##### Chapter 2 Ultrasound Terms

Absorption

conversion of sound to heat

Acoustic

Having to do with sound

Acoustic Variable

Pressure, density, and particle vibration: sound wave quantities that vary in space and time.

Amplitude

Maximum variation of an acoustic variable or voltage

Attenuation

Decrease in amplitude and intensity with distance as a wave travels through a medium

Attenuation Coefficient

Attenuation per centimeter of wave travel

Backscatter

Sound scattered back in the direction from which it came

Bandwidth

Range of frequencies contained in an ultrasound pulse; range of frequencies within which a material, device, or system can operate.

Compression

Reduction in differences between small and large amplitude. Region of high density and pressure in a compressional wave

Constructive Interference

Combination of positive or negative pressures

Continuous Wave

CW

A wave in which cycles repeat indefinitely; not pulsed

Contrast Agent

A suspension of bubbles or particles introduced into circulation to enhance the contrast between anatomical structures, thereby improving their imaging

Coupling Medium

A gel used to provide a good sound path between echoes of slightly different intensities

Cycle

One complete variation of an acoustic variable

Decibel

Unit of power or intensity ratio; the number of decibels is 10 times the logarithm (to the 10 base) of the power or intensity ratio

Density

Mass divided by volume

Destructive Interference

Combination of positive and negative pressures

Duty Factor

Fraction of time that pulsed ultrasound is on

Echo

Reflection

Energy

capability to do work

Fractional Bandwidth

Bandwidth divided by operating frequency

Frequency

Number of cycles per second

Fundamental Frequency

The primary frequency in a collection of frequencies that can include odd and even harmonics and subharmonics

Harmonics

Frequencies that and odd multiples of another

sometimes called Fundamental or operating Frequency

Hertz

Hz

Unit of frequency, one cycle per second; units of pulse repetition frequency, one pulse per minute

Impedance

Density multiplied by the sound propagation speed

Incidence Angle

Angle between incident sound direction and a line perpendicular to the boundary of a medium

Intensity

Power divided by area

Intensity Reflection Coefficient

Reflected intensity divided by incident intensity; the fraction of incident intensity reflected

Intensity Transmission Coefficient

Transmitted intensity divided by incident intensity; the fraction of incident intensity transmitted into the second medium

Interference

Combination of positive and/or negative pressure

Kilohertz

kHz

One thousand hertz

Longitudinal Wave

Wave in which the particle motion is parallel to the direction of wave travel

Medium

material through which a wave travels

Megahertz

MHz

One million hertz

Nonlinear propagation

Sound propagation in which the propagation speed depends on pressure causing the wave shape to change and harmonics to be generated

Oblique Incidence

Sound direction that is not perpendicular to the media boundaries

Penetration

imaging depth

Period

time per cycle

Perpendicular

Geometrically related to 90 degrees

Perpendicular Incidence

Sound direction that is perpendicular to the boundary between media

Power

Rate at which work is done; rate ate which energy is transferred

Pressure

force divided by an area in a fluid

Propagation

progression or travel

Propagation Speed

Speed at which a wave moves through a medium

Pulse

A brief excursion of a quantity from it's normal value; a few cycles

Pulse Duration

Interval of time from beginning to end of a pulse

Pulse Repetition Frequency

PRF

Number of pulses per second; sometimes called pulse repetition rate

Pulse Repetition Period

Interval of time from the beginning of one pulse to the beginning of the next

Pulsed Ultrasound

Ultrasound produced in pulsed form by applying electric pulses or voltage of on or a few cycles to the transducer

Range Equation

relationship between round-trip pulse travel time, propagation speed, and distance to a reflector

Rarefaction

region of low density and pressure in a compressional wave

Rayl

unit of impedence

Reflection

portion of a sound returned from a media boundary; echo

Reflection Angle

Angle between the reflected sound direction and a line perpendicular to the media boundary

Reflector

Media boundary that produces a reflection; reflecting surface

Refraction

change of sound direction on passing from one media to another

Scatterer

AN object that scatters sound because of its small size or its surface roughness

Scattering

Diffusion or redirection of sound in several directions upon encountering a particle suspension or rough surface

Sound

traveling wave of acoustic variable

Spatial Pulse Length

length of space over which a pulse occurs

Speckle

The granular appearance of images and spectral displays that is caused by the interference of echos from the distribution of scatterers in tissue

Specular Reflection

Reflection from large (relative to wavelength), flat, smooth boundary

Stiffness

Property of a medium; applied pressure divided b the fractional volume change produced by the pressure

Strength

Non specific term referring to amplitude or intensity

Transmission Angle

Angle between the transmitted sound direction and a line perpendicular to the media

Ultrasound

A form of sound

Sound that has a higher frequency than the sound we can hear

Over 20 kHz

Wave

is a traveling variation in one or more quantities, such as Pressure

Wavelength

length of space over which a cycle occurs

Work

Force multiplied by displacement

A wave is a traveling variations in quantities called wave _________________.

A) length

B) variables

C) cycles

D) periods

B) variables

Sound is a traveling variations in quantities called _________________ variables.

A) wave

B) pressure

C) density

D) acoustic

D) acoustic

Ultrasound is a sound with a frequency greater than ____________ Hz.

A) 2

B) 15

C) 20,000

D) 1540

C) 20,000

Acoustic variables include __________________, ____________, and particle vibration.

A) stiffness, density

B) hardness, impedance

C) amplitude, intensity

D) pressure, density

D) pressure, density

Which of the following frequencies is in the ultrasound range?

A) 12 Hz

B) 15,0000 Hz

C) 15 kHz

D) .004 MHz

D) .004 MHz

Which of the following is not an acoustic variable?

A) Pressure

B) Propagation speed

C) Density

D) Particle Motion

B) Propagation speed

Frequency is the number of ______________ an acoustic variable goes through in a second.

A) cycles

B) amplitude

C) pulse lengths

D) duty factors

A) cycles

The unit of frequency is ________________, which is abbreviated _______________.

A) hertz, Hz

B) megahertz, mHz

C) kilohurts, khts

D) cycles, cps

A) hertz, Hz

Period is the _________that it takes for one cycle to occur.

A) length

B) amplitude

C) time

D) height

C) time

Period decreases as _____________ increases.

A) wavelength

B) pulse length

C) frequency

D) bandwidth

C) frequency

Wavelength is the length of ________________ over which one cycle occurs.

A) time

B) space

C) propagation

D) power

B) space

Propagation speed is the speed with which a(n) ___________ moves though a medium.

A) wave

B) particle

C) frequency

D) attenuation

A) wave

Wavelength is equal to _______________, ____________ divided by ___________.

A) propagation speed, frequency

B) media density, stiffness

C) pulse length, frequency

D) wave amplitude, period

A) propagation speed, frequency

The _______________ and _____________ of a medium determine propagation speed.

A) amplitude, intensity

B) wavelength, period

C) impedance, attenuation

D) density, stiffness

D) density, stiffness

Propagation speed increases if ____________ is increased.

A) amplitude

B) frequency

C) density

D) stiffness

D) stiffness

The average propagation speed in soft tissue ___________m/s or ______________ mm/μs.

A) 10, 3

B) 1540, 1.54

C) 3, 10

D) 1.54, 1540

B) 1540, 1.54

Propagation speed is determined by the ___________.

A) frequency

B) amplitude

C) wavelength

D) medium

D) medium

Place the following in order of increasing sound propagation speed:

A) gas, solid liquids

B) solid, liquid, gas

C) gas, liquid, solid

D) liquid, solid, gas

C) gas, liquid, solid

The wavelength of 7 MHz ultrasound in soft tissue is ___________________ mm.

A) 1.54

B) .54

C) .22

D) 33.33

C) .22

(λ=1.54/7)

Wavelength in soft tissue _________ as frequency increases.

A) is constant

B) decreases

C) increases

D) weakens

B) decreases

It takes _______ μs for ultrasound to travel 1.54 cm in soft tissue

A) 10

B) .77

C) 1.54

D) 100

A) 10

Propagation speed in bone is ____________ that in soft tissue.

A) lower than

B) equal to

C) higher than

D) 10 m/s greater than

C) higher than

Sound travels fastest in ________________.

A) air

B) helium

C) water

D) steel

D) steel

Solids have higher propagation speeds than liquids because they have greater ____________.

A) density

B) stiffness

C) attenuation

D) propagation speed

B) stiffness

Sound travels slowest in _______________.

A) gases

B) liquids

C) tissue

D) bone

A) gases

Sound is a ________ ________ wave.

mechanical, longitudinal

If propagation speed is doubled (a different medium) and frequency is held constant, the wave-length is _________________.

doubled

If frequency in soft tissue is doubled, propagation speed _________________.

unchanged

If wavelength becomes 2 mm and frequency is doubled the wavelength becomes _______________mm.

1

Waves can carry ____________ from one place to another.

information

From given values for propagation speed and frequency, which of the following can be calculated?

A) Amplitude

B) Impedance

C) Wavelength

D) A and B

E) B and C

C) Wavelength

True or False?

If two media have different stiffnesses, the one with the higher stiffness will have the higher propagation speed.

True

The second harmonic of 3 MHz is ________________.

6

The odd harmonics of 2 MHz are ________________.

A) 1, 3, 5

B) 2, 4, 6

C) 6, 9, 12

D) 6, 10, 14

E) 10, 12, 14

D) 6, 10, 14

The even harmonics of 2 MHz are ___________.

A) 1, 3, 5

B) 2, 4, 6

C) 4, 8, 12

D) 6, 10, 14

E) 10, 12, 14

C) 4, 8, 12

Nonlinear propagation means ________________.

A) the sound beam does not travel in a straight line

B) propagation speed depends on frequency

C) propagation speed depends on pressure

D) the waveform changes shape as it travels

E) more than one of the above

E) more than one of the above

C) propagation speed depends on pressure

D) the waveform changes shape as it travels

As a wave changes from sinusoidal form to sawtooth form, additional _____________ appear that are ______ and _________ multiples of the __________. They are called ________________.

Frequency, even , odd, fundamental, harmonics

If Density of a mediu is 1000 kg/m^3 and the propagation speed is 1540 m/s, the impedance is _________ rayls

1,540,000

True or False?

If two media have the same propagation speed but different densities, the one with the higher density will have the higher impedance.

True

If two media have the same density but different propagation speeds, the one with the higher propagation speed will have the higher impedance.

True

Impedance is _______________ multiplied by __________ ____________.

Density, propagation speed

The abbreviation CW stands for _______________.

Continuous wave

Pulse repetition frequency is the number of _________ occurring in 1 second.

Pulses

Pulse repetition _______________ is the time from the beginning of one pulse to the beginning of the next.

Period

Pulse repetition period _________________ as pulse repetition frequency increases.

Decreases

Pulse duration is the _________________ it takes for a pulse to occur.

time

Spatial pulse length is the ___________ of ___________ that a pulse occupies as it travels.

length, space

_________________ ________________ is the fraction of time that pulse ultrasound is actually on.

Duty factor

Pulse duration equals the number of cycles in the pulse multiplied by __________________.

Period

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

wavelength

The duty factor of continuous wave sound is ______________.

1 (100%)

If the length is 2 mm, the spatial pulse length for a three-cycle pulse is ______________ mm.

6

3 cycles x 2 mm

The spatial pulse length in soft tissue for a two-cycle pulse of frequency 5 MHz is _____________ mm.

.616

(1.54 mm/μs x 2) / 5 MHz

The pulse duration in soft tissue for a two-cycle pulse of frequency 5 MHz is _______________ μs.

.4

2 / 5 MHz

For a 1-kHz pulse repetition frequency, the pulse repetition period is ________________ ms.

1

1 /1 kHz

The pulse duration in soft tissue for a two-cycle pulse of frequency 5 MHz is _______________ μs.

For a 1-kHz pulse repetition frequency, the pulse repetition period is ________________ ms.

The duty factor is ____________________.

.0004 (.04%)

.4 μs x .001 μs = .0004

How many cycles are there in a 1 second of continuous wave 5-MHz ultrasound.

A) 5

B) 500

C) 5000

D) 5,000,000

E) none of the above

D) 5,000,000

How many cycles are there in a 1 second of pulsed 5-MHz ultrasound with a duty factor of .01 (1%).

A) 5

B) 500

C) 5000

D) 5,000,000

E) none of the above

E) none of the above

5,000,000 x .01 = 50,000

How many cycles are there in a 1 second of pulsed 5-MHz ultrasound with a duty factor of .01 (1%).

How many cycles did pulsing eliminate?

A) 100%

B) 99.9%

C) 99%

D) 50%

E) 1%

C) 99%

For pulsed ultrasound, the duty factor is always ____________ __________________ one.

less than

_____________ is a typical duty factor for sonography.

A) .1

B) .5

C) .7

D) .9

A) .1

Amplitude is the maximum _________ that occurs in an acoustic variable.

variation

Intensity is the ________________ in a wave divided by ________________.

Power, area

The unit for intensity _____________.

W/cm^2

Intensity is proportional to _____________ squared.

amplitude

If power is doubled and area remains unchanged, intensity is _______________.

doubled

If area is doubled and power remains unchanged intensity is ________________.

halved

If both power and area are doubled, intensity is ___________.

unchanged

If amplitude is doubled, intensity is ______________.

quadrupled

If a sound beam has a power of 10 mW and a beam area of 2 cm^2, the spatial average intensity is __________________ mW/cm^2.

5 mW/cm^2

10mW/2cm2= 5

Attenuation is the reduction in _____________ and _______________ as a wave travels through a medium.

amplitude, intensity

Attenuation consists of _______________, ______________, and ______________.

absorption, reflection, scattering

The attenuation coefficient is attenuation per ____________ of sound travel.

centimeter

Attenuation and the attenuation coefficient are given in units of _____________ and _______________ respectively.

dB. dB/cm

For soft tissues, there is approximately ___________ dB of attenuation per centimeter for each megahertz of frequency.

.5 dB

3 MHz/.5dB

For soft tissue the attenuation coefficient at 3 MHz is approximately ________________.

1.5 dB/cm

The attenuation coefficient in soft tissue __________ as frequency increases

increases

For soft tissue, if frequency is doubled, attenuation is ________________. If path length is doubled attenuation is ________________. If both frequency and path length are doubled, attenuation is __________________.

doubled, doubled, quadrupled

If frequency is doubled and path length is halved attenuation is ________________.

unchanged

Absorption is the conversion _________ to _______________.

sound, heat

Can absorption be greater than attenuation in a given medium at a given frequency?

No

Is attenuation in bone higher or lower than in soft tissue?

higher

The imaging depth (penetration) ____________ as frequency increases.

decreases

If intensity of 4-MHz ultrasound entering soft tissue is 2 W/cm^2, the intensity at a depth of 4 cm is ______________W/cm^2

.32

(.5 * 4 MHz) * 4cm = 8 dB attenuation

intensity ratio is .16 * 2 W/cm2 = .32 W/cm2

If the intensity of 40-MHz ultrasound entering soft tissue is 2 W/cm^2, the intensity at a depth of 4 cm is ______________ W/cm^2

.000 000 02

(.5 *40 MHz) * 4 cm = 80 dB attenuation

.000 000 01 * 2 W/cm2 = .000 000 02 W/cm2

The depth at which half-intensity occurs in soft tissue at 7.5 MHz is _________________.

A) .6 cm

B) .7 cm

C) .8 cm

D) .9 cm

E) 1.0 cm

C) .8 cm

.5 * 7.5 MHz * .8 cm = 3 dB

When ultrasound encounters a boundary with perpendicular incidence, two ___________ of the tissue must be different to produce a reflection (echo).

impedances

With perpendicular incidence, two media _____________ and the incident ____________ must be known to calculate the reflected intensity.

impedances, intensity

with perpendicular incidence, two media ___________ must be known to calculate the intensity reflection coefficient.

impedances

For an incident intensity of 2 mW/cm^2 and impedances of 49 and 51 rayle, the reflected intensity is ____________ mW/cm^3

.0008, 1.9992

True or False

If the impedance of the media are equal, there is not reflection.

True

for perpendicular incidence

With perpendicular incidence, the reflected intensity depends on the _________________.

A) density difference

B) impedance difference

C) impedance sum

D) b and c

E) a and b

D) b and c

B) impedance difference

C) impedance sum

Refraction is a change in ______________ of sound when it crosses a boundary, Refreaction is caused by a change in __________ ____________ at the boundary.

Direction Propagation speed

Under what two conditions does refraction not occur?

Perpendicular incidence, equal media propagation speeds

The low speed of sound in fat is a source of image degradation because of refraction. If incidence angle at a boundary between fat (1.45 mm/μs) is 30 degrees, the transmission angle is ______________ degrees.

32

Redirection of sound in many directions as it encounters rough media junctions or particle suspensions (heterogeneous media) is called __________.

scattering

True or False?

Back scatter helps make echo reception less dependent on incident angle.

True

What must be known to calculate the distance to a reflector?

A) attenuation, speed, and density

B) attenuation and impedance

C) attenuation and absorption

D) travel time and speed

E) density and speed

D) travel time and speed

No reflection will occur with perpendicular incidence if the media ________________ are equal.

impedances

True or False?

Scattering occurs at smooth boundaries and within homogeneous media.

False