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179 Cards in this Set
- Front
- Back
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what is stroke?
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an event where the brain is deprived of oxygen causing ishemia to brain cells and neurnal loss. This is usually caused by a blockage of arterial flow, but occasionally it is caused by venous thrombus.
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what is a thrombotic stroke, what are the symptoms of it?
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-caused by a build up of plaque and thrombus within an artery that results in reduction of flow to the brain. THis is a process that usually occurs over a number of years, so symptoms may be subtle or non-existant over most of the time.
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where does thrombotic disease usually develop?
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in larger arteries such as the CCA, ICA, or circle of willis, and may lead to emolic stroke.
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what is small vessel disease?
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results due to occlusion from thrombi in the small branches of the circle of illis or basilar arteries.
-as a result of lipid and/or fibrin build up due to aging and hyprension. |
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what are lacunar strokes?
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occlusion of small arteries(branches of circle of willis or basilar arteries)
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what is an embolic stroke?
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a traveling substance through the blood that lodges in a major artery resulting in ischemia. Emboli are usually blood clots, but they are occasionally fat, plaque, or cancer cells
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what are some symptoms of embolic strokes?
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sudden and pronounced symptoms(loss of control, function, or sensation)
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what are the usual sources of embolic strokes/
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from a cardiac or arterial source. the cadiac causes are related to arrythmias, endocarditis, recent myocardial infact, or valve diseases.
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what is a watershed stroke?
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blockage of supply to brain tissue supplied by small end arteries. It is caused by hypoperfusion such as large arter occlusions, systemic hypotension, or cardiac failure.
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what is a venous thrombosis stroke?
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intracranial thrombosis can cause stroke because of intracranial pressure from the backup of blood.
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what is a hemorrhagic stroke?
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when blood is forced to bleed into surrounding tissue instead of toward capillaries of target tissue. This causes tissue to be deprived of blood, as well as pressure from pools of blood restricing tissue and causing it to be deprived of oxygen.
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where do intercerebral hemorrages originate? what are they caused by?
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orignate in small arteries, and are cuased by:
-hypertension -cocaine -trauma -bleeding disorders - |
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what is a subarchnoid hemorrage?
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a rupture of a larger artery ito the cerebrospinal fluid of the subarchnoid space. THey cause intracerebral aneurysms or arterial malformations
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what is a TIA?
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tranisent Ischeic attack:
considered a prelude to stroke and has the same syptoms of stroke but lasts less than 24 hours. |
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what is RIND?
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reversable ischemic neurologic deficit:
stroke symptoms that last longer than 24 hours, but rapidly improve to full function. |
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what is arterial insuffieciency?
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insufficient arterial supply to tissue causes lack of o2 to these areas, cell death, and ultimately tissue death. THere s a difference btw arterial and venous insufficiency.
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what happens when tissue is deprived of arterial blood?
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Tissue breakdown, or loss of function which results in pin or ulcerations in the effected area
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what happens when a person with arterial insufficiency tries to excersize?
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Since tissue is deprived of oxygen, a resting person's arteries will dialate in order to get the maximum amount of blood to tissue. When a person tries to excersize, there arteries will already be dialated, so, there won't be sufficient O2 supplied to the muscle causing pain, and inability to continue exercising that muscle. If this continues, muscle tissue wastes, ulcers form and become infected and the tissue dies(becomes gangrenous)
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what are some symptoms of arterial disease?
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-gradial onset of symptoms
-pasle extremity -poor tissue healing -claudication -unpalpable/weak pulse -lack of hair, scaly skin, thick toenails. |
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which 4 vessels supply the brain?
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Right and Left Vertebral, Right and Left Internal Carotid
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The 1.----- artery lies on the right side of the aortic arch and divides into the Carotid and Subclavian.
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brachiocephalic
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The caroticotympanic and meningohypophyseal branches arise from the 1.-----.
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ICA
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which artery is not within the circle of willis?
Ophthalmic Anterior Cerebral Posterior Communicating Posterior Cerebral |
ophthalamic
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T/F the posterior circulation includes the internal carotid arteries?
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false
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what is a collateral pathway?
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an alternate blood flow route
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why do we have the circle of willis?
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to provide an alternate path if there is a blockage
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what is the most common variation of the circle of willis?
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the hypoplasia of the communicating arteries.
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what do the branches of the basilar artery supply?
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-lateral aspects of the cerebrum
-pons -cerebellum |
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Adequate perfusion relies on systemic blood pressrue, cardiac output, and blood volume."
How does this statement relate to Carotid artery stenosis? |
Carotid stenosis may decrease perfusion and lead to tissue death.
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what are the intracranial branches of the ICA?
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caroticotympanic
ophthalmic meningohypophyseal |
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what do the vertebral arteries lie within?
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the foramina transversarium
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the occipital branch of the ECA may connect with the?
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atlantic branch of the vertebral artery
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what is the difference btw ischemic and hemmorhhagic strokes?
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Ischemic strokes are where blood flow is blocked and Hemorrhagic strokes are caused by blood "flooding" the brain tissue.
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the anatomic variation that most decreases collateral potential for the brain is what?
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absent or hypoplastic posterior and anterior communicating arteries
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T/F the ECA supplies the cerebrum
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false
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why is atherosclerotic plaque evaluated?
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Technological advances in ultrasound may prove more correlation between ultrasound characteristics and the clinical symptoms.
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intima/media thickness calculations are said to be a marker for cardiovascular disease. Why is this?
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Atherosclerosis is widespread, therefore arterial changes in the carotid artery may indicate changes in the coronary arteries.
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how should the extent and severity of plaque be evalueated?
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length and thickness
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what is the sequence of events in plaque formation?
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lipid infiltration, formation of foam cells, transformation of muscle cells into fibroblasts
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what is inflammation?
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The ongoing process within plaque that leads to the breakdown of materials within.
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there is a fibrous cap associated with plaque. When is it formed?
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smooth muscle cells from the muscular layer are transformed into fibroblasts
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large plaques are associated with what?
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-embolization
-stenosis -plaque disruption due to inflammation |
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Dangerous plaque that may result in permanent sequelae, may NOT cause stenosis according to our Doppler study.
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True
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heterogenous plaque may be described as
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focal and scattered areas of low and high echogenicities with in the plaque
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what is the clinical presentation of acute venous disease?
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suddden symptoms
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why is the acute phase of blood clot formation critical?
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it's at this time when thrombus is most suseptible to moving away and potentiallly lodging in the lungs which may lead to deadly respiratory distress.
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what is the frontline study to diagnose DVT/
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venous doppler studey
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what is considered acute, subacute, chronic?
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acute-the first 14 days
subacute-14 days to 6 months chronic-longer than 6 months |
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thrombus
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the formation of a blood clot
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what is vascular testing used to determine?
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overall heath of the tissue supplied or drained.
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what diseases can lead to arterial occlusions?
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injury, inflammatory disease, tumors, clotting disorders, atheroscleriss.
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what happens when there is occlusion or narrowing of veins?
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poor tissue health due to lack of blood flow and fluid away from the tissue. fluids and toxins accumulate around tissue cells leading to poor ransportation of oxygen and nutrients to target cells tissue degrades and chronic skn ulcerations may result.
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What are some clinical presentations of venous leg ulcers?
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-dry itchy leg
-brown staining -pain later in day -ankle swelling -ulcer at malleolus -moderate copious drainage -minimal slough -irregular edges -shallow -red granulation |
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explain non-ultrasound modalities that are used for vascular testing?
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-blood pressure
-limb volume changes -oxygen saturation |
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explain the working conditions and training required for vascular technologsts
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-usually work in a hospital setting, but can work in clinics, physicians offices, free standing laboratories, and usually work 40 hour weeks, and some are on call.
-lots are trained on the job, but can be trained formally. |
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what are the credential organizations?
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ARDMS-meet clinical experience and educational requirements
CCI-cardiovascular credentialing international ICAVL-intersocietal commission for the accredaitation of vascular laboratories |
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what instraments are used for scanning vessels?
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5-10 mHZ transducer
-spectral doppler with velocity measurement capabilities. |
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what is the usefulness of transverse carotid scannign?
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important for th assessment of the thickness of plaque and for visual measurement of luminal narrowing.
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what is the best approach for the ICA?
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posterolateral
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name the approaches for biffercation examination?
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-posterolateral-posterior to sternocloidomastoid muscle
-Anterior-probe btw trachea and sternocloidomastoid, an is more upright. Patients head is more upright, and is used with big necks and deep vessels -Lateral approach-patients head turned 45 degrees away, and probe is wiming up at vessels from the back of the sternocloidomastoid muscle. -posterior approach-allows more distal ICA-from back of sternocloidomastoid muscle |
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what is the best doppler angle to flow? What is used for diagnostic purposes? How shoudld the sample volume be placed?
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0degrees, 60degrees Should be placed midstream with the angle parallel to flow.
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how do you ensure that you are on the right artery?(ICA vs ECA)
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note spectral waveform
anatomical placement ECA tap |
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what are the general categories of cerebral vascular disease?
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coronary artery disease
cerebrovascular disease peripheral arterial disease |
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Explain the process of plaque formation?
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1. Platelets release growth factos, smooth muscle cells move in
2. changes in muscle cell metabolism promotes accumulation of CHO in their cytoplasm 3. smooth muscle cells die or change to foam cells 4. when smooth muscle cells die, lipid is released into interstitial spaces and either oxydized, degraded, or deposited into cholesterol crystals 5. macrophages move in and transform into foam cells to release cytokines and biologically active substances 6. macrophages secrete: TFN, and other destructive substances 7. collagen deposits 8. sclerotic part surrounds the atheroma causing it to be both hard and soft. 9. atheromas bulge, and the surface capsule may burst causing an ulceration 10. blood clots form within ulceration 11. calcification |
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what do macrophages secrete?
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TFN, and other cell destructive substances
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what happens when blood clots form within the ulceration?
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-fibrotic scars in large arteries and may cause occlusion or emboli
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what is calcification? what is it caused by?
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hardening caused by fat released by dead cells
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what are common atherosclerotic sight? What is the most common sight for plaque?
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-branching points of the aortic arch
-origins of vertebral artery from subclavian -bifercation of CCA -carotid siphon -origins of anterior and middle cerebral arteries -basilar artery THE MOST COMMON LOCATION FOR PLAUE TO DEVELOP IN THE CEREBROVASCULATURE IS TH ECAROTID BIFERCATION |
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what are some risk factors associated with atherosclerosis?
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-age
-sex -heredity -lipid metabolism\ -hyperlipidemia -secondary lipidemia -diabetes mellitis -hypertension -clotting factors -cigarette smoking -behavior |
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how does diabetes mellitis contribute to atherosclerosis?
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aggravates the course of the disease
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how does hypertension contribute to atherosclerosis?
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ishemia of endothelial cells, force lipid to filtrate into the vessel wall.
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how does cigarette smoking contribute to atherosclerosis?
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roughens the lining of the arteries/
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unilateral paresis?
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weakness or paralysis on one side of the body
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unilateral paresthesis
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tingling, numbing, or lack of feeling on one side of the body.
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dysphasis
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impared speech
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aphasia
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inability to speak.
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behavioral abnormallities
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frequently accompany ischemia of the temproal lobe caused usually by infation of the MCA
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Amourosis fugax
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temporary partial or total blindness(usually only in one eye), described as a blind being pulled over one eye
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homonymous heianopia
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blindness in the corresponding right and left visual fields.(loss of 1/2 of the visual field of both eyes that may occur after a stroke)
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Explain anterior circulation/
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synonymous with carotid circulation:
Perfusion of the eyes, and from the tops, and sides of the cerebral hemispheres. Perfusion through the ICA< ACA, MCA, and ACA |
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Explain posterior circulation?
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-synonymous with vertebrobasilar cirulation:
profuses the brainstem, cerebellum, back, and uncersurface of cerebral hemispheres. Veretebral, basilar, and posterior cerebral and posterior communicating arteries supply blood to the brain stem, cerebellum, and occipital lobes. |
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what are the symptoms of a posterior circulation stroke?
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-vertigo(sensation of moving around in space)
-ataxia(muscular in co-ordination(especially with hands)) -bilateral visual blurring -diplopia(double vision) -bilateral parethesia(tingling and numbing) -drop attack(falling) |
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where does the CCA lie in relation to the jugular vein?
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medial
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what kind of flow does the carotid artery exibit?
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cephalad flow and a pulsatile flow pattern. Constant calebre. thick walled, and a distinct intimal reflection is visible.
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what kind of flow is flow in the jugular vein?
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caudad and cahracteristic by a continuous low velocity signal. calebre changes with respiration. thin walled and easily compressible.
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What are the characteristics of uncomplicated plaque?
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smooth surface
mixed echogenicities within |
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What are the characteristics of complicated plaque
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-necrosis
-hemorrhage -calcification -disruprion of the fibrous capsule -disruption of the endothelial layer -ulceration |
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What can cause plaque severity to be underestimated?
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by looking at longitudinal images.
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What should you note when looking at plaque?
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weather it is eccentric or circufrential(extending around the circumference)
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What is another name for uncomplicated plaque? what can happen to it?
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stable- can be transformed into complicated plaque through chronic inflammation and an injury process.
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why are large plaques more dangerous?
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they tend to be complicated, cause embolization, and stenosis more than smaller plaque
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What may cause plaque to have low echogenicities?
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-fresh thrombus, or it may not be evident until doppler is applied to it.
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what are the characteristics of moderately echogenic plaque?
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-developing plaque
-smooth, unruptured plaque |
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what are the characteristics of strongly echogenic plaque?
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-contains scar tissue
-may contain thrombus material -most often irregular shaped with mixed echogenicities -may be very densly shadowed with poor ultrasound penetration |
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What kind of plaque are TIA and stroke more common with?
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heterogenous plaque
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How do the echogenicities of plaque compare to the fat content in them?
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low echogenic plaque is fatty, and moderately echogenic plaque is more fibrous
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what are common sources of emboli that cause stroke?
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ulcerated plaque
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How easy is it for sonographers to identify ulcers? what has to be seen in order for an ulcer to be identified?
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Large ulcers are easier to see, but small ones, are rarely seen.
In order for an ulcer to be confirmed, the following has to be seen: -cavity is truly within plaque -cavity is sharply marginated -blood flow within cavity |
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Artery
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carries relativly high presure blood from the heart to the arterioles
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arteriole
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connnects the artery to a capillary, has a capability for vasoconstriction, and vasodialation
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venule
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thinner wall, less smooth muscle and elastic tissue than an arteriole. Connects a capillary to a vein
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vein
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thinner walled than an artery, but similar layers. The middle layer is more poorly developed, some with flap like valves. carries relativley low blood pressures from a venule to the heart. Valvesprevent back flow, veins serve as a reservoir.
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describe the flow of blood from the heart, back to the heart?
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heart
large arteries muscular arteries small arteries arterioles capillaries(l red blood cell at a time) small veins venules larger veins heart |
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what vessels are part of the extracerebral gross anatomy?
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-aorta
-brachiocephalic -left common carotid -left sublclavian |
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explain the divisions of the aorta
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ascending-rt and lt cca
arch-brachocephalic -CCA -Lt subclavian Descendind:thoracic,and abdominal |
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describe the branches of the aortic arch?
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1. Brachiocephalic:
-first branch -divides into Rt CCA and Rt sublavian 2. Lt CCA -2nd larges branch -Courses cephalad -lies lateral to the thyroid gland, larynx, pharynx -lies medial to the jugular vien -Divides into ECA and ICA at the upper border of the thyroid 3. Lt subclavian: -Courses upward and lateral to supply the lt extremity and portions of the brain -its branches are: Vertebral, thyrocervical trunk, intrenal thoracic, superior intercostals trunk, costocervcical trunk |
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What are the 4 segments of the ICA?, and explain them?
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1. Cervical(carotid bulb)-goes from the bifercation to the entrance of the carotid canal in the petrous bone where it has a fusiform dialation. (no branches)
2. Petrous segment:Courses from carotid canal vertically, anteromedially, and up to dural layer forming the floor of the cavernous sinus. Branch: typanic artery 3. Cavernous segment: Courses in an S shape forming the floor and roof of the cavernous sinus. 4. supraclinoud segment: forms roof of cavernous sinus, and courses posteriorly, superiorly, and lateraly to its bifercation into the anterior and middle cerebral arteries. Branches:anterior and middle cerebral artery, anterior choroid, posterior communicating artery |
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Describe the ECA and its branches
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These branches primarily profuse the face and scalp;
-Anterior:Superior thyroid, lingual, and facial -posterior:occipital, posterior auricular -ascending:ascending pharyngeal -terminal: superficial temporal, internal maxillary |
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What do the vertebral arteries profuse?
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the brainstem, cerebellum, back, and undersurface of the cerebral hemispheres.
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What are the 4 segments of the VA?
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1. extravertbral segment: from origin of VA at subclavian to transvers foramina
2. intervertebral segment:through the transvers foramina and courses btw C-6 and C-1 3. Horizontal segment: courses into the cranium before they peirce the dura mater. Courses medially and posteriorly. Branches into the posterior meningeal, and muscular branches 4. Intracranial segment:ascends from dura mater anteromedially through the foramen magnum and joins with the contralateral VA from the basilar confluence. |
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what are the arteries of the circle of willis?
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-anterior communicating:joins left and right ACA's, and provides flow across the left and right hemispheres
-ACA(anterior cerebral artery):A-1-begins at ICA, courses anteromedially.A-2-begins after PcommA bif, and courses superiorly and around corpus collosum. -PCommA-Arisses from supraclinoid ICA, and courses posteriorly to anastomose with PCA -PCA-Terminal branch of basilar artery: P-1-basilar-PcommA P-2-Distal PcommA-around midbrain |
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Why is the middle cerebral artery important for the brain?
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supplies 80%
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What does cerebral mean when refering to arteries.
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very important because it supplies the cerebrum.
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What are the arteries related to the circle of willis?
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-Middle cerebral artery:
M-1-ICA-MCA, then laterally, horizontal, and inferior M-2-MCA bif-superioposterior within sylvian fissure and has branches -basilar artery(BA)-originates from the VA confluence and courses anteriorly, and superiorly then branches into RT and LT PCA. Branches: superior creebellar arteries, posterior creebral arteries. |
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what are the variations for the circle of willis?
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-classic circle of willis is only pressent in 50 % of people
--25 % have hypoplastic ACA which may result in a loss of collateral blood flow across hemispheres |
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what are the anatomical variations of the carotid artery?
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-Lt CCA originates from right brachiocephalic trunk(9%)
-Rt and LT brahciocephalic trunks(1%) -ICA tortuous and kinky -bifercation levels in the neck -various configurations of carotid bulb. |
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what are some variations of the vertebral artery?
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-VA entrance into cervical vertebra may vary
-size may vary(lt is larger in 45% of population -Rt VA originates from brachiocephalic trunk -Lt VA arise off the arch. - |
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What are the routes for intracranial collateral circulation?
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-large interarterial connections
-intracranial-extracranial anastomoses -smaller interarterila communications |
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If there is ICA obstruction, what are some possible collateral routes?
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-circle of willis-only hypoplastic communicating arteries will prevent this flow
-ECA anastamoses -branches of the major cerebral arteries that connect across each vascular territory(called leptomeninges) -Transdural branches that are the surface arteries of the brain may connect to provide flow to starving tissue.(wonderful net/rete mirable? |
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If there is obstruction in the subclavian artery, what are some collaterals?
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-Blood from one VA to another
-Anterior and posterior circulations via the VA -ECA to ICA to VA -Occipital artery to deep cervical artery. -Cross over of inferior thyroid arteries -thryrocrevical trunk and spiral arteries -cross over via internal thoracic arteries -intecostal arteries and internal thoracic arteries |
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what are some collaterals if there is vertebral obstruction?
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-Contralateral VA
-Occipital branch provides flow via VA -thryocervical trunk and muscular branches of vertebral artery |
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what happens if there is basilar obstruction?
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arterior to posterior circulations
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What is the most important distinguishing feature for vessel differentiation?
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spectral waveform
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what are normal vascular varients most commonly seen in the neck/
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-level of carotid bifercation
-tortuosities of the arteries -various sizes and locations of the carotid bulb -inverse relationsphip of the ICA and ECA lie |
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Explain kinking?
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kinking usually occus 2-4 cm above the bifercation and is bilateral in 50% of patients. Spectral analysis will display all of the usual characteristics of stenosis.
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What is a plaque that has sonolucent zone near its base thought to contain?
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a small hemorrhage
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A focal hyperechoic zone in the midst of the plaque likely represents what?
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healing or fibrotic reaction at the site of a previous hemorrhage.
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Calcium Deposition is detected as an area of what?
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acoustic shadowing.
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When plaque is complex, what does this suggest?
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more than one cycle of hemorrhage and repair.
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how does diameter of a tube affect flow rate? Why is this?
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flow rate increases in short segment of diameter reduction, but in long diameter reduction, flow rate slows because there is more shear force against the wals of the tube slowing overall flow rates.
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What is resistance?
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the opposition to flow.
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what is the formula for resistance?
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the pressure difference divided by the volume flow.
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What is low resistance flow? what arteries have this?
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-flow of continuous nature in systole and diastole feeding a dialted vascular bed.
-the ICA, VA, renal, celiac, splenic and hepatic arteries |
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what is high resistance flow? What arteries have this?
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pusatile(triphasic) flow.
-ECA, Aorta, iliac, extremeity arteries and fasting SMA |
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what is pulsititity?
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the pressure variation in the flow of blood.
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when is the pressure gradient the greatest?
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the first half os systole(also the greatest velocity)
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How is forward flow maintined during diastole?
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due to the energy stored within the walls of the arteries which recoil and propel blood forward.
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Explain pressure changes when blood leaves the LV?
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a bolus of blood leaves the LV, but there is little loss of pressure from friction in large and distributing arteries . They offer little resistance to flow, and the mean pressure decreases only slightly btw the aorta and small arteries of the limbs.
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What are the characteristics of a pressure wave?
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-amplification of pressure distally
-refected waves due to stiffness or bifercation -pulsitility seen even in microcirculation -pulsitility in peripheral arteries is reduced by vasodialtion due to reduced resistance -systolic pressure at the periphery increases compared to brachial pressure |
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what substances contribute to the density and viscosity of blood?
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plasma, cells(white, red, platelets), water, proteins
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What is the normal density for blood? How does it compare with water?
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1.05g/ml it is slightly higher than water
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What is the normal blood viscocity? at 37 degrees?
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.035 poise
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What is another name for the character of flow?
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flow profiles-cells within blood move against eachother and against walls of the blood vessels to create certain resistance to flow.
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What are some flow characteristics in a constant steady state that can be made?
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-blood flows in parallel layers called laminar flow
-blood layers move slower agains the vessel walls -the layer that moves fastest is at the center of flow. |
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Where is laminar flow found? what is it?
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found in steady straight tubes. This is parallel flow where the average flow speed is equal to half the speed in the center
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What is plug flow? wherre is it found?
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in larger tubes,or at their entrance. Flow velocity is constant through the diameter due to decreased frictional forces.
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what is disturbed flow? where does it occur?
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the streamlines become disorganized but forward flow is maintained. Occurs at biffercations, and or tortuosities.
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During collateralization, what changes are made to the spectral waveform, and 2D appearence of the collateralizing vessel?
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-vessel enlarges to accomodate flow
-spectral waveform appears low resistance with high diastolic flow. -Overall PSV increases |
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Describe turbulent flow, and where it is found?
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Chaotic flow with different directions and speed. Occurs in association with stenosis
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how does the resistance of the waveform of the CCA compare to the ICA and ECA
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it is a low resistant waveform compared to the ECA, but high resistant compared to ICA
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Describe the waveform of different sections of the ICA?
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-proximal ICA has normal flow separation
-mid and distal portions have low resistant waveforms compared with ICA and ECA |
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explain the flow of blood in the subclavian artery?
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it supplies the upper extremities which are highly resistant vascular beds. High resistant triphasic waveform is demonstrated(typically flow reversal in diastole)
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Explain the flow of blood in the vertebral artery?
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-they supply the posterior brain which is a low resistant vascular bed, therefore, the flow is low resistant and low velocity
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what is the difference btw antegrade and retrograde?
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antegrade-flow toward the brain
retrograde-flow within them |
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Define stenosis
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narrowing of a passage or opening
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severe stenosis of the carotid artery has several affects on blood flow to the brain. what are they?
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-reduction in blood flow through stenosed vessel
Collaterization via: -ECA -contralateral carotid artery -posterior circulation via the circle of willis |
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what is the stenotic zone?
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the flow speeds up at the narrowed region, and becomes turbulent just post it. The amount of flow acceleration a dn turbulence is directly proportional to the degree of narrowing.
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when might the spectral doppler criterial not be valid?
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-if ther is tandem stenosis
-there is contralateral high grade stenosis -there is hyperdynamic flow -low cardiac output -CCA stenoiss -tortuosities -inaproppriate angle or estimate measurements |
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When there is a 50 percent or less diameter reduction, what is the velocity of blood in the vessel, ICA-CCA ratio, and ICA EDV?
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125m/sec, <2.0, and <40 cm/sec
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When there is a 50-69% diameter reduction, what is the velocity of blood in the vessel, ICA-CCA ratio, and ICA EDV?
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125-230cm/sec, 2-4, 40-100cm/sec
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when there is a diameter reduction of 70% or more, what is the velocity of blood in the vessel, ICA-CCA ratio, and ICA EDV?
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>230cm/sec, >4, >100cm/sec
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How is critical stenosis detemined with the ICA-CCA ratio?
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anytime the velocity doubles, there is critical stenosis(50-60% diameter reduction)
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what is trickle flow?
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when there is a diameter reduction greater than 95% where the frictional factors cause velocity to be very slow.
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what shows up on ultrasound with stenosis?
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2D-plaque within lumen
Color-color aliasing associated with the narrowest point Spectral-sampling of flow before, during and after |
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What happens to resistance before, during and after a stenosis?
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before-resistance increases causing pusitility and lower velocities
during-very high velocities after-if critical, low velocities and low resistance. |
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How many cycles are used for pulsed doppler?
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3-30
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What does range gating mean?
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sonographer can determine where in the body sampling takes place
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What button corrisponds to PRF, or pule echo cycle?
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scale
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When does aliasing occur?
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when the doppler frequency shift exceeds one half of the PRF. (niquist limit)
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What is refraction?
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when the beam is diverted away from its course when encountering an interface of different propegation speed
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when may aliasing occur?
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-inappropriate display of doppler spectrum due to low sampling rate for PRF.
-system is sampling deep into tissue(increases PRF) |
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What is blooming or blossoming?
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overgain of the doppler signal so the display shows echos outside the regions of the spectrum(may cause overestimation of peaksystolic velocity)
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What is a bruit, how is this ignored?
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low frequency high amplitude echo that may interfere with displayed doppler signal. Can increase wall filter
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When is mirror image artifact commonly seen?
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when imaging the subclavian vein.
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What is partial volum affect or slice thickness artifact?
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objects close to the edge of the beam width are displayed in the middle,so it may mimic thrombus or plawue.
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How can spectral broadening be helped?
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decrease the insonification angle
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What is range ambiguity?
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where flow may be detected from a deeper depth but displayed as a shallow vessel.
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What are the 3 components of color doppler?
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-Hue-BART
-Saturation-saturation is greater with less white present -luminence-brighness within the hue that represents echo intensity |
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what are some applications of color doppler?
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-assessment of blood flow(health of vessel)
-characterization of masses -to facilitate placement of doppler sample volume -determine vascular variations |
