PHY Q
596. Which two of the following devices convert ultrasound energy into heat? A. a calorimeter B. a thermocouple C. a hydrophone D. a Schlieren
A and B. The calorimeter and the thermocouple are two devices that use the principle of converting acoustic energy into thermal energy to estimate the energy in a sound beam. A hydrophone converts acoustic energy into pressure. A Schlieren uses the interaction of sound and light to evaluate a sound beam profile.
514. The information that is processed by a standard duplex ultrasound system includes all of the following except. A. attenuation B. amplitude C. frequency D. time of arrival
A. A duplex ultrasound system provides both image and Doppler information. Included in the data processing is the amplitude of the reflected signal, its time of arrival, and its frequency content. The pulse's attenuation is not recorded or processed.
520. A system has three transducers with frequencies of 7.5 MHz, 5 MHz, and 3.25 MHz. Aliasing appears while using the 5.0 MHz transducer during a pulsed Doppler exam. What should the sonographer do? A. use the 3.25 MHz transducer B. use the 7.5 MHz transducer C. nothing; the other transducers do not provide solutions to the problem
A. A transducer producing ultrasound at a lower frequency will produce smaller Doppler shifts, which are less likely to alias. Thus, one potential solution for aliasing is to use a lower frequency transducer.
524. Which of the following determines the gray scale in a Doppler spectrum? A. number of reflectors B. velocity C. frequency shift D. laminar flow
A. Gray scale in a Doppler spectrum is related to the number of red blood cells creating the reflection.
601. Some ultrasonic bioeffects studies are performed in vivo. What is the meaning of the term in vivo? A. observable in a living body B. observations based on an experiment C. discernible in a test tube D. estimated in a computer simulation
A. In vivo observations are made in a living body. For example, increased tissue temperatures in patients following exposure to ultrasound are considered in vivo observations.
609. Which of the following terms best describes the mechanistic investigation of bioeffects? A. cause-effect B. exposure-response C. cause-response D. exposure-cure
A. The mechanistic approach to the study of bioeffects is properly called cause and effect. For example, a researcher might propose that vibration causes harmful bioeffects and then conducts research to see whether this is indeed the case.
623. Which of the following epidemiologic studies is considered most likely to produce meaningful results? A. retrospective and prospective B. prospective and randomized C. retrospective and empirical D. prospective and mechanistic
B. A clinical trial that is both prospective and randomized is most likely to reach a valid and meaningful endpoint.
500. 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. 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 sound wave, with higher frequencies yielding higher Doppler shifts.
621. What is epidemiology the study of? A. large groups B. the prevalence of disease C. acoustic bioeffects on the fetus D. in vitro effects
B. Epidemiology is a division of medicine that is devoted to the study of the prevalence of diseases or pathology in a defined population.
613.Which of the following is not a potential mechanism for production of bioeffects from ultrasound exposure to the body? A. temperature elevation B. fractionation C. cavitation D. vibration
B. Fractionation means "to separate a mixture into its ingredients" and has nothing to do with bioeffects. The other choices are potential mechanisms for acoustic bioeffects.
610. Which of these terms best describes the empirical investigation of bioeffects? A. cause-effect B. exposure-response C. cause-response D. exposure-cure
B. The empirical approach to the study of bioeffects searches for a biologic response following an exposure to ultrasound. An example of an empirical study is the assessment of a newborn child following an ultrasound study performed while in utero.
624. What is the highest SPTA intensity of an unfocused ultrasound wave where there have been no observed bioeffects? A. 1 mW/cm? B. 100 mW/cm2 C. 1000 mW/cm2 D. 1 W/cm?
B. There have been no independently confirmed significant bioeffects in mammalian tissue exposed to unfocused ultrasound with intensities below 100 mW/cm2.
617. Which of the following statements regarding cavitation is true? A. it has never been observed in any biologic media B. stable cavitation relates to oscillating bubbles while transient relates to bursting bubbles C. it is a nonlethal bioeffect produced in animal experiments D. waves with peak pressures less than 100 MPa can never induce cavitation
B. This is the principal difference between the two forms of cavitation: stable cavitation means that the microscopic gas bubbles in the tissues are rhythmically swelling, whereas transient cavitation means the microscopic gas bubbles burst.
532. The two most common color maps used in color flow imaging are: A. variance and direct B. variance and velocity C. turbulence and variance D. power and velocity
B. Two common modes of color Doppler are velocity and variance modes.
96. 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. 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.
512. A duplex ultrasound system displays information. A. M-mode, two-dimensional image, and A-mode B. A-mode and B-mode C. two-dimensional image and Doppler D. two-dimensional image and M-mode
C. A duplex scanner displays both Doppler and two-dimensional image data.
602. Certain studies of bioeffects are performed in vitro. What is the meaning of in vitro? A. visible in a living organism B. observations based on experiments C. discernible in a test tube D. perceptible in a living human being
C. An in vitro experiment is performed out of the body and in an artificial environment. The observations may be described as "in a test tube."
614. Which of the following ultrasound beams has a characteristic that is most likely to cause temperature elevation in soft tissue? A. strongly focused B. medium focused C. unfocused
C. An unfocused beam is most likely to cause temperature elevation in soft tissues. Temperature elevation with unfocused beams results from the broad area over which the beam spreads. With narrower, focused beams, the area insonated by the beam is smaller and therefore heats a smaller mass of tissue.
616. Research has indicated that cavitation A. never occurs B. cannot occur with long pulses C. can be lethal to living things D. effects are purely theoretical
C. Cavitation resulting from ultrasound exposure is lethal to the fruit fly. Cavitation has the potential for significant and harmful bioeffects under specific circumstances.
513. All of the following are associated with a CW Doppler transducer except: A. narrow bandwidth B. increased sensitivity C. backing material D. high Q-factor
C. Compared to pulsed transducers, continuous wave transducers do not use backing material. As a result, CW has increased sensitivity and is more able to detect small Doppler shifts.
501. When using a 4 MHz transducer, a Doppler shift of 3,000 Hz is recorded. What will the Doppler shift be when a 2 MHz transducer is used? A. 3,000 Hz B. 2 Hz C. 1,500 Hz D. 6,000 Hz
C. Doppler shifts are directly related to transducer frequency. When the frequency is halved, the Doppler shift will be halved.
What will the Doppler shift be when a 2 Doppler shift of 3,000 Hz is recorded. 501. When using a 4 MHz transducer, a MHz transducer is used? A. 3,000 Hz В. 2 Hz C. 1,500 Hz D. 6,000 Hz
C. Doppler shifts are directly related to transducer frequency. When the frequency is halved, the Doppler shift will be halved.
97. What information does the Doppler shift furnish concerning the blood cells that produce it? A. frequency B. speed C. velocity D. density
C. 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.
525. Which choice relates to the presence of gray shades in a Doppler spectrum? A. velocity B. frequency shift C. amplitude of the echo D. laminar flow
C. Gray scale in a Doppler spectrum is related to the number of red blood cells creating the reflection. The num of red blood cells determines the amplitude of the reflected signal.
502. 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. Included in the Doppler equation is the cosine of the angle between the direction of motion and the direction of the sound beam.
620. Which sound wave is least likely to create cavitation? A. 5 MHz, 2 MPa B. 2 MHz, 4 MPa C. MHz, 2 MPa D. 2 MHz, 2 MPa
C. Low values of mechanical index indicate low likelihood of cavitation. Derived mathematically from a sound wave's frequency and pressure, mechanical index is lowest with high frequency and low pressure.
sine tangent C. cosine D. cotangent Two 505. 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. Maximum Doppler shifts occur when red blood cells travel directly toward or directly away from a transducer. An angle of 180 between the sound source and the direction of motion exists when the cells travel directly away from the transducer.
A. 2 m/s B. 4 m/s C. 1 m/s D. cannot be determined
C. Maximum velocities are measured at a zero degree angle. Only one-half of the true velocity is measured when the angle is 60 degrees.
629. A comprehensive and scholarly review of bioeffects is performed by the American Institute of Ultrasound in Medicine for all of the following reasons except: A. ultrasound is a versatile technique B. ultrasound has proven widespread clinical utility C. ultrasound is considered highly toxic D. applications of ultrasound are growing considerably
C. The AIUM examines bioeffects research because diagnostic ultrasound is a clinically relevant, popular, and widely used imaging technique. Diagnostic ultrasound is not, however, considered highly toxic or likely to expose patients to substantial risks.
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 motion relative to each other. Frequency may be expressed as hertz, Hz, cycles/sec, or per second.
504. 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. The Doppler shift is related to the angle between the directions of the blood flow and the sound wave. The cosine of this angle indicates the percentage of the true velocity that is measured by Doppler. Normal incidence indicates a 90° angle between blood flow and the sound beam. The cosine of 90° is zero. Therefore, zero percent of the velocity is measured; the Doppler shift is absent.
522. During a pulsed Doppler exam, aliasing is observed. All of the following may eliminate aliasing except. A. selection of another imaging view with a shallower sample volume B. selection of another transducer with a lower frequency C. selection of another imaging view that provides a greater pulse repetition period D. use of a continuous wave system
C. The actions that will reduce the likelihood of aliasing are: 1. selecting a shallówer imaging depth to increase the PRF 2. using a transducer with a lower frequency, and 3. using a continuous wave Doppler system that cannot alias If the sonographer selects an imaging view with a greater pulse repetition period, the pulse repetition frequency will decrease and the likelihood of aliasing will increase.
612. Of the following choices, which is considered the most important for the sonographer with regard to bioeffects? A. pulse repetition frequency B. frequency C. duration of the study D. imaging mode
C. The exam duration is most significant because the sonographer directly controls it. Exams should always be of high quality and should provide relevant diagnostic information with a secondary goal of minimizing output power level and time exposure to the patient.
619. Which selection has the highest mechanical index? A. high frequency, high power B. high PRF, high intensity C. low frequency, high pressure D. high spatial pulse length, high PRF
C. The mechanical index is derived mathematically from the pressure in a sound beam and the sound's frequency. Mechanical index is highest with a high pressure sound beam of low frequency.
597. The measures beam intensity at specific locations, whereas a measures the entire energy in a sound beam. A. calorimeter, thermocouple B. Schlieren, thermocouple C. thermocouple, calorimeter D. thermometer, hydrometer
C. The thermocouple is a small electronic thermometer that measures the sound beam's energy at specific locations. The calorimeter absorbs all the beam's energy, converting it to heat. The calorimeter measures all the beam's energy.
499. 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. 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.
499. 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 ultrasound
C. 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.
Sed blood cells are traveling toward a aransducer, the trequency emitted by the transducer is the frequency reflected trom the red blood cells. A greater than B. equal to -C. ess than
C. When red blood cells approach a transducer, a positive Doppler frequency shift results. The emitted frequency is less than the reflected frequency.
511. All of the following are related to dedicated continuous wave Doppler transducers өхсept A. wide bandwidth B. high quality factor C. higher sensitivity D. range ambiguity ultrasound system
Continuous wave transducers have a narrow bandwidth. Backing material in pulsed wave transducers creates a wide bandwidth. Since dedicated continuous wave transducers do not use backing material, they have a narrow bandwidth.
603. Which component of an ultrasound system exposes a patient to greatest risk? A. the CRT B. the electric cord C. the pulser D. the transducer
D. Although the risk is small, the transducer exposes the patient to the greatest risk during an ultrasound scan. However, the risk will be substantially greater if the system is not functioning properly or being used in a responsible manner.
611. When studying bioeffects, which research approach is more important? A. empirical B. mechanistic C. neither is important D. both are equally important choices,
D. Both the empirical and the mechanistic approaches are important. The strongest bioeffects conclusions are reached when the results of both approaches are in agreement.
498. Blood moving at a velocity of 2 m/s creates a Doppler frequency of 3,000 Hz. What will the Doppler shift be if the velocity increases to 4 m/s? A. 3,000 Hz B. 2 Hz C. 1,500 Hz D. 6,000 Hz
D. 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.
615. According to the AIUM, at what in situ tissue temperature is there danger to a fetus? A. 100° C B. 98.6° F C. 1° F over normal temperature D. 41° C
D. Elevation of fetal tissue in excess of 41° C is considered potentially harmful.
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,
516. With pulsed Doppler, what term is used to describe a very high positive Doppler shift that is displayed as a negative waveform? A. attenuation B. filtering C. demodulation D. aliasing
D. In pulsed Doppler exams, the phenomenon where high velocities are displayed as negative velocities is called aliasing. The term alias means "having a false identity".
600. Under which condition is it permissible to perform a diagnostic ultrasound exam? A. when the patient will benefit B. when the patient has insurance C. when the exam is perfectly safe D. when the benefits outweigh the risks
D. It is proper to perform a diagnostic ultrasound exam when the benefit to the patient outweighs the risks that may be present.
622. Epidemiologic studies of in utero exposure to ultrasound have included all of the following findings except A. birth weight B. cancer C. structural abnormalities D. none of the above
D. Many epidemiologic studies on the effects of ultrasound have been reported. End points birth weight, cancer, and structural abnormalities have all been studied. There is no correlation between ultrasound exposure and these events.
517. The highest Doppler frequency without the appearance of aliasing is called the and is equal to A. aliasing limit, half of the emitted frequency B. pulse repetition frequency, the pulse repetition frequency C. Nyquist limit, half of the emitted frequency D. Nyquist limit, half of the emitted PRF
D. The Nyquist limit is the highest Doppler shift that can be displayed without aliasing. The Nyquist limit is equal to half of the pulse repetition frequency (PRF).
521. The frequency of a pulsed Doppler wave is 6 MHz, and the PRF is 5 kHz. What is the maximum Doppler shift that can be recorded without aliasing? A. 6 MHz B. 5 kHz С. З МНz D. 2.5 kHz
D. The frequency at which aliasing occurs is called the Nyquist limit and is one-half the pulse repetition frequency. In this example, the pulse repetition frequency is 5 kHz or 5,000 pulses/sec. Thus, the Nyquist limit is 2.5 kHz. Aliasing will occur when Doppler frequencies exceed this value.
625. The upper limit for the SPTA intensity of a focused ultrasound wave where there have been no observed bioeffects is. A. 1 mW/cm? B. 10 mW/cm?2 C. 100 mW/cm2 D. 1 W/cm2
D. There have been no independently confirmed significant bioeffects in mammalian tissue exposed to focused ultrasound with intensities below 1 W/cm?.
498. Blood moving at a velocity of 2 m/s creates a Doppler frequency of 3,000 Hz. What will the Doppler shift be if the velocity increases to 4 m/s? A. 3,000 Hz В. 2 Hz C. 1,500 Hz D. 6,000 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.
25. 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
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.
607. True or False? A bioeffect identified through the mechanistic approach rather than the empirical approach is more likely to have clinical significance.
False. A bioeffect identified only by a mechanistic methodology is not likely to have greater clinical significance than a bioeffect identified empirically. The most clinically relevant bioeffect would be one identified both mechanistically and empirically.
508. Problems with aliasing significantly limit its clinical utility.
False. Aliasing is an artifact where high Doppler shifts are misidentified as flow in the opposite direction. Aliasing is produced in pulsed Doppler exams when the PRF is low compared to the Doppler frequency. Aliasing does not appear with CW Doppler.
519. True or False? The higher the pulse repetition frequency of a Doppler exam, the more likely aliasing is to occur.
False. Aliasing is less likely to occur with high PRF. Aliasing occurs when the Doppler frequency exceeds half of the PRF. If the PRF is high, it is less likely that the Doppler shift will reach a value that is greater than half the PRF. producing
604. True or False? The AIUM suggests that in vitro research confirming bioeffects is valuable and valid. Their results are significant and should be directly applied to the clinical arena.
False. Although in vitro experiments results are extremely important, it is difficult to assess their direct clinical significance. Further studies should be performed before applying these conclusions clinically.
531. True or False? Absence of color on a color Doppler image always indicates a region of no blood flow.
False. Although this statement may be true, it is not always true. Even with blood flow, if the direction of the sound beam is 90° to the direction of blood flow, no Doppler shift will be created. The region will remain colorless even when flow is present.
530, True or False? On a color Doppler image, red always represents flow toward the transducer, whereas blue indicates flow away from the transducer.
False. Although this statement may be true, it is not always true. The color associated with flow toward the transducer appears in the upper half of the color map. The color associated with flow away from the transducer appears in the lower portion of the color map.
515. True or False? The appearance of negative velocities in a pulsed Doppler display always indicates that red blood cells are moving away from the transducer.
False. Negative velocities on the spectral display a pulse Doppler exam may indeed indicate that red blood cells are traveling away from the transducer. However, aliasing may also cause negative velocities in the spectrum. Aliasing occurs when very high Doppler shifts are processed incorrectly as flow in the opposite direction.
598. True or False? The biological effects of ultrasound are thought to be negligible and thus, few investigations have been performed on the subject.
False. The biological effects of ultrasound are studied extensively by scientists throughout the world. Under specific circumstances, bioeffects have been confirmed and are the subject of many discussions, investigations, and publications.
528. True or False? Color flow Doppler relies on pulsed Doppler principles and is immune to aliasing artifact.
False. The first portion of the statement is true: color flow does indeed rely on pulsed Doppler principles. However, the second part of the statement is false. It is continuous wave Doppler, not pulsed Doppler, that is immune to aliasing.
535. True or False? Velocity mode color Doppler and variance mode color Doppler will produce identical images when blood flow patterns are turbulent.
False. The principal difference between velocity and variance modes is that variance mode maps are able to identify turbulent flow. Turbulent flow appears on the image as a third color, such as green, that is located on the right side of the color map. When turbulent flow exists, the variance color will appear, Since there is no variance color with velocity mode, the variance and velocity mode images will differ.
599. True or False? It is generally believed that the effects of ultrasound on biologic media are minimal.
False. Ultrasonic bioeffects are substantial under certain conditions, including, but not limited to, therapeutic ultrasound and lithotripsy.
618. Which of the following is related to cavitation bioeffects? A. TIS B. MI C. cavitation index D. pulsatility index
The MI, or mechanical index, is related to cavitation bioeffects. Higher values of MI are associated with increased likelihood of cavitation.
94. in standard Doppler, what is true about the reflected frequency produced by blood cells traveling away from the transducer? A. tis in the audible range B. it is ultrasonic C. it exceeds the transmitted frequency D. it equals the transmitted frequency
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.
618. Which of the following is related to cavitation bioeffects? A. TIS B. MI C. cavitation index D. pulsatility index
This is the principal difference between the two forms of cavitation: stable cavitation means that the microscopic gas bubbles in the tissues are rhythmically swelling, whereas transient cavitation means the microscopic gas bubbles burst.
608. True or False? The AIUM considers an ultrasound-induced biologic tissue temperature rise of less than 2° Centigrade above normal body temperature as safe for clinical studies.
True. AIUM guidelines state that an exam is considered free of the potential for thermally induced bioeffects if the tissue temperature is within 2° C of normal.
506. True or False? The appearance of negative velocities on the spectral display of a continuous wave Doppler exam always indicates that red blood cells are moving away from the transducer.
True. Aliasing does not occur with continuous wave Doppler. Negative velocities appear on the spectral display only when red blood cells travel away from the transducer.
606. True or False? The empirical approach to True. the study of bioeffects and ultrasonic safety surveys data involves finding a relationship between exposure and toxic effects.
True. An empirical study is one where investigators look for a relationship between two events without necessarily understanding the fundamental cause and effect that relates the two factors. An example of an empirical study is examining the possibility that changes in fetal birth weight and ultrasound exposure are associated. Note that no specific mechanism for this relationship is postulated. The empirical approach is considered "exposure-response."
523. True or False? TGC cannot be used with continuous wave Doppler.
True. CW Doppler is not associated with TGC. Unlike pulsed ultrasound, attenuation effects cannot be remedied with continuous wave Doppler.
509. Frequencies measured at the transducer are produced from many different locations along the ultrasonic beam.
True. One of the characteristics of CW Doppler is that the frequencies received by the transducer can come from anywhere along the region of overlap between the transmitted and received beams. This is called range ambiguity, which is the inability to distinguish the absolute depth where the Doppler shift was created.
527. True or False? Color flow Doppler imaging incorporates pulsed Doppler principles and provides range resolution.
True. One of the greatest advantages of color flow Doppler is its ability to superimpose two-dimensional color velocities upon a two-dimensional gray scale image of anatomy. Color flow Doppler provides range resolution and is based on pulsed Doppler principles.
627. True or False? Focused sound beams are considered less likely to create bioeffects because the beams will strike fewer gas bubbles that could potentially cavitate.
True. Small gas bubbles, or gaseous nuclei in tissues, serve as sites of cavitation. When a beam is focused, its diameter is smaller and is less likely to strike cavitation nuclei.
526. True or False? Color flow Doppler exams tend to have lower temporal resolution than traditional two-dimensional, real-time imaging.
True. Temporal resolution is the ability to accurately locate moving structures. Color flow technology reduces the number of pictures produced each second. Color flow Doppler suffers from poor temporal resolution because of this low frame rate.
518. True or False? In a pulsed Doppler exam, the use of a higher transducer frequency increases the likelihood that aliasing will appear.
True. The Doppler shift depends on the frequency of the incident sound wave. The statement is true because a higher emitted frequency produces a higher Doppler shift, and a high Doppler shift is more likely to alias.
510. The duty cycle of the continuous wave is 100%.
True. The duty cycle is the percentage of time that the ultrasound transducer is producing sound. With CW Doppler, one crystal is transmitting continuously and the duty cycle is 100%.
605. True or False? The mechanistic approach to the study of bioeffects and safety includes the identification of a theoretical construct that could produce an effect.
True. The mechanistic approach is based on developing a theory as to how something happens. If the theoretical mechanism is proven correct, it provides great insight into the system and its component factors. The development of a computer simulation of tissue temperature and its relation to exposure is such an example. The mechanistic approach is considered "cause and effect."
True or False? Color flow Doppler systems display anatomical data in gray scale while simultaneously displaying flow information in color.
True. This is the fundamental process by which color flow mapping works. A two- dimensional black and white image provides data on anatomical structures. A two-dimensional color image is displayed simultaneously on top of the black and white image. The color data deals with the Doppler frequencies produced by moving blood cells in the imaging plane.
628. True or False? It is generally believed that the ultrasound bioeffects are minimal at intensity levels typical of those produced by diagnostic imaging equipment.
True. Ultrasound is considered safe at levels typical of current diagnostic imaging equipment. The likelihood of significant, harmful bioeffects is extremely low.
533. True or False? Variance mode color maps may be identified by de-to changes in the color bar, whereas velocity mode color maps only change color vertically.
True. Variance mode maps change colors side to side as well as from top to bottom. Velocity mode maps only change color from top to bottom.
507. A minimum of two distinct piezoelectric crystals are in the transducer.
True. With continuous wave ultrasound, one crystal is constantly producing sound. A second crystal is required to listen for reflections. In some pulsed ultrasound systems, the same crystal may be used for both pulsing and receiving.
626. True or False? One reason focused ultrasound beams with low intensities are less likely to cause bioeffects is that a focused beam is less efficient in heating a large mass of tissue to a critical temperature.
True. With focused beams, only a small mass of tissue heated, and the heat flows rapidly to cooler neighboring tissues. There is limited accumulation of heat energy and the temperatures tend to stay below critical levels.
534. True or False? Velocity mode color Doppler and variance mode color Doppler will produce identical images when blood flow patterns are laminar.
principal difference between velocity and variance modes is that variance mode maps identify turbulent flow. Turbulent flow appears on the image as a third color, such as green, that is located on the right side of the color map. If turbulent flow is not present, then the third color will not appear on the image and the velocity and variance mode images will look identical.
