2a. CT - Head Radiology Flashcards
in a imaging studies the patients left side is my ___ side
right
how do your know an image is a CT scan and not another modality
bones of skull is white (high intensity) in CT
opposite of MRI where bones of skull would be black
on CT what colour/intensity would bone be
high intensity - white
on CT what colour/intensity would white matter of the brain be
darker grey
on CT what colour/intensity would CSF be
hypointense (black/dark)
on CT what colour/intensity would fat be
very dark - hypointense
on CT what colour/intensity would muscle be
mid grey
on CT what colour/intensity would blood be
high-low intensity depending on freshness of blood
fresh blood = bright/intense
old blood = dark/hypointense
what are the 4 things to describe in terms of a lesion on a CT scan
which side the lesion is on
lesion appearance
location of lesion
other features of lesion
what are the components in your description of a lesion
x6 things
shape of lesion (eg biconvex)
intensity (hyper/hypo)
size (eyeball cmxcm)
where in the brain structures is the lesion located (eg ant cranial fossa)
where the lesion borders are extending to (eg extends to midline)
is it compressing the brain/is the midline skewed - what side is it displacing the midline to
what are the 3 cross sectional imaging modalities
CT, MRI, ultrasound
which of the 3 cross sectional imaging modalities can be used with contrast?
all of the 3
what are the 5 advantages of CT scans
fast (1-20min)
relatively widely avail
3D reformatting and reconstruction
intermediate cost
what are 3 uses of CT scans
acute trauma
stroke to rule out bleed
angiography with contrast media
how does the CT work
CT anode produces a narrow continuous fan shaped stream of xrays as it rotates around the head
anode is paired with a detector array which also rotates at a constant 180* to the anode
the image is reconstructed into stack of 2D images using a number of algorithms
is the CT scan technique quantitative or qualitative why
quantitative as the scale is a linear transformation of the original tissue attenuation
Quantative as intensity on screen can give a number to it - Hounsfield unit
what is the hounsfield unit
can give it a number to the intensity on screen
what is the hounsfield unit for water and air
water = 1 air = -1000
what can the hounsfield unit used for
density quantifications
does the hounsfield number change with windowing
no
calcium has what hounsfield unit relative to bone
high value sim to bone
what are the 2 main types of disease
congenital and acquired
what are the 2 types of acquired disease
infectious and non-infectious
what are 4 examples of infectious diseases
bacteria
viruses
parasites
fungi
what are 4 examples of non-infectious diseases
trauma
malignancy
inflammatory
degenerative
what is intra-vascular contrast media
compounds injected to increase the contrast of structures or fluids on imaging
does contrast media cross the blood brain barrier
usually dont cross the BBB unless it is not intact
what xrays need contrast media and what type of contrast media do CT use
xray = angiography CT = iodinated media
what does the image look like when there is a pathology that allows the contrast media to enter the tissues/vessels, how does this happen
what is the wash out rate
in areas of apthology eg tumour/stroke leaky vessels means contrast agent enters the abnormal tissue
wash out is slow
visualized as high signal - bright
iodinated media can do what to poor renal function and what is the rate of contrast reaction
exacerbate poor renal function
rate is high
what can gadolinium based media rarely cause and why
nephrogenic systemic fibrosis when used in large dose in patients with poor renal function due to gadolinium deposition in tissues
if non hemorrhagic the stroke can be treated wiht what 2 ways
tissue plasminogen activator/TPA
neuro-radiological intervention/clot removal
if the stroke is haemorrhagic what does the image look like and is TPA used
blood seen on bright signal on CT
TPA withheld as will likely cause more haemorrhage
what are the 2 disadvantages of CT
uses high ionising radiation
intermediate cost
what is an early sign of ischemia on CT
3 signs
loss of definition between grey and white matter
ill-defined internal capsule
hyperdense middle cerebral artery not always seen
are acute signs of ischaemia seen on CT
sometimes changes take 24hrs to develop
what are acute signs of acute bleed on CT
hyperintensity
if concern of bleeding and CT doesnt show anything what happens next
patient may go to MRI for diffusion weighted imaging (DWI)
which is more sensitive to ischemic changes - CT, MRI, DWI
DWI
what is epidural bleed in terms of where the blood is between what structures of the head/skull
traumatic collection of blood between the inner aspect of the skull and the stripped of dura
what is epidural bleed in terms of the bleeding is from what vessel
usually trauma and bleeding from the middle meningeal artery
what is subdural bleed in terms of shape and edge of bleed shape
lentiform shape
clean edge of bleed
what is subdural bleed in terms of where the blood is between what structures of the head/skull
what vessel type is injured
traumatic injury to veins between dura mater and arachnoid mater leading to collection of blood in subdural space
what is epidural bleed in terms of shape and edge of bleed shape
crescent shape
jagged, irregualr edge of bleed
what do chronic bleeds in the head do to the brain
squishes material of the brain itself
for a sub arachnoid bleed where is the blood collection in the brain
between arachnoid mater and pia mater
for a sub arachnoid bleed what does the blood look like on the surface of the brain in images and where is the blood also seen after bleed
bright signal
seen in basal cisterns immediately after bleed
what is the basal cisterns in the brain in terms of location and shape
what is the blood intensity on the image
circle structure with projections like a star
seen in the center of the brain in a axial scan
bright blood/high intensity
what 2 things causes subarachnoid hemorrhages
hypertension
rupture of aneurysms of cerebral vessels
what are meningiomas and how fast does it grow and is it dangerous
tumors arising from meninges
slow growing
90% benign
on a CT scan what does a lesion look like before and after the contrast is applied
before = grey circle similar to surrounding healthy brain tissue
after = high intensity very bright
what is a glioblastoma tumor in terms of appearance when contrast is applied and what other injury is associated with it
most common malignant brain tumor
enhancing lesion associated with surrounding oedema (doesnt enhance very well)
what is a glioblastoma tumor and is it dangerous, how fast does it grow
most common malignant brain tumor
slow growing less aggressive
what are vessels of aggressive tumors like compared to slow growing tumors and what does this mean for contrast uptake
aggressive tumors = vessels are more leaky
blood leaks and contrast gets into it so more bright
what are the key characteristics of abscess on CT
rim enhancing lesion with oedema
middle of lesion has pretty dark intensity
what is the rim like in appearance of abscess on CT images
very thin uniform enhancing edge
what is the oedema like in appearance of abscess on CT images
slightly darker area outside rim enhancement
slightly darker than normal tissue
Why is CT good for imaging facial trauma
3 reasons
CT scan avoids superimposing of bones so can see structure really well
high contrast between bone and soft tissue enables easy segmentation and 3D reconstruction
good visualization for surgeon when planning surgery
when there is a fracture of the infraorbital wall what happens to the contents of the orbit
what is clinically significant about this
contents of orbit pushed down
may have bit of blood in maxillary sinus and fat in orbit gets trapped and eye muscles trapped in sinus so eyes dont work together as well so get double vision clinically
