Shared Flashcard Set

Details

Understanding Ultrasound Physics/Edelman Ch 19 Part 1
Understanding Ultrasound Physics - Part One
66
Medical
09/27/2010

Additional Medical Flashcards

 


 

Cards

Term
The frequency of sound changes when the sound source and the receiver move closer together or further apart. What is this called?
Definition
Doppler Shift
Doppler Frequency
Term
What is doppler shift used to measure
Definition
Velocity of Blood Flow
Term
As sound approaches a receiver, what seems to happen to its frequency/pitch?
Definition
Increases
Term
As sound departs a receiver, what seems to happen to its frequency/pitch?
Definition
Decreases
Term
Demodulation
Definition
The process of extracting low doppler frequency from the higher transducer frequency
Term
What is the doppler shift range?
Definition
20Hz - 20,000Hz (20kHz)
Term
If the transmitted signal is 5,000,000 Hz and the received signal is 5,003,000 Hz, what is the doppler shift? Which direction is the blood moving?
Definition
3,000Hz (positive, so...)
Toward Transducer
Term
When RBCs move toward the transducer, is the doppler shift negative or positive?
Definition
Positive
Term
When RBCs move away from the transducer, is the doppler shift negative or positive?
Definition
Negative
Term
Speed
Definition
This is purely a magnitude, indicating the distance traveled
Term
Velocity
Definition
This is magnitude, indicating the distance traveled, and the direction traveled
Term
Speed is reported in what units?
Definition
cm/s (any distance divided by time)
Term
Doppler provides a (quantitative|qualitative) measurement
Definition
Quantitative
Term
Spectral Doppler (Color Flow) provides a (quantitative|qualitative) measurement
Definition
Qualitative
Term
The ideal transducer angle (angle correction/cosine) for taking doppler measurements is what?
Definition
0 - 60 Degrees
(0 or 180 degrees is ideal)
Term
What is the relationship between doppler shift and blood flow velocity?
Definition
Directly Related
Term
Why is there a "2" in the doppler shift equation?
Definition
Transmit/Receive Time
Term
What is the relationship between doppler shift and transducer frequency?
Definition
Directly Related
Term
When blood flow is ___ to the sound beam, the entire doppler shift is measured, making the velocity measurement 100% accurate
Definition
Parallel
(0 or 180 Degrees)
Term
When blood flow is ___ to the sound beam, the no doppler shift is measured, making the velocity measurement 0% accurate
Definition
Perpendicular
(90 Degrees)
Term
The % of true velocity that is measured depends on the ___ of the angle between the sound beam and the direction of flow
Definition
Cosine
Term
A Doppler system that measure the presence of blood flow without distinguishing its direction is called what?
Definition
Nondirectional Doppler
Term
A ___ doppler shift indicates flow ___ the transducer whereas a ___ doppler shift represents flow ___ the transducer
Definition
+ / towards
- / away from
Term
A doppler system that measures the presence of blood flow and its direction is called what?
Definition
Bidirectional Doppler
Term
Nondirectional doppler uses how many speakers?
Definition
1
Term
Bidirectional doppler uses how many speakers?
Definition
2 (one for flow in each direction)
Term
When flow toward the transducer is displayed graphically, above the baseline, and flow moving away from the transducer is shown below the baseline, what is this called?
Definition
Phase Quadrature
Quadrature Detection
Term
When assessing adjacent artery and veins with doppler, how can we determine which is which?
Definition
The artery & vein will each be heard from a different speaker. The arterial signal will have a higher velocity.
Term
How many crystals are needed for continuous wave doppler?
Definition
Two - one for transmitting, one for receiving
Term
What is the greatest advantage of continuous wave doppler?
Definition
Its ability to accurately measure very high velocities
Term
What is the primary disadvantage of continuous wave doppler?
Definition
Range Ambiguity - its inability to determine the exact location of the moving RBCs
Term
With continuous wave doppler, at which part of the beam are velocities measured?
Definition
Velocities are measured along the entire beam
Term
Another disadvantage of continuous wave doppler is its lack of ___: doppler shifts from deeper RBCs may be incorrectly interpreted as having been created by ___ RBCs
Definition
TGC
Fewer
Term
Simultaneous anatomic imaging and doppler imaging is called what?
Definition
Duplex Imaging
Term
A transducer which contains only two crystals and no backing material is called what?
Definition
Dedicated Continuous Wave
(Pedoff)
Term
Which kind of transducer offers these advantages:
- higher sensitivity
- high quality factor
- narrow bandwidth
- undampened signal strength
Definition
Dedicated Continuous Wave
(Pedoff)
Term
How many crystals are needed for pulsed wave doppler?
Definition
One - alternates between transmit & receive
Term
With pulsed wave doppler, at which part of the beam are velocities measured?
Definition
Gate
Sample Volume
Term
What is the greatest advantage of pulsed wave doppler?
Definition
Ability to select the exact location to assess
- Range Resolution/Specificity
- Freedom from Range Ambiguity Artifact
Term
What is the primary disadvantage of pulsed wave doppler?
Definition
Inaccurate measurement of high velocity signals (aliasing)
Term
What is it called when high velocity flow in one direction is displayed as traveling in the opposite direction?
Definition
Aliasing
Term
Which kind of transducer offers these advantages:
- low quality factor
- low sensitivity
- wide bandwidth pulses
Definition
Pulsed Wave Doppler Transducers
Term
Can pulsed wave doppler transducers produce images as well?
Definition
Yes
Term
Aliasing only occurs with what type of doppler?
Definition
Pulsed Wave Doppler
Term
This is the highest doppler frequency or velocity that can be measured without the appearance of aliasing
Definition
Nyquist Limit
Term
Half the PRF is also called what?
Definition
Nyquist Limit
Term
The Nyquist Limit is measured in what units?
Definition
Hz
Term
Deeper sample volumes create more ___
Definition
Aliasing
Term
The sampling rate of pulsed wave doppler is the ___
Definition
PRF
Term
Will the following result in more or less aliasing?
- slower blood velocity
- lower transducer frequency
- shallow gate
Definition
Less Aliasing
Term
Will the following result in more or less aliasing?
- faster blood velocity
- higher transducer frequency
- deep gate
Definition
More Aliasing
Term
What happens to the PRF/Nyquist Limit when the sample volume gate is shallow?
Definition
High PRF/Nyquist Limit
Term
What happens to the PRF/Nyquist Limit when the sample volume gate is deep?
Definition
Low PRF/Nyquist Limit
Term
What type of transducers create more aliasing?
Definition
High Frequency Transducers
Term
What type of transducer is less likely to create doppler shifts that exceed the Nyquist Limit?
Definition
Low Frequency Transducers
Term
These 5 techniques can be used to avoid what?
1. Adjust scale to maximum
2. Use lower freq transducer
3. Use shallower sample volume gate
4. Use CW Doppler
5. Adjust baseline (appearance only)
Definition
Aliasing
Term
What is an advantage of adjusting doppler scale to its maximum?
Definition
Doing so increases PRF & Nyquist Limit to maximum values, thus reducing the chances of aliasing
Term
What is a disadvantage of adjusting doppler scale to its maximum?
Definition
1. Higher PRF reduces sensitivity to low velocities
2. Aliasing can still occur
Term
What is an advantage of selecting a lower frequency transducer?
Definition
Lower doppler shifts are less likely to exceed the Nyquist Limit and alias
Term
What is a disadvantage of selecting a lower frequency transducer?
Definition
Nothing significant, although lower quality grayscale anatomical images can occur during duplex imaging
Term
What is an advantage of using a shallower sample volume gate?
Definition
The PRF/Nyquist Limit increases, reducing the chances of aliasing
Term
What is a disadvantage of using a shallower sample volume gate?
Definition
Nothing really, although in some cases the sonographer may be unable to adjust the view to allow for a shallower sample volume gate
Term
What is an advantage of using CW doppler?
Definition
Aliasing never happens with CW
Term
What is a disadvantage of using CW doppler?
Definition
Range Ambiguity - the entire beam is measured
Term
What is an advantage of using baseline shift?
Definition
High velocity flows are displayed in the proper direction. Although no more accurate, it is more pleasing to the eye
Term
What is a disadvantage of using baseline shift?
Definition
1. Nothing changes other than visual appearance - audio signal will still come from the wrong speaker
2. Aliasing can still occur