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21 Cards in this Set
- Front
- Back
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What is the typical range of Doppler shift found in diagnostic imaging examinations? |
Between 20 Hz and 20 kHz |
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The phenomenon where high velocities appear in the opposite direction is called? |
Aliasing |
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The frequency at which aliasing occurs is called? |
Nyquist limit |
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The area of interrogation in a pulsed Doppler exam is called? |
Sample volume |
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True or False Shallower sample volumes result in more aliasing. |
False |
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T-F The higher the emitted frequency, the more likely a pulsed wave signal is to alias. |
True |
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T-F Only pulsed wave Doppler exams have a sample volume. |
True |
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An 8 MHz transducer with a PRF 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.The actual Nyquist limit is one-half of the pulse repetition frequency, 2.5 kHz or 2,500 hertz |
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An 8 MHz transducer with a pulse repetition frequency 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 MHz C. 4 kHz D. 3.5 dB E. 3,500 Hz |
E. 3,500 Hz The measured Doppler shift is directly related to the transducer frequency. in this example, the transducer frequency is halved. The Doppler shift will be halved as well. |
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T-F A successful Doppler exam cannot be performed on a severely anemic patient. |
False. Within the physiologic range, variations in red blood cell concentration will not effectthe ability to successfully perform a Doppler exam. |
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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 |
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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 |
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Which of the following terms is synonymous with spectral broadening? A. plug flow B. parabolic flow C. laminar flow D. turbulent flow |
D. With turbulent flow the spectral window is filled in. A filled in pattern is called spectral broadening. |
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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. |
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Why are dedicated continuous wave 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. |
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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 towrd and away colors. The center of the lumen will be black. |
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The Doppler effect is observed as a change in ---- and has units of------. A. amplitude, watts B. power, watts C. frequency, per second D. wavelength, millimeters |
C. The doppler effect is a change in a wave's frequency when the sound source and the receiver of the sound are in motionrelative to eachother. Frequency may be expressed as Hz, hertz, cycles/second, or per second. |
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In clinical imaging, which reflectors produce most relevant Doppler shifts? A. blood vessels B. blood plasma C. platelets D. red blood cells |
D. 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. |
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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. When red blood cells approach a transducer, a positive Doppler frequency shift results. The emitted frequency is less than the reflected frequency. |
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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 |
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What is the range of Doppler shifts commonly measured in clinical exams? A. -10 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 |
