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Vascular > Chapter 2: Ultrasound Principles > Flashcards

Chapter 2: Ultrasound Principles Flashcards

1
Q

echoes on the image that were not caused by actual reflectors in the body

A

artifacts

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2
Q

ultrasound has the ability to cause changes to the tissue if proper settings are not used

A

bioeffects

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3
Q

principle of constantly transmitting a sound wave into the patient to obtain a spectral Doppler waveform

A

continuous wave

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4
Q

Tool for measuring blood flow quantitatively or qualitatively using pulsed-wave or continuous-wave techniques

A

Doppler

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5
Q

Principle of sending in a small group of sound waves and then waiting for that pulse to come back so that an image can be displayed. Also used for spectral and color Doppler.

A

pulsed wave

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6
Q

the part of the ultrasound machine that transmits and receives sound via an array of piezoelectric elements

A

transducer

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7
Q

pressure/mechanical waves

A

sound waves

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8
Q

a series of reflectors along one vertical line

A

scan line

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9
Q

all the scan lines displayed on the screen

A

frame

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10
Q

propagative of wave is parallel to the movement of molecules within the medium

A

longitudinal wave

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11
Q

simplest unit of a wave

A

cycle

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12
Q

can be measure by height, length, and other parameters

A

cycle

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13
Q

the number of cycles that occur in 1 second

A

frequency

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14
Q

the frequency of a pulsed wave transducer is determined primarily by:

A

thickness of piezoelectric element

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15
Q

other names for frequency

A

operating frequency
center frequency
resonating frequency

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16
Q

units for frequency

A

Hz

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17
Q

typical range of frequency in ultrasound

A

2-20 MHz

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18
Q

time taken for one cycle to occur in milliseconds

A

period

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19
Q

speed at which sound moves through a medium

A

propagation speed

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20
Q

What is propagation speed determined by?

A

only by the medium through which sound is traveling

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21
Q

What is the average propagation speed of soft tissue?

A

1540 m/s

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22
Q

length in (mm) of one cycle of sound, from the beginning of the wave to the end of the wave

A

wavelength

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23
Q

What is wavelength determined by?

A

propagation speed divided by the operating frequency

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24
Q

height of a cycle, from the baseline to the peak of the cycle

A

amplitude

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25
Q

Units of amplitude

A

pressure (pascals)
density (kg m^3)
particle motion (mm)

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26
Q

acoustic impedance unit

A

Rayls

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27
Q

property of the medium

A

acoustic impednace

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28
Q

What is acoustic impedance determined by?

A

the product of the density and propagation speed

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29
Q

With a difference in impedances between adjacent tissues,

A

no reflection is generated

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30
Q

The larger the differences in impedances, the _____ the return echo.

A

larger

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31
Q

pulse is sent into the body by the transducer, and machine waits for that pulse to return before transmitting the next pulse

A

Pulsed-wave ultrasound

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32
Q

number of pulses per second in Hz or kHz

A

pulse repetition frequency

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33
Q

inversely related to depth of reflector and unrelated to operating frequency

A

pulse repetition frequency

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34
Q

length of the pulse

A

spatial pulse length

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35
Q

equal to the wavelength multiplied by the number of cycles in a pulse

A

spatial pulse length

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36
Q

time taken for a pulse to occur, including dead time

A

pulse repetition period

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37
Q

measurement of only the transmission part of the pulse and does not include dead time

A

pulse duration

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38
Q

percentage of time machine is transmitting sound into patient

A

duty factor

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39
Q

equal to PD/PRP

A

duty factor

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40
Q

one element constantly receiving and one element constantly transmitting

A

continuous-wave ultrasound

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41
Q

DF of continuous wave

A

100%

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42
Q

used only for spectral Doppler

A

continuous wave

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43
Q

sound travels through tissue, some energy is lost

A

attenuation

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44
Q

may result from absorption of the beam

A

attenuation

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45
Q

conversion of sound to heat

A

absorption

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46
Q

lowest attenuation

A

water

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47
Q

highest attenuation

A

air

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48
Q

average attenuation rate through soft tissue

A

0.5 dB/cm/MHz

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49
Q

attenuation increases with ____.

A

frequency

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50
Q

larger than the wavelength of the transmitted beam and includes broad strucutres

A

specular reflectors

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51
Q

sound strikes perpendicularly, reflectors show up on ultrasound as a bright white line

A

specular reflector

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52
Q

sound strikes at an angle other than 90 degrees is not reflected back to the transducer and is not displayed

A

specular reflector

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53
Q

sound encounters a structure that is smaller than the transmitted beam’s wavelength

A

nonspecular reflector

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54
Q

scattering of a sound wave, beam spread out over many directions

A

nonspecular reflector

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55
Q

What reflector in not angle dependent?

A

nonspecular

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56
Q

Rayleigh scatterer

A

nonspecular reflector

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57
Q

occurs when reflector is very small compared with beam’s wavelength

A

Rayleigh scatterer

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58
Q

amount of scatter proportional to frequency to the fourth power

A

Rayleigh scatterer

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59
Q

the boundary of two tissues adjacent to one another

A

interface

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60
Q

occurs when two condition are met:
an angle of incidence perpendicular to interface
difference in acoustic impedance of two media

A

reflection

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61
Q

Amount of reflection is proportional to:

A

impedance mismatch

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62
Q

The farther apart two impedances are, the _____ the reflection

A

stronger

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63
Q

May occur if two different conditions met:
nonperpendicular, or oblique angle of incidence
difference in propagation speeds between two media

A

refraction

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64
Q

sound will be transmitted into the tissue at the same angle with no change in direction at the interface

A

perpendicular incidence

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65
Q

transmitted sound will change direction, assuming disparate propagation speeds

A

oblique incidence

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66
Q

if propagation speed of second medium greater than 1540 m/s, angle of the transmitted angle will be _____ than the incident angle.

A

greater

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67
Q

used by machine to determine travel time of pulse

A

range equation

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68
Q

measure time taken for a transmitted pulse of sound to return to the transducer and calculates the distance to the reflector

A

range equation

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69
Q

d- ct/z

A

range equation

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70
Q

sometimes called “curved” or “convex” array

A

curvilinear array transducer

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71
Q

commonly called linear array

A

linear sequential array

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72
Q

typically a small rectangular of square footprint transducer

A

phased array

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73
Q

curved near field with sloped sides

A

curvilinear array transducer

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74
Q

have ability to displayed at two image shapes
rectangular: rectangle with a flat top and bottom and straight sides
vector: slopes sides of rectangle to form a trapezoid; sometimes called virtual convex

A

linear array transducer

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75
Q

may have sector or vector image
both shaped like slices of pie

A

phased array transducers

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76
Q

piezoelectric elements are most commonly made of:

A

lead zirconate titanate

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77
Q

What is used on transducer to limit number of cycles in the pulse

A

damping material

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78
Q

improve transmission of sound into patient

A

damping material

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79
Q

source of electricity from a part of the machine

A

pulser

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80
Q

initial amount of power used to shock elements determines ______ or strength of sound wave.

A

amplitude

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81
Q

ALARA

A

as low as reasonably achievable

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82
Q

production of heat in tissue as sound travels

A

thermal bioeffects

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83
Q

creation of bubbles in the tissue

A

cavitation

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84
Q

Two indices used by manufacturers to provide information on risk of bioeffects at given technical settings

A

Mechanical index and thermal index

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85
Q

SPTA intensity no bioeffects unfocused transducer

A

100 mW/cm^2

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86
Q

SPTA intensity no bioeffects focused transducer

A

less than 1 W/cm^2

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87
Q

No bioeffects noted if temperature increase remains below:

A

1.5 degrees Celcius

88
Q

resolution of reflectors that are parallel to the beam

A

axial resolution

89
Q

shorter pulse = _____ axial resolution

A

better

90
Q

The ____ the operating frequency, the better the axial resolution

A

higher

91
Q

involves reflectors perpendicular to the beam
determined by the width of the beam

A

lateral resolution

92
Q

Where is the best lateral resolution?

A

in region of focal zone

93
Q

width of the beam

A

slice-thickness or elevational plane

94
Q

frame rate; number of images produced per second

A

temporal resolution

95
Q

influencers of temporal resolution

A

depth of image
width of image
number of focal zones
use of color Doppler

96
Q

completed when a series of scan lines have been created

A

frame

97
Q

The deeper the depth, the ____ the frame rate.

A

worse

98
Q

The more focal zones used, the ____ the frame rate.

A

worse

99
Q

the difference between the transmitted frequency of the ultrasound transducer and the returned frequency of the reflector

A

Doppler shift

100
Q

Doppler shift: if a reflector is stationary

A

reflected frequency will be identical to transmitted frequency and Doppler shift will be zero

101
Q

If a reflector is moving in a direction that is toward the transducer, then the reflected frequency will be greater than the transmitted frequency

A

Positive Doppler shift

102
Q

reflector is moving away from the transducer, reflected frequency will be lower than the transmitted frequency

A

Negative Doppler shift

103
Q

Doppler equation

A

V=c(Fd)/2f(cos0)

104
Q

The most accurate Doppler shift

A

0 degrees

105
Q

____ will provide the highest doppler shift

A

0 degrees

106
Q

At ___, the Doppler shift is zero.

A

90 degrees

107
Q

displays the signal information on a graph in which the frequency shift (converted to velocity) is displayed on the y-axis and time on the x-axis

A

spectral Doppler

108
Q

wraparound of the spectral waveform causing positive shifts to be displayed as negative

A

aliasing

109
Q

maximum frequency shift that can be sampled is equal to the ______ which is ____ of the PRF

A

Nyquist limit
1/2

110
Q

elimination of aliasing

A

increase PRF or decrease Doppler shift

111
Q

converts complex information into spectral waveform

A

Fast Fourier Transform

112
Q

filling in of spectral window

A

spectral broadening

113
Q

type of PW Doppler in which information regarding direction of flow and mean velocity is displayed as a color on top of the B-mode display

A

color Doppler

114
Q

BART

A

blue away, red towards

115
Q

created by sending multiple pulses of sound down the scan lines of a color gate to determine movement of the reflectors

A

color Doppler

116
Q

processing algorithm used to process color Doppler

allows for identification of only mean velocity information, not peak systolic and end diastolic information obtained by spectral Doppler

A

autocorrelation

117
Q

display of positive shift information as a negative shift

A

aliasing

118
Q

also called
amplitude Doppler
color power angio

A

power Doppler

119
Q

provides flow information that relies on the amplitude of the Doppler shift, but not the shift itself

A

power Doppler

120
Q

What is amplitude determined by?

A

the number of red blood cells moving through the vessel, with higher amplitudes causing a stronger signal

121
Q

movement artifact that obscures the image and makes it less or nondiagnostic

A

flash

122
Q

adjusts brightness of all the dots on the screen equally

used when overall appearance of image is too bright or too dark

A

overall gain

123
Q

adjusted when only part of the iamge is too bright or too dark

adjusts for attenuation in the far field

A

Time gain compensation

124
Q

set number and location of focal zones

lateral resolution best

at or below area of interest

A

focal zone

125
Q

determined by thickness of the element

A

frequency

126
Q

controlled by PRF

should be set where area of interest is fully displayed

A

depth

127
Q

produces images using sound energy returning from the patient that is double the operating frequency

produces images with better lateral resolution and fewer artifacts

A

tissue harmonic imaging

128
Q

transducer sends beam into patient from different directions to minimize image artifacts and improve appearance of soft tissue

A

spatial compounding

129
Q

permits measurement of higher velocities without aliasing

A

increasing scale/PRF

130
Q

should be optimized so that spectral waveform should occupy about two-thirds of spectral window without touching the top or bottom of the display

A

PRF/scale

131
Q

controls brightness of spectral waveform

A

spectral gain

132
Q

permits sample depth selection

A

sample volume/range gate

133
Q

used to stretch out a waveform so that individual parts of waveform can be more accurately measured

A

fast sweep speed

134
Q

represents part of spectral waveform where velocity is zero

A

zero flow baseline

135
Q

flips waveform so that negative shifts are displayed above the baseline and positive shifts below it

A

invert

136
Q

The larger the gate, the _____ the frame rate

A

slower

137
Q

The wider the gate, the ____ scan lines required

A

more

138
Q

should be increased when a vessel not filling well with color, and scale is appropriately set

A

color gain

139
Q

negative shifts displayed on top, positive shifts displayed below

A

invert

140
Q

common aritfact consisting of linear repeating echoes

appears as a result of a strong specular reflector near the surface

A

reverberation

141
Q

type of reverberation artifact

commonly caused by small bits of calcium or surgical clips

A

comet tail

142
Q

occurs as the result of the attenuation of the sound

seen in presence of calcified plaque and overlying bone

A

shadowing

143
Q

when sound travels through an area of decreased attenuation compared to the surrounding tissue, the tissue deep to the week attenuator appears brighter

A

enhancement

144
Q

sound travels in the region of a strong specular reflector and causes a duplication of a reflector deep to the original structure

associated with array transducers

A

Grating lobes

145
Q

caused by wall motion

produces a high-amplitude, low-frequency noise along baseline

eliminated with use of high-pass filters, also called a wall-filter

A

clutter

146
Q

the principle of sending in a small group of sound waves and then waiting for that pulse to come back so an image can be displayed

A

pulsed-wave

147
Q

The part of the ultrasound machine that transmits and receives sound via an array of piezoelectric elements

A

transducer

148
Q

Tool for measuring blood flow quantitatively or qualitatively using pulsed-wave or continuous-wave techniques

A

Doppler

149
Q

Echoes on the image not caused by actual reflectors in the body

A

artifacts

150
Q

principle of constantly transmitting a sound wave into the patient to obtain a spectral-Doppler waveform

A

continuous-wave

151
Q

The ability of ultrasound to cause changes to the tissue if proper settings are not used

A

bioeffects

152
Q

What is the number of cycles that occur in 1 second?

A

frequency

153
Q

What is the time taken for one cycle to occur?

A

period

154
Q

What determines the propagation speed of sound?

A

the medium through which the sound is moving

155
Q

What is the height of a cycle from baseline to the peak of the cycle?

A

amplitude

156
Q

What is the number of pulses per second emitted by an ultrasound system?

A

pulse repetition frequency

157
Q

What information is needed in order to determine spatial pulse length?

A

wavelength and the number of cycles per pulse

158
Q

What is the percentrage of time the machine is transmitting sound in to the patient?

A

duty factor

159
Q

What is the minimum number of piezoelectric elements necessary to perform continuous wave Doppler?

A

two

160
Q

Which of the following has the highest attenuation?
a. water
b. muscle
c. bone
d. air

A

d

161
Q

What type of reflection results when sound encounters structures that are smaller than the transmitted beam’s wavelength?

A

nonspecular

162
Q

Which of the following must be present for reflection to occur?
a. acoustic impedance mismatch
b. difference in propagation speeds between two media
c. structures much smaller than the ultrasound beam’s wavelength
d. a change in the direction of the sound beam

A

a

163
Q

What is a change in direction of the transmitted beam at an interface?

A

refraction

164
Q

Assuming soft tissue, how long does it take an ultrasound pulse to reach a depth of 1 cm and return to the transducer?

A

13 milliseconds

165
Q

Which transducer is most commonly used for peripheral and cerebrovascular examinations?

A

linear sequential array

166
Q

Which transducer creates a “pie slice” shaped image?

A

phased array

167
Q

Which of the following is added to a transducer to limit the number of cycles in a pulse?
a. damping material
b. matching layer
c. attenuation layer
d. lead zirconate titanate

A

a

168
Q

After removing gel and fluids from a nonintracavitary transducer, what should the next step be in cleaning the transducer?

A

wipe down with a low-level transducer

169
Q

What is the part of the ultrasound machine that provides the electricity that shocks the transducer?

A

pulser

170
Q

What does the acronym ALARA stand for?

A

as low as reasonably achievable

171
Q

What does the TI indicate?

A

risk of thermal bioeffects

172
Q

Which term describes the resolution parallel to the beam?
a. temporal
b. axial
c. lateral
d. transverse

A

b

173
Q

Where is the lateral resolution the best?

A

focal zone

174
Q

A reflector moving toward a transducer would result in what type of Doppler shift?

A

positive shift

175
Q

What angle results in the most accurate and highest Doppler shift?

A

0 degrees

176
Q

On a spectral display, what is represented on the vertical axis?

A

velocity

177
Q

What is complex processing technique that converts complex frequency shifts into a spectral waveform?

A

fast Fourier transform

178
Q

Which of the following describes sending multiple pulses down one scan line to create a color Doppler image?

A

autocorrelation

179
Q

What is a Doppler technique that provides flow information based on amplitude of the Doppler shift and not the shift itself?

A

power Doppler

180
Q

Which control adjusts the overall brightness of the B-mode image?

A

gain

181
Q

Which processing technique results in better lateral resolution and reduces reverberation artifact?

A

tissue harmonic imaging

182
Q

Which control should be adjusted to permist the display of higher velocities in a spectral Doppler display?

A

PRF/scale

183
Q

Which control should be adjusted if color is either not filling the vessel or is bleeding outside the vessel wall?

A

color gain

184
Q

During an ultrasound evaluation of the aorta, a surgical clip is ecountered. What artifact would likely be present owing to this clip?

A

comet tail

185
Q

What is an artifact caused by wall motion that can be released by using a wall filter?

A

clutter

186
Q

Sound waves are ______ indicating that the movement of the molecules within the wave is parallel to propagation direction.

A

longitudinal

187
Q

The typical frequency range used in medical diagnostic ultrasound is ____ MHz.

A

2-20

188
Q

The average propagation speed in soft tissue that ultrasound machines assume is ____.

A

1,540 m/s

189
Q

The property of the medium that is determined by the product of density and propagation speed that helps determine reflection of echoes is _____.

A

acoustic impedance

190
Q

The parameter that primarily determines pulse repetition frequency and pulse repetition period is ______.

A

imaging depth

191
Q

The loss of some energy in the sound beam as it travels through tissue is ______.

A

attenuation

192
Q

The average rate of attenuation through soft tissue is _____.

A

0.5 dB/cm/MHz

193
Q

The diaphragm is an example of a _____ reflector.

A

specular

194
Q

A red blood cell is an example of a _____ scatterer.

A

Rayleigh

195
Q

If the propagation speed in the transmitted medium is greater than the propagation speed in the incident medium, the angle of the transmitted beam will be _____ than the incident angle.

A

greater

196
Q

The ultrasound machine uses the _____ equation to determine the travel time of an ultrasound pulse.

A

range

197
Q

Modern transducers are ______, meaning they have the ability to use different frequencies that are present in the beam.

A

broadband

198
Q

The _____ layer of a transducer is used to improve the transmission of sound into the patient.

A

matching

199
Q

The piezoelectric elements within a transducer are usually made of _______.

A

lead zirconate titanate (PZT)

200
Q

The measure of the amount of power in an ultrasound beam divided by the area of the beam is the _____.

A

intensity

201
Q

A bioeffect of ultrasound that results in the creation of bubbles in the tissue is ______.

A

cavitation

202
Q

No thermal bioeffects have been noted with an unfocused transducer with an SPTA intensity below ___ mW/com^2.

A

100

203
Q

Lateral resolution is determined by the _____ of the beam.

A

width

204
Q

Axial resolution is improved by increasing the _____ of the transducer.

A

frequency

205
Q

The number of images produced per second is called the ______.

A

frame rate/temporal resolution

206
Q

The ______ is the difference between the transmitted frequency of the ultrasound transducer and the returned frequency of the reflector when motion is present.

A

Doppler effect

207
Q

A Doppler angle of _____ degrees results in no detectable shift.

A

90

208
Q

A common artifact of PW spectral Doppler is _____ or wraparound of the spectral waveform causing positive shifts to be displayed as negative.

A

aliasing

209
Q

The maximum frequency shift that can be sampled during PW Doppler is known as the ______/

A

Nyquist limit

210
Q

Filling in of the spectral window because of a wide range of velocities at a given point in time is called _____.

A

spectral broadening

211
Q

The process used in color Doppler to identify mean velocity and direction is called ______.

A

autocorrelation

212
Q

Slider controls used to achieve uniform brightness across an image are known as _____.

A

TGCs

213
Q

A processing technique that sends the beam into the patient from different directions to improve the appearance of soft tissue is known as ______.

A

spatial compounding

214
Q

A Doppler control that allows the display of more or fewer spectral waveforms on the screen at one time is _____.

A

sweep speed

215
Q

______ artifact occurs as a result of increased attenuation of sound and is often seen posterior to bone or calcified plaque.

A

comet tail

216
Q
A

Vascular (33 decks)

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