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6494 Regional Anesthesia > 2.1 Ultrasound Physics > Flashcards

2.1 Ultrasound Physics Flashcards

1
Q

Ultrasound is:

A

mechanical energy (vibration) that travels through a medium (tissues)

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2
Q

what is the unit of measurement for ultrasound?

A

Hz (the number of sound waves/second)

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3
Q

medical ultrasound is in the range of:

A

2.5-15 MHz (Mega Hz)

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4
Q

human hearing is in the range of:

A

20-20,000 Hz

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5
Q

main physical property behind ultrasound:

A

the piezoelectric effect

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6
Q

the piezoelectric effect

A

Property of certain materials to create voltage when mechanically deformed; * produced by passing an electrical current through a piezoelectrical crystal

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7
Q

pulse repetition frequency

A

the number of pulses per unit of time

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8
Q

amplitude

A
  • The strength of the sound beam.
  • The difference between the maximum value and the average
  • NOT the difference between the maximum and minimum values of the wave.
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9
Q

power

A
  • Rate of work, ability to do work.
  • Units: Watts
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10
Q

Power ______ as the sound propagates through the body?

A

decreases

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11
Q

Intensity

A
  • Concentration of energy in a sound beam.
  • Units: watts/cm2
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12
Q

Intensity is _______ proportional to power.

A

directly

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13
Q

compression

A

high pressure waves

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14
Q

rarefraction

A

low pressure waves

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15
Q

Zones: near

A

the region of a sound beam in which the beam diameter decreases as the distance from the transducer increases

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16
Q

Zones: focal

A

the region where the beam diameter is most concentrated giving the greatest degree of focus

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17
Q

Where is the BEST (sharpest) image obtained?

A

It depends on the transducer

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18
Q

Zones: Far

A

the region where the beam diameter increases as the distance from the transducer increases

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19
Q

absorption

A

loss of US energy due to its conversion to another form, such as heat or intracellular vibration

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20
Q

acoustic impedance

A

the resistance to sound transmission through a medium

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21
Q

attenuation

A

loss of sound energy when the wave travels through tissue due to absorption, reflection, and scattering of sound energy

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22
Q

doppler effect

A

a change in sound frequency due to motion (i.e. flow) between a sound source and the receiver (target)

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23
Q

doppler effect: change in sound frequency is said to be POSITIVE when…

A

the receiver is moving toward the source

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24
Q

doppler effect: change in sound frequency is said to be NEGATIVE when…

A

the receiver is moving away from the source

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25
Q

echnogenicity

A

degree of brightness displayed in an ultrasound image

influenced by the amount of beam returning to the transducer (reflected) after it encounters a target structure

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26
Q

frequency

A

number of cycles/sec

INVERSE of wavelength

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27
Q

interface

A

boundary layer between tissue layers of different acoustic properties – why we use gel
(i.e. change in medium from one type to another)

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28
Q

resolution

A

ability to distinguish 2 structures that lie close to each other

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29
Q

high resolution, two structures appear:

A

separate

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30
Q

low resolution, two structures appear:

A

like one

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31
Q

scattering

A

process by which ultrasound waves are force to deviate from reflection due to irregularities in the reflective surface

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32
Q

wavelength

A

distance between two consecutive peaks or troughs of a wave

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33
Q

period

A

the time required to complete a single cycle

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34
Q

unit of measurement for period:

A

time units—seconds, hours, milliseconds

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35
Q

the period is determined by:

A

the sound source (transducer)

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36
Q

frequency (repeat)

A

the number of cycles of acoustic variable that occur in one second

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37
Q

unit of measurement for frequency:

A

Hzf

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38
Q

Frequency and period are __________ related

A

inversely

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39
Q

frequency is determined by:

A

the sound source (transducer)

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40
Q

wavelength

A

length or distance of a single cycle

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41
Q

unit of measurement for wavelength

A

any length unit—meter, mm, micrometers

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42
Q

wavelength influences ___________ (hint: image quality)

A

resolution

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43
Q

wavelength is determined by:

A

the sound source (transducer)

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44
Q

propagation speed

A

the rate at which sound travels through a medium

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45
Q

unit of measurement for propagation speed:

A

m/s, mm/μs

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46
Q

propagation speed is determined by:

A

medium

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47
Q

by convention, the speed of sound through body tissues is:

A

1540 m/s

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48
Q

what determines how far US waves can travel?

A

the frequency of the transducer

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49
Q

the HIGHER the frequency, the ____ it can penetrate

A

LESS

50
Q

the LOWER the frequency, the ______ it can penetrate

A

DEEPERA

51
Q

Attenuation is _______ related to frequency

A

directly

52
Q

what is the speed of sound through bone?

A

4000 m/s

53
Q

what is the speed of sound through air? lung?

A

300; 500

54
Q

The ___________ the frequency of the beam, the _________ resolution the image will have. But, the penetration into tissue will be _________.

A

HIGHER
MORE
LESS

55
Q

Hyperechoic tissues appear _______ on the screen

A

bright

56
Q

hypoechoic tissues appear _______ on the screen

A

opaque

57
Q

the reason that frequency and tissue penetration are inversely proportional is because velocity through a medium is ___________

A

constant

58
Q

So, if frequency increases or decreases, the wavelength must increase or decrease in the _____________ direction to maintain the constant velocity

A

OPPOSITE

59
Q

most ultrasound waves are _______; therefore, they ______ enter the body.

A

reflected; never

60
Q

what is gel used?

A

to prevent a large difference in impedance when ultrasound passes through two very different materials and causes the majority of US waves to be reflected

61
Q

which transducer design is best used for vascular structures and small parts?

A

Linear

62
Q

which transducer design is best used for cardiac, upper body, abdomen, and pelvis?

A

phased array

63
Q

what is the curved array best used for?

A

abdominal, OB, renal, urologic
Ex: gastric ultrasound

64
Q

which transducer design has a higher frequency, linear or curvilinear?

A

linear

65
Q

which transducer design is better for looking at a smaller area and gauging depth, linear or curvilinear?

A

linear

66
Q

this probe gives a wider angle of view:

A

curvilinear

67
Q

hyperechoic structures that tend to appear white on screen and why?

A

bone; pleura (diaphragm), and tendons

reflects majority of sound waves

68
Q

isoechoic structures that tend to appear in various shades of gray on screen and why?

A

most solid organs; thick fluid

allow some sound waves through but reflect others

69
Q

another term for isoechoic

A

echogenic

70
Q

hypoechoic structures appear black on screen and why?

A

fluid within a cyst, urine, blood

allow most sound waves through

71
Q

how do veins and arteries appear on screen?

A

anechoic, round structures

72
Q

distinguish how veins and arteries appear on screen:

A

veins are collapsible with increased pressure

arteries are pulsatile and non-compressible

73
Q

how does fat and muscle appear on ultrasound?

A

hypoechoic background with hyperechoic streaks

74
Q

how to distinguish fat and muscle on ultrasound

A
  • fat is primarily superficial
  • muscle tissue has a “different appearance” …
75
Q

how does bone appear on ultrasound?

A

hyperechoic and bright, with an acoustic shadow below

76
Q

why does an acoustic shadow occur below bone?

A

due to the inability of ultrasound waves to penetrate the structures below

77
Q

how do nerves appear in the supraclavicular area?

A

HYPOechoic and in bundles

(d/t nerve fibers within the nerve)

78
Q

how do infraclavicular and lower extremity nerves appear on ultrasound? on long axis?

A

HYPERechoic

on long axis they appear speckled

79
Q

distinguish supraclavicular from infraclavicular nerves:

A

supraclavicular = hypoechoic

infraclavicular = hyperechoic

80
Q

how do tendons appear on ultrasound?

A

hyperechoic; but the “streaks” appear longer than the nerves

(this is due to the composition of the tendon’s outer layer)

81
Q

how do tendons appear on long axis view?

A

with internal hyperechoic lines

82
Q

Short Axis AKA…

A

cross-sectional

83
Q

Long Axis AKA…

A

longitudinal

84
Q

what does PART stand for when it comes to image acquisition?

A

P: Pressure
A: Alignment
R: Rotation
T: Tilt

85
Q

alignment

A

SLIDING of the transducer along the body part/surface being examined

86
Q

rotation

A

TWISTING of the probe during examination

87
Q

tilt

A

CHANGING THE ANGLE of the transducer while keeping it in place

88
Q

which movement of the transducer is most useful to align the needle with the transducer beam?

A

ROTATION

89
Q

which movement of the transducer is most useful in aligning the beam PERPENDICULAR to the target in order to improve image quality?

A

TILT

90
Q

which movement of the transducer is most helpful in locating the target and needle?

A

ALIGNMENT

91
Q

the three basic adjustments on the ultrasound machine settings are:

A

depth, gain, and focus

92
Q

if the depth is set too high, the _________ and _______ of the target structure are decreased

A

definition; resolution

93
Q

the depth should be set __________ (____ cm) the distance at which the structure is located

A

just below; 1-2 cm

94
Q

what is the purpose of gain?

A

allows for compensating the attenuation of the signal as it travels deep into tissues

95
Q

too low of gain will not allow for:

A

tissue differentiation

96
Q

too high of gain will cause:

A

loss of resolution

97
Q

the ideal gain setting is one that allows for:

A

tissue differentiation

98
Q

the gain should be ________ as the distance to the probe increases

A

increased

99
Q

increase gain = _______ image
decreased gain = _______ image

A

brighter; darker

100
Q

focus

A

allows for the concentration of the beam to be at its sharpest when it reaches the area of interest

101
Q

focus is based on the:

A

focal zone of the ultrasound beam

102
Q

focal zone of the ultrasound beam

A

where the beam is at its narrowest (diameter) and density of the waves is highest

103
Q

crossbeam

A

method by which the beams from the transducer form a cross-weave

(this allows for better definition and sharper images)

104
Q

doppler or color flow allows for:

A

identification of blood vessels based on flow

105
Q

doppler: red color typically indicates

A

flow TOWARDS the transducer

106
Q

doppler: blue color typically indicates

A

flow AWAY from the transducer

107
Q

in-plane needle insertion

A

refers to the needle being inserted and followed in the same plane as the ultrasound beam, AKA PARALLEL

108
Q

out of plane needle insertion

A

needle is inserted perpendicular to the beam

109
Q

which type of needle insertion allows for visualization of the entire needle during the procedure?

A

in plane

110
Q

which type of needle insertion is a more difficult approach, since you can only see a portion of the needle shaft?

A

out of plane

111
Q

what are the 3 basic ergonomic principles to maximize patient and provider comfort when using ultrasound?

A

patient positioning
equipment positioning
operator positioning

112
Q

artifacts

A

false images or shadows that may confuse what you see

ex: acoustic, anatomic, optical illusion

113
Q

acoustic shadows are caused by:

A

bone

114
Q

acoustic enhancement is seen as:

A

shadows usually under blood vessels

115
Q

tissue reverberation is caused by:

A

strongly reflective tissues such as the pleura, seen as an area of brightness under the structure

116
Q

reverberation artifacts

A

caused by needles and other structures

117
Q

air artifact is usually seen when (2):

A

1- the transducer loses contact with the skin
2- there is not enough conductive media

118
Q

what are the most common sources of confusion that cause anatomic artifact?

A

tendons and nerves

119
Q

how can the provider identify nerves?

A

nerve stimulator

120
Q

blood vessels with thrombi can be confused with:

A

neural structures

121
Q

enlarged lymph nodes can be mistaken for:

A

neural tissue, occluded vessels

122
Q

how can edema cause artifact? (2)

A

1- may disfigure the appearance of anatomic structures, including nerves

2- may change the electrical thresholds, making the location of nerve tissue difficult

6494 Regional Anesthesia (5 decks)

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