Doppler Flashcards
What is Doppler
broad category which includes spectral Doppler, waveform Doppler, audio Doppler, color flow imaging
Doppler Effect
Shift in frequency
what is Doppler effect used for
The mechanism by which blood flow is detected, measured, and monitored noninvasively within the body
how is the doppler effect exemplified?
change in pitch that occurs as a high-speed train or car approaches and then speeds past
what is the apparent shift in frequency the result of?
changes that occur to the wavelength because of the relative motion
If the object is moving towards the observer
The wavelength will be shorter
If the object is moving away from the observer
The wavelength will be longer
Therefore, since a shorter wavelength produces a higher frequency
The motion towards the observer produces a higher frequency than the original wave
Motion away from the observer
Produces a lower frequency than the frequency of eh transmitted wave
Doppler shift is proportional to what
The relative velocity
The doppler shift increases as what increases?
velocity increases
Doppler shift is also affected by what?
Parameters that affect the wavelength
when the distance between the source and the observer is increasing
Relative motion is away
Decompression occurs
When the distance between the source and observer is decreasing
Relative motion is towards
compression occurs
Compression leads to what?
Higher frequency and a positive frequency shift
Decompression
Lower frequency and a negative frequency shift
Shift can be what?
Positive or negative
A greater shift only tells what?
only amount, not direction
Unless we know what, we cannot tell if the shift was positive or negative
Must know the relative motion
If the relative motion is towards
the greater shift implies an increasing higher frequency
If the relative motion is away
greater shift implies an increasing lower frequency
what is the doppler shift
Relative difference between the detected frequency and transmitted frequency
when the detected frequency is higher than the transmitted frequency
Doppler shift is positive
If the velocity of the train doubles, the frequency shift A) Halves
B) Doubles
C) Cannot be determined because direction is not known
B) If the velocity of a train doubles, the frequency shift doubles
If the velocity of the train doubles, the positive frequency shift
A) Halves
B) Doubles
C) Cannot be determined because direction is not known
C) Cannot because determined because direction is not known
Which represents a greater Doppler shift, +2kHz or -3 kHz
A) 2 KHz
B) 3kHz
C) cannot be determined
B) -3kHz
As the relative motion increases
Doppler Effect also increases
wavelength and operating frequency have what kind of relationship
Inverse proportional
As operating frequency increases
Doppler shift also increases
As propagation velocity increases
Doppler shift decreases
Roundtrip effect
Measurement is not made by the observer but rather by measuring the reflected frequency back to the transducer
As the wave travels to the moving structure
there is an associated shift
why is there a doubling effect?
Structure acts as the source of the reflected wave
The structure is moving as it reflects the wave back to the transducer
The doppler shift
Can be both positive or negative depending on the direction of motion relative to the observer
Simplified Doppler Equation
Doppler shift frequency=2transmit frequency velocity of the target through medium/speed of interrogating beam through medium
Doppler shift frequency is proportional to
Velocity
Doppler shift frequency is proportional to
transmit frequency
Doppler shift frequency is inversely proportional to
speed of interrogating beam through medium
For a given interrogating frequency, if the velocity triples, what happens to the doppler shift frequency?
Doppler shift is proportional to the velocity therefore a tripling of the velocity implies a tripling of the Doppler shift
If the transmit frequency is changed from 2MHz to 10 MHz, what happens to Doppler shift frequency
Doppler shift is proportional to operating frequency an increase in the operating frequency by a factor of 5 implies an increase in the Doppler shift by a factor of 5
What is the usual target in diagnostic ultrasound
Red blood cells
What is the usual observer in diagnostic ultrasound
transducer
what is the simplified equation for velocity
v=c*fdop/2f0
The _______ ________ is a shift in frequency caused by relative motion between the observer and target
Doppler Effect
A positive shift is caused by motion _____________the observer
Towards
A __________shift is caused by motion away from the observer
negative
A Doppler shift will ______if both the target and observer are moving away from each other faster
Increase
A Doppler shift will _____if both the target and observer are moving towards each other faster
Decrease
The _______the target moves, the higher the Doppler shift
faster
The Doppler shift is to the operating frequency
Proportional
The Dopplere shift is _______to the propagation velocity
inversely proportional
Because the Doppler effect is based on motion relative to an observer
The angle between the observer and the motion affects the Doppler Effect
what is the optimal transmit frequency for red blood cells deeper than 3cm?
Below 3MHz
At shallower depths, high frequencies produce what?
Stronger Doppler signals because of increased reflectivity
At deeper depths, lower frequencies produce what?
Stronger Doppler signals because of the increased absorption that occurs with higher transmit frequencies
red blood cells produce what kind of scattering?
Rayleigh scattering
The amount of scattering increases with….
Increased frequency
how is Rayleigh scattering related to the frequency
Non-linearly
What is the problem with increasing frequency
Increasing the frequency increases reflectivity but also results in significantly increased attenuation
what is spontaneous contrast
rouleau formation which allows for the visualization in blood in 2D
Spontaneous contrast
Can indicate a pathology/hemodynamic problem
what is the Doppler Angle
The angle that is formed between the observer’s line of sight and the direction of the target object
what is the doppler angle also referred to as?
Insonification angle or angle of insonification (measured between the beam steering direction and the direction of flow)
why is the correct insonification angle important
- Ability to determine flow direction
2) Ability to measure doppler measurement accurately
3) Ability to minimize Doppler Error sources
4) Ability to assess the likelihood of artifact related issues (spectral broadening)
