The Doppler effect is observed as a change in ________ And has units of _________.
A. Amplitude, Watts
B. power, Watts
C. frequency, per second
D.
... [Show More] wavelength, millimeters
C. frequency, per second
The Doppler effect is a change in a waves frequency when the sound source and the receiver of the sound are in motion relative to each other. frequency may be expressed as Hertz, Hz, cycles/sec, or per second.
In clinical imaging, which reflectors produce most relevant Doppler shifts?
A. Blood vessels
B. blood plasma
C. platelets
D. red blood cells
D. red blood cells
In clinical imaging, red blood cells are the primary reflectors that produce Doppler shifts. Blood cells constantly move through the circulatory system and make up nearly 45% of the volume of the blood.
If red blood cells are traveling toward a transducer, the frequency emitted by the transducer is ______ the frequency reflected from the red blood cells.
A. greater than
B. Equal to
C. less than
C. less than
When red blood cells approach a transducer, a positive Doppler frequency shift results. The emitted frequency is less than the reflected frequency.
In standard Doppler, what is true about the reflected frequency produced by blood cells traveling away from the transducer?
A. It is in the audible range
B. it is ultrasonic
C. it exceeds the transmitted frequency
D. it equals the transmitted frequency
B. it is ultrasonic
The frequency of the sound wave reflected by red blood cells back to the transducer is ultrasonic (having a frequency greater than 20,000 Hertz). although the difference between the transmitted and reflected frequencies is audible, the reflected wave has a frequency in the ultrasonic range.
What is the range of Doppler shifts commonly measured in clinical exams?
A. -1 kHz to 1 MHz
B. -0.5 MHz to 0.5 MHz
C. -0.02 MHz to 0.02 MHz
D. None of the above
C. -0.02 MHz to 0.02 MHz
Doppler shifts in clinical imaging typically range from -20,000 Hz to + 20,000 Hz. Choice C has units of megahertz, but when we examine the values of -0.02 to +0.02 MHz closely, We see that this means exactly the same as -20,000 Hz to +20,000 Hz.
When red blood cells move away from a transducer, the frequency of the wave reflected from the red cells is _______ the frequency emitted by the transducer.
A. Greater than
B. Less than
C. Equal to
B. Less than
When red blood cells are moving away from a transducer, the Doppler shift is negative. The reflected frequency is less than the originally transmitted frequency from the transducer.
What information does the Doppler shift furnish concerning the blood cells that produce it?
A. Frequency
B. speed
C. velocity
D. density
C. velocity
Doppler shifts produce information regarding velocity.
What is the difference between speed and velocity? Speed is purely a number such as 400 m/s. velocity is both a number and a direction, such as 200 m/s away from the transducer. Doppler shifts indicate direction And a magnitude.
Blood moving at a velocity of 2 m/s create a Doppler frequency of 3000 Hz. what will the Doppler shift be if the velocity increases to 4 m/s?
A. 3000 Hz
B. 2 Hz
C. 1500 Hz
D. 6000 Hz
D. 6000 Hz
Doppler shifts are directly related to reflector velocity. Higher velocities create higher Doppler shifts. Lower velocities create lower Doppler shifts.
When the velocity doubles, the Doppler shift doubles.
Two ultrasound transducers are used to perform Doppler exams on the same patient. The exams are identical except that the transducer frequencies are 5 and 2.5 MHz. which exam will measure the highest velocities?
A. The 2.5 MHz exam
B. the 5 MHz exam
C. neither
D. cannot be determined
C. neither
The velocities measured by Doppler exams are the same, Regardless of the frequency of the transducer. Although the Doppler shifts associated with the velocities may vary with different transmitted frequencies, the measured velocities are identical.
Two ultrasound transducers are used to perform Doppler exams on the same patient. The exams are identical except that the transducer frequencies are 5 and 2.5 MHz. Which exam will measure the highest Doppler shift?
A. The 2.5 MHz exam
B. the 5 MHz exam
C. neither
D. cannot be determined
B. the 5 MHz exam
Doppler shifts are directly related to the transmitted frequency. Higher frequency transducers produce a greater Doppler shift. Using lower frequency ultrasound will result in lower Doppler shifts.
For a specific velocity, the Doppler shift produced will depend on the frequency of the incident Soundwave, with higher frequencies yielding higher Doppler shifts.
When using a 4 MHz transducer, a Doppler shift of 3000 Hz is recorded. What will the Doppler shift be when a 2 MHz transducer is used?
A. 3000 Hz
B. 2 Hz
C. 1500 Hz
D. 6000 Hz
C. 1500 Hz
Doppler shifts are directly related to transducer frequency. When the frequency is halved, the Doppler shift will be halved.
Doppler does not always provide a valid estimate of the speed of blood cells because the shift is related to the _______ of the angle between the direction of the beam and the direction of blood flow.
A. Sine
B. Tangent
C. cosine
D. cotangent
C. cosine
Included in the Doppler equation is the cosine of the angle between the direction of motion and the direction of the sound beam.
2 otherwise identical Doppler studies are performed, except that the angle between flow and the sound beam is zero degrees in the first study and 60 degrees in the second. the velocity measured in the first study is 2 m/s. what velocity will be measured in the second study?
A. 2 m/s
B. 4 m/s
C. 1 m/s
D. Cannot be determined
C. 1 m/s
Maximum velocities are measured at a zero degree angle. only one half of the true velocity is measured when the angle is 60 degrees.
What is true of the Doppler shift when the sound beam is normally incident to the velocity of the red blood cells?
A. It is at maximum
B. it is half of maximum
C. it is absent
D. it is at minimum
C. it is absent
the Doppler shift is related to the angle between the directions of the blood flow and the Soundwave. The cosine of this angle indicates the percentage of the true velocity that is measured by Doppler. Normal incidence indicates a 90 degree angle between blood flow and the soundbeam. The cosine of 90 degrees is zero. Therefore, 0% of the velocity is measured; the Doppler shift is absent.
A maximum Doppler shift is obtained when the angle between the direction of blood flow and the direction of the sound beam is ______ .
A. 10 degrees
B. 90 degrees
C. 180 degrees
D. 270 degrees
C. 180 degrees
Maximum Doppler shifts occur when red blood cells travel directly toward or directly away from a transducer. An angle of 180 degrees between the sound source and the direction of motion exists when the cells travel directly away from the transducer. [Show Less]