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55 Cards in this Set
- Front
- Back
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Which of the following describes an angle with a measure of 45°?
A. orthogonal B. acute C. obtuse D. normal |
B. any angle that measures less than 90° is an acute angle
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Which of the following describes an angle with a measure of 123°?
A. orthogonal B. acute C. obtuse D. normal |
C. any angle that measures greater than 90° is an obtuse angle
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The angle between the direction of propagation and the boundary between two media is 90°. What term describes the form of incidence of the wave?
A. not normal B. direct C. oblique D. orthogonal |
D. orthogonal incidence is attained when a sound wave strikes a boundary between media at exactly 90°
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Which term does not belong in the group below?
A. orthogonal B. at right angles C. oblique D. 90° E. normal F. perpendicular |
C. the five terms: orthogonal, at right angles, 90°, normal, and perpendicular are synonymous. Their meanings are identical
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A sound wave strikes a boundary between two media at a 60° angle. This is called ____ incidence.
A. orthogonal B. angular C. obtuse D. oblique |
D. oblique incidence is always present when the angle between the direction of a wave's propagation and the boundary between two media is different than 90°.
oblique incidence is a definition of exclusion. that is, if the incidence is not perpendicular, it is oblique. |
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Which term has a meaning other than normal incidence?
A. orthogonal incidence B. perpendicular incidence C. oblique incidence |
C. oblique incidence has a meaning that is different from normal incidence. oblique incidence occurs when a wave strikes a boundary at any angle other than 90°, while normal incidence occurs when the wave strikes a boundary at exactly 90°
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What is the maximum possible value for both the intensity reflection coefficient and the intensity transmission coefficient?
A. 100 B. 1% C. 1 D. infinity |
C. the maximum percentage of the incident intensity that either reflects or transmits is 1.0 or 100%. at the extremes, total reflection occurs (intensity reflection coefficient = 1.0) or complete transmission occurs (intensity transmission coefficient = 1.0). the upper limit of both of these coefficients is 1.0
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if the ______ of two media are different and sound strikes a border between the media at 90° incidence, then reflection will occur.
A. conductances B. densities C. impedances D. propagation speeds |
C. under the conditions of orthogonal or normal incidence, reflection depends on differences in the acoustic impedances of the media on either side of the boundary. with normal incidence, as long as the impedances are dissimilar, reflection will always occur
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True or False. The proportion of the incident intensity that is reflected at a border between two media will increase as the impedances of the media become increasingly dissimilar.
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True. As sound waves strike the border between two media, reflection occurs if their impedances are different. Greater differences between the two impedances create stronger reflections. If the impedances are only slightly , then a weak reflection will be produced.
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Two acoustic waves strike a boundary between two media. The waves are traveling in a direction 90° to the boundary. Reflection of these waves depends on differences in the ______.
A. frequencies of the two waves B. propagation speeds of the two media C. amplitudes of the two waves D. impedances of the two media |
D. With normal incidence, reflection will occur at a boundary when the media on either side of the boundary have different acoustic impedances. Reflection is not dependent on the waves' characteristics such as amplitude and frequency. With normal impedance, only one condition must be met for reflection to take place: the impedance of the media on either side of the boundary must be different.
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An ultrasound waves strikes an interface between two media at a 90° angle. The propagation speed of the media are identical. However, the densities of the true media are different. Which is true?
A. reflection will definitely occur B. reflection will definitely not occur C. refraction may occur D. none of the above |
A. Reflection will definitely occur. With normal incidence, reflection will occur when the impedances of the media on either side of the boundary are different from each other. In this example, the densities of the media are different while their propagation speeds are the same. Since impedance is propagation speed multiplied by density, it follows that the acoustic impedances of media bordering the interface are indeed different. Reflection will occur.
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True or False. When reflection occurs with oblique incidence, the angle of reflection equals the angle of incidence. This is known as Snell's Law.
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False. It is indeed true that the angle of reflection is equal to the angle of incidence when reflection occurs at an oblique incident angle. The falsehood in this statement is that this is not Snell's Law.
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What event does Snell's Law govern?
A. transmission B. refraction C. impedance |
B. Snell's Law defines the physics of refraction
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True or False. Refraction occurs at the border between two media if and only if there is oblique incidence of the wave at the boundary.
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True. Refraction cannot occur if a wave is normally incident to the boundary between two media. It can occur only if the incident wave is oblique to the boundary.
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What conditions are necessary for refraction to occur at a boundary between two media?
A. unequal acoustic impedances and normal incidence at the boundary B. unequal densities of the media and normal incidence at the boundary C. dissimilar propagation speeds and oblique incidence at the boundary D. different elasticities of the media and oblique incidence |
C. The two conditions required for refraction are:
1. a sound wave must be obliquely incident to the border between two media, and 2. the media on either side of the border must have dissimilar propagation speeds. Refraction occurs during transmission of a wave from one medium to another. |
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How long does it take for sound to make a round trip to and from the skin's surface to a reflector depth of 1 cm in soft tissue?
A. 13 µs B. 150 ms C. 15 µs D. 2 seconds |
A. In soft tissue, sound can travel to and return from a depth of 1 cm (a total distance of 2 cm) in 13 microseconds (13 millionths of a second).
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In soft tissue, sound travels to a reflector and back to the transducer in 39 µs. How deep is the reflector?
A. 2 cm B. 6 cm C. 3 cm D. cannot be determined |
C. For each 13 µs, sound travels a round trip depth of 1 centimeter. Thus, in 39 µs, sound travels to and returns from a depth of 3 cm.
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One reflector is 5 times deeper than another. The time of flight of sound to the deeper structure is _____ the time of flight of the shallower reflector.
A. one fifth as much as B. equal to C. less than D. five times more than |
D. Time of flight and reflector depth are directly related. When a reflector is five times deeper than another, the pulse's time of flight is five times greater.
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Axial resolution describes the accuracy related to visualizing two structures that are ______ to a sound beam's main axis.
A. parallel B. perpendicular C. oblique D. normal |
A. Axial resolution is related to structures that are parallel to the beam's main axis. In other words, the structures are arranged front to back.
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Two systems are undergoing evaluation. System A has 1,000,000 pixels, each with 4 bits. System B has 750,000 pixels, each with 12 bits. Which system has the best longitudinal resolution?
A. system A B. system B C. both are the same D. cannot be determined |
D. The longitudinal resolution of an ultrasound system is determined primarily by the pulse duration or the spatial pulse length. Since no information is provided on the length of the pulse, it is impossible to determined which of the systems will have superior longitudinal resolution.
HINT: Longitudinal resolution is also called axial resolution |
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True or False. The lower the numerical value of the longitudinal resolution, the worse the picture.
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False. Higher quality images are associated with lower values of longitudinal resolution. The numerical value indicates how close two structures can be and still produce two distinct images on the ultrasound display. Lower numbers identify ultrasound systems that display images with fine detail.
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True or False. One way that a sonographer can alter the axial resolution achieved during an exam is to adjust the maximum imaging depth.
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False. Depth of view and axial resolution are unrelated. A sonographer cannot adjust imaging depth to change a system's axial resolution.
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True or False. With a specific ultrasound system and transducer, the system's axial resolution is invariant, and the sonographer can do nothing to improve it.
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True. Axial resolution is determined only by the components of the system. When you are using a particular ultrasound system, axial resolution remains constant.
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True or False. The shorter the pulse duration, the better the picture.
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True. This restates one of the fundamental principles of ultrasonic imaging. The shorter the pulse duration, the higher the quality of the images.
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Which transducer has the best axial resolution?
A. 2 cycles/pulse, 4MHz B. 4 cycles/pulse, 4MHz C. 4 cycles/pulse, 2MHz D. 2 cycles/pulse, 2MHz |
A. Pulses with the fewest cycles and the highest frequency have the best axial resolution.
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Which transducer has the worst axial resolution?
A. 2 cycles/pulse, 4MHz B. 4 cycles/pulse, 4MHz C. 4 cycles/pulse, 2MHz D. 2 cycles/pulse, 2MHz |
C. Pulses with the most cycles and the lower frequency have the worst axial resolution.
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Two ultrasound systems produce pulses. One pulse is 0.4 µsec in duration and the other is 0.2 µsec long. Which pulse is most likely to provide the best radial resolution?
A. 0.4 µsec system B. 0.2 µsec system C. they are the same D. cannot be determined |
B. Radial (or axial) resolution is determined by the pulse duration or the spatial pulse length. The shorter the time span that a pulse exists (or the shorter the length of the pulse), the better the radial resolution.
The device producing the shorter pulse, 0.2 µsec, has the best radial resolution. Radial resolution is also called axial, depth, longitudinal, or range resolution. |
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True or False. The shorter the pulse length, the better the picture.
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True. This is the fundamental concept of longitudinal resolution. Shorter pulses produce better pictures.
One of the most important design criteria for ultrasound systems and transducers is to minimize the pulse duration and spatial pulse length. |
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Which component of an ultrasound system is made of lead zirconate titanate (PZT)?
A. transducer's matching layer B. transducer's active element C. transducer's damping material D. scan converter's computer chips |
B. Lead zirconate titanate, abbreviated PZT, is man-made piezoelectric material commonly used as the active element of ultrasound transducers
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True or False. The purpose of the backing material of an ultrasound transducer is to shorten the pulses, thereby creating images with better quality.
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True. Diagnostic imaging transducers are especially effective in creating excellent images when their pulses are short. The backing material reduces the ringing of the active element and shortens the pulse duration.
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The main purposes of a transducer's case are (more than one may be correct):
A. to protect the patient from shock B. to protect the patient from heat C. to protect the internal components of the transducer D. to protect the patient from radiation |
A and C. The case of a transducer protects the patient from electrical shock and also protects the internal components of the transducer from damage.
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Which component of an ultrasound transducer is made from a slab of epoxy embedded with tungsten particles?
A. the matching layer B. the piezoelectric crystal C. the damping material D. the computer chips |
C. The backing material, or damping material, of a transducer assembly is often fabricated of tungsten-embedded epoxy.
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True or False. The characteristic impedance of acoustic gel is greater than the matching layer's impedance but less than the piezoelectric element's impedance.
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False. The acoustic impedance of gel is lower than the impedances of both the active element and the matching layer. The gel increases the efficiency of sound transmission at the transducer/skin boundary. Consequently, the gel must have an impedance that is between those of the matching layer and the skin.
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The impedance of a transducer's matching layer is 2.6 MRayls and the impedance of the piezoelectric crystal is 3.4 MRayls. If this is assumed to be a good imaging system, what is the best estimate for the impedance of the skin?
A. 1.5 MRayls B. 3.8 MRayls C. 3.4 MRayls D. 2.8 MRayls |
A. The impedance of a transducer's matching layer should be between the impedance of skin and the impedance of the piezoelectric crystal.
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True or False. The piezoelectric crystal of a transducer typically has an impedance higher than the impedance of skin.
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True. The impedance of piezoelectric crystals typically exceeds the impedance of skin. To calculate impedance, multiply the density of a material by the propagation speed of the material. The density of lead zirconate titanate (a common piezoelectric material) is greater than the density of skin. The propagation speed of piezoelectric crystals are usually three to four times greater than skin.
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Which of the following lists orders the impedance from highest to lowest?
A. skin, gel, matching layer, PZT B. PZT, gel, matching layer, skin C. gel, PZT, matching layer, skin D. PZT, matching layer, gel, skin |
D. To maximize the transmission of sound energy between the transducer and the body, the impedances of the active element, matching layer, gel, and skin much be in decreasing order. The impedance of the piezoelectric crystal is the highest, the matching layer's impedance is a bit lower, the gel's impedance is lower yet, the impedance of skin is the lowest of all.
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Assume that the frequency of sound with the greatest power emitted by a transducer is 5MHz. However, the pulse contains acoustic energy with frequencies as low as 3.5 MHz and as high as 6.5 MHz. What is the bandwidth of the transducer?
A. 6.5 MHz B. 5.0 MHz C. 3.5 MHz D. 3.0 MHz |
D. The bandwidth of a pulse is defined as the range of frequencies that are present within the pulse. To calculate bandwidth, subtract the lower frequency from the highest frequency in the acoustic signal (6.5 - 3.5 = 3.0Mhz). The bandwidth is 3.0 MHz. The natural or center frequency of this transducer is 5 MHz.
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Which of the following actions would cause PZT crystal to lose its special properties?
A. breaking it in pieces B. exposing it to high temperatures C. exposing it to electrical current D. exposing it to low pressures |
B. When a piezoelectric crystal is exposed to high temperatures, it will depolarize and permanently lose its piezoelectric properties.
This temperature is known as the Curie temperature or Curie point. |
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What helps to determine the frequency of the sound produced by the transducer of a continuous wave ultrasound system?
A. piezoelectric crystal diameter B. piezoelectric crystal thickness C. damping material density D. ultrasound system electronics |
D. A continuous wave (CW) transducer produces an acoustic wave with a frequency equal to the frequency of the electrical signal that excites the crystal. When the pulser's electrical signal has frequency of 6 MHz, then the emitted acoustic wave is also 6 MHz. The electronics of a CW system determine the frequency of the sound wave.
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With pulsed wave ultrasonic imaging, what helps to establish the primary frequency of the acoustic energy discharged by the transducer?
A. piezoelectric crystal diameter B. piezoelectric crystal thickness C. damping material density D. ultrasound system electronics |
B. The frequency of sound produced by a standard pulsed wave imaging instrument is partly determined by the thickness of the piezoelectric element. Just as different tones are produced when a musician plays different bars on a xylophone, piezoelectric crystals of various thicknesses produce acoustic pulses of different frequencies.
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An ultrasonic pulse is traveling in soft tissue. Which of the following is most important in the determination of the frequency of sound?
A. the propagation speed of the ultrasound transducer's matching layer B. the thickness of the transducer's backing material C. the impedance of the transducer's matching layer D. the propagation speed of the transducer's active element |
D. The two characteristics that determine the frequency of sound in a pulse are:
1. the thickness of the ultrasound crystal and 2. the propagation speed of the crystal. The speed and impedance of the matching layer and the thickness of the backing material are unrelated to the frequency of an ultrasound pulse. |
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Which properties of the piezoelectric crystal of an imaging transducer result in the highest emitted acoustic wave frequency?
A. thin, high propagation speed B. thick, slow propagation speed C. thin, slow propagation speed D. none of the above |
A. Only pulsed wave transducers can create images. The crystal's thickness and propagation speed determine the frequency of sound created by these transducers.
Highest frequency sound is created by thin crystals in which sound travels quickly. |
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What is the region form the transducer to the smallest cross-sectional area of a sound beam is called?
A. focus B. half-value thickness C. near zone D. Fraunhofer zone |
C. The region from the transducer to the narrowest portion of an ultrasound beam is defined as the near zone, or Fresnel zone.
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The area that starts at the beam's smallest diameter and extends deeper is:
A. the distant zone B. the Fresnel zone C. the Fraunhofer zone D. the depth of penetration |
C. The region that extends deeper from an ultrasound beam's narrowest diameter and deeper is called the far zone, or Fraunhofer zone.
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Which of these terms have the same meaning?
1) far zone 2) near zone 3) Fresnel zone 4) focal zone 5) Fraunhofer zone 6) lateral zone A. 1 and 2, 3 and 4 B. 1 and 4, 2 and 3 C. 4 and 6, 5 and 1 D. 2 and 3, 5 and 1 |
D. Another name for the Fresnel zone is the near zone. the Fraunhofer zone can also be called the far zone.
(HINT: Fresnel is the short name - it is the near zone. Fraunhofer is the long name - it is the far zone.) |
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What is the point or location where a beam reaches its smallest dimension?
A. near zone B. focus C. penetration depth D. focal zone |
B. The actual location where an ultrasound beam reaches its minimum diameter and cross-sectional area is called the focus
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All of the following are true of the focus except:
A. it is at the end of the near zone B. it is at the beginning of the Fraunhofer zone C. it has the highest spatial peak intensity D. it is at the start of the Fresnel zone |
D. The focus is located at the end of the near or Fresnel zone. The Fresnel zone starts at the transducer.
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As sound travels deeply into the far zone, the beam diverges, or spreads out. Which of the following will result in a minimum beam divergence deep in the far zone?
A. small diameter, high frequency B. high frequency, large diameter C. large diameter, low frequency D. low frequency, small diameter |
B. Large diameter crystals of high frequency tend to produce sound beams that diverge less in the deep far zone.
In contrast, waves from small diameter, low frequency crystals are more divergent in the deep far zone. |
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The focus of an ultrasound beam is the location where the ______.
A. beam is the broadest B. optimum transverse resolution is C. frequency is the highest D. finest depth resolution is obtained |
B. The focus of an ultrasound beam is the location where the beam is most narrow. The narrowest portion of the beam provides the optimal transverse or lateral resolution.
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What will lower the value of an ultrasound system's lateral resolution?
A. decrease the # of cycles in the pulse B. increase the effective damping material C. increase the pulse repetition period D. use an acoustic lens |
D. To lower the numerical value of lateral resolution of an ultrasound system, the diameter of the beam must be reduced. A commonly used technique to decrease the diameter of the beam is to focus the beam with an acoustic lens.
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Which of the following focusing techniques is different from the others?
A. lens B. curved crystal C. fixed D. phased |
D. Phased focusing is achieved with the electronics of an ultrasound system. Phased focusing is adjustable.
Focusing with either a lens or curved crystal is fixed. |
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Which of the following techniques is internal focusing?
A. lens B. curved crystal C. electronic |
B. Focusing with a curved PZT crystal is known as internal focusing
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Which of these terms means adjustable focusing or multi-focusing?
A. dynamic aperture B. harmonics C. frequency agility D. phased array |
D. All phased array transducers share one of these two features:
1. they have multi-focus capabilities or 2. the focal depth can be changed by the sonographer |
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Which of these techniques is consistent with variable or multi-focusing?
A. lens B. curved crystal C. electronic |
C. Electronic focusing is achieved with phasing of electronic signals. Electronic focusing, unlike internal or external focusing, is adjusted by the sonographer. In addition, it is multi-focus.
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In which region of a sound beam is focusing most effective?
A. the very shallow near zone B. the end of the near zone C. very deep in the far zone D. throughout the entire length |
B. The region of a beam that is most affected by focusing is close to the end of the near zone at the beginning of the far zone. This region is called the focal zone.
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