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67 Cards in this Set
- Front
- Back
List the propagation speed of tissue from slowest to fastest
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Air-->Fat--> Water--> Soft tissue--> Blood--> Muscle-->Bone
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Elasticity and compressibility are opposite of __?
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Stiffness
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What is another term for stiffness?
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Bulk Modulus
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What is the incident beam a sum of?
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The transmitted beam and reflected beam
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Describe Luez's Law
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Angle of Incidence = Angle of Reflection
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What does Snell's Law determine?
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Amount of refraction that will occur
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Given Snell's Law, what will happen to the beam if the c of medium 2 is greater than the c of medium 1?
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The beam will be bent away from normal, the transmission angle will be greater than the incident angle
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Given Snell's Law, what will happen to the beam if the c of medium 1 is greater than the c of medium 2?
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The beam will bend toward normal, the transmission angle would be less than that of the incident angle
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What does harmonics do?
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Creates an image using reflections which are 2x that of the frequency of transmitted sound
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As you increase your depth, what happens to harmonics?
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^ depth, ^ harmonics
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For harmonics to occur, the mechanical index has to be great than __?
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0.1
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What is the purpose of harmonics?
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Improves lateral resolution
Eliminates grating lobes Degrades axial resolution |
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If you increase crystal diameter or frequency, what happens to the far zone?
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Increase aperature, or increase frequency you decrease the far zone
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Where is the best lateral resolution found?
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At the focal zone
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Where does diffraction occur?
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In the far zone
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Define A-modes y-axis and x-axis
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Y-axis= echo strength
X-axis= increasing depth |
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Define B-modes y-axis and x-axis
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Y- axis= depth
X- axis= time |
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What is a voxel?
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3D picture element, used to create 3D images
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How is 3D accomplished?
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Using many parallel 2D images
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Give the formula for Reflector depth
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Reflector depth= c * (t/2)
t- round trip time |
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What happens to your PRF as you decrease the depth?
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Your PRF increases as depth decreases
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Relate image depth, # of scan lines, # of focal zones, and frame rate
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image depth * # scan lines * # of focal zones * frame rate <77,000
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Frames less than __ will create a flicker?
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15-20 frames/sec
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What is the typical frame rate used?
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30-60 frames/ sec
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What can you do to improve frame rate?
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Increase the PRF
Decrease the Depth Decrease the sector angle Decrease # of focal zones |
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What form of artifact does harmonics help prevent?
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Reverberation artifacts
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What affects blood flow?
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Cardiac motion
Compliance Capacitance Muscle Tone Radius/diameter of vessel wall |
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What is compliance?
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Rate at which volume increases with respect to change in pressure
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What is capacitance?
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rate volume increases with respect to time
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What is stroke volume?
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Amount of blood in the forward direction
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Give the formula for stroke volume
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Stroke volume= end diastolic volume - end systolic volume
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What is the formula for cardiac output?
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Cardiac output= stroke volume * heart rate
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Give the equation of Poiseuille's law
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Q= (change in pressure* pi*r^4)/8*L*viscosity
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What part of the vessel is the primary source of peripheral resistance?
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Arterioles
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Define viscosity
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The fluids ability to resist change in shape of flow
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If you increase viscosity what happens to flow?
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Flow decreases as viscosity increases
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Define inertia
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ability for blood to resist change in direction or speed
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What causes inertia?
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Pulsatile flow of arterial circulation
Phasic flow of venous circulation Velocity changes d/t narrowing of the vessel |
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Describe Bernolulli's Principle
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Total energy= potential energy + kinetic energy
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What is potential energy?
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Stored energy
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What is kinetic energy?
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Energy in motion
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Describe the potential energy distal to a stenosis
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It increases but never reaches the level prior to stenosis
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What is plug flow?
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When velocity of blood is constant throughout
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Give an example of a vessel with plug flow
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Aorta
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Define parabolic flow
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average speed across the vessel is equal to half the maximum flow at the vessel center
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What does Reynold's number have to exceed in order to get turbulent flow?
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2,000
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Give the formula for Reynold's number
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Re= velocity*density*2r/viscosity
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What happens to resistance and flow when the vessel dilates?
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Dilation increases vessel radius, therefore decreasing resistance and increasing flow
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What happens to resistance and flow when the vessel constricts?
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Constriction decreases the vessel radius, therefore, increasing resistance and decreasing flow
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What is hydrostatic pressure?
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pressure related to blood pushing on vessel (i.e gravity)
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As gravity increases what happens to the hydrostatic pressure?
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Increase gravity, increase hydrostatic pressure
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Give the hydrostatic pressure at the different levels of the body when standing
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Top of head: -30mmHg
Mid chest: 0 mmHg Waist: + 50 mmHg Knee: + 75 mmHg Ankle: + 100 mmHg |
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How many crystals does a continuous wave transducer have?
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2 crystals, one transmitting one receiving
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In continuous wave where will the Doppler signal be picked up?
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At the beam overlap, where receiving crystal signal and transmitting crystal signal intersect
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What is range ambiguity?
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Inability to tell where the Doppler signal is coming from
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What is the biggest disadvantage of continuous wave Doppler?
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Range ambiguity
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What it the biggest advantage of continuous wave Doppler?
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No aliasing
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How many crystals are there in pulsed wave Doppler?
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1 crystal
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When will aliasing occur?
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When the nyquist limit = 1/2 PRF
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What can you do to eliminate aliasing?
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Decrease depth
Decrease frequency Increase scale Decrease baseline Use continuous wave |
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What is a Duplex image?
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Combination of color and pulsed wave Doppler
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What is the purpose of phased quadrature?
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compares transmitting and receiving wave phase, resultant phase tells direction of frequency
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What is FFT?
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mathematical technique, breaks down complex frequencies into individual frequencies
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Give the formula for the pulsitility index
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PI= PSV-EDV/ mean
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Give the formula for the resistive index
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RI= PSV-EDV/PSV
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How many pulses are in a color packet?
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3-30 per line of color
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What is saturation
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Degree of color is diluted with white
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