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57 Cards in this Set
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What is volume flow rate?

Volume flow rate is the volume of flow passing through a vessel or location per unit time.


VFR formula/Pousille's equation

Q= Delta P x Pie x Radius cubed/8nl


What are the 4 factors that affect volume flow rate?

The 4 factors affecting volume flow rate are:
Pressure difference, tube diameter, tube length, viscosity 

Define the relationship of VFR with resistance.

VFR and resistance have an inverse relationship. If resistence goes up then VFR will go down.


Resistence formula

Resistance ...
8nl/pie x radius cubed 

What is the most important component that affects the VFR in Poiseuille's equation?

The most important component affecting VFR in poiseuille's equation is vessel size (diameter/radius). This is because it is cubed so any change in diameter/radius will have a big effect.


What is plug flow?

Plug flow is flow at the vessel origin or enterance. The viscosity is constant across the width of the vessel.


What is laminar/parabolic flow?

Laminar/parabolic flow is stead flow. Flow is fastest in the center due to low resistence and slower near the walls due to friction from the walls (higher resistence). Flow is in straight and parallel lines running in layers. Laminar flow is used for velocity check (sample)


What is disturbed flow?

Disturbed flow is when parallel streamline flow is altered or "disturbed" from their straight form. In natural setting it is seen at bif and in pathology it is seen prestenosis.


What is turbulent flow?

Turbuelent flow is random and chaotic flow. Speed AND direction are chaotic. Flow creates circles/swirling patterns known as Eddie currents. Turbulent flow is seen poststenosis.


What is reynolds number?

Reynolds number predicts the onset of turbulence. If reynolds number exceeds 2000 turbulence occurs.
** 1800  2000 = disturbed flow 

Reynolds number formula

reynolds number formula
Velocity x density x diameter/viscosit 

Define continuity rule.

According to continuity rule, volume flow must be CONSTANT pre at and post stenosis. Blood is neither created nor destroyed as it flows through stenosis.


Define Bernoulli's effect.

Bernoulli's effect ... There is a drop in pressure at stenosis associated with increased flow speed. This decreased pressure in regions of high flow speed is known as bernoulli's effect.


What happens to pressure and velocity at stenosis?

At stenosis, pressure decreases and velocity increases in order to maintain continuity rule.


If the pressure gradient increases, flow _____

If the pressure gradient increases, flow INCREASES


If the resistence increases, VFR ________

If the resistence increases, VFR DECREASES


List the variables on which flow resistence depends upon.

Flow resistence depends on...
Length (increasing) Viscosity (increasing) Diameter (decreasing) all resulting in INCREASED resistence 

Flow resistence decreases with an _____ in vessel radius.

Flow resistence decreases with an INCREASE in vessel radius


What happens to energy at stenosis?

At stenosis, pressure energy is converted into kinetic energy.


List the variables increase which decrease VFR (those with inverse relationship)

Viscosity increased and/or length increased results in a decrease in VFR


What happens to the speed of flow at stenosis?

At stenosis velocity INCREASES, the flow speeds up


At stenosis the pressure is _____ than the proximal and distal locations

At stenosis the pressure is LOWER than the proximal and distal locations


What happens to the VFR at Stenosis?

At stenosis VFR stays CONSTANT (continuity rule)


Define velocity.

Velocity is the speed and direction of flow.


Define doppler effect.

Doppler effect is a change in received frequency as a result of relative motion (motion can be with the receptor, reflector or sound source)


Define doppler shift.

Doppler shift is the difference between emitted frequency and received frequency.


When the received frequency is smaller than the initial frequency, what kind of doppler shift happend?

In doppler shift, if the received frequency is smaller than the initial frequency, the result is NEGATIVE doppler shift. Flow is going AWAY from the Tx.


Define positive doppler shift.

Positive doppler shift is when the received frequency is greater than the initial frequency (flow is coming TOWARDS the Tx


Smaller angle results in what kind of doppler shift?

Smaller angle results in BIGGER doppler shift. (0 degrees is the max and 90 degrees is nothing)


What happens when you scan at 90 degree angle?

At 90 degree there is NO doppler shift. You are inside the vessel


Doppler equation formula

Fd= 2 x operating frequency x velosity x cosine theta/ prop speed


Define doppler equation and their relationship with one another

Doppler equation relates to the variables that result in doppler shift and is related to flow speed and frequency. When speed and frequency increase doppler shift increases.


What kind of relationship do doppler shift and angle have?

Doppler shift and angle have an inverse relationship.


What kind of relationship do angle and cosine theta have?

Angle and cosine theta are homies, what one does the other does too.


A stationary sound source and a stationary listener _____ result in doppler shift.

A stationary sound source and a stationary listener DO NOT result in doppler shift.
**THERE IS NO MOVEMENT. Doppler shift requires movement. 

A doppler shift is a change in ______ of the ____ or ______ as a result of relative motion.

A doppler shift is a change in received frequency of the SOURCE or RECEPTOR as a result of relative motion.


A 3 MHZ transducer produces 2 Khz doppler shift frequency. If all parameters remain the same and we double operating frequency, what will be the new doppler shift?

Doubling operating frequency will double doppler shift.


Maximum negative doppler shift will be caused by the reflecftor which is ____ from the source

Maximum negative doppler shift will be caused by the reflector which is MOVING AWAY from the source


Maximum positive doppler shift will be caused by the reflector which is moving _____ the trandsducer

Maximum positive doppler shift will be caused by the reflector which is moving TOWARDS the transducer


The reflector which is ____ to the sound source will not produce any doppler shift.

The reflector which is PERPINDICULAR (90 degrees) to the sound souce will not produce any doppler shift


What are the limitations for color doppler?

Color doppler limitations are ...
Increased dwell time due to multiple pulses per scan line Decreased frame rate to increase packet size aliasiing seen in form of mosaics 

What is aliasing?

Aliasing is color artifact due to improper settings. Aliasing occurs when doppler shift exceeds the nyquist limit (1/2 PRF). Aliasing is AKA undersampling


List the reasons for aliasing

Aliasing occurs due to ...
Scanning deep samples Higher frequency selected than necessary Improper doppler shift (results in low angle) Undersampling Exceeding nyquist limit 

List the ways to reduce aliasing

Reduce aliasing by...
Scanning shallower increase scale (PRF) Lower frequency Increase scanning angle Use a smaller sample size (will increase frame rate) Switch to CW doppler (requires no PRF) 

What is auto correlation?

Auto correlation is the automatic assignment of color according to strength. Done by the machine.


What is power doppler used for?

Power doppler is used to indicate the prescence or abscence of flow in small.tiny vessels (does not alias)


List the limitations of power doppler.

Power doppler cannot tell you the type of flow, direction of flow or velosity (speed) of flow


List the differences between PW and CW

PW has 1 crystal, CW has 2
PW has damping and PRF, CW does not PW has aliasing @ high velocity, CW has NO aliasing PW has image and waveform, CW has waveform only PW has a duty factor of 1%, CW is 100% PW has range resolution, CW has range ambuiguity 

What are the drawbacks of CW?

Drawback of CW...
No Image Blind modality Too much information/overlapping 

Do you see any color at 90 degrees? which one?

At 90 degrees you do not see red or blue, you will only see black


What does lack of color indicate?

Lack of color indicates ...
Abscence of flow poor probe position occulded vessel poor color gain high wall filter setting poor angle (90 degree) 

Define spectral broadening.

Spectral broadening are wide spectral traces indicating multiple velocities are present in the sample. Vertical thickening of spectral trace. Spectral broadening is seen at stenosis and is AKA window filling.


What is Fast Fourier Transform?

FFT is the mathematical technique the ultrasound machine uses to calculate the doppler shift in spectral instruments. It shows the individual velosities in the signal. It is the PW & CW demodulation for spectral analysis


What is the unit for Viscosity?

The unit for viscosity is POISE


Pulsatile flow is controlled by ______

Pulsatile flow is controlled by the HEART


Phasic flow is controlled by _____

Phasic flow is controlled by RESPIRATION
