Chapter 1 Essentials of Ultrasound

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"Mechanical energy transmitted by pressure waves in a medium" is an accurate description for:

A) audible sound only
B) all types of sound
C) ultrasound waves only
D) High-energy sound waves only

B) all types of sound

this is a general definition applicable to any sound wave


SOund waves can travel through each of the following except?

A) air
B) water
C) vacuum
D) steel

C) vacuum

a vacuum has no molecules or "particle" to transmit sound waves


Which of the following properties are common to all sound sources

A) They are larger than a wavelength
B) They cause vibrations in the medium
C) They produce transverse waves
D) they can not move back and forth

B) They cause vibrations in the medium

the only property applicable to all sound sources is they vibrate and consequently produce vibrations in the medium


The speed of sound depends on which of the following?

A) wavelength
B) frequency
C) Medium
D) amplitude

C) Medium

sound speed depends on the density and stiffness of the medium


In a sound wave, regions where the pressure is higher than normal are called regions of:

A) rarefraction
B) attenuation
C) compression
D) amplitude

C) compression

regions of compression have a higher density and higher pressure. The opposite is regions of rarefaction.


Which of the following is a type of sound wave that can propagate through soft tissue?

A) transverse wave
B) longitudinal wave
C) shear wave
D) radio wave

B) longitudinal wave

only longitudinal sound waves travel through soft tissue; transverse waves (another name for shear waves) are severely attenuated; radio waves are not sound waves


Units for pressure are:

A) Joules
B) Newtons
C) Pascals
D) None of these; pressure is unitless

C) Pascals

joules are units of energy
Newtons are units of force


The time for one cycle of a wave is the

A) Duty factor
B) Period
C) wave duration
D) phase

B) Period


If the frequency is 1 MHz, the period is

A) 1,000,000s
B) 100s
C) .01s
D) .000001

D) .000001

period is 1/frequency = 1/1,000,000 = .000001


Deci-, centi-, milli-,and micro- mean?

A) 100, 1000, .1, and .000001
B) .1, 100, .001, and .000001
C) .1, .01, .001, and .000001
D) 10, 100, .001, and .000001

C) .1, .01, .001, and .000001

deci = 1/10
centi = 1/100
milli = 1/1000
micro = 1/1,000,000


WHich of the following lists correctly arranges the materials according to their speeds of sound, from lowest to highest?

A) water, tissue, bone, air
B) bone, air, tissue, water
C) air, bone, water, tissue
D) air, water, tissue, bone

D) air, water, tissue, bone

air has the lowest and bone has the highest, water has a lower speed than average soft tissue


The average speed of sound in soft tissue is taken to be?

A) 1300 m/s
B) 1460 m/s
C) 1540 m/s
D) 450 m/s

C) 1540 m/s

1540 m/s = 1.54 mm/μs = .154 cm/s


The distance a wave travels during one period of oscillation of the source is the:

A) period
B) wavelength
C) speed of sound
D) depth of penetration

B) wavelength

wavelength is also sound speed divided frequency and for soft tissue it 1.54 mm/f(MHz) where f(MHz) is the frequency given in MHz


The wavelength for 5MHz sound wave in tissue is about?

A) .3 mm
B) 3 mm
C) 1.54 m
D) 1.54 mm

A) .3 mm

wavelength = 1.54 mm / f(MHz) = 1.54 mm / 5 = .3mm


If the frequency doubles the wavelength?

A) double
B) halves
C) increases four times
D) does not change

B) halves

wavelength is inversely proportional to frequency


The acoustic impedance is found by multiplying the

A) attenuation
B) density by the speed of sound
C) density by the wave amplitude
D) speed of sound by the particle displacement

B) density by the speed of sound

this is the definition for the characteristic impedance of material


If the density of Material B is 10% greater than that of Material A, and they have equal speeds of sound and attenuation values, the impedance of B is ___________ that of A.

A) the same as
B) 1% higher than
C) 10% lower than
D) 20% higher than

C) 10% lower than

impedance is directly proportional to the density, so if latter increases by 10% so does the impedance


If the impedance on one side of an interface is two times the impedance on the other, the amplitude reflection coefficient is?

A) 1
B) .33
C) .1
D) .033

B) .33

call the impedance of material 1 "1" that of material 2 "2".
R= (2-1)/(2+1) = .33
any other number will work as long as material 2's impedance is two times that of material 1


About what percent of the incident intensity is reflected at a soft tissue-bone interface?

A) 2% or lower
B) between 10% and 60%
C) 100%
D) 200%

B) between 10% and 60%

which can be verified by using impedance values in the text


About what percent of the incident intensity is reflected at a soft tissue-soft tissue interface?

A) 2% or lower
B) between 10% and 60%
C) 100%
D) 200%

A) 2% or lower


About what percent of the incident intensity is reflected at a soft tissue-air interface?

A) 2% or lower
B) between 10% and 60%
C) 100%
D) 200%

C) 100%

essentially all the sound is reflected at a tissue-air interface


In order to produce refraction what condition(s) must be met at an interface?

A) perpendicular incidence, different sound speeds
B) perpendicular incidence, same sound speeds
C) nonperpendicular incidence, different sound speeds
D) perpendicular incidence, different acoustic impedance

D) perpendicular incidence, different acoustic impedance

for refraction to occur, the sound must be incident at an angle that is not perpendicular and the sound speeds must be different at the interface.


Snell's law predicts?

A) the direction of the reflected beam
B) the amplitude of the incident beam
C) the directions of the transmitted beam
D) the amplitude of the transmitted beam

C) the directions of the transmitted beam

Snell's law relates the transmitted beam direction to the incident beam angle and the speeds of sound at the interface. Given any three of the four quantities lets you solve for the forth


For angle between 0 degrees and 9 degrees, as the angle increases, the sine of that angle?

A) does not change
B) increases
C) decreases

B) increases

the sine increases as the angle increases from 0 to 90 degrees


The best way to describe the role of ultrasonic scattering in diagnostic imaging is it

A) gives rise to diagnostic information
B) is responsible for echo enhancement
C) must be eliminated to give clear detail
D) results in greater acoustic exposure to the patient

A) gives rise to diagnostic information

scattering is the main source of echo signals in ultrasonography


Interfaces that scatter ultrasonic energy are usually considered those that

A) are much larger than the ultrasonic beam
B) are much larger than the wavelength
C) are the size of or smaller than the wavelength
D) surround soft tissue-bone interface

C) are the size of or smaller than the wavelength

we usually say scatterers are smaller than the wavelength


One advantage a diffuse reflector provides over a specular reflector is

A) exhibits less angular dependence of the reflection
B) does not attenuate the ultrasound beam
C) exhibits a greater acoustic impedance change
D) intersects only a small fraction of the beam

A) exhibits less angular dependence of the reflection

it reflects sound waves in all directions, so there is less of a dependance of the detected echo amplitude on the angle of the surface


Decibels provide a convenient way to express the ________ two amplitudes of intensities

A) sum of
B) differences between
C) product of
D) ratio of

D) ratio of

decibels are used to quantify the ratio of two amplitudes or intensities


Which statement is incorrect regarding ultrasound absorption?

A) it is part of attenuation
B) sound energy is converted to heat
C) it increases when the frequency increases
D) it is greater in fluid cavities

D) it is greater in fluid cavities

at MHz frequencies, sound absorption is very low in fluid cavities in the body, such as the bladder, compared to absorption in soft tissue


The rate of attenuation, or attenuation coeffient, is expressed in?

A) µW/cm^2
B) µW
C) dB/cm
D) dB/cm^2

C) dB/cm

dB/cm is used to express the attenuation coefficient


If the attenuation coeffient of a tissue is .5 dB/cm at 1 MHz, it is probably _____ at 5 MHz

A) .1 dB/cm
B) .5 dB/cm
C) 2.5 dB/cm
D) 12.25 dB/cm

C) 2.5 dB/cm

attenuation can be assumed to be proportional to frequency. you are given the attenuation coeffient at 1 MHz, so multiply by 5 to get the value at 5 MHz


Echo "enhancement" results from a structure having a:

A) Higher speed of sound than adjacent material
B) higher acoustic impedance than adjacent material
C) lower attenuation than surrounding material
D) Greater absorption rate than surrounding material

C) lower attenuation than surrounding material

enhancement results from good through-transmission in a mass or fluid-filled cavity


The attenuation of an ultrasound pulse traveling 12 cm in a tissue that has an attenuation coefficient of 1 dB/cm is?

A) 1/12 dB
B) 1 dB
C) 12 dB
D) 13 dB

C) 12 dB

attenuation (in dB) is the attenuation coeffient
(dB/cm) x distance (cm) = 1 dB/cm x 12 cm


WHich of the following conditions are minimal requirements for a sound wave to be classified as ultrasonic?

A) frequency above 10 kHz
B) frequency above 20 kHz
A) frequency above 10 kHz; intensity greater than 1 W/m^2
A) frequency above 20 kHz; longitudinal wave
A) frequency above 10 kHz; underwater propagation.

B) frequency above 20 kHz

high-frequency (grater than 20 kHz) sound waves traveling through media besides water are still ultrasound; the waves can be other than longitudinal if the medium will support their transmission.


Calculate the wavelength for a 2 MHz ultrasound beam in soft tissue.
speed of the sound is 1540 m/s
f = 2 MHz = 2x10^6 s

card image

.77 mm

λ = (1540 m/s) / (2 x 10^6) = .00077 m = .77 mm


Calculate the wavelength for a 2 MHz ultrasound beam in soft tissue.

.154 mm

λst = 1.54 mm /f(MHz)
λst = 1.54 mm/10
λst = .154 mm

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