ct head Flashcards
(21 cards)
give the average hounsfiled units for the following: air, bone, brain, csf
air = -1000
bone = +1000
brain = -30 to 40
csf = -10 to 20
images reconstructed into multiplayer reconstructions axial, sag, coronal
xrays are absorbed to different degrees by different tissues, known as ‘densities’ and brain is the reference density, what are the 3 levels of densities and how do they appear on image
higher density - hyper dense (bright)
lower density - hypotenuse (dark)
same density - isodense (same)
what is the average head scanning protocol
- axial image acquisition
- 5mm slices (standard brain window good for pathology)
- reconstruct back 1.25mm (soft tissue)
- reconstruct back 0.625mm (bone window)
brain anatomy :
supratentorial = frontal, temporal, parietal and occipital lobe
infratentorial = cerebellum, brainstem
sulcus (furrow b/w gyro)
gyrus (fold of brain)
what is the goal of a non contrast ct head
- exclude intracranial haemorrhage
- find early features of ischaemia
- find dense vessels
- exclude other intracranial pathologies
what is a CT fast stroke (angiogram)
from aortic arch to cortex to look for occluded vessels (not all blood clots can be seen pre contrast)
- green cannula
- IV administered
- bolus tracked
when is the scan triggered in CT fast stroke
- when optimal contrast is in ascending aorta
what is the aim of delayed angiographic ct brain imaging, what does it help determine
- ascertain extent of infarct
- deterring perfusion of surrounding brain and if theres salvageable brain
- helps determine if thrombectomy (surgical removal of clot) or thrombolysis (drug prescribed to dissolve clot) is needed
what is a dedicated CT perfusion for
determine if patients are suitable for repercussion therapy
- identifies the infarcted tissue and the although ischaemic but perhaps salvageable tissue
acute ischaemic stoke is significantly improve by IV thrombolysis (limited with short treatment window) or mechanical thrombectomy (can be done up to 24 hours post insult)
what are visible signs of early infarction on CT scan
- dense vessel
- subtle loss of grey/white matter
what are visible signs of acute infarction on CT scan
- swelling/oedema (darker region)
what are visible signs of subacute infarction on CT scan
- swelling subsides
- small petechial haemorrhage
- fogging effect (initially hypodense ischemic areas transiently become isodense to normal brain)
what are visible signs of chronic infarction on CT scan
- swelling subsides
- gliosis sets in (hypertrophy of glial cells)
- low density (dark) no mass effect
what is haemorrhage transformation
a common complication in patients with acute ischemic stroke. It occurs when peripheral blood extravasates across a disrupted blood brain barrier (BBB) into the brain following ischemic stroke.
what does acute and chronic haemorrhage look like on ct scan
acute = hyper dense (bright)
chronic = (hypodense (dark)
but as bleed resolves going from acute to chronic, it’ll go isodence (same as brain) before going hypodense
BUT active bleeding can also appear hypodense
what do intraaxial haemorrhages (contusions (blow to head), intra parenchymal (bleed into brain)) look like on ct
look like focal areas of high density within brain parenchyma
what is vasogenic oedema and what is the typical ct sighting for vasogenic oedema
Vasogenic cerebral oedema refers to a type of cerebral oedema in which the blood brain barrier (BBB) is disrupted
- low density effecting white matter
know that lesions in brain typically are ring enhanced when given contrast
why is fresh blood bright on ct
when a blood clot retracts, its water content decreases and its hematocrit may raise up to 90%. As a result, fresh blood clots typically appear hyperdense.
