Studying for the SPI Part 2 of 6

d) The relative velocities of sound in the two media Explanation: Snell's law dictates the angle of transmission that will occur at an interface with refraction of the sound beam. Refraction (bending) of the sound beam will occur whenever there is oblique incidence and different propagation speeds between two media.

According to Snell's law, the angle of transmission is related to the incident beam angle and: a) The amount of acoustic impedance mismatch at an interface b) The change in frequency that occurs at an interface c) One-half the angle of incidence d) The relative velocities of sound in the two media e) The percentage of diffraction distal to the interface

c) Specular reflector Explanation: With specular reflection, the angle of reflection is equal to the angle of incidence. So, in order to get most of the reflected sound to be angled back at the transducer, the transducer must be oriented so that the sound will strike the interface perpendicularly. That is why we get the best images of the kidney, aorta, etc. when we have them positioned horizontally on the ultrasound image.

An echo from which one of the following sound reflectors is most dependent on the angle of incidence? a) Rayleigh scatter b) diffuse reflector c) specular reflector d) acoustic scatterer e) nonspecular reflector

a) Renal capsule Explanation: A specular reflector is a large, smooth interface such as the renal capsule or diaphragm. Specular reflection is primarily responsible for the bright interfaces seen at organ boundaries.

An example of a specular reflector is: a) Renal capsule b) Liver parenchyma c) Red blood cells d) Ascites e) Hematoma

a) constructive interference

An interaction of echoes that leads to reinforcement rather than to partial or total cancellation is known as: a) constructive interference b) refraction c) destructive interference d) autocorrelation e) rarefaction

d) scattering Explanation: Specular reflection occurs when the interface is large and smooth. Nonspecular reflection or scattering occurs when the interface is small, less than several wavelengths across.

Another term for nonspecular reflection is: a) destructive interference b) refraction c) diffraction d) scattering e) absorption

c) stiffness

As a general observation about media of concern in diagnostic ultrasound, sound propagates faster in materials with greater: a) compressibility b) acoustic impedance c) stiffness d) refractive index e) all of the above

c) intensity Explanation: Pressure is force divided by area in a fluid. If pressure is increased, intensity is increased. In fact, intensity can be determined by measuring acoustic pressure with a hydrophone.

As acoustic pressure increases, so does: a) speed of sound b) wavelength c) intensity d) acoustic impedance e) attenuation

a) double attenuation rate, one-half wavelength Explanation: If frequency is doubled but the wavelength will be halved. Remember, as frequency is increased wavelength is decreased resulting in improved resolution, but penetration is decreased due to increased sound absorption.

As you perform an abdominal ultrasound examination, you switch from a 3.5 MHz transducer to a 7.0 MHz transducer to image a pancreatic mass. Compared to those of the previous transducer, what will the new attenuation rate and wavelength be? a) double attenuation, one-half wavelength b) double attenuation rate, double wavelength c) one-fourth attenuation rate, one-half wavelength d) one-half attenuation rate, double wavelength e) one-half attenuation rate, one-fourth wavelength

e) All of the above Explanation: Attenuation coefficient is the amount of attenuation for each centimeter of sound propagation. Anything that increases attenuation will increase attenuation coefficient.

Attenuation increases with increasing: a) path length b) absorption c) frequency d) acoustic impedance e) all of the above

e) The great acoustic impedance mismatch between the cranium and soft tissue causes most of the sound to be reflected at the interface. Explanation: This acoustic impedance mismatch causes nearly all of the sound to be reflected at the bone-soft tissue interface and leaves very little energy for transmission into the brain. Since attenuation is greatest with high-frequency transducers, imaging of the adult brain must be limited to very low frequencies to enhance penetration. This results in poor spatial resolution.

Diagnostic ultrasound is limited in its diagnostic application to the adult brain because: a) the speed of sound in the brain is much faster than that in the soft tissue resulting in a range artifact. b) Nearly all of the sound is transmitted at the interface between bone and soft tissue with no reflection to create an image. c) Diffraction of the sound beam occurs because of the irregular surface of the brain, resulting in little transmission of sound through the cranial interface. d) Bending of the sound beam due to refraction results in a multipath artifact that distorts the image, making it non-diagnostic at high frequencies. e) The great acoustic impedance mismatch between the cranium and soft tissue causes most of the sound to be reflected at the interface.

d) absorption Explanation: Absorption is the conversion of sound into heat. It does contribute to attenuation, but does not redirect the sound beam. All of the other interactions will redirect the sound beam.

During an abdominal ultrasound examination, you encounter all of the interactions of ultrasound and tissue listed below. Which one will NOT cause a redirection of part of the ultrasound energy? a) reflection b) scattering c) divergence d) absorption e) refraction

d) gallstone

During an abdominal ultrasound, you image the following structures. Which is the MOST attenuating? a) blood b) bile c) liver parenchyma d) gallstone e) spleen

b) Transverse view of the gallbladder. Explanation: Refraction occurs whenever there is oblique incidence at an interface in which propagation speeds are different. It can be seen with a transverse view of the gallbladder in many instances because of the curved interface and the different propagation speeds between the liver parenchyma and the bile-containing gallbladder.

During the performance of an abdominal ultrasound examination, you would most expect to encounter refraction in this view? a) diaphragm below liver parenchyma b) transverse view of the gallbladder c) Sagittal view of the abdominal aorta d) transverse view of the pancreas e) refraction is not encountered during an abdominal sonogram.

b) oblique incidence Explanation: Normal incidence is also known as perpendicular incidence. It occurs when the sound beam strikes the interface at a 90 degree angle.

During ultrasound examination of the aorta, a 45 degree beam-to-vessel angle would be called: a) Normal incidence b) oblique incidence c) perpendicular incidence d) Snell's incidence e) none of the above

d) density Explanation: The equation for acoustic impedance is z = pc, where z is the rayl (unit for acoustic impedance). p is density, and c is the speed of sound. Since the speed of sound in tissue is relatively constant (1540 m/s), the main factor determining acoustic impedance is changes in tissue density.

For soft tissue, one of the factor responsible for determining acoustic impedance is: a) attenuation b) frequency c) absorption d) density e) amplitude

c) Decreased spatial resolution Explanation: This is the classic tradeoff in ultrasound. High frequencies have better spatial resolution but greater attenuation than low frequencies. So in order to gain penetration, one must sacr4ifice some spatial resolution by using a lower frequency. If improved spatial resolution is desired, then one must sacrifice penetration by using a higher frequency.

If you choose a lower-frequency transducer to image a highly attenuating liver, what tradeoff are you making? a) Decreased penetration b) Decreased beam intensity c) Decreased spatial resolution d) Increased beam refraction e) Increased round-trip travel time

c) Diffuse reflection

Reflection of the sound beam from a large interface with a rough surface is called: a) scattering b) diffraction c) diffuse reflection d) specular reflection e) Rayleigh scattering

b) the angle of sound transmission at an interface with oblique incidence and different propagation speeds. Explanation: Snell's law related the angle of transmission of the sound beam to the relative velocities of sound in the two media. Refraction of sound at an interface obeys Snell's law.

Snell's law describes: a) The percentage of reflection at an interface with normal incidence and different densities. b) The angle of sound transmission at an interface with oblique incidence and different propagation speeds. c) The amount of attenuation of sound in tissue with depth. d) The amount of backscatter from a diffuse reflector. e) The angle of sound reflection at an interface with oblique incidence and nonspecular reflection.

e) compression Explanation: Attenuation includes all sound interactions that result in a weakening of the beam. These include reflection, scattering, absorption, and, to a lesser extent, refraction. Absorption is the conversion of sound to heat in tissue. Refraction results in a bending of the beam.

Sound may be attenuated by all of the following EXCEPT: a) reflection b) scattering c) conversion of sound to heat d) absorption e) compression

b) interference

The algebraic summation of waves is called: a) scattering b) interference c) absorption d) refraction e) diffusion

c) 0.5 Explanation: Sound attenuation increases with frequency. It is approximately 1 dB/cm/MHz.

The attenuation of ultrasound propagating through soft tissue is approximately _____________ dB/cm/MHz.

b) decreased attenuation through a fluid-filled structure Explanation: Acoustic enhancement results from decreased attenuation through a fluid-filled structure compared to the adjacent tissue. Changes in propagation speed do not produce acoustic enhancement. The sound absorption in the region distal to the fluid-filled structure is not affected. A high acoustic impedance mismatch at the cyst-tissue interface would result in greater reflection of sound with possible shadowing instead of enhancement. The shadowing seen posterior to the lateral border of the cyst is refraction due to bending of the sound beam with oblique incidence.

The hyperechoic region in this image results from: a) increased acoustic velocity through a fluid-filled structure b) decreased attenuation through a fluid-filled structure c) decreased sound absorption in the region distal to the fluid-filled structure d) a high acoustic impedance mismatch between the cyst and adjacent tissue e) bending of the sound beam due to oblique incidence

a) Reflection Explanation: Due to the large acoustic impedance mismatch between soft tissue and calcium, most of the sound is reflected at the stone-tissue interface. There is very little sound transmitted through the stone to provide reflections from tissue distal to the stone. This results in shadowing distal to the calcification.

The shadow depicted in this image of the kidney is primarily a result of the following sound-tissue interaction: a) reflection b) refraction c) destructive interference d) cavitation e) diffraction

c) specular reflection

The term for reflection from a large, smooth interface is: a) Rayleigh scattering b) diffraction c) specular reflection d) diffusion e) refraction

a) the reflected bandwidth will be shifted down in frequency due to the increase attenuation of higher frequencies. Explanation: Since higher frequencies are absorbed more quickly than lower frequencies, the reflected bandwidth of the beam will be shifted down compared to the transmitted bandwidth.

The transducer you are using to image the liver transmits a wide-bandwidth beam of 3-5 MHz. Which of the following most correctly describes the reflected beam after it has traversed the liver? a) the reflected bandwidth will be shifter down in frequency due to the increased attenuation of higher frequencies. b) the reflected beam will be of reduced intensity but will have the same frequency content as the transmitted beam. c) the reflected bandwidth will be shifted upward in frequency due to the increased absorption of the lower frequencies. d) only the center frequency component of the bandwidth will be reflected back to the transducer. e) the reflected beam will be identical to the transmitted beam.

c) Scan with perpendicular incidence Explanation: With specular reflectors, the angle of reflection is equal to the angle of transmission. So the greatest reflection will be received back to the transducer whenever perpendicular incidence is used. Increasing the amount of received energy will enhance the visibility of the reflector.

What can be done to enhance visibility of a specular reflector? a) scan with the lowest possible frequency. b) scan with oblique incidence. c) scan with perpendicular incidence. increase the d) distance of the reflector. e) scan with an incident angle of 45 degrees.

a) Density and propagation speed of the medium. Explanation: Acoustic Impedance is determined by the density and propagation speed of the medium as expressed i this equation: z = pc where z represents acoustic impedance, p represents density, and c represents propagation speed.

What determines acoustic impedance? a) Density and propagation speed of the medium b) Frequency and propagation speed c) Frequency and interface size d) Angle of incidence and media propagation speed e) Frequency and media density

e) scattering

What interaction of ultrasound and tissue is primarily responsible for Imaging the internal structure of organs? a) specular reflection b) refraction c) diffraction d) destructive interference e) scattering

b) If frequency is doubled, absorption is doubled. Explanation: There is a direct relation between absorption and frequency. As frequency is doubled, the rate of absorption doubles. That is why there is less penetration with higher frequencies--absorption is increased.

What is the relationship of frequency to absorption? a) If frequency is halved, absorption is doubled. b) If frequency is doubled, absorption is doubled. c) If frequency is doubled, absorption is halved. d) If frequency is halved, absorption is quartered. e) the rate of sound absorption is not frequency-dependent.

d) propagation speed Explanation: Frequency, period, and intensity are all determined by the ultrasound system. Only propagation speed is determined by the medium.

What sound parameter is determined only by the medium? a) frequency b) period c) intensity d) propagation speed e) none of the above

c) reflection

What sound-tissue interaction is necessary to form an ultrasound image? a) rarefaction b) refraction c) reflection d) diffraction e) interference

b) TGC Explanation: TGC (time gain compensation) and DGC (depth gain compensation) are two names for the same system control. TGC is a method of increasing amplification to echoes from a specific depth to account for the weakening (attenuation) of the sound beam with depth. If the TGC is adjusted appropriately, like structures will appear with the same brightness even if they are located at different depths.

What system control should you adjust to account for sound attenuation with depth? a) Dynamic Range b) TGC c) Transmit Power d) Frame averaging e) Focus position

a) acoustic enhancement

What term describes the hyperechoic region seen beneath this testicular cyst? a) acoustic enhancement b) acoustic shadowing c) reverberation d) refraction e) acoustic impedance

e) attenuation

What term is used to describe the reduction in the intensity of sound as it propagates through tissue? a) diffraction b) refraction c) reflection d) absorption e) attenuation

c) oblique incidence and different media propagation speeds Explanation: Both must be present for refraction to occur. Reflector size does not affect refraction. Refraction does not occur with perpendicular incidence.

What two conditions must be present to cause refraction of a sound wave? a) perpendicular incidence and identical media propagations speeds b) perpendicular incidence and reflector size smaller than one length c) oblique incidence and different media propagation speeds d) oblique incidence and reflector size smaller than one wavelength e) normal incidence and reflector size smaller than one wavelength

d) The angle of reflection will be oriented away from the transducer resulting in decreased visualization of the aorta. Explanation: With specular reflectors, the angle of reflection is equal to the angle of incidence, but will be oriented in the opposite direction. So, if perpendicular incidence is used, most of the sound will be reflected back at the transducer. But if oblique incidence is used, most of the sound will be reflected at an angle equal to the transmitted angle oriented away from the transducer.

What would be the result of imaging the aorta at an angle of 45 degrees? a) a very strong reflection will occur since this is the optimal angle for imaging. b) all of the sound will be reflected due to the poor scanning angle. c) all of the sound will be transmitted due to the poor scanning. d) The angle of reflection will be oriented away from the transducer resulting in decreased visualization of the aorta. e) The amount of scattering will be reduced with a scanning angle of 45 degrees resulting in a cleaner image with reduced artifactual echoes.

b) lateral misregistration Explanation: Refraction is a bending of the sound beam that results in lateral misregistration of the structures posterior to the refracted beam.

When the sound beam is refracted during an ultrasound examination, which of the following will you detect on the ultrasound image? a) axial misregistration b) lateral misregistration c) reverberations posterior to a reflector d) enhancement of a reflector e) electric interference

c) diffraction

Which interaction is associated with divergence of the sound beam after passing through a small aperture? a) scattering b) absorption c) diffraction d) interference e) diffuse reflection

a) The reflected beam is scattered in various directions. Explanation: With diffuse reflection, the beam is weakened due to incoherence. Diffuse reflection occurs when the sound beam strikes a large, rough surface. The beam is reflected at many different angles because it strikes the rough surface at varying angles of incidence. This has the result of causing the reflected waves to be incoherent (out of phase) with each other, weakening and defocusing the beam.

Which of the following describe diffuse reflection? a) The reflected beam is scattered in various directions b) The reflected frequency is altered by the Doppler effect. c) The reflected beam is amplified by the focusing effect of scatterers. d) The reflected beam is weakened by the large acoustic impedance mismatch at the tissue interface. e) There is no reflection at a tissue interface because of a disorganized transmit beam.

e) all of the above Explanation: All of these interactions will decrease the intensity of the transmitted beam.

Which of the following interactions of sound and tissue decreases the intensity of the transmitted beam? a) absorption b) reflection c) scattering d) conversion of sound to heat e) all of the above

e) scattering intensity is proportional to frequency raised to the fourth power.

Which of the following statements is true regarding the effect of frequency on Rayleigh scattering? a) The amount of scattering is not affected by frequency. b) scattering intensity doubles if frequency is doubled c) doubling the frequency results in having the scattering intensity. d) doubling the frequency results in quartering the scattering intensity. e) scattering intensity is proportional to frequency raised to the fourth power.

a) Redirection of the sound beam at an interface with different propagation speeds and a curved surface. Explanation: The shadowing seen posterior to the lateral borders of a cyst is due to oblique incidence and different media propagation speeds between the cyst and the surrounding tissue. This is known as refraction.

While imaging a breast cyst, you notice shadowing posterior to each lateral border of the cyst. What is the source of the shadows? a) redirection of the sound beam at an interface with different propagation speeds and a curved surface. b) bending of the sound beam due to different media densities c) increased attenuation of the sound beam at the borders of the cyst d) lateral misregistration of the cyst due to a multipath artifact e) diffraction of the sound beam resulting in a weakened signal at the lateral borders of the cyst

c) liver/bowel gas Explanation: Reflected signal strength depends on acoustic impedance mismatch. A small reflected signal will occur when the acoustic impedance mismatch is negligible, as it is, for example between spleen and kidney , liver and pancreas, liver and bile duct, and renal cortex and renal sinus, all of which are soft tissue. A large reflected signal will occur when the acoustic impedance mismatch is large, as it is between liver (i.e., soft tissue) and bower gas (air)

While performing an abdominal ultrasound examination, you encounter the following interfaces. Which will produce the strongest reflected signal? a) spleen/kidney b) liver/pancreas c) liver/bowel gas d) liver/bile duct e) renal cortex/renal sinus

a) difference in acoustic impedance and angle of incidence. Explanation: The amplitude of the reflected signal depends on the difference in acoustic impedance between two tissues. The greater the difference, the greater the reflection. Specular reflection is highly angle-dependent. The beam strikes the interface at a right angle (90 degrees), the reflected energy will be directed back to the transducer. But if the beam strikes the interface at another angle, the reflected energy will be directed at the same angle AWAY from the transducer.

With specular reflection, the strength of the received signal depends on the following two factors: a) Difference in acoustic impedance and angle of incidence. b) Difference in acoustic velocity and interface size. c) Difference in acoustic velocity and motion of reflector. d) angle of incidence and tissue temperature e) bulk modulus and interface size.

e) all of the above Explanation: Refraction will occur due to the oblique incidence (round surface) and different propagation speed. Reflection will occur since the acoustic impedance will be different (different density and propagation speed). Absorption occurs as sound propagates through tissue so it will be present. Scattering will occur with the liver parenchyma.

You are imaging a regular round mass in the liver that has a much slower propagation speed than liver tissue. What sound-tissue interaction will be encountered as the ultrasound propagates through this interface? a) refraction b) reflection c) absorption d) scattering e) all of the above

b) Axial misregistration of the mass on the screen caused by the slower propagation speed through fat Explanation: Since sound travels slower in fat than in soft tissue, a large mass composed primarily of fat may cause axial misregistration of the mass on the ultrasound image. This occurs because the system must assume a constant sound propagation speed of 1,540 m/s. If sound travels slower through a medium then a longer round-trip travel time will result and the system will place the structure deeper on the image. Conversely, if sound travels through a medium with a faster propagation speed compared to soft tissue, then a shorter round-trip travel time will result and the structure will be placed shallower on the image.

You are scanning a large abdominal mass that is composed primarily of fat. Which of the following are you most likely to encounter? a) posterior acoustic shadowing caused by increased attenuation through the fat b) axial misregistration of the mass on the screen caused by the slower propagation speed through fat. c) lateral misregistration of the mass on the screen because of refraction d) total reflection of the sound beam caused by a large acoustic impedance mismatch e) diffraction of the sound beam due to a virtual small aperture though the mass

d) There will be no reflected sound. Explanation: Normal Incidence is another term for perpendicular incidence. No reflection will occur with this scenario. Sound reflection requires an interface in which there is a change in acoustic impedance from one media into the next.

You are scanning an interface at normal incidence in which the acoustic impedance is unchanged from one media into the other. a) all of the sound will be reflected. b) some of the sound will be transmitted and some of the sound will be reflected. c) Refraction of the sound beam will occur. d) There will be no reflected sound. e) Most of the sound will be absorbed at the interface

d) 10 MHz Explanation: Since the thyroid is a superficial structure, it is best imaged with a high-frequency transducer that will provide superior spatial resolution

You have been asked to perform an ultrasound study of the thyroid gland. A transducer of the following frequency would be most appropriate for this study: a) 2.25 MHz b) 1 MHz c) 3.5 MHz d) 10 MHz e) 5 MHz

a) 3.0 MHz Explanation: Sound absorption (one cause of attenuation) increases with increasing frequency. Therefore the use of a lower-frequency transducer will decrease attenuation.

You have selected an multi-frequency transducer to perform an abdominal ultrasound examination. For this study, you wish to reduce attenuation as much as possible. Which frequency selection would reduce sound attenuation most effectively? a) 3.0 MHz b) 3.5 MHz c) 4.0 MHz d) 5.0 MHz e) Attenuation is not affected by frequency

b) Decreasing transmit power Explanation: Attenuation of the sound beam in the body is increased as frequency is increased due to greater absorption. Altering the receiver gain changes the amplification of the received signal and does not affect attenuation. Decreasing transmit power would result in a weaker sound beam that would attenuate more quickly. Dynamic range does not affect attenuation. Decreasing focusing would decrease beam intensity and therefore would not reduce sound attenuation.

which of the following adjustments would reduce sound attenuation in the body the most? a) increasing receiver gain b) decreasing transmit power c) increasing dynamic range d) decreasing frequency e) decreasing focusing