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AJT Physics > PHYSICS - US > Flashcards

PHYSICS - US Flashcards

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1
Q

PACS (acronym)

A

Picture Archiving and Communication System

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2
Q

DICOM (acronym)

A

Digital Imaging and COmmunications in Medicine

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3
Q

Speed of sound in soft tissue

A

1540 m/s

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4
Q

Terms for areas of high and low pressure created by sound waves

A

compression and rarefaction, respectively

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5
Q

Bone - higher or lower speed of sound

A

higher speed of sound (dense, less compressible)

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6
Q

Air - higher or lower speed of sound

A

lower speed of sound (less dense, more compressible)

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7
Q

Change in decibels equivalent to a 50% loss in sound intensity

A

-3 dB

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8
Q

Half value thickness definition

A

thickness of tissue that attenuates sound intensity by 3 dB (50%)

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9
Q

Strength of returning echoes is influenced by…

A

magnitude of impedence difference and angle of incidence

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10
Q

Distance traveled in US

A

twice the depth of the reflector (lesion)

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11
Q

No refraction occurs if…

A

incident waves are perpendicular to tissue boundary or no impedence difference between tissues

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12
Q

Snell’s Law

A

angle of refraction increases with increasing speed difference between tissues and increasing angle of incidence

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13
Q

“Edge shadowing”

A

refraction artifact (distal to curvilinear surface); computer assumes linear progression of sound waves

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14
Q

Specular scatter

A

a.k.a. smooth scatter (not really scatter, just reflection); occurs when reflector dimensions are larger than wavelength

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15
Q

Non-specular scatter

A

a.k.a. diffuse scatter; occurs when reflector dimensions are smaller than wavelength

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16
Q

Non-specular scatter increases with…

A

decreasing wavelength (smaller waves “see” more small irregular surfaces which cause scatter)

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17
Q

Relationship between scatter and frequency

A

directly proportional; increased TF => decreased wavelength => increased scatter

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18
Q

Attenuation increases with…

A

TF and tissue depth

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19
Q

Attenuation coefficient for soft tissue

A

0.5 (dB/cm)/MHz

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20
Q

Effect of increasing frequency on HVT

A

decreased HVT (less tissue required to attenuate a higher frequency beam by 50%)

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21
Q

Components of transducer

A

piezoelectric crystals, dampening block, matching layer

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22
Q

Frequency at which maximum intensity waves are produced

A

center (resonance) frequency

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23
Q

Transducer crystal thickness is equal to…

A

half of the wavelength (or wavelength is equal to 2x crystal thickness)

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24
Q

Effect of thinner crystal on frequency

A

thinner crystal => smaller wavelength => higher transducer frequency

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25
Q

Effect of thicker crystal on frequency

A

thicker crystal => longer wavelength => lower transducer frequency

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26
Q

Thin dampening block used for…

A

Doppler imaging (longer SPL, narrow bandwidth)

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27
Q

Thick dampening block used for…

A

B-mode (shorter SPL, broader bandwidth)

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28
Q

Low Q

A

thick dampening block; good for B-mode, broad bandwidth

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29
Q

High Q

A

thin dampening block; good for Doppler, narrow bandwidth

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30
Q

Purpose of matching layer

A

to minimize impedence differences between transducer and patient (gel also helps with this)

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31
Q

Optimal matching layer thickness

A

1/4 of wavelength (or 1/2 of crystal thickness)

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32
Q

Activation type where crystal groups are pulsed sequentially

A

linear array activation (linear or curvilinear probes)

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33
Q

Sector transducers

A

a.k.a. phased array transducers

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34
Q

Activation type where crystal groups are pulsed simultaneously

A

phased array activation (firing times can be adjusted to create constructive and deconstructive effects)

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35
Q

Fresnel zone

A

a.k.a. near field

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36
Q

Fraunhofer zone

A

a.k.a. far field

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37
Q

Length of near field influenced by…

A

transducer frequency and crystal diameter

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38
Q

Divergence in far field influenced by…

A

transducer frequency and crystal diameter

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39
Q

Effect of higher TF on near field and far field

A

longer near field, less divergence in far field (better lateral resolution)

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40
Q

Effect of increased crystal diameter on near field and far field

A

longer near field, less divergence in far field (better lateral resolution)

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41
Q

Best lateral resolution at the…

A

focal zone

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42
Q

Spatial pulse length (SPL) definition

A

of waves per pulse; generally 2 waves (so 2 * wavelength)

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43
Q

Formula for axial resolution

A

SPL / 2 - note that smaller axial resolution is better

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44
Q

Pulse repetition period (PRP) definition

A

time between the beginning of subsequent pulses

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45
Q

Relationship between PRP and depth of FOV

A

directly related; greater PRP => increased depth of FOV

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46
Q

Relationship between PRF and depth of FOV

A

inversely related; greater PRF => decreased depth of FOV

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47
Q

How to: correct aliasing in spectral Doppler

A

increase PRF, increase Doppler angle, decrease TF, increase the scale

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48
Q

Relationship between PRF and frame rate

A

increased PRF => increased frame rate

49
Q

Disadvantage of broadband transducers

A

spectral broadening; this is why thin dampening blocks are used for Doppler imaging

50
Q

Advantages of broadband transducers

A

produce smaller SPLs, can use multiple frequencies, can perform harmonic imaging

51
Q

Bandwidth definition

A

range of frequences produced by a transducer

52
Q

Minimum required separation to differentiate two adjacents objects

A

1/2 of the SPL; a.k.a. the AXIAL RESOLUTION

53
Q

How to: get a smaller SPL (better axial resolution)

A

increase frequency, thicker dampening block, broad bandwidth

54
Q

T/F - axial resolution is depth dependent

A

false - axial resolution is NOT depth dependent

55
Q

Factors affecting lateral resolution

A

beam width, transducer frequency, scan line density

56
Q

Relationship between beam width and lateral resolution

A

thinner beam => better lateral resolution

57
Q

T/F - lateral resolution is depth dependent

A

true - lateral resolution is depth dependent

58
Q

Elevational resolution is dependent on…

A

transducer element thickness

59
Q

Maximum frame rate equation

A

PRF / # of scan lines per frame

60
Q

Effect of increasing number of scan lines

A

improved lateral resolution, slower frame rate

61
Q

Effect of decreasing PRF

A

increased depth of FOV, slower frame rate

62
Q

Effect of using multiple focal zones

A

better lateral resolution, slower frame rate

63
Q

Pixel depth for B-mode, M-mode, and color Doppler

A

8 bits for B-mode and M-mode, 24 bits for color Doppler

64
Q

Setting where echoes that are multiples of the center frequency are collected

A

harmonics

65
Q

Benefits of harmonics

A

improved axial and lateral resolution, increased SNR, decreased reverberation and side lobe artifact

66
Q

Drawback of harmonics

A

echoes are attenuated more rapidly (decreased visualization of deep tissues), more shadowing

67
Q

Benefits of compound imaging

A

edge sharpening, less shadowing

68
Q

Cyst appears more like a hypoechoic mass with…

A

compound imaging

69
Q

Hypoechoic mass appears more cystic with…

A

harmonics

70
Q

Positive Doppler shift indicates flow in which direction?

A

towards transducer; positive Doppler shift = increase in frequency

71
Q

Negative Doppler shift indicates flow in which direction?

A

away from transducer; negative Doppler shift = decrease in frequency

72
Q

Ideal Doppler angle

A

30-60 degrees (relative to long axis of vessel)

73
Q

High frequency transducers are more or less sensitive to blood flow?

A

more sensitive

74
Q

Magnitude of Doppler shift is proportional to…

A

cos(theta), velocity of flowing blood, and TF

75
Q

How to: increase sensitivity for slow flowing blood

A

decrease PRF, increase TF, switch to power Doppler, smaller Doppler angle

76
Q

Wall filter

A

only displays Doppler shifts above a set threshold; removes artifacts, but may also remove signal from slow flowing blood

77
Q

Doppler technique that uses a single gate to yield a spectrum of Doppler shifts

A

spectral Doppler

78
Q

Doppler technique that displays an average of Doppler shifts

A

color Doppler

79
Q

Doppler technique that displays the total number of Doppler shfits

A

power Doppler

80
Q

Doppler technique(s) that demonstrate direction of flow

A

spectral and color Doppler

81
Q

Doppler technique(s) that are susceptible to aliasing

A

spectral and color Doppler

82
Q

Effect of increased power

A

increased SNR, brighter image, greater depth of FOV; may result in artifacts, risk for potential bioeffect

83
Q

ALARA prefers increasing power or gain?

A

gain (no extra energy imparted to patient)

84
Q

Time gain compensation

A

progressive amplification of returning echoes from increasing depths

85
Q

Persistence definition

A

frame averaging to decrease noise; drawback is decreased temporal resolution

86
Q

Thermal index (TI)

A

maximal increase in temperature secondary to energy deposition

87
Q

TI for OB imaging

A

<0.7

88
Q

TI where US should not exceed 30 min

A

1.0-1.5

89
Q

TI where US should not exceed 1 min

A

2.5-3.0

90
Q

TI where US should not be used

A

> 3.0

91
Q

Mechanical index (MI)

A

likelihood of cavitation

92
Q

Relationship between MI and frequency

A

inversely related; high frequency => lower MI

93
Q

FDA limits for MI

A

1.9 for an adult, 1.0 for OB

94
Q

Cavitation type resulting in tissue damage - stable or transient

A

transient cavitation

95
Q

Cavitation is most likely to occur with ____ frequency and ____ pressure

A

low frequency and high pressure

96
Q

All US equipment required to display TI and MI by who?

A

FDA

97
Q

Tissue damage is proportional to…

A

TI, MI, and exposure time

98
Q

1st trimester US recommendations

A

no Doppler, keep TI <1.0; scanning uterine arteries is ok

99
Q

Equipment testing QC interval

A

semi-annual (per ACR)

100
Q

Artifact: echoes outside main beam are erroneously placed in main beam

A

side lobe artifact; due to radial expansion of piezoelectric crystals; occurs more with linear array transducers

101
Q

Artifact: duplicated SMA

A

refraction artifact; computer assumes linear progression of sound waves

102
Q

Nyquist limit

A

1/2 of the PRF; Doppler shifts above Nyquist limit result in aliasing

103
Q

Burst of color (Doppler) filling the screen

A

flash artifact; due to transducer or patient motion

104
Q

Effect of increasing power (or transmit gain) on resolution

A

increased power => beam widening => worse lateral resolution

105
Q

Relationship between Doppler imaging and axial resolution

A

longer SPLs are required to determine Doppler shifts => worse axial resolution

106
Q

Risk-benefit discussion required at what TI and MI?

A

TI >1.0 and MI >0.5

107
Q

Difference between reverberation and comet tail artifact

A

distance between reflective surfaces in comet tail artifact is <1/2 SPL

108
Q

Artifact: multiple evenly spaced lines in the axial direction

A

reverberation artifact

109
Q

Typical depth of penetration for 3 MHz

A

20 cm

110
Q

Typical depth of penetration for 10 MHz

A

6 cm

111
Q

Effect of increasing TF on Doppler shift, sensitivity to slow flow, and aliasing

A

increased TF => increased magnitude of detected Doppler shift, increased sensitivity to slow flow, more prone to aliasing

112
Q

Determinants of impedance

A

density and speed of sound in a given tissue

113
Q

Sound intensity reduction with -10, -20, and -30 dB

A

reduction to 10%, 1%, and 0.1 %, respectively

114
Q

TF affects axial resolution, lateral resolution, or both?

A

both

115
Q

Effect of frequency on tissue heating and cavitation

A

increasing frequency => increases heating, decreases cavitation

116
Q

Cause of posterior acoustic enhancement and shadowing

A

material attenuates sounds less than or greater than that of surrounding tissue

117
Q

Cause of tissue vibration artifact

A

turbulent flow

118
Q

Speed displacement artifact

A

echoes traveling through an area of decreased speed (e.g. fat) are erroneously placed at increased depth (due to longer round trip time)

AJT Physics (7 decks)

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