which anatomical basline of the head is used for a ct brain?
- supraorbital meatal line or glabellomeatal line
- it used to be the oml
why is beam hardening artifact common in the posterior fossa of the brain?
because of the dense bone of the skull
which two things can you do to compensate for beam hardening artifact in the posterior fossa of the brain?
- decrease slice thickness
- increase kvp
why are narrow window widths used to demonstrate the brain?
because there is only a small difference in attenuation between the gray matter and the white matter
why does the gray matter attenuate more of the xray beam compared to the white matter?
because of its lower water content and higher blood volume
what is the x-ray attenuation in hounsfield units for water?
what is the x-ray attenuation in hounsfield units for CSF?
what is the x-ray attenuation in hounsfield units for gray matter?
what is the x-ray attenuation in hounsfield units for white matter?
what is the x-ray attenuation in hounsfield units for circulating blood?
what is the x-ray attenuation in hounsfield units for clotted blood?
what is the x-ray attenuation in hounsfield units for tissue calcification?
what is the x-ray attenuation in hounsfield units for fat?
-60 to -70
what is the x-ray attenuation in hounsfield units for air?
as a rule, intracranial hemorrhage will appear hyperdense to normal brain tissue for approximately how many days?
what happens to the ICH (intracranial hemorrhage) after 3 days?
- It will decrease in density starting at the periphery of the hematoma
- density loss will continue until the whole hematoma is hypodense to the brain tissue
what does the ICH look like from onset to 3 days?
what does the ICH look like from 4 to 10days?
contains a hyperdense center and surrounded by concentric areas of hyperdense and hypodense tissue
what does the ICH look like from 11 days to 6 months?
contains an isodense center surrounded by hypodense tissue
what does the ICH look like by 6 months?
will be hypodense to the brain
ct of the neck mainly focuses on which structures?
- aryepiglottic folds
- pyriform sinuses
- lymph nodes
- pathological tissue
what type of bolus technique is used for scanning the neck?
why is split bolus used for scanning the neck?
it takes time for the mucosa, lymph nodes, and pathology tissues to be enhanced
how do you use the split bolus technique for scanning the neck?
- administer half of the contrast and a delay of about 2 minutes for it to enhance the structures of interest
- then give the 2nd half of the contrast then scanning is innitiated soon after the 2nd injection is given to highlight the vessels
what does the CTA of the head and neck look for?
- accurately measure stenosis of the carotid and vertebral arteries and their branches
- evaluate the circle of willis
- dissections or occlusions
which modality is the gold standard for visualizing vasculator in the neck and brain?
what makes CT better than IR for evaluating vascular disease?
- widely available
- time-saving (most important)- can get treated right away especially for acute stroke patients
CT is better than MRI at imaging the spine because of what?
it can demonstrate bony abnormalities very well
scans of the spine are often obtained after what type of fluoroscopic exam?
myelography with intratechal contrast
ct scan of the spine after intratechal contrast is given is helpful for diagnosing what?
degenerative disk disease
most reports suggest a delay time of ______ between intratechal injection (for myelography) and scanning
1 to 3 hours
why is there a delay time between intratechal injection (myelography) and ct scanning?
to dilute the contrast and avoid masking intradural structures
why is it recommended for the patient to roll once or twice before scanning the spine after a myelogram?
to mix the contrast that may have settled since the myelogram
what are the two main types of strokes?
what is the main type of stroke?
ischemic - 80%
what are two types of ischemic stroke?
- thrombotic - caused from a blood clot (from atherosclerosis) or a fatty deposit within one of the brain's arteries
- embolic - traveling particle that forms elsewhere and is too large to pass through small vessels and eventually lodges in a smaller artery
what are the common sites for CVA atherosclerosis (thrombotic stroke)?
- proximal common carotid artery
- the origin of the internal carotid artery
- the carotid siphon
- the proximal middle cerebral and vertebral arteries
what is an embolytic stroke?
when an artery in the brain is blocked by an embolus, usually a thrombus that developed elsewhere in the body
an embolytic stroke accounts for how many percent of all strokes?
which conditions can cause an embolytic stroke?
atrial fibrillation- abnormal rhythm of the heart causes blood to remain in the atrium of the heart which can clot and can break off and travel to the brain. 15% of all embolytic strokes
At the site of artificial heart valves or as a result of heart valve disorders
After a heart attack or heart failure as a result of areas of the ventricles that do not move properly, allowing blood to stagnate and clot
From fat particles, tumor cells, or air bubbles that travel through the bloodstream. This type of emboli is rare.
what is a lacunar stroke?
blockage in the small arteries of the brain like deep cerebral white matter.
No other blood vessels exist in these deep parts to help supply that region therefore blockage results in tissue death in that area.
what are signs for lacunar strokes?
- emotional variability
sometimes serve as a warning sign that a major stroke may be imminent
lacunar strokes account for how many percent of all strokes?
what is a hemorrhagic stroke?
rupture of a blood vessel in the brain causes leakage of blood into the brain parenchyma, CSF spaces around the brain, or both
hemorrhagic strokes account for how many percent of all strokes?
how are hemorrhagic strokes classified?
by how and where they occur
what is an intracebral hemorrhage?
- stroke that occur within the brain parenchyma itself and a hematoma often results.
- Accounts for more than half of hemorrhagic strokes
- most often result from hypertension
what is a subarachnoid hemorrhage?
- occur when there is bleeding into the subarachnoid spaces and the CSF spaces
- Usually caused by the rupture of an aneurysm
what is an arteriovenouso malformation (AVM)?
- tangles of arteries and arterialized veins
- blood is shunted directlyl from the arterial system to the venous system which allows oxygenated blood to enter the veins. This abnormality comes with high pressure which can rupture the vessels
what is a hypotensive stroke?
blood pressure that is too low can cause a stroke.
primary areas of damage are within the circle of willis between the anterior and middle cerebral arteries and between the middle and posterior cerebral arteries in the parieto-occipital regions of the cerebral hemispheres
what is a transient ischemic stroke (TIA)?
- a reversible symptom of stroke that can last for a few minutes to a few hours.
- caused by a tiny emboli that lodge in an artery and then quickly break up and dissolve with no damage.
- warning signs for major stroke and a heart attack, due to the relationship of strokes to atherosclerosis and coronary disease.
diffrent types of TIA symptoms occur based on what?
- based on where the emboli lodges
- TIAs in the carotid arteries- more common, affects the retinal artery = poor vision. Also affects the cerebral hemisphere= problems with speech, partial and temporary paralysis, tingling, numbness typically on one side of the body
- TIAs in the basilar arteries- both hemispheres can be affected which means both sides of the body. Blurry or complete loss of vision, tingling or numbness in the mouth, cheeks or gums, headache in the back of the head, dizziness, nausea and vomitting, difficulty swallowing, inability to speak clearly, weakness in the arm and legs
what are some of the symptoms of a major ischemic stroke?
- large embolus in an artery of the brain- headache and seizures can occur within seconds
- thrombus in a narrow artery- symptoms manifest more gradually, during mins to hours or days to weeks
- a thrombus in one side of the brain will usually affect the opposite side of the body, this includes:
- unilateral weakness
- loss of feeling on one side of the face or in an arm or leg
- blindness in one eye
- If the left hemisphere of the brain is affected, speech problems occur.
- inability to express thought verbally or understand spoken words
what is the difference of an early ischemic stroke symptom to a TIA?
- TIA symptoms are reversible
- Ischemic early symptoms do not resolve
what are the symptoms of a hemorrhagic stroke?
- depends on where and how it occurs
- usually begins very suddenly and evolve over the course of several hours
- nausea and vomitting
- altered mental state
- subarachnoid hemorrhage may produce warning signs from the leaky blood vessel a few days to a month before the aneurysm fully develops and ruptures. warning signs may include:
- abrupt headaches
- nausea and vomitting
- altered state of consciousness
- eyes that become fixed in one direction or a loss of vision
what are symptoms of hypertensive stroke?
- loss of vision
- decreased alertness
- weakness that affects the shoulder, hand and thigh
hypertension contributes to how many percent of all strokes?
stroke risk factors (pg 246 CT for technologist)
what is the tissue plasminogen activator (t-PA)?
treatment for acute ischemic stroke
what does the t-PA treatment do to acute ischemic strokes?
- targets the tissue called the penumbra. The penumbra is ischemic tissue that is destined for infarction but is still salvageable.
- Fully infarcted tissue will not benifit from t-PA treatment and may increased the risk for hemorrhage.
administering of t-PA is only effective when?
administered within 3 hours of the first signs of stroke.
what is the main contraindication of t-PA treatment?
what does a non contrast CT of the brain look for when a pt is suspected of a stroke?
- differentiate ischemic stroke from hemorrhagic stroke
- assess the state of the cerebral circulation and tissue
- secondarily, assess the underlying disease
why are CT perfusion and CT angiography done along with a non con CT brain?
a regular CT noncon brain will remain the same for up to 6 hours because the ischemia does not reach the critical level of structural integrity. The CT perfusion and CTA asess the state of the cerebral circulation and tissue.
what does a CT perfusion scan of the head accomplish?
- measures cerebral blood flow
- perfusion studies are obtained by monitoring the passage of iodinated contrast through the cerebral vasculature
what is calculated during a CT perfusion scan?
Cerebral Blood Volume(CBV)= Cerebral Blood Flow (CBF) x Mean Transit Time (MTT)
what are the clinical indications for a CT perfusion scan?
- acute stroke
- tumor grading
- determine cerebrovascular reserve
- in conjunction with temporary balloon occlusion
what is the technique used for a CT perfusion scan?
- non con brain first
- 50ml of contrast @ 4 or 5ml/sec
- Helical scan
- 5 sec scan delay
- 5mm thick
- Scan duration 40-45 secs
- reformatted to 10mm thick