Podcast
Questions and Answers
What causes the change in frequency observed in the Doppler effect?
What causes the change in frequency observed in the Doppler effect?
- Variations in the amplitude of the sound wave
- Changes in the temperature of the medium
- Motion of the sound source, receiver, or reflector (correct)
- Interference patterns between sound waves
In Doppler ultrasound, what aspect is of primary interest regarding the Doppler effect?
In Doppler ultrasound, what aspect is of primary interest regarding the Doppler effect?
- The reflector (correct)
- The receiver
- The sound source
- The medium
What is measured in order to determine the velocity of blood flow using the Doppler effect?
What is measured in order to determine the velocity of blood flow using the Doppler effect?
- The density of the blood
- The temperature of the blood
- The change in frequency of the sound waves (correct)
- The amplitude of the reflected sound waves
During a Doppler ultrasound exam, if the sound wave sent into the body has a frequency of 5,000,000 Hz and the sound returning from the blood has a frequency of 5,003,000 Hz, what is the Doppler shift, and what does it indicate?
During a Doppler ultrasound exam, if the sound wave sent into the body has a frequency of 5,000,000 Hz and the sound returning from the blood has a frequency of 5,003,000 Hz, what is the Doppler shift, and what does it indicate?
How does the frequency of an echo change when a moving reflector is moving away from the transducer?
How does the frequency of an echo change when a moving reflector is moving away from the transducer?
Under which condition does the Doppler shift provide the most accurate measurement of the actual velocity of red blood cells?
Under which condition does the Doppler shift provide the most accurate measurement of the actual velocity of red blood cells?
What is the relationship between the Doppler shift and the operating frequency?
What is the relationship between the Doppler shift and the operating frequency?
While performing a Doppler ultrasound, if the ultrasound beam is not aligned parallel to blood flow, what adjustment can be made to obtain a more accurate velocity measurement?
While performing a Doppler ultrasound, if the ultrasound beam is not aligned parallel to blood flow, what adjustment can be made to obtain a more accurate velocity measurement?
How do ultrasound systems determine blood velocity?
How do ultrasound systems determine blood velocity?
What does a positive Doppler shift indicate about the movement of red blood cells relative to the transducer?
What does a positive Doppler shift indicate about the movement of red blood cells relative to the transducer?
What happens to the measured velocity when the ultrasound beam and blood flow direction are not parallel?
What happens to the measured velocity when the ultrasound beam and blood flow direction are not parallel?
What does the '2' represent in the context of the simplified Doppler equation relating blood velocity and frequency shift?
What does the '2' represent in the context of the simplified Doppler equation relating blood velocity and frequency shift?
If the Doppler angle is increased, what generally happens to the cosine of that angle and the accuracy of the Doppler shift measurement?
If the Doppler angle is increased, what generally happens to the cosine of that angle and the accuracy of the Doppler shift measurement?
If blood flow is parallel to the ultrasound beam but moving away from the transducer, what is the Doppler angle?
If blood flow is parallel to the ultrasound beam but moving away from the transducer, what is the Doppler angle?
Which of the following is true regarding the relationship between the Doppler shift and blood flow velocity?
Which of the following is true regarding the relationship between the Doppler shift and blood flow velocity?
Under what condition is the calculated velocity from a Doppler measurement 100% accurate?
Under what condition is the calculated velocity from a Doppler measurement 100% accurate?
What is the cosine of the Doppler angle at 90 degrees, and what does this imply for velocity measurements?
What is the cosine of the Doppler angle at 90 degrees, and what does this imply for velocity measurements?
If the frequency difference (Doppler shift) between the transmitted and reflected waves is 7,000 Hz, what is notable about this frequency?
If the frequency difference (Doppler shift) between the transmitted and reflected waves is 7,000 Hz, what is notable about this frequency?
When red blood cells are moving away from the transducer, what type of Doppler shift occurs?
When red blood cells are moving away from the transducer, what type of Doppler shift occurs?
A reflector remains stationary relative to the transducer. What form of Doppler shift will the ultrasound detect?
A reflector remains stationary relative to the transducer. What form of Doppler shift will the ultrasound detect?
How is Doppler shift calculated?
How is Doppler shift calculated?
When an echo source is moving perpendicular to the transducer, what type of Doppler shift is observed?
When an echo source is moving perpendicular to the transducer, what type of Doppler shift is observed?
Within what range do Doppler shifts typically fall in clinical studies?
Within what range do Doppler shifts typically fall in clinical studies?
How does increasing the ultrasound transducer frequency typically affect the magnitude of the Doppler shift?
How does increasing the ultrasound transducer frequency typically affect the magnitude of the Doppler shift?
What are other common names for the Doppler effect?
What are other common names for the Doppler effect?
In vascular imaging, is the ultrasound beam Parallel to blood flow?
In vascular imaging, is the ultrasound beam Parallel to blood flow?
If the Doppler angle is greater than 60 degrees, are the Doppler measurements reliable?
If the Doppler angle is greater than 60 degrees, are the Doppler measurements reliable?
If the blood is moving parallel to the ultrasound beam, will the velocity measurement be accurate?
If the blood is moving parallel to the ultrasound beam, will the velocity measurement be accurate?
What are the best angles to get reliable Doppler measurements?
What are the best angles to get reliable Doppler measurements?
If there is a 45° angle between direction of flow and the ultrasound beam how much percet of the velocity measured by the Doppler shift?
If there is a 45° angle between direction of flow and the ultrasound beam how much percet of the velocity measured by the Doppler shift?
Complete this equation: Doppler shift (kHz) =
Complete this equation: Doppler shift (kHz) =
Doppler shifts result from reflected sound bouncing off of which of the following?
Doppler shifts result from reflected sound bouncing off of which of the following?
During Doppler Effect, frequency of sound changes when the sound source and the ________ move closer together or further apart
During Doppler Effect, frequency of sound changes when the sound source and the ________ move closer together or further apart
What do ultrasound systems measure to see the change in frequency?
What do ultrasound systems measure to see the change in frequency?
What does the computer programmed measure for in Doppler systems?
What does the computer programmed measure for in Doppler systems?
What happens when velocity is doubled?
What happens when velocity is doubled?
The Doppler Equation gives important information that needs to be considered when measuring speed of ___.
The Doppler Equation gives important information that needs to be considered when measuring speed of ___.
If the Doppler angle is 180°, blood flow is still Parallel to the ultrasound beam, but the flow is moving ____ from the transducer.
If the Doppler angle is 180°, blood flow is still Parallel to the ultrasound beam, but the flow is moving ____ from the transducer.
Compared to Cos 0°, what does Cos 180° equal?
Compared to Cos 0°, what does Cos 180° equal?
What is the typical range of Doppler shifts observed during clinical ultrasound studies?
What is the typical range of Doppler shifts observed during clinical ultrasound studies?
If a reflector is moving toward the transducer, which of the following will likely be observed?
If a reflector is moving toward the transducer, which of the following will likely be observed?
In Doppler ultrasound, how is the Doppler shift calculated?
In Doppler ultrasound, how is the Doppler shift calculated?
In the context of the Doppler equation, what does 'c' generally represent?
In the context of the Doppler equation, what does 'c' generally represent?
According to the Doppler equation, what happens to the Doppler shift if the velocity of blood flow increases?
According to the Doppler equation, what happens to the Doppler shift if the velocity of blood flow increases?
What happens to the accuracy of the velocity measurement when the ultrasound beam is perpendicular to the direction of blood flow?
What happens to the accuracy of the velocity measurement when the ultrasound beam is perpendicular to the direction of blood flow?
In vascular imaging, why is it important to account for the Doppler angle?
In vascular imaging, why is it important to account for the Doppler angle?
If the Doppler angle is 60 degrees, what percentage of the true velocity will be measured?
If the Doppler angle is 60 degrees, what percentage of the true velocity will be measured?
What is the best Doppler angle to get the most reliable Doppler measurements?
What is the best Doppler angle to get the most reliable Doppler measurements?
How do the ultrasound systems use the change in frequency of the ultrasound to calculate velocity of blood?
How do the ultrasound systems use the change in frequency of the ultrasound to calculate velocity of blood?
What does the ultrasound system measure?
What does the ultrasound system measure?
When the reflector is moving diagonally what type of Doppler shift is there?
When the reflector is moving diagonally what type of Doppler shift is there?
What is the relationship between the Doppler shift (frequency) and the velocity?
What is the relationship between the Doppler shift (frequency) and the velocity?
What are the units that Doppler shift are measured by?
What are the units that Doppler shift are measured by?
What happens to the measurements of Doppler shift and velocity as Doppler angle (0) increases?
What happens to the measurements of Doppler shift and velocity as Doppler angle (0) increases?
Flashcards
Doppler Effect
Doppler Effect
Change in sound wave frequency when the source and reflector move relative to each other.
Doppler Ultrasound
Doppler Ultrasound
Change in frequency due to the relative motion between the source and receiver/reflector.
Doppler Effect Use
Doppler Effect Use
Used to measure the velocity of blood in the body.
Doppler shift
Doppler shift
Signup and view all the flashcards
Positive Doppler Shift
Positive Doppler Shift
Signup and view all the flashcards
Negative Doppler Shift
Negative Doppler Shift
Signup and view all the flashcards
No Doppler Shift
No Doppler Shift
Signup and view all the flashcards
Doppler Shift Example
Doppler Shift Example
Signup and view all the flashcards
Frequency moving toward transducer
Frequency moving toward transducer
Signup and view all the flashcards
Frequency moving away from transducer
Frequency moving away from transducer
Signup and view all the flashcards
Doppler Shift Sounds
Doppler Shift Sounds
Signup and view all the flashcards
Doppler Shift
Doppler Shift
Signup and view all the flashcards
Doppler Equation
Doppler Equation
Signup and view all the flashcards
Ultrasound Calculation
Ultrasound Calculation
Signup and view all the flashcards
Doppler Shift Correlation
Doppler Shift Correlation
Signup and view all the flashcards
Doppler Angle
Doppler Angle
Signup and view all the flashcards
Accurate measurement
Accurate measurement
Signup and view all the flashcards
Sound beam direction
Sound beam direction
Signup and view all the flashcards
Measured velocity
Measured velocity
Signup and view all the flashcards
Measurement Reliability
Measurement Reliability
Signup and view all the flashcards
Study Notes
Doppler Effect and Frequency
- Doppler is used to measure blood velocity.
- The change in sound sound frequency is heard when source and reflector move closer/further.
- The change in frequency is identified as the Doppler Effect.
- Other names for Doppler Effect: Doppler shift, and Doppler frequency.
- Only the reflector is relevant in Doppler ultrasound.
- Doppler shift is how the velocity of flow of blood is measured.
Doppler Shift
- Doppler shifts range from -10 kHz to + 10 kHz in clinical studies.
- Audible shifts caused by sound bouncing off red blood cells.
- Doppler shift = Reflected frequency – Transmitted frequency.
- Doppler shift also equals received frequency minus source frequency.
- Doppler shift occurs when sound waves hit moving RBCs.
- Transducer sends sound into the body at a frequency e.g. 5,000,000 Hz.
- Sound hits blood and returns to transducer at frequency e.g. 5,003,000 Hz.
- Doppler shift (change in frequency) is +3,000 Hz in this example.
- Blood is traveling toward the transducer because the reflected sound had a higher frequency than the transmitted sound.
- A reflector moving towards the transducer will send back a echo with a higher frequency.
- A reflector moving away from the transducer will send back a echo with a lower frequency.
Doppler Equation
- Blood velocity and Doppler (frequency) shift have a direct relationship.
- Velocity is doubled, Doppler shift is doubled.
- Velocity is halved, Doppler shift is halved.
- Ultrasound systems are used to measure the Doppler shift (change in frequency).
- The computer within the ultrasound instrument calculates the velocity of blood using the Doppler equation.
- Spectral Doppler has a Doppler shift scale in KHz on the left side with a velocity scale on the right.
- Formula:
- ΔF = 2Fo * V * Cosθ / C
- ΔF = Doppler shift frequency (kHz)
- F0 = Ultrasound transmission frequency (MHz)
- V = Blood cell velocity (cm/sec)
- Cos Θ = Cos of angle between US & flow direction
- C = Speed of sound in soft tissue (1 540 m/sec)
- ΔF = 2Fo * V * Cosθ / C
- Doppler shift is proportional to operating frequency.
- Doppler shift and velocity have a direct relationship, increased flow velocity = increased Doppler shift.
- Relationship between the direction that blood is traveling and the direction in which the ultrasound beam propagates is referred to as the Doppler angle and affects accuracy.
- Identical velocities are calculated even when Doppler of different frequencies are utilized as Doppler shifts also change.
Doppler angle
- The most accurate velocity measurement is obtained when red blood cells are traveling in a direction parallel to the ultrasound beam.
- The Doppler shift measures the actual velocity of the red blood cells when travel directly forward or directly away from the transducer.
- If there is an angle between the direction of flow and direction of pulse, less than the true velocity is measured.
- 0 degrees, i.e. parallel to beam, is best but sometimes not possible.
- You must correct it!
- Doppler angle θ the angle between the direction of flow and the sound propagation direction.
- Sound beam direction vs. flow direction
- The velocity measurement is 100% accurate if the blood is moving parallel to the ultrasound beam
- Beam is usually parallel in cardiac imaging -Beam is likely not parallel in vascular imaging
- Calculation: Measured velocity = true velocity x cos θ
- At 0°, (blood flow parallel to sound beam) where cos θ = 1, calculated velocity is 100% accurate.
- At 60°, where cos θ = 0.5, so calculated velocity is 50% of true velocity.
- At 90° (perpendicular) where cos θ = 0, the velocity cannot be measured.
- As Doppler angle (θ) increases, cos θ decreases, and the Doppler (frequency) shift decreases, so your measurements of Doppler shift and velocity are less accurate.
- If the Doppler angle is 180°, blood flow is still parallel to the ultrasound beam, but the flow is moving away from the transducer.
- cos 0°=1 AND cos 180°= -1.
- Blood flow is parallel to the sound beam will provide true velocity as the measures.
- Flow moving directly toward the sound beam, 0°, cos θ = 1, measures true positive velocity.
- Flow moving directly away from the sound beam, 180°, cos θ = -1, measures true negative velocity.
- Blood flow is 90° (perpendicular) to the sound beam.
- cos θ = 0
- No doppler signals and velocities measured
- Blood flow is >0° but <90°
- Only a portion of the true velocity is measured
- Doppler measurements are not reliable if the Doppler angle is >60 degrees.
- At less than 30 degrees beam doesn't hit blood, and is reflected at vessel wall/blood boundary.
- Best angles are between 30 and 60 degrees, except cardiac where 0 degrees is used.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
