Midterm Flashcards
stroke can be caused by blockage of:
- thrombosis
- arterial embolism
- hemorrhage of an aneurysm
what may stroke result in?
affected area of brain cannot function because without oxygen, cells die
- inability to move one or both limbs on one side of the body
- or inability to understand or formulate speech (slurred or jumbled)
- inability to see one side of visual field
- face may be drooping
ischemic stroke
a blood clot blocks a blood vessel, cutting off the oxygen supply
Transient ischemic attack (TIA)
a temporary blood clot blocks a blood vessel
is a patient comes in with symptoms of stroke, TIA, or vascular then what do we do as sonographers?
use cerebral vascular doppler study to visualize:
- areas of plaque and characterization
- high grade stenosis
- complete occlusion
- collaterization
Rt cerebral hemisphere stroke symptoms
- paralysis of Lt side of body
- difficulty reasoning and thinking out simple solutions
Lt cerebral hemisphere stroke symptoms
- paralysis of Rt side of body
- disrupts ability to speak
cerebellar stroke symptoms
- lack of coordination (ataxia)
- imbalance, shaking, muscular difficulty
brainstem stroke symptoms
involuntary function/vegetative state
syncope
transient loss of consciousness-faintness
which side of the body are the symptoms experienced during a stroke?
contralateral side of the body
amaurosis fugax
exception to the symptoms of stroke being on ipsilateral side of body
what does stenoses usually involve?
the bulb and ICA
what is considered a warning sign for a stroke?
TIA
what are signs of a stroke?
- weakness
- aphasia (trouble speaking)
- vision problems
- headache
- dizziness
what does the acronym FAST stand for?
F-face-ask person to smile
A-arms-can you raise both arms
S-Speech-slurred or jumbles
T-Time- call 911
what is the treatment for a stroke?
Medication
how do stroke drugs work?
- aim to break up existing blood clots
- thin the blood to prevent clots from starting or worsening
- lesson bleeding in a hemorrhagic stroke
Anticoagulants
drugs that thin the blood
what are types of anticoagulents?
- Aspirin
- Warfarin
Aspirin
prevents platelets from clotting the blood
-can be used to avoid stroke
Warfarin
blood thinner used to prevent blood clots from forming or to prevent existing clots from growing larger
antiplatelet drugs
helps prevent blood clots from forming
Tissue Plasminogen activator:(TPA)
common emergency treatment for people having an ischemic stroke. immediately breaks up clot
-injected into vein or artery
Statins
blocks an enzyme in the body needed to produce cholesterol that may clog arteries
prescribes to people with high cholesterol which may lead to TIA’s, heart attacks, e.t.c
what statins are commonly used?
Lipitor or crestor
Blood pressure medications
used to help lower blood pressure which can play a major role in hemorrhagic stroke
what blood pressure medications are commonly prescribed?
- beta-blockers
- angiotensin-converting enzyme (ACE) inhibitors
- calcium channel blockers
what are the indications for doing an ultrasound for stroke?
- identify patients who are at risk
- facilitate treatment
- document progressive treatment
- detect nonatherosclerotic
Indications
Dissection Fibromuscular dysplasia Trauma Arteritis Aneurysms Radiation effects Stroke/TIA symptoms Bruit
Bruit
an abnormal swishing sound heard
why do we measure?
- measure of doppler waveform allow for quantification of disease
- determination of severity
- grading allows for future treatment
- predict situation of prox stenosis when disease is not easily seen (bowel gas)
- comparisons can be made
is velocity constant across a vessel?
no
what is velocity dependant on?
- left ventricular output
- resistance of the arterioles
- cross-sectional area of vessel
- coarse of the vessel (kinked, tortuous)
what does PSV stand for?
peak systolic velocity
PSV
maximum velocity at any given time
what can be used in ratio calculations when the angle correct is employed at 60 degrees?
PSV
what does EDV stand for?
end diastolic velocity
EDV
velocity measured in the diastolic phase immediately prior to the systolic upstroke
what can measurement of EDV be used for?
grading a severe internal carotid stenosis
what is the outcome when EDV exceeds 140cm/s?
stenosis is in the 80-99% occluded range
what are ratios used for?
compensate for poor cardiac function
what must be used for carotid doppler?
angle correct (most accurate)
what must the angle correct be compared to the vessel?
parallel to the vessel walls in the CCA and ICA
where is the PSV measured?
distal CCA-this represents the segment proximal to the critical stenosis in the ICA
The PSV within a stenosis in the prox ICA is obtained taking how many measurements?
at least 3 to ensure highest measurements is recorded
what is the ratio in carotid artery?
PSV ICA/PSV distal CCA
a ratio of what is significant?
greater than 2
what does a ratio greater than 2 represent?
this means the flow has doubled in velocity between the segments and is now hemodynamically significant
the higher the ratio=______
the greater the severity of the disease
what are ratios used for in peripheral?
estimate degree of stenosis in the femoral vessels
what else in peripheral arteries must the PSV be measured?
proximal segment to the stenosis that exhibits normal flow
what is the ratio in peripheral arteries?
stenotic zone PSV/proximal PSV
when can ratios not be used?
ratios cannot be used if there is disease in the proximal segment (this is true for any ratio measurement including carotids)
when is the angle correct at 60 degrees used?
both measurements
what is the ratio dependant on?
angle dependant
why is optimization important?
to provide accurate hemodynamic information concerning vessel patency and direction of flow which facilitates clinical management of the patient
what contributes to the best possible exam regarding optimization?
- transducers
- scanning techniques
- knobology
what does interpretation of the doppler spectrum rely on?
topnotch technique
what does the frequency of the transducer determine?
the axial image resolution and useable image depth
what happens as the frequency increases to the resolution and depth?
resolution also increases but depth decreases
what transducer is used for carotid and venous studies?
5-10 mHZ
spectral anaylisis
allows for visualization of the doppler signal
what info is needed to provide quantitiavie data for evaluating doppler shift?
spectral analysis
what gives rise to different spectral displays?
high and low impedance conditions downstream
what converts doppler shift information into a visual spectral analysis?
uses a fast fourier transform (FFT)
what does FFT break down?
complex signals of the doppler shift into individual frequencies
what does FFT’s display as?
velocity rather than frequency
what are advantages for spectral analysis?
- allows measurement of peak,mean,diastlic velocities
- minimum flow velocities, flow direction, and characteristics of blood flow
- presents doppler shift frequencies in frequency order
what is the disadvantages to spectral analysis?
cannot accurately measure high velocities without aliasing
what is displayed in the sample volume?
instantaneous spectrum
what will happen if angle correction is applied?
the spectrum will represent the range of velocities in the sample volume
where is the range of frequencies displayed in each spectrum?
on the vertical axis
what is the power of each frequency component presented as?
as a shade of grey
how many heart cycles are measurements best made over?
5 heart cycles
what should the colour scale velocities match?
velocities of the expected study
what button alters scale?
PRF
will PRF be higher or lower for arteries?
higher than venous flow
what arteries may require higher PRF?
aorta rather than renal arteries
what does colour above the baseline indicate about flow?
toward transducer
what can colour shades indicate on spectral?
magnitude of the velocity (mean doppler shift)
light red
high velocity
dark red
low velocity
what may a range of velocities in each sample be presented as?
turbulence
how do you correct aliasing?
increase PRF
can the velocity scale on spectrum be changed?
yes, increased or decreased
what velocity size should be displayed?
not too small or too large
what button adjusts doppler gain?
D
if the spectral signal is weak what must be adjusted?
- gain
- angle of insonation by altering the window used
what does grading of carotid stenosis rely heavily on?
using a different window to get a cleaner signal
how should the colour box field of view be?
field of view should be adjusted to cover only the region of interest (maximized frame rate)
what is an issue with colour box? length or depth?
length is not an issue but depth is
aliasing
- misrepresenting the pulse wave doppler shift in a negative direction
- wrap around
- exceeding Nyquist limit
what is aliasing caused by?
- the doppler shift exceeding one half of the PRF
- under sampling of the doppler shift
what does aliasing manifests as?
- improper representation of the information sampled
- wraps around of the pulse wave or colour doppler display
- incorrect flow direction
what are methods of overcoming aliasing?
- increase PRF (velocity scale)
- increase doppler angle
- adjust baseline closer to 0
- decrease operating frequency
- decrease depth of sample volume
- change to continuous wave
flash
sudden bursts of colour (colour bleeding)
what is flash caused by?
tissue and transducer motion
what is the manifestation of flash?
extension of colour beyond the region of blood flow
what are the methods of overcoming flash?
- increase PRF
- decrease colour gain
- increase filtering of low flow velocities
range ambiguity
doppler shifts received are not all from the same vessel
what is range ambiguity caused by?
improper placement of sample volume
what is the manifestation of range ambiguity?
improper representation of doppler shift
what are methods of overcoming range ambiguity?
readjust placement of sample volume
mirror imaging
duplication of a vessel or Doppler shift on the opposite side of a strong reflector
what is the cause of mirror imaging?
doppler gain is set too high
what is manifestation of mirror imaging?
added vessel or doppler shift
what are methods of overcoming mirror imaging?
- decrease doppler or colour gain
- use a different acoustic window
