Ch. 17-20 Final Exam Review Flashcards
The energy at the beginning of the vessel must be __ than the energy at the end of the vessel for blood to flow.
Greater
Contrast agents are used to improve image quality by changing the __ properties of the tissue that it resides in.
Acoustic
What is characterized by chaotic flow patterns in many different directions and at many different speeds?
Turbulent flow
Blood flows from regions of __ energy to __ energy.
High; low
What imaging technique sends a positive and then a negative pulse down each scan line?
Pulse inversion harmonics
Where are harmonics generated?
In tissue
Resistance to blood flow is primarily controlled by __.
The radius of the vessel
MI is proportional to ___ pressure.
Rarefactional
MI is inversely proportional to __.
Frequency
What uses the amplitude of the Doppler shift and the intensity of the red blood cells to be able to generate color on the image independent of the angle of insonation.
Power Doppler
What form of Doppler has a large sample volume that obtains signals from all vessels within?
CW Doppler
What is the best obtainable angle of insonation to produce the most accurate Doppler shift information?
60 degrees
When is Doppler shift the highest?
When the beam angle is parallel to the direction of flow
What is the smallest number of crystals a PW Doppler device may have?
One
According to Bernoulli Principle, where will you find the highest velocity in a vessel with stenosis?
At the site of stenosis
If blood pressure increases with no change in resistance, what happens?
Increased flow rate
What is the type of blood flow typically visualized in arteries?
Pulsatile
What type of blood flow is normally associated with veins?
Phasic
A Reynolds number __ indicates turbulent flow on color Doppler evaluation.
Greater than 2000
Resistance increases in a vessel:
Smaller vessels, increased viscosity, longer vessels, and closer to the vessel wall
What happens when spectral Doppler gain is too high?
Overmeasurement of the velocities
Which controls affect the amount of color fill in a vessel evaluated with color Doppler?
Color Doppler scale settings, sample size, and sample angle
Does aliasing occur with color Doppler?
Yes
The brightness of the reflection on the Doppler tracing represents __.
The number of red blood cells moving at each velocity displayed
What type of blood flow is predicted with a Reynold’s number less than 1500?
Laminar flow
Which mathematical processing technique is used to analyze the data and produce a spectral waveform?
Fast Fourier Transform
What does increasing the PRF/scale setting on spectral Doppler do?
Decreases the potential for aliasing
Can color Doppler measure peak systolic and end diastolic velocities?
No
In tissue harmonic imaging, what frequency is used to produce the image?
Double the fundamental frequency
What is the term used to describe the cocentric layers of blood flow within a normal vessel.
Laminar flow
As blood vessel radius decreases, __.
The resistance increases
Pressure __, when a vein is fully expanded?
Increases
What is the cosine of 60 degrees?
0.5
What can you do to eliminate aliasing?
Increasing PRF, increasing the Nyquist limit above the frequency shift, and decreasing the sample depth
What are the benefits of harmonic imaging?
Improves image quality, aids in visualization of borders, and lateral resolution improves
No flow is detected while performing a color Doppler evaluation of a normal patient vein. What will improve the color display?
Increase the color packet size
What is the cosine of 90 degrees?
0
What does the brightness of the dots that make up the spectral display represent?
The number of red blood cells present
What is the term used to describe the thickness of blood?
Viscosity
What is the name of the flat flow profile that is seen at the entrance of vessels
Plug flow
What is defined as the specific area or location where Doppler shift information is being obtained.
Sample volume
Blood flow that varies with respiration is __.
Phasic
What is an abnormality that would lead to an increase in the Reynolds number?
Stenosis of the vessel
What are the advantages of CW Doppler over PW Doppler?
Not limited by PRF, no aliasing, and the ability to evaluate deeper vessels
What is the signal processing technique used for color Doppler that is not as accurate as, but is faster than the technique used for spectral Doppler?
Autocorrelation
Blood flow at a focal stenosis will demonstrate:
Increased resistance, increased velocity, and decreased pressure
What must be increased in order to see an increase in flow volume?
Pressure difference
During inspiration the flow in the veins of the upper extremities __.
Increases
The speed of sound in soft tissue is __ related to the Doppler shift.
Inversely
In a standing patient, where is the hydrostatic pressure the highest?
In the feet
The Doppler shift is lowest at what angle to flow?
90 degrees
What happens if blood flow is sampled in the center of laminar flow?
There will be a higher velocity than if sampled towards the edges
What is the filling in of the spectral window on a Doppler tracing that is caused by turbulence?
Spectral broadening
What is the Nyquist limit if the PRF is 5000 Hz?
2.5 kHz
If the harmonic frequency is 10 MHz, what most likely is the fundamental frequency?
5 MHz
In a vessel with a focal stenosis, where is the lowest pressure point found?
At the narrowest point in the vessel
What is defined as the physiology of blood flow?
Hemodynamics
The sonographer may avoid aliasing by altering the __.
Image depth
What is the point at which Reynolds number predicts turbulence?
2000
The harmonic signal __.
Is produced by the patient (tissues)
When imaging in tissue harmonic imaging __.
The fundamental frequency is filtered out
Flow moving away from the transducer will be demonstrated __.
Below the baseline
The low velocity component is missing on a spectral waveform. What should be adjusted to fix this?
Wall filter
What does Bernoulli’s Principle describe?
In a stenosis, velocity increases and pressure decreases
The Doppler shift is zero when the angle between the incident and the flow direction is __.
90 degrees
When a reflector moves toward the transducer, what will happen to the reflected frequency?
It increases
Blood flow moves in layers with the highest velocity layer in the center of the vessel describes __.
Parabolic flow
The green or yellow color on the variance color map indicates __.
Turbulent flow
With normal circulation, inspiration:
Increases venous return from the heart to the upper body
How many crystals are needed for CW doppler devices?
At least two
In an exercising patient, what is the response to peripheral resistance with arteriolar dilation?
The peripheral resistance decreases
Artifacts related to propagation speed occur because:
The machine assumes 1,540 m/s for all tissue
If the reflector is moving away from the sound source, the resulting reflected waves will exhibit:
A decrease in frequency
In order to maintain flow as a constant, if the area of a vessel increases what must happen to the velocity?
It decreases
When evaluating a suspected arterial stenosis, a Doppler angle of __ degrees will produce the MOST accurate flow velocity.
0
What is a disadvantage of power Doppler?
Lack of information of blood flow direction
In order to assess low velocity flow, what system adjustment should be made?
Decrease the rejection and wall filter setting
The term __ refers to when all layers of blood flow are moving relatively the same speed.
Plug flow
Assuming flow is constant, what happens in a region of blood vessel narrowing?
There is an increase in the velocity along with a corresponding decrease in pressure
What type of energy relates to hydrostatic pressure?
Gravitational
Intravascular contrast agents __ the reflectivity of selected tissues?
Increase
Pulse inversion harmonic imaging __ spatial resolution and __ temporal resolution.
Increases; decreases
Harmonic waves behave in a __ fashion.
Nonlinear
Frequency will __ if the sound source and/or reflector move towards each other.
Increase
Audible flow is termed __, while palpable flow is termed __.
Murmur or bruit; thrill
Where does the blood travel the fastest when there is a stenosis?
In the stenosis
Name the two types of laminar flow.
Plug and parabolic
If the number of ultrasound pulses per scan lines increases:
The color packet size will increase
Why does aliasing NOT occur with CW Doppler systems?
CW probes use two separate elements so they are not limited by pulse echo parameters like PRF and the Nyquist limit
What system adjustment would increase the size of the spectral window?
Changing from 4 mm to 2 mm sample size
What is a system adjustment that is made when changing from a lower extremity arterial exam to a lower extremity venous exam on the same patient?
Decrease doppler scale
What will increase spectral broadening on the image?
Increases sample volume size
Pulse inversion harmonics uses __ bandwidth transducers.
Wide
Harmonics are __ the transducer frequency.
Twice
Why do contrast agents reflect sound?
Because the impedance of the agent is different than the impedance of soft tissue
