartate (NAA)
choline (Cho)
creatine (Cr)
lactic acid (Lac) |
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Term
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Definition
N-acetyl- aspartate
found in normally functioning neurons
decreases with irreversible neuronal injury |
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Term
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Definition
choline
component of cell membranes (phospholipid)
increases in any process that causes cellular turnover (tumor, acute infections...) |
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Definition
creatine
marker of cellular energy |
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Term
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Definition
lactic acid
byproduct of anaerobic glycolysis
seen in ischemic cells
not present in normal brain tissue |
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Term
| markers of normal MR spec |
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Definition
NAA, Cho, Cr peaks
absence of lactic acid peak |
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Term
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Definition
increased Cho
decreased NAA
can help differentiate enhancing lesion on an MRI that could be consistent with either tumor or necrosis |
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Term
| multiple sclerosis MR spec |
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Definition
| spectra reflect acute demyelination products to help differentiate between tumor and MS plaque on MRI |
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Term
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Definition
used for guidance to percutaneous biopsy lesions that previously required an open surgical procedure
-intracranial
-spinal
-transfacial |
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Term
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Definition
acquire hemodynamic maps as bolus of contrast passed through specific portions of the brain
get rapid slices as contrast is being injected
reflects how well different portions of the brain are being perfused
can calculated cerebral perusion parameters:
-MTT: mean transit time
-CBV: cerebral blood volume |
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Term
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Definition
can help identify penumbra
decreased CBV ~ MR diffusion
increased MTT ~ MR perfusion |
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Term
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Definition
rapidly scan through head and neck while contrast material is being injected, time scanning so that peak concentration of contrast in in arterial vessels
multislice scanner and thin sections
stack images and delete background info |
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Term
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Definition
| images are similar to catheter angiogram with ~0% risk of causing stroke |
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Term
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Definition
intrinsic vascular detail not as good (but often adequate to answer clinical questions)
radiation |
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Term
CTA
different pathologies imaged |
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Definition
atherosclerosis
dissection (need blood flow moving a certain speed)
aneurysms - 1st choice over MRA |
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Term
| new angiography techniques |
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Definition
coiling of aneurysms
carotid stenting
treatment of intraluminal thrombus |
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Term
angiography
aneurysm coiling |
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Definition
| instead of an open surgical clipping of an aneurysm, coils can be passed through an intravascular catheter into the aneurysm, obliterating the aneurysm lumen and eliminating the risk of future rupture |
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Term
angiography
carotid stenting |
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Definition
| treatment of narrowed atherosclerotic vessels with an intravascular catheter with a balloon that can be dilated to expand the vessel lumen followed by placement of a stent to maintain patency |
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Term
angiography
treatment of intravascular clots |
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Definition
acute occlusion of a cerebral blood vessel can lead to death of downstream tissue; if vessel can be re-opened quickly, downstream brain may be salvaged
-intra-arterial thrombolysis
-mechanical clot removal |
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Term
| intra-arterial thrombolysis |
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Definition
new angiography technique to treat intravascular clots
"clot-busting" agents like TTPA can be directed injected into a clot via a catheter
(not yet FDA approved) |
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Term
| mechanical clot retrieval |
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Definition
new angiography technique to treat intravascular clots
Merci cath - capture and remove clot
Penumbra cath - break up and aspirate clot
(both are FDA approved) |
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