Chapter 19 Book Flashcards
Change in frequency due to doppler shift is also called what?
Doppler frequency
The motion between the sound _______ and the _________ creates a frequency change.
source, receiver
The process of extracting the low Doppler frequency from the transducer’s carrier frequency is called _________.
Demodulation
Doppler shift = _____________ - _____________
reflected frequency - transmitted frequency
A positive doppler shift occurs when a receiver moves __________ the source.
towards
What is the doppler equation?
∆ƒ = (2 x v x ƒo x cos ø) / propagation speed
Doppler shift is directly related to what property of RBCs?
Velocity
The entire velocity of blood cells are measured when the sound beam is pointed _________ to them.
Parallel
The measured velocity of RBCs = the ____________ x _________.
true velocity x cos ø
cos 0º = _______
1.0
cos 30º = _______
0.87
cos 60º = ________
0.50
cos 45º = _________
0.71
cos 90º = __________
0
What is the greatest advantage of continuous wave doppler?
its ability to accurately measure very high velocities
The fact that signals arise from all blood cells in the region of overlap in continuous wave doppler is known as __________ _____________.
range ambiguity
Simultaneous anatomic imaging and Doppler is called ___________ ____________.
Duplex imaging
The greatest advantage of pulsed wave doppler is what?
being able to select the exact location where velocities are measured
Describe Aliasing
the false representation of very high velocities going in the opposite direction
The very top of a spectral display is called the ________ ___________.
Nyquist limit
When does aliasing occur?
when the Doppler smiling rate is too low in comparison to the velocities
What are ways to avoid aliasing?
Increase the scale decrease the frequency adjust the baseline Select a shallower sample volume Use continuous wave doppler
Color Doppler measures ________ velocity, whereas pulsed and continuous wave Doppler measure ________ velocity.
mean, peak
Colors above the black stripe on a velocity mode color map indicate what?
blood cells moving toward the transducer
Colors above the black stripe on a variance mode color map indicate what?
blood cells moving toward the transducer
In addition to direction and speed, Variance mode also does what?
distinguishes lamer flow from turbulent flow
Colors on the left side of a variance mode color map indicate what?
laminar flow
Colors on the right side of a variance mode color map indicate what?
turbulent flow
Power doppler is also known as ______________ color doppler
non-directional
Power doppler is also called _______ mode or ________ __________.
energy, color angio
What are the three advantages of power mode?
- increased sensitivity to low flow or velocity, such as venous flow or flow in small vessels
- unaffected by Doppler angles, unless exactly 90º
- No aliasing since velocity is ignored
What are two structures that can cause clutter in spectral displays or a ghosting artifact in color Doppler?
heart muscle, pulsating vessel walls
What is used to eliminate clutter or ghosting?
a wall filter
What is crosstalk and when does it happen?
Crosstalk is a mirror image of a wave that appears on a spectral display, and it occurs when the gain is set too high or the incident angle is near 90º.
With turbulent flow, the used Doppler spectral window is filled in, this is known as what?
spectral broadening
The Doppler effect is presented as a _________ when the source and the receiver are __________.
Frequency shift, in motion relative to each other
Starting from the same point, the sound source is moving toward the east at 12 miles/hour and the receiver is moving toward the west at 10 miles/hour. the Doppler shift is _______ (+ or -)
Negative, the source and receiver are moving apart
Starting from the same point, the receiver is moving toward the west at 12 miles/hr and the source is moving toward the west at 10 miles/hr. The Doppler shift is ________ (+ or -)
Negative, the source and receiver are still moving apart despite moving in the same direction
Doppler shift produces information about ______.
Velocity
At what angle between the sound beam and the direction of motion will the Doppler shift be the highest?
0º or 180º, parallel
At what angle between the sound beam and direction of motion will the Doppler shift be closest to zero?
90º, cosine of 90º = 0
What is the difference between speed and velocity?
Speed has only a magnitude. Velocity has magnitude and direction
What is the current method of processing Doppler signals?
The Fast Fourier Transform (FFT) method of spectral analysis is used for used and CW. Autocorrelation is the method of spectral analysis for color flow Doppler.
What is the typical range of Doppler shift found in diagnostic imaging examinations?
Between 20 Hz and 20 kHz (audible range)
The phenomenon where high velocities appear in the opposite direction is called ________.
aliasing
The frequency at which aliasing occurs is called ______.
Nyquist limit
The area of interrogation in a pulsed Doppler exam is called _________.
Sample Volume
T/F. The higher the emitted frequency, the more likely a pulsed wave signal is to alias.
True
T/F. Shallower sample volumes result in more aliasing.
False
T/F. Only pulsed wave Doppler exams have a sample volume
True
An 8 MHz transducer with a pulse repetition frequency of 5,000 Hz is imaging to a depth of 7 cm. What is the Nyquist frequency? A. 4 MHz B. 3.5 Hz C. 2.2 kHz D. 2.5 dB E. 5 kHz
C. Nyquist limit = 1/2 of PRF, 2,500 Hz or 2.5 kHz
C is the closest to the actual answer
An 8 MHz transducer with a PRF of 5,000 Hz measures a Doppler shift of 7 kHz. The study is repeated with a 4 MHz transducer. What Doppler shift will be measured? A. 4 MHz B. 3.5 Hz C. 4 kHz D. 3.5 dB E. 3,500 Hz
E. 3,500 Hz or 3.5 kHz. Transducer frequency is halved, Doppler shift will be halved as well.
T/F. A successful Doppler exam cannot be performed an a severely anemic patient.
False. Within the physiologic range, variations in RBC concentration will not affect the ability to successfully perform a Doppler exam.
Which technique is used to perform spectral analysis on color Doppler data? A. autocorrelation B. demodulation C. Fast Fourier Transform D. pulse inversion
A. autocorrelation. Autocorrelation is the digital technique used to analyze color flow Doppler
Which technique is used to perform spectral analysis on pulsed Doppler data? A. autocorrelation B. demodulation C. Fast Fourier Transform D. pulse inversion
C. Fast Fourier Transform. The FFT performs spectral analysis on used and CW Doppler data
Which of the following terms is synonymous with spectral broadening? A. plug flow B. parabolic flow C. laminar flow D. turbulent flow
D. Turbulent flow. With turbulent flow, the spectral window is filled-in. A filled-in pattern is called spectral broadening.
Which of the following is an advantage of a large packet size? A. less aliasing B. increased frame rate C. improved lateral resolution D. increased Doppler accuracy
D. increased Doppler accuracy. Doppler is more accurate with larger packets
Why are dedicated continuous wave Doppler transducers so sensitive? A. absence of the matching layer B. increased electrical conductance C. Absence of backing material D. inclusion of demodulator
C. absence of backing material. A CW transducer does not create anatomic images and does not contain backing material This increases the sensitivity of dedicated CW Doppler transducers.
T/F. The lumen of a horizontal vessel evaluated with a color Doppler, sector shaped image contains a single color
False. The vessel will have both the toward and away colors. The center of the lumen will be black.
