Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Radiology Residency > Ultrasound Physics > Flashcards

Ultrasound Physics Flashcards

1
Q

Sound is a traveling variation in ______.

A

Pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Sound involves ______ motion in the medium through which it travels.

A

Mechanical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the 3 acoustic variables?

A

Pressure
Density
Particle vibration
- they are the quantities that vary in a sound wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are rarefactions & compressions?

A

Rarefactions = regions of low pressure & density

Compressions = regions of high pressure & density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is density?

A

Density = concentration of matter (mass per unit volume)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Sound is a _______, _________ wave in which back-and-forth particle motion is parallel to the direction of travel

A

Mechanical, longitudinal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

If the up and down motion of a water surface is perpendicular to the direction of wave travel it is what type of wave?

A

Transverse or shear wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the definition of frequency? And what is it’s unit?

A

Freq = # of cycles that occur in 1 second

Hertz (1 Hz =1 cycle/sec)
1 kHz = 1000Hz
1 MHz = 1,000,000Hz

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The positive and negative halves of a pressure cycle correspond to what, respectively?

A

Regions of compression & rarefaction

(Higher pressure = denser medium & vice versa)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the definition of period? And what is it’s unit?

A

Period = time it takes for 1 cycle to occur

Common unit for period = microseconds ( 1 microsecond = 0.000001 second) e.g. the period for 5MHz U/S = 0.2 microseconds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the equation for period?

A

T (period in microseconds) = 1/ freq (Mhz)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

If the period decreases, what happens to freq?

A

If period decreases –> freq increases.

If freq inc –> period dec

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the definition of wavelength? what is the common unit of wavelength?

A

Wavelength = length of SPACE/DISTANCE that 1 cycle takes up

Aka the length of cycle from front to back

Millimeters (1 mm = 0.001m)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

For a propagation speed of 1.54 mm/s and a freq of 5MHz, what is the wavelength?

A

0.31mm

(Eq:: wavelength = propagation speed [mm/us] / freq [MHz])

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is propagation speed (c)? What is it’s unit?

A

The speed with which a waves moves through a medium

Units = m/s and mm/microsecond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the relationship between wavelength, propagation speed, & freq?

A

Wavelength = propagation speed (mm/microsecond) / freq (MHz)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

If wavelength increases —> freq ________

A

Decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What primarily determines propagation speed?

A

The medium, specifically it’s stiffness (hardness)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is stiffness?

A

Stiffness = resistance of a material to compression

Stiffer media –> HIGHER sound speeds (gas < liquid < solid)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the average propagation speed in soft tissues?

A

1540 m/s or 1.54 mm/microsecond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Shear waves travel ______ in comparison to longitudinal waves.

A

More slowly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

The average propagation speed in fat is approximately what percentage in comparison to soft tissue?

A

~6% lower

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Propagation speed in any medium depends on the ______ and ______ of the medium.

A

density (p) and stiffness

Density = mass density = mass per unit volume

Stiffness aka hardness or bulk modulus of elasticity (B)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the equation to for propagation speed?

A

c (m/s) = [ B (N/m^2) / density (kg/ m^3) ] ^ 0.5

*In general, stiffness differences dominate the effect on propagation speed more than mass density (therefore solids have higher propagation speeds than liquids)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How does propagation speed affect pressure and therefore the overall wave shape?

A

Higher pressure portions of the wave travel faster than lower pressure portions –> non sinusoidal shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the term for propagation in which speed depends on pressure & changes wave shape?

A

Nonlinear propagation

  • nonlinear propagation results in additional freq that are even & odd multiples of the fundamental freq ( a continuous - not pulsed - sinusoidal waveform is characterized by a SINGLE freq [this freq equals the # of cycles/second]
  • while the shape becomes less sinusoidal, the harmonic become STRONGER
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is pulse repetition freq (PRF)? What is the common unit of measurement?

A

PRF = # of PULSES that occur in 1 second

kHz ( 1kHz = 1000Hz)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the pulse repetition period (PRP)? What is the common unit of measurement?

A

PRP = time from the beginning of 1 pulse to the beginning of the next

Milliseconds (0.001 seconds)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the formula for PRP?

A

PRP (ms) = 1 / PRF (kHz)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

If PRP decreases, what happens to PRF?

A

PRP decreases while PRF increases b/c when more pulses occur in 1 second, the time between them decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is pulse duration (PD)?

A

Pulse duration is the time it takes for one pulse to occur

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is pulse duration (PD) equal to? / what is the formula?

A

PD = period (T, the time for 1 cycle) x # of cycles in the pulse (n)

PD = T (microseconds) x n
- expressed in microseconds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What occurs to PD if the # of cycles is decreased? what about if the freq is increased?

A

Pulse duration DECREASES if the # of cycles is decreased

Pulse duration DECREASES if the freq is increased (inc freq reduces the period)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Slower pulses _________ image quality

A

Improve

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What is duty factor (DF)?

A

DF = the fraction of time that pulsed U/S is on

  • In CW U/S the DF = 1 (b/c U/S is on 100% of the time)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

DF is the _______ of the _____ that the sound is on

A

fraction; PRP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Higher PRFs —> ______ DF

A

Increased DF (b/c less listening time between pulses)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What is the effect on DF is the PRF is increased? what is the period is increased?

A

Inc PRF –> Inc DF

Inc period –> Inc DF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What is the equation for DF?

A

DF = PD / PRP

DF = PD (microseconds) x PRF (kHz) / 1000 (KHz/MHz)
….this factor of 1000 converts KHz to MHz to be consistent with microseconds of PD

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

DF for Doppler ultrasound is ______in comparison to sonography?

A

Higher (0.5 - 5%) b/c of longer PDs

(typical sonography ranges from 0.1-1.0% DF)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What is spatial pulse length (SPL)? What is the unit?

A

SPL = length of a pulse from front to back

Millimeters (mm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

If freq is increased, what happens to SPL? What if # of cycles increases?

A

SPL decreases (b/c wavelength decreases with inc freq)

If # of cycles inc –> Inc SPL

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

The actual # of cycles that occur in 1 second in pulsed U/S depends on the _____.

A

DF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

If the DF is 0.01 and the freq is a 5MHz pulsed wave, what is the actual # of cycles per second?

A

0.01 DF = 1%

0.01 x 5,000,000 = 50,000 cycles/second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

What is bandwidth?

A

Range of freq contained in a pulse

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

How does a few # of cycles affect the bandwidth?

A

Fewer # of cycles = shorter pulses –> higher # of freq = broader bandwidth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

What is fractional bandwidth?

A

Fractional bandwidth = Bandwidth / operating freq

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

_______ and ______ are indicators of strength of the sound.

A

Amplitude; intensity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What is amplitude?

A

Amplitude = maximum variation that occurs in an acoustic variable aka how far a variable gets away from its normal, undisturbed value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

What is power?

A

Power is the rate of at which energy is transferred from one part of a system to another

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

What is the equation for power? What is the unit of measurement?

A

Power = Energy transferred / time required to transfer energy

Watts (W) & milliwatts (mW)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What is intensity?

A

Intensity = the rate at which energy passes through a unit area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

What is the equation for intensity? What are the units of measurement?

A

Intensity = power [mW] / area (over which power is distributed) [cm^2]

Miliwatts per centimeter squared (mW/ cm^2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

What happens to the intensity if the power is increased? Area is increased? Area is decreased?

A

Inc intensity

Dec intensity (power less concentrated)

Inc intensity (power more concentrated)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

Intensity is proportional to __________

A

Amplitude^2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

If amplitude is double, intensity is ________.

A

Quadrupled

Intensity = Amplitude^2

(and vice versa, if amplitude is halved, intensity is quartered)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Intensity is NOT constant across a sound beam, but is usually highest in the ______ and falls off near the ________. Also, intensity is NOT constant within pulses, but rather starts out _____ and then _______ towards the end of the pulse.

A

Center; periphery

High; decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

What is the relationship between temporal average intensity, pulse average intensity, and DF.

A

I(TA) = I(PA) x DF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

As an unfocused sound beam travels through a medium, the _______ and _______ will decrease. This is termed __________.

A

Amplitude; intensity; attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

What is absorption?

A

Absorption = conversion of sound to heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

Attenuation can occur by what 3 means?

A

Absorption; reflection; scatter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

What is the dominant factor that contributes to attenuation of sound in soft tissues?

A

Absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

Scatter occurs when sound encounters ____ ______ and _____ _______.

A

tissue surfaces; heterogeneous tissues

64
Q

The generation of echoes by the ______ and ______ of sound is crucial to image production.

A

Reflection; scattering

65
Q

What is the unit of measurement of attenuation?

A

Decibel (dB)

66
Q

What is the attenuation coefficient? and what are its units?

A

Attenuation coefficient = attenuation that occurs with EACH centimeter the sound wave travels

Units = dB/cm

67
Q

3 dB corresponds to an intensity ratio of ______.

10dB corresponds to an intensity ratio of ____.

A

3dB = intensity ratio of 1/2 (aka 50% reduction in intensity)

10dB = intensity ratio of 1/10 (aka 90% reduction in intensity)

68
Q

What is the formula to determine attenuation in dB?

A

Attenuation (dB) = attenuation coefficient (dB/cm) x L (cm)

L = path length (aka how far the sound has traveled in cm)

69
Q

If path length increases, attenuation _______. If freq increases, attenuation _______.

A

Increases; increases

70
Q

_____dB of attenuation per centimeter for each MHZ of freq

A

0.5

71
Q

What is the average attenuation coefficient (dB/cm) in soft tissues?

A

Attenuation coefficient (dB) = 1/2 x freq (MHz) x L (cm)

72
Q

If 4MHz U/S with 10mW/cm^2 intensity is applied to a soft tissue surface, what is the intensity 1.5cm into the tissue?

A

1) Multiple freq by 1/2 to yield attenuation coefficient of 2 dB/cm.
2) Multiple attenuation coefficient by (2 dB/cm) by path length (1.5cm) to yield an attenuation of 3 dB.
3) An attenuation of 3dB corresponds to an intensity ratio of 0.5. (aka 50% of the original intensity remains after sounds travels through this path).
4) Multiple intensity ratio (0.5) by original intensity (10mW/cm^2) to yield end intensity of 5mW/cm^2

73
Q

With respect to perpendicular incidence, sound may be _________ or ________. Most often, _______ occur.

A

reflected back into 1st medium; transmitted into 2nd medium; both

74
Q

True or false, in the case of perpendicular incidence the transmitted sound changes direction.

A

False

75
Q

When discussing incidence, the intensities of the reflected sound (the echo) & the transmitted sound depend on the ____________ at the boundary and the _________ of the media on either side of the boundary.

A

Incident intensity; impedances

76
Q

What is the definition of impedance?

A

Impedance determines how much of an incident sound wave is reflected back into 1st medium & how much is transmitted into 2nd medium

77
Q

What is the formula for impedance? And what are its units?

A

Impedance = density (p) of a medium x propagation speed

Rayls (z)

z = p (kg/m^3) x c (m/s)

78
Q

What happens to impedance if density increases? If propagation speed increases?

A

Increases; increases

79
Q

The sum of the reflection and transmission coefficients must equal ____.

A

One (e.g. 100%)

80
Q

The _____ the difference between the impedances, the _____ the echo.

A

Greater; stronger

81
Q

If media impedances are the same, what happens?

A

No echo is produced

82
Q

For impedances of 40 and 60 rayls, determine the intensity reflection (IRC) & transmission coefficients (ITC) .

A

IRC = [ 60 - 40 / 60 + 40] ^2
= (20 / 100) ^2
= (0.2) ^2 –> 0.04

ITC = 1 - 0.04 –> 0.96

83
Q

_____ angle always equals the ______ angle.

A

Reflection; transmission

84
Q

A change in the direction of sound when it crosses a boundary is called ____.

A

Refraction

85
Q

If the propagation speed in the 2nd medium is GREATER than the 1st medium, the transmission angle is ______ than the incidence angle

A

greater

Propagation speed (c)
c1 < c2 –> Incidence angle < transmission angle

c1 > c2 –> incidence angle > tranmission angle

86
Q

What are the two requirements for refraction to occur?

A

1) Oblique incidence
2) Different propagation speed on either side of the boundary

87
Q

What is scatter?

A

The redirection of sound in many directions by rough surfaces or by heterogeneous media

88
Q

How do contrast agents produce echoes?

A

Due to the impedance mismatch between suspended particles & suspending medium (impedance of gas is MUCH LESS than that of the suspending liquid)

89
Q

The distance to a reflector is calculated by the range equation, which is what?

A

d (mm) = 1/2 [ c (mm/us) x t (us)]

distance = 1/2 (propagation speed x ROUND TRIP
time)

90
Q

What is the purpose of damping (backing) material?

A

Reduces pulse duration & spatial pulse length –> improves axial resolution

  • Additionally, reduces U/S amplitude therefore decreasing the efficiency & sensitivity of the system (aka the ability to detect weak echoes….this is the tradeoff for better resolution)
91
Q

What is purpose of the matching layer?

A

Improve sound transmission through tissues

92
Q

Operating freq (resonance freq) is determined by what?

A

1) Propagation speed of the element material
2) Transducer element thickness

93
Q

Operating/resonance freq is such that the _______ of the element corresponds to _______ a wavelength in the element material.

A

thickness; 1/2

94
Q

____ elements –> higher frequencies

A

Thinner (b/c wavelength decreases while freq inc)

95
Q

What is the equation relating resonance freq to transducer element thickness?

A

Freq = propagation speed (mm/us) / 2 x thickness

96
Q

what is the advantage of voltage excitation when used selectively with wide bandwidth transducers?

A

Can operate the same transducer at more than 1 freq

97
Q

Wide bandwidth transducers allow use of harmonic imaging, which is what?

A

In harmonic imaging, echoes of 2x the freq ae sent into the body & received to improve the image

98
Q

Reducing the # of cycles in ultrasound pulses _______ their bandwdth.

A

Broadens

99
Q

The width in the scan plane determines the _______resolution.

A

Lateral

100
Q

What does the width perpendicular to the scam plane determine?

A

The extent of the section thickness artifact

101
Q

Bea width at any location depends on _______, _______, and _______.

A

Wavelength
Aperture
Distance from the transducer

102
Q

While the element or lens is increasingly curved, the focus moves ______ to the transducer.

A

Closer
(this causes beam width at the focus to decrease)

103
Q

The limit of beam narrowing depends on _______, _______, and ________.

A

Wavelength
Aperture
Focal length

104
Q

For a rectangular aperture, how does one calculate the minimum beam width?

A

Focal beam diameter =
2 ( wavelength x focal length) / aperture

105
Q

Beam width narrows to ___ the disk diameter at the near zone length and then ______ to the disk diameter at twice the near zone length.

A

1/2

widens

106
Q

Why do lenses focus?

A

B/c the propagation speed through them is higher than in tissues

107
Q

_______at the surface of the lens forms the beam so that a focal region occurs.

A

Refraction

108
Q

The ______ is the size of the group of elements energized to produce each pulse.

A

Aperture

109
Q

Multiple focal zones can be acquired leading to improved detail resolution, however this degrades what?

A

Temporal resolution ( b/c the frame rate is reduced due to the multiple pulses per scan line)

110
Q

An Increased or decrease in the curvature of the delay pattern moves the focus ______ or _______, respectively.

A

Shallower; deeper

111
Q

To maintain the same focus beam width at increasing focal lengths, the aperture must be _______.

A

Increased

112
Q

What is apodization and how does it work?

A

Reduces the effect of grating lobe artifact.
Outer elements are driven at lower amplitudes than inner elements (downside is loss of resolution)

113
Q

Axial and lateral resolution depend on the ______ and ______ of the ultrasound pulses, respectively.

A

Length; width

114
Q

What is axial resolution?

A

The minimum reflector separation required along the direction of sound travel to produce separate echoes.

115
Q

What is the most important factor for determining axial resolution?

A

Spatial pulse length

116
Q

What is the formula for determining axial resolution?

A

AR (mm) = SPL (mm) / 2

117
Q

How are the number of cycles in each pulse reduced?

A

Transducer damping

118
Q

What is lateral resolution?

A

The minimum reflector separation in the direction perpendicular to the beam direction that can produce 2 separate echoes

(this is equal to the beam width)

119
Q

What is the equation for lateral resolution?

A

LR (mm) = beam width (mm)

120
Q

To avoid ______ _______, all echoes from one pulse must be received before the next pulse is emitted.

A

Echo misplacement

121
Q

Imaging depth (aka penetration) in cm multiplied by PRF (kHz) must not exceed _____ if echo misplacement is to be avoided

A

77 cm/ms

122
Q

While operating frequency is reduced & penetration increases –> PRF is _____to avoid echo misplacement

A

Reduced

123
Q

Power ratio (dB) = ???

A

Voltage ratio squared
I.e. If input voltage amplitude to an amplifier is 2mV and the output voltage is 200 mV, the voltage ratio is 200/2, or 100. The power ratio is 100^2 = 10,000

124
Q

3 dB corresponds to a power gain of ?
10 dB corresponds to a power gain of ?

A

3 db = power gain x2
10 dB = power gain x 10

125
Q

What is time gain compensation?

A

Equalizes differences in received echo amplitudes caused by different reflector depths (aka increased attenuation from greater imaging depths is compensated for)

126
Q

The time gain slope can be expressed in what units?

A

Decibels of gain per cm of depth
The slope should correspond to the average attenuation coefficient in the tissue if properly adjusted

127
Q

_____ and ______ determine the maximum imaging depth

A

Attenuation; maximum amplifier gain

128
Q

What is the maximum amplifier gain determined by?

A

Noise

129
Q

The _____ ________ of the digitizer is determined by the digitizing frequency

A

Temporal precision

130
Q

Each cycle of voltage must be interrogated at least _____ to determine its frequency/

A

2 times

131
Q

What is the average soft tissue attenuation?

A

0.5 dB/cm-MHz
(Average attenuation is 1dB/cm-MHz when the centimeter value is the distance from the transducer to the reflector; sound must travel twice this distance so the attenuation # doubles)
*Typical TCG slopes ~1 dB/cm-MHz

132
Q

What are the 3 functions of a signal processor?

A

Amplitude detection
Bandpass filtering
Compression (dynamic range reduction)

133
Q

A smaller dynamic range presents a _____ contrast image.

A

Higher

134
Q

What is persistence?

A

The averaging of sequential frames (frame averaging) to provide a smoother image appearance & to reduce noise

135
Q

Speckle reduction improves _______ _____ and _____ ______.

A

Dynamic range
Contrast resolution

136
Q

Detail resolution is usually limited by _________ and _______ rather than by pixel density in the memory.

A

Spatial pulse length
Beam width

137
Q

The analog-to-digital converter (ADC) is part of the ____ _____. And the digital-to-analog converter (DAC) is part of the ____ _______.

A

Beam former
Image processor

138
Q

How does an a change in the number of bits per pixel affect contrast resolution?

A

More bits per pixel (more gray shades)–> improved contrast resolution

139
Q

Greater # of shades or ______ dynamic range –> improved contrast resolution

A

Reduced

140
Q

What is dynamic range?

A

The ratio of the largest to the smallest amplitude or power that a system can handle
- expressed in dB

141
Q

Greater dynamic range values indicate what?

A

The ability to detect weaker echoes, aka greater sensitivity

142
Q

What is frame rate?

A

The # of images stored per second

143
Q

What is temporal resolution?

A

The ability of a display to distinguish closely spaced events in time & to present rapidly moving structures correctly.
-Expressed in milliseconds

144
Q

If frame rate increases, temporal resolution _____.

A

Increases (less time elapses between one frame to the next)

145
Q

What is the formula for PRF is there are more than 1 focuses?

A

PRF (Hz) = n x LPF x FR (Hz)

n = # of foci
LPF = lines per frame
FR = frame rate

146
Q

Must occur to PRF if you want to increase the # of foci? Increase the # of LPF? Increase the FR?

A

PRF must increase in every instance

147
Q

In order to avoid echo misplacement, what must occur to PRF if penetration increases?

A

PRF must decrease (must ensure that all echoes from one pulse are received before another pulse is emitted)

148
Q

Lower operating frequency –> _____ penetration —> _____ PRF

A

Increased
Decreased

149
Q

When image depth is increased, what happens to FR?

A

FR decreases

150
Q

Echo misplacement is also called what?

A

Range ambiguity artifact

151
Q

Temporal resolution in A and M modes is equal to what?

A

Pulse repetition period (b/c each pulse produces a new line of echo information)

152
Q

What is harmonic imaging?

A

The fundamental (transmitted) frequency echoes are filtered out and the second harmonic frequency echoes are accepted

153
Q

What are the 3 primary ways in which harmonic imaging improves image quality?

A

1) Harmonic beam much narrower –> improves lateral resolution [harmonics are generated only in the highest intensity portion of the beam]
2) Eliminates grating lobe artifacts [extra beams not strong enough to generate the harmonics]
3) Reduced/eliminated image degradation b/c harmonic beam is generated at a depth beyond were some artifactual problems occur (e.g. superficial reverberation)

154
Q

What is spatial compounding?

A

Technique in which scan lines are directed in multiple directions by phasing so that structures are interrogated more than once by the U/S beam

155
Q
A

Radiology Residency (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions