Week 8 Flashcards
B-Mode in Duplex ultrasound visualizes an _________, and is used to study __________.
Image, Anatomy
Doppler in Duplex ultrasound visualizes __________, and is used to study ____________.
Velocity, Physiology
Define the Doppler Effect
A change in Frequency when a reflector or source of sound is moving
The difference between the frequency sent vs the frequency received is the ____________________.
Doppler Frequency Shift
Doppler echoes are evaluated for what three things?
Timing (depth), Strength (amplitude), Frequencies
What is the Doppler Equation?
∆ƒ = [2 v ƒo (cos ø)] / C
Relation. Frequency shift and Cosine of the doppler angle.
Directly
Relation. Frequency shift and Velocity.
Directly
Relation. Speed of Sound and Frequency Shift
Indirectly
Relation. Initial Frequency and Frequency Shift.
Directly
The initial frequency is changed when it encounters what?
Moving reflectors
What is an example of a moving reflector that Doppler would encounter?
RBCs
The speed of blood is heard as _________ and is measured by _____________.
pitch, frequency
The number of blood cells is heard as __________ and is measured by _____________.
loudness, amplitude
Rearrange the Doppler Equation to solve for Velocity.
V = [∆ƒ C] / [2 ƒo (cos ø)]
If there is a positive frequency shift, that means the reflector is moving (TOWARDS/AWAY) from the beam.
TOWARDS
If there is a decrease in frequency, that means the reflector is moving (TOWARDS/AWAY) from the beam.
AWAY
If a 10 MHz Doppler beam creates an echo read by the equipment at 10.005 MHz, what is the frequency shift? A. 10 MHz B. 5 MHz C. 5 kHz D. 10.005 Hz
C. 5 kHz
If a + 3 kHz frequency shift was created by a reflector, the flow direction was \_\_\_\_\_\_\_\_\_\_\_. A. Away from the Doppler Beam B. Away from the head C. Toward the head D. Toward the Doppler Beam
D. Toward the Doppler Beam
If a 2 MHz probe results in an echo of 1.998 MHz, what is the frequency shift? A. + 2 kHz B. -2 MHz C. -2 kHz D. + .998 MHz
C. -2 kHz
Why is there a “2” in the Doppler Equation?
Because there are actually 2 doppler shifts in ultrasound.
1) when the moving RBC meets the sound beam
2) as it sends the echo back
What does the velocity (or how it changes) tell us?
how tight a narrowing is in an artery
What is the average speed of sound in soft tissue (C)?
1540 m/s
What does ø measure?
the angle between the doppler beam and the flow direction
ø must be (,or =) 90˚?
cos 45˚ = ______.
0.71
cos 30˚ = ______.
0.87
cos 90˚ = ______.
0
cos 60˚ = _______.
0.5
cos 0˚ = _______.
1.0
What is the Doppler angle?
the angle between the Doppler beam and the flow direction
A decrease in angle = ____ cos, _____ frequency shift, ________ velocity
increase, increase, decrease
What would the equation look like for calculating frequency shift using a 5 MHz probe, 100 cm/s velocity, and 60 degrees?
Frequency shift = 2 (5000 kHz) (1 m/s) (0.5) / 1540 m/s
For the Doppler equation, frequencies should be measured in what unit? What unit should velocities be measured?
kHz, m/s
If solving for velocity, what unit should your final answer be in?
cm/s
What part of Duplex is used to see an image and study anatomy?
B-Mode
What part of Duplex is used to visualize velocity and study physiology?
Doppler
Define Doppler frequency shift.
The difference between the frequency sent vs the frequency received
What does a moving reflector do?
Change the initial frequency
0.5 = ______
cos 60
0.87 = ______
cos 30
1.0 = __________
cos 0
0.71 = _________
cos 45
0 = _______
cos 90
The process of extracting the low Doppler frequency from the transducer’s carrier frequency is called __________.
Demodulation
Doppler shift = __________ - ____________
reflected frequency - transmitted frequency
Velocity is defined by what?
magnitude AND direction
When an angle exists between the direction of flow and the sound beam, the measured velocity is _______ than the true velocity.
Less
