Chapter 1: Physical Principles

Adding damping to the transducer improves which type of resolution? a. transverse resolution b. temporal resolution c. axial resolution d. elevational resolution

C. Axial resolution (also known as radial, range, longitudinal, or depth resolution) is improved when the pulse is shorter, which occurs when damping is used in a pulsed-wave (PW) transducer.

Density is typically measured in: a. kilograms per centimeter cubed b. millimeters c. watts per square centimeter d. pascals

A. Density is typically measured in kilograms per centimeter cubed.

The prefix "centi" denotes: a. thousandths b. hundredths c. millions d. hundreds

B. "Centi" denotes hundredths.

Which of the following would be considered ultrasonic? a. 10 Hz b. 18 kHz c. 0.5 MHz d. 200 Hz

C. 0.5 MHz is 500,000 Hz, which is an ultrasonic frequency. The ultrasonic range is defined as "greater than 20,000 Hz."

What term is defined as "the power of a wave divided by the area over which the power is distributed?" a. amplitude b. power c. intensity d. absorption

C. Intensity is essentially equal to the power of a wave divided by the area over which the power is distributed.

As imaging depth increases, the PRF must: a. not change b. increase c. decrease d. PRF does not relate to imaging depth

C. Depth and PRF are inversely related. As imaging depth increases, the PRF decreases.

Which of the following is defined as the number of ultrasound pulses emitted in 1 second? a. PRP b. DF c. PRF d. SPL

C. Pulse repetition frequency is defined as the number of ultrasound pulses emitted in 1 second. PRF is determined by imaging depth.

The change in the direction of the original sound wave that occurs when sound interacts with two different tissue types that have a different propagation speed is referred to as: a. wavelength b. scattering c. refraction d. absorption

C. Refraction is the change in direction of the transmitted sound beam that occurs with oblique incidence and dissimilar propagation speeds.

What are the units of DF? a. dB b. dB/cm c. Hz d. unitless

D. Duty factor, the percentage of time that sound is being transmitted, has no units. It is a percentage.

Pressure is typically expressed in: a. frequency b. pascals c. decibels d. kilograms per centimeter cubed

B. Pressure is typically expressed in pascals. You may also see kPa (kilopascals) or MPa (megapascals).

In clinical imaging, the wavelength typically measures between: a. 1 and 10 Hz b. 1540 and 2000 m/s c. 0 and 1 d. 0.1 and 0.8 mm

D. In clinical imaging, the wavelengths measure between 0.1 and 0.8 mm.

Areas of high pressure and density are referred to as: a. compressions b. rarefactions c. diffractions d. refractions

A. Areas of high pressure and density are referred to as compression. Areas of low pressure are referred to as rarefaction.

As a sound wave travels through the human body, the intensity of the sound wave decreases as a result of: a. attenuation b. elevational resolution c. Huygen's principle d. refraction

A. Attenuation is a decrease in the amplitude and intensity of the sound beam as sound travels through tissue. There are three mechanisms of attenuation: absorption, reflection, and scattering.

Damping of the sound beam: a. reduces the SPL b. increases the SPL c. increases the PD d. has no impact on SPL or PD

A. Damping of the sound beam decreases the spatial pulse length by decreasing the number of cycles in a pulse (n).

Density and propagation speed are: a. inversely related b. directly related c. directly proportional d. unrelated

A. Density and propagation speed are inversely related. Propagation speed is directly related to stiffness.

An increase in PF would lead to: a. an increase in DF b. a decrease in PD c. an increase in the number of cycles d. a decrease in resolution

A. Duty factor is equal to pulse duration (PD) divided by pulse repetition period (PRP). PRP is inversely related to pulse repetition frequency (PRF), so an increase in PRF would lead to an increase in duty factor because they are directly related.

Which of the following is determined by the sound source only? a. frequency b. wavelength c. SPL d. propagation speed

A. Frequency is determined by the sound source only. Specifically, it is the thickness of the element and the propagation speed of the element that determines frequency.

Micro denotes: a. millionth b. hundredth c. million d. billionth

A. Micro- is a metric prefix that denotes one-millionth.

All of the following are true of power except: a. as amplitude increases, power remains the same b. power is proportional to amplitude squared c. intensity is proportional to power d. power is measured in milliwatts

A. Power is proportional to the amplitude squared, so power decreases as amplitude decreases.

Which of the following is an appropriate unit of measurement for propagation speed? a. millimeters per microsecond (mm/μs) b. watts per square centimeter (W/cm^2) c. microseconds (ms) d. kilohertz (kHz)

A. Propagation speed an be measured in millimeters per microsecond or meters per second.

Which of the following is described as the ability of an object to resist compression and relates to the hardness of a medium? a. stiffness b. density c. pressure d. inertia

A. Stiffness is the ability of an object to resist compression and relates to the hardness of a medium.

The attenuation coefficient in soft tissue is equal to: a. one-half of the operating frequency b. double the operating frequency c. frequency times path length d. the total decibels

A. The attenuation coefficient (in dB/cm) is the rate at which sound is attenuated per unit depth. It is equal to one half of the frequency (f/2) in soft tissue.

What time is defined as the beginning of one pulse to the beginning of the next pulse and, therefore, includes both the "on" and "off" time? a. PRP b. PD c. DF d. PRF

A. The pulse repetition period is the time from the start of one pulse to the start of the next pulse, and therefore, it includes the "on" (or transmit) and "off" (or listening) times.

Which of the following would have the highest propagation speed? a. air b. bone c. soft tissue d. water

B. Bone, which has a propagation speed of 4080 m/s, has the highest propagation speed.

The major component of attenuation is: a. scatter b. absorption c. transmission d. refraction

B. Absorption, the creation of heat in the tissue as sound travels, is a significant contributor to attenuation.

All of the following relate to the strength of the sound wave except: a. amplitude b. wavelength c. intensity d. power

B. Amplitude, intensity, and power represent the strength of the beam. Wavelength is a parameter of the length of the wave.

What is the total amount of attenuation that occurs if a 6.0-MHz sound beam travels through 4 cm of soft tissue? a. 24 dB b. 12 dB c. 6 dB d. 1.5 dB

B. Attenuation in soft tissue is equivalent to the attenuation coefficient (f/2, in dB/cm) multiplied by the path length (in cm). The total amount of attenuation that occurs if a 6.0-MHz sound beam travels through 4 cm of soft tissue is 12 dB (3 dB/cm x 4 cm).

If only the density of a medium is increased, then the: a. propagation speed will increase b. propagation speed will decrease c. propagation speed will stay the same d. none of the above

B. Density and propagation speed are inversely related. If only the density of the medium is increased, then the propagation speed will decrease.

As imaging depth increases, PRP: a. remains constant b. increases c. decreases d. doubles

B. Depth and PRP are directly related. Therefore, as imaging depth increases, the PRP increases.

The DF for CW ultrasound is: a. 1.0% b. 100% c. 20,000 Hz d. 8 Pa

B. Duty factor is the percentage of time that sound is being transmitted. With continuous wave (CW) ultrasound, there is constant sound transmission. Therefore, the duty factor for CW is 100%.

Which of the following requires an oblique interface and a propagation speed mismatch? a. reflection b. refraction c. normal incidence d. damping

B. In order for refraction to occur, there must be an oblique angle of incidence and different propagation speeds.

What is the change in intensity if the power decreases by half? a. intensity doubles b. intensity is halved c. intensity is one-fourth d. intensity does not change

B. Intensity and power are directly related. If power is decreased by half, intensity is decreased by half.

What are the units for pressure? a. feet, inches, centimeters, or miles b. pascals or pounds per square inch c. kilograms per centimeter cubed d. hertz, kilohertz, or megahertz

B. Pressure is measured in pascals (Pa) or pounds per square inch.

The portion of the sound beam where the molecules are farther apart describes an area of: a. compression b. rarefaction c. refraction d. amplitude

B. Rarefaction is an area in the sound wave where the molecules are spread wider apart. Be careful and not confuse "rarefaction" with "refraction."

If the angle of incidence is 40°, what is the angle of transmission at the interface if medium 1 has a propagation speed of 1320 m/s and medium 2 has a propagation speed of 1700 m/s? a. 0° b. >40° c. <40° d. cannot tell the angle of transmission

B. The angle of transmission is greater than 40° because the propagation speed of medium two is greater than the propagation speed of medium 1 (θ2 > θ1 if c2 > c1).

The typical range of frequency for diagnostic ultrasound imaging is: a. 20 to 20,000 Hz b. 1 to 20 MHz c. 2 to 15 kHz d. 12 to 100 MHz

B. The typical range of frequency for diagnostic ultrasound is 2 to 15 MHz, although some transducers may go as low as 1 MHz and as high as 20 MHz. In this question, 1 to 20 MHz is the best answer. There are transducers for specialized imaging exams that go as high as 70 MHz.

All of the following are true of wavelength except: a. it is determined by both the medium and the sound source b. it is equal to the period divided by the frequency c. it is inversely related to frequency d. it is directly related to period

B. Wavelength (λ) is equal to the propagation speed (c) divided by the frequency (f). Wavelength is inversely related to frequency, a very important concept in ultrasound physics.

SPL can be calculated by: a. multiplying the number of cycles by the frequency b. dividing the period by the frequency c. multiplying the number of cycles by the wavelength d. dividing the number of cycles by the wavelength

C. Spatial pulse length equals the number of cycles in the pulse multiplied by the wavelength.

The percentage of time that the ultrasound system is producing pulses of ultrasound describes the: a. PRP b. PD c. DF d. PRF

C. The duty factor is the percentage of time the ultrasound system is producing a sound.

The inertia of the medium describes its: a. attenuation characteristics b. stiffness c. density d. elasticity

C. The inertia of a medium describes its density.

Transducers have material within them that, when electronically stimulated, produces ultrasound waves. This is most likely some form of: a. tungsten acetate b. dilithium zirconium c. lead zirconate titanate d. barium sulfate

C. Transducers have material within them that, when electronically stimulated, produces ultrasound waves. These materials most likely consist of some form of lead zirconate titanate.

Which of the following is determined by the sound source and medium? a. propagation speed b. frequency c. period d. wavelength

D. Wavelength (λ) is determined by both the sound source (frequency, determined by the transducer) and the medium (propagation speed).

The maximum value or minimum value of an acoustic variable minus the equilibrium value of that variable describes the: a. power b. intensity c. DF d. amplitude

D. Amplitude is the maximum or minimum deviation of an acoustic variable from the average value of that variable.

Which of the following would have the lowest propagation speed? a. water b. soft tissue c. bone d. lung tissue

D. Lung tissue, which has a propagation speed 660 m/s, has the lowest propagation speed. Do not confuse propagation speed with attenuation. Air has the highest relative attenuation, but the lowest propagation speed.

What is the change in power if the amplitude triples? a. it doubles b. it triples c. it quadruples d. it increases nine times

D. Power is proportional to the amplitude squared. They do not have a one-to-one relationship. If amplitude triples, then power increases by nine times.

Which of the following is defined as only the active time? a. DF b. PRF c. period d. PD

D. Pulse duration is the time it takes for a pulse to occur, but only includes the "on" or transmitting time.

Which of the following describes the amount of refraction that occurs at an interface? a. Bernoulli's law b. Poiseuille's law c. Law of reflection d. Snell's law

D. Refraction is a redirection of the transmitted sound beam. Snell's law describes the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media.

Sound is technically a: a. transverse and longitudinal wave b. mechanical and transverse wave c. nonmechanical and pressure wave d. mechanical and longitudinal wave

D. Sound is a mechanical and longitudinal wave. Sound waves are pressure waves, which are created by a mechanical action, like vocal cords or a piezoelectric element vibrating. Longitudinal waves are waves in which the molecules vibrate in a direction that is parallel to the direction of wave travel.

Which of the following is considered the speed of sound in soft tissue? a. 1.54 m/s b. 0.77 m/s c. 100 mW/cm^2 d. 1540 m/s

D. The average speed of sound in all soft tissue is considered to be 1540 m/s or 1.54 mm/μs. This number is the average of all the propagation speeds found within the human body.

Which of the following is described as the distance over which one cycle occurs? a. PD b. DF c. period d. wavelength

D. Wavelength is distance over which one cycle occurs, or the distance from the beginning of one cycle to the end of the same cycle.