Physical Principles

Inertia

Newton's principle that states that an object at rest stays at rest and an object in motion stays in motion, unless acted on by an outside force

Attenuation

a decrease in the amplitude and intensity of the sound beam as sound travels through tissue

Hydrophone

a device used to measure the output intensity of the transducer

Piezoelectric materials

a material that generates electricity when pressure is applied to it, and one that changes shape when electricity is applied to it; also referred to as the element or crystal

Decibels

a unit that establishes a relationship or comparison between two values of power, intensity, or amplitude

An increase in PRF 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. An increase in DF (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.)

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. As amplitude increases, power remains the same (Power is proportional to the amplitude squared, so power decreases as amplitude decreases)

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 (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.)

Areas of high pressure and density are referred to as: a. Compressions b. Rarefactions c. Diffractions d. Refractions

a. Compressions (Areas of high pressure and density are referred to as compression. Areas of low pressure are referred to as rarefaction.)

Which of the following is determined by the sound source only? a. Frequency b. Wavelength c. SPL d. Propagation speed

a. Frequency (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.)

Density and propagation speed are: a. Inversely related b. Directly related c. Directly proportional d. Unrelated

a. Inversely related (Density and propagation speed are inversely related. Propagation speed is directly related to stiffness.)

Density is typically measured in: a. Kilograms per centimeter cubed b. Millimeters c. Watts per square centimeter d. Pascals

a. Kilograms per centimeter cubed (Density is typically measured in kilograms per centimeter cubed.)

Micro denotes: a. Millionth b. Hundredth c. Million d. Billionth

a. Millionth (Micro- is a metric prefix that denotes one-millionth)

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. One-half of the operating frequency (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. PRP (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.)

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

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

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/cm2) c. microseconds (ms) d. kilohertz (kHz)

a. millimeters per microsecond (mm/µs) (Propagation speed can be measured in millimeters per microsecond or meters per second.)

Rarefaction

an area in the sound wave of low pressure and density

Oblique incidence

angle of incidence is less than or greater than 90° to the interface

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. 1 to 20 MHz (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.)

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

b. 100% (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%.)

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. 12 dB (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 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. >40° (The angle of transmission is greater than 40° because the propagation speed of medium two is greater than the propagation speed of medium 1 (~ > 01 if c2 > c1)

The major component of attenuation is: a. Scatter b. Absorption c. Transmission d. Refraction

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

Which of the following would have the highest propagation speed? a. Air b. Bone c. Soft tissue d. Water

b. Bone (Bone, which has a propagation speed of 4080 m/s, has the highest propagation speed.)

The prefix "centi" denotes: a. Thousandths b. Hundredths c. Millions d. Hundreds

b. Hundredths ("Centi" denotes hundredths.)

As imaging depth increases, PRP: a. Remains constant b. Increases c. Decreases d. Doubles

b. Increases (Depth and PRP are directly related. Therefore, as imaging depth increases, the PRP increases)

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 is halved (Intensity and power are directly related. If power is decreased by half, intensity is decreased by half.)

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. It is equal to the period divided by the frequency (Wavelength (A) 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.)

Pressure is typically expressed in: a. Frequency b. Pascals c. Decibels d. Kilograms per centimeter cubed

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

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

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 (Rarefaction is an area in the sound wave where the molecules are spread wider apart. Be careful not to confuse "rarefaction" with "refraction:')

Which of the following requires an oblique interface and a propagation speed mismatch? a. Reflection b. Refraction c. Normal incidence d. Damping

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

All of the following relate to the strength of the sound wave except: a. Amplitude b. Wavelength c. Intensity d. Power

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

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

Giga (G)

billion (10^9)

Nano (n)

billionth (10^-9)

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

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 (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.)

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

c. DF (The duty factor is the percentage of time the ultrasound system is producing a sound.)

As imaging depth increases, the PRF must: a. Not change b. Increase c. Decrease d. PRF does not relate to imaging depth

c. Decrease (Depth and PRF are inversely related. As imaging depth increases, the PRF decreases.)

The inertia of the medium describes its: a. Attenuation characteristics b. Stiffness c. Density d. Elasticity

c. Density (The inertia of a medium describes its density.)

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

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

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. Multiplying the number of cycles by the wavelength (Spatial pulse length equals the number of cycles in the pulse multiplied by the wavelength.)

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

Acoustic variables

changes that occur within a medium as a result of sound traveling through that medium

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 to 0.8 mm

d. 0.1 to 0.8 mm (In clinical imaging, the wavelengths measure between 0.1 and 0.8 mm.)

Which of the following is considered the speed of sound in soft tissue? a. 1.54 m/s b. 0.77 mis c. 100 mW/cm2 d. 1540 m/s

d. 1540 m/s (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.)

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

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. It increases nine times (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 would have the lowest propagation speed? a. Water b. Soft tissue c. Bone d. Lung tissue

d. Lung tissue (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.)

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. Mechanical and longitudinal wave (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 defined as only the active time? a. DF b. PRF c. Period d. PD

d. PD (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. Snell's law (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.)

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

d. Unitless (Duty factor, the percentage of time that sound is being transmitted, has no units. It is a percentage.)

Which of the following is determined by the sound source and medium? a. Propagation speed b. Frequency c. Period d. Wavelength

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

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

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

Path length

distance to reflector

Pressure

force per unit area or the concentration of force

Distance

how far apart objects are; may also be referred to as vibration or displacement

Hecto (h)

hundred (10^2)

Centi (c)

hundredth (10^-2)

Snell's law

law used to describe the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media

Density

mass per unit volume

Mega (M)

million (10^6)

Micro (u)

millionth (10^-6)

Frequency

number of cycles per second

Specualr reflections

reflections that occur when the sound impinges upon a large, smooth reflector at a 90° angle

Nonspecular reflectors

reflectors that are smaller than the wavelength of the incident beam

Backscatter

scattered sound waves that make their way back to the transducer and produce an image on the display

Rayleigh scatterers

small scattering reflectors

Continuous wave

sound that is continuously transmitted

Capacitive micromachined ultrasound transducers

technology used to create comparable transducer technology to piezoelectric materials

Deca (da)

ten (10^1)

Deci (d)

tenth (10^-1)

Stiffness

the ability of an object to resist compression

Axial resolution

the ability to accurately identify reflectors that are arranged parallel to the ultrasound beam

Compression

the area in the sound wave of high pressure and density

Refraction

the change in the direction of the transmitted sound beam that occurs with oblique incidence angles and dissimilar propagation speeds

Absorption

the conversion of sound energy to heat

Half-value layer thickness

the depth at which sound has lost half of its layer thickness; also known as half-intensity depth

Interface

the dividing line between two different media

Reflection

the echo; the portion of sound that returns from an interface

Acoustic speckle

the interference pattern caused by scatterers that produces the granular appearance of tissue on a sonographic image

Spatial pulse length

the length of a pulse

Wavelength

the length of a single cycle of sound

Amplitude

the maximum or minimum deviation of an acoustic variable from the average value of that variable; the strength of the reflector

Particle motion

the movement of molecules due to propagating sound energy

Pulse repetition frequency

the number of pulses of sound produced in 1 second

Intensity reflection coefficient

the percentage of sound reflected at an interface

intensity transmission coefficient

the percentage of sound transmitted at an interface

Duty factor

the percentage of time that sound is actually being produced

Scattering

the phenomenon that occurs when sound waves are dispersed into different directions because of the small reflector size compared with the incident wavelength

Intensity

the power of the wave divided by the area over which it is spread, the energy per unit area

Damping

the process of reducing the number of cycles of each pulse in order to improve axial resolution

Attenuation coefficient

the rate at which sound is attenuated per unit depth

Power

the rate at which work is done or energy is transformed

Beam uniformity ratio

the ratio of the center intensity to the average spatial intensity; also referred to as the SP/SA factor or beam uniformity coefficient

Impedance

the resistance to the propagation of sound through a medium

Propagation speed

the speed at which a sound wave travels through a medium

Pulse duration

the time during which the sound is actually being transmitted; the "on" time

Period

the time it takes for once cycle to occur

Pulse repetition period

the time taken for a pulse to occur

Total attenuation

the total amount of sound (in dB) that has been attenuated at a given depth

Hertz

the unit of frequency, equal to one cycle per second

Kilo (k)

thousand (10^3)

Milli (m)

thousandth (10^-3)

Propagate

to transmit through a medium

Normal incidence

Angle of incidence is 90° to the interface