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SPI > Chapters 1-24 > Flashcards

Chapters 1-24 Flashcards

1
Q

reciprocal relationship

A

when two numbers with a reciprocal relationship are multiplied together, the result is one. EX: 2 x 1/2 = 1

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2
Q

increase by a factor means

A

multiply by that number

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3
Q

decrease by a factor means

A

divide by that number

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4
Q

10^9 means…..

A

giga, G, billion

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5
Q

10^6 means…..

A

mega, M, million

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6
Q

10^-3 means….

A

milli, m, thousandth

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7
Q

10^-6 means…

A

micro, u, millionth

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8
Q

10^-9 means….

A

nano, n, billionth

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9
Q

10^3 means….

A

kilo, k, thousand

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10
Q

sound is …..

A
  • a mechanical wave
  • travels in a straight line
  • sound waves are longitudinal
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11
Q

acoustic propagation properties are…

A

the effects of the medium upon the sound wave

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12
Q

Biologic effects are….

A

the effects of the sound wave upon the biologic tissue through which it passes

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13
Q

acoustic variables

A

the way sound waves are identified

  1. pressure - pascals (Pa)
  2. density - kg/cm^3
  3. distance - cm, mm
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14
Q

acoustic parameters

A

a waves features or characteristics

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15
Q

Decibels are what?

A

-a relative measurement, a comparisson, a ratio, logarithmic

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16
Q

Negative decibels describe what?

A

Signals that are decreasing in strenght or are getting smaller

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17
Q

Attenuation is determined by what two factors?

A

Path length and frequency of sound

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18
Q

How are frequency and attenuation related?

A

Directly

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19
Q

What 3 processes contribute to attenuation?

A

Reflection, scattering & absorption

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20
Q

Specular reflection is?

A

When the beam reflected hits a smooth boundary

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21
Q

Diffuse reflection (rough boundary) is aka?

A

Backscatter

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22
Q

intensity =

A

power (w) / area (cm^2)

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23
Q

Power is related to?

A

amplitude squared

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24
Q

Intensity is related to?

A

amplitude squared

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25
Q

Power is related to?

A

intensity

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26
Q

Wavelength (mm) =

A

1.54 mm/us /frequency (MHz)

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27
Q

speed (m/s) =

A

frequency (Hz) x wavelenght (m)

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28
Q

as stiffness increases…..

A

speed increases

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29
Q

as denstiy increases….

A

speed decreases

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30
Q

bulk modulus is the same as?

A

stiffness

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31
Q

which 5 parameters describe pulsed sound?

A
  • pulse duration
  • pulse repetition period
  • pulse repetition frequency
  • duty factor
  • spatial pulse length
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32
Q

what is duty factor?

A

the percentage of time that the system transmits a pulse

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33
Q

With shallow imaging we have….

A
  • less listening
  • shorter PRP
  • higher RRF
  • higher duty factor
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34
Q

With deep imaging we have….

A

-more listening
-longer PRP
-lower PRF
lower duty factor

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35
Q

what is the duty factor for continuous wave sound?

A

1.0 (100%)

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36
Q

what is the typical value for duty factor for pulsed wave sound?

A

0.2 -0 .5%

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37
Q

what are the intensity measurement methods?

A
  • SPTP
  • SATP
  • SPTA (tissue heating & bioeffects)
  • SATA
  • SPPA
  • SAPA
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38
Q

all intensities have units of ?

A

W/cm^2

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39
Q

What are the temporal intensities from largest to smallest?

A

Itp, Imax, Ipa, Ita

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40
Q

What is the rank of intensities from largest to smallest?

A

SPTP, Im, SPPA, SPTA, SATA

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41
Q

What happened to sound as he travels in the body?

A

It attenuates

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42
Q

What are the units of attenuation?

A

dB

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43
Q

Decibels require what?

A

2 intensities

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44
Q

Positive decibels report signals that or what?

A

Increasing and strength or getting larger

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45
Q

Decibel notation is?

A

A relative measurement, a comparison, a ratio,logarithmic

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46
Q

Negative decibels describe signals that are what?

A

Decreasing and strength are getting smaller

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47
Q

Attenuation is determined by what two factors?

A

Path length and frequency of sound

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48
Q

More attenuation happens with?

A

Longer distances and higher frequencies

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49
Q

Less attenuation happens with?

A

Shorter distances and lower frequencies

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50
Q

What the processes contribute to attenuation?

A

Reflection, scattering, and absorption

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51
Q

What are the two forms of reflection?

A

Specular and diffuse

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52
Q

Diffuse reflection a.k.a.?

A

Backscatter

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53
Q

What is scattering?

A

Random redirection of sound in many directions

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54
Q

What is the relation between frequency and Rayleigh scattering?

A

Proportional to frequency to the fourth power

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55
Q

What is the attenuation Coefficient?

A

Is the number of decibels of attenuation that occurs when sound travels 1 cm

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56
Q

What are the units of attenuation coefficient?

A

dB/cm

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57
Q

What is the half-value layer thickness?

A

Is the distance sound travels in a tissue that reduces intensity of sound to one half its original value

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58
Q

What are the bases for ultrasonic imaging?

A

Reflection and transmission

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59
Q

What are the units of impedance?

A

Rayls

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60
Q

What is normal incidence also called?

A

Perpendicular, Orthogonal, right angle, 90°

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61
Q

What is incident intensity?

A

Is the sound wave’s intensity immediately before it strikes a boundary

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62
Q

What percentage of a sound waves intensity is reflected at a boundary between two Soft tissues?

A

Very little 1% or less

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63
Q

What percentage of a sound wave’s intensity is transmitted at a boundary between two soft tissues?

A

Most 99% or more

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64
Q

When we have normal incidence reflection occurs only if?

A

The media on either side of the boundary have different impedances

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65
Q

What to physical principles always apply to reflection with oblique incidence?

A

Conservation of energy and reflection equals incident angle

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66
Q

Refraction occurs only you?

A

Oblique incidence and different propagation speeds of the two media

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67
Q

What is Snell’s law?

A

It’s quantifies the physics of refraction

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68
Q

If speed 1 equals speed 2….

A

No refraction, transmission angle equals incident angle

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69
Q

Speed 2 greater than speed 1…..

A

Transmission angle greater the incident angle

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70
Q

Speed 2 less than speed 1…

A

Transmission angle less than incident angle

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71
Q

What is the go return time?

A

The elapsed time from pulse creation to pulse reception

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72
Q

What is the 13 µs rule?

A

For every 13 µs of go return time the object creating the reflection is 1 cm deeper in the body

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73
Q

What does the backing material enhance?

A

Axial resolution

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74
Q

In decreasing order of impedance….

A

PZT>Matching layer>gel>skin

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75
Q

What are 3 consequences of backing material?

A

Decrease sensitivity, wide bandwidth,and low-quality factor

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76
Q

What are the characteristics of damping material?

A

High degree of sound absorption and acoustic impedance similar to PZT

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77
Q

What is bandwidth?

A

The range frequency found in a pulse

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78
Q

With continuous wave transducers, electrical frequency equals……

A

Acoustic frequency

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79
Q

What 2 characteristics of the active element combine to determine the frequency of sound?

A

Speed of sound in the PZT and thickness of the PZT

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80
Q

What are the characteristics of high frequency waves imaging transducers?

A

Thinner PZT crystals & PZT with higher speeds

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81
Q

What are the characteristics of low. Frequency pulsed wave imaging transducers?

A

Thicker PZT crystals and PZT with lower speeds

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82
Q

What gives us a shallow focus?

A

Small diameter PZT & lower frequency

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83
Q

What gives us a deep focus?

A

Large diameter PZT and higher frequency

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84
Q

What gives us less divergence?

A

A larger diameter and higher frequency

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85
Q

What gives us more divergence?

A

Smaller diameter and lower frequency

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86
Q

What are HUYGEn’s wavelets aka?

A

Spherical waves, or diffraction patterns (v shaped waves)

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87
Q

What is axial

resolution?

A

It deals with structures that are parallel to the sound beam

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88
Q

LARRD stands for?

A

Longitudinal, axial, range, radial and depth

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89
Q

What is better axial resolution associated with?

A

Shorter spatial pulse lenght, shorter pulse duration, higher frequencies (shorter wavelength), fewer cycles per pulse (less ringing) and lower numerical values

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90
Q

What is lateral resolution?

A

It relates to structures that are positioned perpendicular to the sound beam

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91
Q

What does LATA stand for?

A

Lateral, angular, transverse, and azimuthal

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92
Q

Where is lateral resolution Best at?

A

At the focus

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93
Q

What does focusing do?

A

It concentrates the sound energy into a narrower beam and thus improve lateral resolution

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94
Q

Fixed focusing is aka?

A

Conventional or mechanical focusing

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95
Q

What are the effects of focusing?

A

Beam diameter in near field and focal zone is reduced, focal depth is shallower, beam diameter in the far zone increases and focal zone is smaller.

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96
Q

What are the three basic modes oh viewing ultrasound information?

A

Amplitude mode, brightness mode, and motion mode

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97
Q

With M-mode….

A

X-axis displays time

Y-axis displays depth

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98
Q

With B-mode….

A

X-axis displays depth

Z-axis displays amplitude

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99
Q

With A-mode….

A

X-axis displays depth

Y-axis displays amplitude

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100
Q

What are the US system’s main components?

A

Transducer, pulser and beam former, receiver, display, storage, and master synchronizer

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101
Q

What is the pulser’s function?

A

It creates electrical signals that excite the transducers PZT crystals and create sound beams

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102
Q

what are array transducers?

A

they contain multiple active elements; an array comprises a single slab of PZT cut into a collection of separate pieces called elements

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103
Q

3 types of array transducers are:

A

linear, annular and convex

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104
Q

phased array always means what?

A

adjustable or multi-focus

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105
Q

What creates electronic steering?

A

slope

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106
Q

slice thickness or elevational resolution is what?

A

it deals with shallow to deep

side to side and above to below the imaging plane

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107
Q

side and grating lobes degrade what?

A

lateral resolution

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108
Q

side lobes are created by what?

A

mechanical transducers

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109
Q

grating lobes are created by what?

A

array transducers

110
Q

What is apodization?

A

when stronger electrical signals are used to excite the inner crystals and progressively weaker electrical spikes excite the outer crystals. Lobes are diminished

111
Q

What is subdizing?

A

when a crystal is divided into a group of smaller crystals called sub-elements. These sub-elements are electrically joined and act as if they are a single crystal, which reduces grating lobes

112
Q

what is dynamic aperture aka variable aperture?

A

it can be used to make a sound beam narrow over a greater range of depths and thus optimize lateral resolution

113
Q

frame rate is determined by what 2 factors?

A
  • sound’s speed in the medium

- the depth of imaging

114
Q

Tframe and frame rate are?

A

inversely related

115
Q

what system settings affect frame rate?

A

imaging depth (deeper, lower FR) and number of pulses per frame (less pulses, higher FR)

116
Q

what factors determine the number of pulses per frame?

A
  • number of focal points
  • sector size
  • line density
117
Q

multifocusing does what to FR?

A

it decreases FR and disminishes temporal resolution

118
Q

multifocus improves what?

A

lateral resolution

119
Q

Sector size aka FOV, does what to FR?

A

if narrow this means less pulses, so it increases FR

120
Q

What does line density do to FR?

A

If we increase line density, we decrease FR

121
Q

What does high line density do?

A

it increases spatial resolution, but decreases temporal resolution

122
Q

what type of resolution does multi-focusing improve?

A

lateral resolution

123
Q

To have higher FR, we need to have?

A
  • shallower imaging
  • single focus
  • narrow sector
  • low line density
124
Q

To have lower FR, we need to have?

A
  • deeper imaging
  • multiple focal points
  • wide sector
  • high line density
125
Q

What is the transducer output aka?

A

Output gain, acoustic power, pulser power, energy output, transmitter output power or gain.

126
Q

what are the six components of an US system?

A
  • Transducer
  • Pulser and beam former
  • receiver
  • display
  • storage
  • master sychronizer
127
Q

what is the function of the pulser?

A

it determines amplitude, PRP, and PRF

128
Q

what is the function of the beam former?

A

determines the firing delay patterns for phased array systems

129
Q

output power increases what?

A

signal to noise ratio

130
Q

what are the receiver operations?

A
  • amplification (remember alphabetical order)
  • compensation
  • compression
  • demodulation
  • rejects
131
Q

what happens with amplification (dB)?

A

all electrical signals in the receiver are affected identically by amplification

132
Q

what is compression?

A

it alters the gray scale mapping of an us image; aka log compression or dynamic range

133
Q

what does demodulation do?

A

a 2 part process that changes the electrical signal into a form more suitable for display; rectification and smoothing (or enveloping)

134
Q

what does reject affect?

A

only weak signals affected; strong signals remain unchanged

135
Q

what is contrast?

A

a control that determines the range of brilliances within the displayed image. Bistable images are high contrast

136
Q

what are some limitations of analog scan converters?

A

image fade, image flicker, instability, deterioration

137
Q

what are some advantages of digital scan converters?

A

uniformity, stability, durability speed, and accuracy

138
Q

what is pixel density?

A

the number of picture elements per inch

139
Q

what’s a bit?

A

the smallest amount of computer memory

140
Q

what is a byte?

A

a group of 8 bits such as 10011111

141
Q

what do get with fewer bits per pixel?

A

fewers shades of gray and degraded contrast resolution

142
Q

what do we get with more bits per pixel?

A

more shades of gray and improved contrast resolution

143
Q

EX: how many possible shades of gray are displayed with 5 bits of memory?

A

multiplying 2 by itself 5 times yields = 32

144
Q

coded excitation provides what?

A
  • higher signal to noise ratio
  • improved axial resolution
  • improved spatial resolution
  • improved contrast resolution
  • deeper penetration
145
Q

what is coded excitation?

A

creates very long sound pulses containing a wide range of frequencies; it occurs in the pulser

146
Q

what does PACS stand for?

A

picture archiving and communications system

147
Q

what does DICOM stand for?

A

digital imaging and computers in medicine

148
Q

what is dynamic range?

A

a method of reporting the extent to which a signal can vary and still be accurately measured; units dB

149
Q

what are the mathematics of compression?

A

add or subtract

150
Q

with fewer shades of gray we have….

A
  • few choces
  • black and white (bistable)
  • narrow dynamic range
  • high contrast
151
Q

with more shades of gray we have….

A
  • many choices
  • gray scale
  • wide dynamic range
  • low contrast
152
Q

tissue harmonics are

A
  • created in tissues
  • created during transmission
  • created by non-linear behavior
  • primarily created along the beams main axis
153
Q

what is pulse inversion harmonics?

A

it’s designed to utilize harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections; a positive and then a negative pulse is transmitted down each scan line.

154
Q

modulation harmonics is what?

A

another imaging technique specifically disigned to augment harmonic reflections, while eliminating distorted fundamental reflections.

155
Q

contrast agents must must meet what requirements?

A
  • safe
  • metabolically inert
  • long lasting
  • strong reflector of ultrasound
  • small enough to pass through capillaries
156
Q

What is contrast harmonics?

A

they are created because microbubbles act in a non-linear manner when struck by sound waves; they are created during reflection

157
Q

what are contrast agents (aka microbubbles)?

A

they are gas bubbles encapsulated in a shell; they are designed to create strong reflections that actually “light up” blood chambers, vessels or other anatomic regions

158
Q

Contrast bubbles…..

A

expand to a greater extent than they shrink

159
Q

what is the Mechanical Index?

A

the amount of contrast harmonics produce may be estimated by this number

160
Q

higher MI increases with?

A

large pressure variation and lower frequency

161
Q

lower MI increases with?

A

small pressure variation and higher frequency

162
Q

With the highest MI, greater than 1, we get?

A
  • strongest harmonics
  • bubble disruption
  • extreme nonlinear behavior
  • lowest frequency sound
  • highest beam strength
  • bubbles expands greatly
163
Q

flow aka volume flow rate indicates what?

A

the volume of blood moving during a particular time; units are volume divided by time, ex: 5L/min

164
Q

what is velocity?

A

speed that indicates direction

165
Q

what is pulsatile flow?

A

when blood moves in variable velocity, blood accelerates and decelerates as a result of cardiac contraction; associated with arterial circulation

166
Q

what is phasic flow?

A

when blood moves in variable velocity, blood accelerates and decelerates as a result of respiration; associated with venous circulation

167
Q

what is steady flow

A

when fluid moves at a constant speed or veloctiy

168
Q

what is laminar flow

A

when the flow streamlines are aligned and parallel; associated with normal physiologic states

169
Q

what are the 2 types of laminar flow?

A

plug and parabolic (bullet shaped)

170
Q

what is the Reynold’s number?

A

it predicts whether flow is laminar or turbulent

171
Q

what is turbulence?

A

chaotic flow patterns in different directions and speeds; (eddie current or a vortex); associated with pathology

172
Q

what is a murmur or a bruit?

A

sound associated with turbulence

173
Q

what is a thrill?

A

tissue vibration associated with turbulence

174
Q

what is the Reynold’s number for turbulence flow?

A

greater than 2000

175
Q

what are the 3 forms of energy?

A
  • kinetic (moving object)
  • pressure(stored or potential energy)
  • gravitational(stored or potential energy associated with elevated objects)
176
Q

what are the 3 energy losses in the circulation?

A
  • viscous loss (units of Poise)
  • frictional loss
  • inertial loss
177
Q

what are the effects of a stenosis?

A
  • change in flow direction
  • increased velocity as vessel narrows
  • turbulence downstream from the stenosis
  • pressure gradient across the stenosis
  • loss of pulsatility
178
Q

Where is pressure lowest at a stenosis?

A

at the vessel’s narrowest point (stenosis)

179
Q

where is velocity of blood the highest?

A

at the stenosis

180
Q

what is Bernoulli’s principle?

A

describes the relationship between velocity and pressure in moving fluid

181
Q

pressure gradient increases when either what?

A
  • flow increases

- resistance increases

182
Q

flow increases when either what?

A
  • pressure gradient increases, or

- resistance decreases

183
Q

in the circulatory system, what are the resistance vessels called?

A

arterioles

184
Q

electrical resistance is reported in units of?

A

ohms

185
Q

what is the shape of a vein as pressure increases?

A

hourglass shape(lower pressure), oval shape (intermediate pressure) and round shape(higher pressure)

186
Q

what is hydrostatic pressure?`

A

it’s related to the weight of blood pressing on a vessel measured at the height above or below heart level

187
Q

in a supine individual, what is the hydrostatic pressure ?

A

in this case, all parts of the body are at the same level of the heart, hydrostatic pressure is zero everywhere

188
Q

in a standing individua, what is the hydrostatic pressure? depends upon whether the measurement is made above or below heart level

A

depends upon whether the measurement is made above or below heart level;-50 ( finger when the patient fully extends an arm toward the sky) -30 (top of head), 0 (at the level of the heart), 50 (at the level of the hips) 75 (at the level of the knees and 100 at the level of the ankle)

189
Q

what happens with inspiration?

A
  • diaphragm moves downward the abd
  • thoracic pressure decreases
  • abd pressure increases
  • venous return to the heart increases
  • venous flow in legs decreases
190
Q

what happens with expiration?

A
  • diaphragm moves upward into the thorax
  • thoracic pressure increases
  • abdominal pressure decreases
  • venous return to the heart decreases
  • venous flow in leg increases
191
Q

Doppler shift, aka doppler frequency is what?

A

a change in frequency, the frequency of sound changes when the sound source and the receiver move closer together or farther apart

192
Q

what is a positive doppler shift?

A

when blood cells move toward the transducer, they reflect sound with a higher frequency

193
Q

what is negative doppler shift?

A

when blood cells move away from the transducer, they reflect sound with a lower frequency

194
Q

Doppler shift?

A

2 x velocity of blood x transducer frequency x cos / propagation speed

195
Q

Doppler shift is directly related to what?

A

velocity

196
Q

when does the first shift occur?

A

when the sound wave from the transducer strikes moving blood cells

197
Q

when does the second doppler shift occur?

A

it results from the transducer’s reception of the sound wave from moving red blood cells

198
Q

what do the x and y axis of a doppler spectrum represent?

A
  • x-axis = time

- y-axis = doppler shift or velocity

199
Q

Doppler shift is directly related to what?

A

frequency of the transmitted sound

200
Q

when does the doppler shift represent 100% of the true velocity?

A

when blood flow is is parallel to the sound beam

201
Q

what happens when an angle exists between the direction of flow and the sound beam?

A

the measured velocity is less than the true velocity

202
Q

what determines how much of the velocity is measured, when the sound beam and flow direction are not parallel?

A

it depends on the cosine of the angle between the sound beam and the direction of motion

203
Q

How is doppler shift related to cosine?

A

directly related, when the cosine doubles, the doppler frequency doubles; the cosine increases as angles approach zero degrees

204
Q

doppler shift and velocites cannot be measured when?

A

with a perpendicular incidence, 90 degrees

205
Q

when is flow parallel to the sound beam?

A

when the angle between the direction of motion and sound is 0 or 180 degrees

206
Q

cosine 0 degrees is 1, this indicates?

A

flow toward the the transducer

207
Q

cosine 180 degrees is -1 indicates?

A

flow away from the transducer

208
Q

Since the cosine of 60 degrees is 0.5, the measure velocity at 60 degrees is what

A

one half the actual velocity

209
Q

what is bidirectional doppler?

A

spectral doppler tracing flow toward and away from the tranducer (above and below the baseline)

210
Q

what is phase quadrature aka quadrature detection?

A

a commonly used signal processing technique for bidirectional doppler

211
Q

a pulsed doppler transducer is characterized by?

A
  • at least one crystal
  • damped PZT
  • low Q-factor
  • wide bandwidth
  • lower sensitivity
212
Q

a CW doppler transducer is characterized by?

A
  • at least 2 crystals
  • undamped PZT
  • high Q-factor
  • narrow bandwidth
  • higher sensitivity
213
Q

pulsed doppler gives us?

A
  • range resolution
  • sample volume
  • limited maximum velocity- Nyquist limit
  • aliasing
214
Q

CW doppler gives us?

A
  • range ambiguity
  • region of overlap
  • unlimited maximum velocity
  • no asiasing
215
Q

with imaging we have?

A
  • normal incidence- 90 degrees
  • higher frequency, improves resolution
  • pulsed wave only
  • minimum of 1 crystal
216
Q

with doppler we have?

A
  • 0 or 180 degrees
  • lower frequency-avoids aliasing
  • pulsed or CW
  • min. of 1 (pulsed ) or 2 (CW) crystals
217
Q

what is aliasing?

A

the most common error associated with doppler ultrasound; it happens when very high velocities in one direction are incorrectly displayed as going in the opposite diretion

218
Q

what is the Nyquist limit aka Nyquist frequency?

A

is the highest Doppler frequency or velocity that can be measured without the appearance of aliasing

219
Q

we get less aliasing with?

A
  • slower blood velocity
  • lower frequency transducer
  • shallow gate (high PRF)
220
Q

we get more aliasing with?

A
  • faster blood velocity
  • higher frequency transducer
  • dep gate (low PRF)
221
Q

what two methods to eliminate aliasing, increase PRF?

A

increasing the scale and moving to a new view with a shallower sample volume (increase the Nyquist limit

222
Q

what do the following techniques to eliminate aliasing do?

  1. lower transducer frequency
  2. zero baseline shift
  3. CW doppler
A
  1. decreases Doppler shift
  2. aliasing remains but display more appealing
  3. never aliases, but range ambiguity
223
Q

what does eliminating aliasing improve?

A

the ability to measure the maximum velocity with Doppler

224
Q

what does color doppler measure?

A

mean or average velocity

225
Q

what does spectral doppler measure (pulsed and CW) measure?

A

peak velocity

226
Q

what are the two mot commonly used doppler color maps used?

A

velocity mode and variance mode

227
Q

with a variance mode, what do colors on the Lt represent?

A

laminar flow

228
Q

with variance mode, what do colors on the Rt represent?

A

turbulent flow

229
Q

with any color flow image that is sector-shaped, the horizontal vessel will display what?

A

both the toward and away colors, the center of the lument will be black

230
Q

with any color flow image that has a rectangular shape, the horizontal vessel will display what?

A

1 color, and one can determine the direction of flow by placing an imaginary line in the upper corner and placing one’s finger her and slide it away from the imaginary line

231
Q

what are doppler packets aka ensemble?

A

multiple ultrasound pulses used to accurately determine blood velocities

232
Q

packets composed of a larger number of pulses have what 2 advantages?

A
  • more accurate velocity measurements

- increased sensitivity to low flow

233
Q

what disadvantages are there with packets with more pulses?

A
  • more time needed to acquire data
  • reduced frame rate
  • decreased temporal resolution
234
Q

what is power doppler aka energy mode or color angio?

A

it identifies the presence of a doppler shift, but does not evaluate speed or direction

235
Q

what are 3 advantages of power mode?

A
  • increased sensitivity to low flow or velocity
  • unaffected by doppler angles, unless the angle is exactly 90 degrees
  • no aliasing, since the velocity information is ignored
236
Q

what are 3 disadvantages of power mode?

A
  • no measurement of velocity or direction
  • lower frame rates
  • suscepitble to motion of the transducer, pt, or soft tissues
237
Q

what does a wall filter aka high pass filter do?

A

eliminates low frequency doppler signals near the baseline (ghosting and clutter)

238
Q

what is crosstalk?

A

a mirror image artifact

239
Q

what is spectral analysis?

A

a tool that breaks the complex signal into its basic “building blocks” and identifies the individual velocities that make up the reflected doppler signal

240
Q

what does Fast Fourier Transform used for?

A

to process both pulsed and continous wave doppler signals

241
Q

what are the advantages of FFT?

A

exceedingly accurate and displays all individual velocity components that make up the complex reflected signal

242
Q

what is autocorrelation aka correlation function used for?

A

to analyze color flow doppler

243
Q

for color to appear in a vessel, what must be created?

A

an angle other than 90 degrees must be created between the direction of flow and the direction of the sound beam

244
Q

when will color NEVER appear in a vessel?

A

when the directions of flow and sound are perpendicular

245
Q

what happens when we have a color flow images and our color gain level is too high?

A

color appears throughout the box, color confetti

246
Q

what happens when our color gain is too low?

A

all color disappears from the image

247
Q

what happens when we have a spectral display, and our pulsed doppler gain is too high?

A

gray scale noise appears throughout the spectrum

248
Q

what happens when we have a spectral display, and our pulsed doppler gain is too low?

A

all gray scale will disppear

249
Q

when should aliasing be considered?

A

when we have peculiar color variation

250
Q

how can we distinguish bidirectional flow from aliasing with color flow doppler?

A

flow reversal is present in a vessel when the colors red, black and blue are next to each other; if the colors that touch each other go around the outside of the map, aliasing is present

251
Q

how can we eliminate or reduce aliasing from a color doppler image?

A

the most effective way is to increase the velocity scale

252
Q

what other effect does increasing the scale have on a color doppler image?

A

it decreases the sensitivity to slow flows

253
Q

what happens when we increase the walter filter in a color flow image?

A

ghosting artifact disappears and removal of color from the slow flow states; increasing the wall filter leaves the high velocity flows inchanged

254
Q

in a doppler spectrum, what happens when we increase the wall filter?

A

the wall filter, selectively eliminates low frequency doppler shifts near the baseline; this does not affect the appearance of higher velocity flows

255
Q

if we have a color flow image and increase the wall filter, what happens?

A

it eliminates low frequency doppler shifts; is does not get rid of aliasing

256
Q

what happens when we increase the scale in a color flow image?

A

aliasing disappears and so does the low frequency flows

257
Q

what are the 6 assumptions of imaging systems?

A
  1. sound travels in a straight line
  2. sound travels directly to a reflector and back
  3. sound travels in soft tissue @ exactly 1,540 m/s
  4. reflections arise only from structures positioned in the beam’s main axis
  5. the imaging plane is very thin
  6. the strength of a reflection is related to the characteristic of the tissue creating the reflection
258
Q

when are reverberations created?

A

when a sound wave bounces back and forth between two strong reflectors; the first two reflections are real, the others are artifacts; assum #2

259
Q

when does comet tail aka ring down artifact appear?

A

when a sound wave bounces back and forth between two very closely spaced objects; assum #2

260
Q

when does shadowing artifact happen?

A

when sound hits a highly attenuating object such as bone; assum #6

261
Q

when are edge shadows created?

A

as sound beams refract and diverge along the edge of a curved structure; assump #6

262
Q

what is enhancement artifact?

A

a hyperechoic region that extends beneath structures with abnormally low attenuation; assum # 6

263
Q

what is focal enhancement aka focal banding?

A

is a hyperechoic horizontal region at the depth of the focus; assum #6

264
Q

when does mirror image artifact appear?

A

when sound reflects off a strong reflector (mirror), and is redirected toward a second structure; assum # 1 and 2

265
Q

what is crosstalk?

A

it’s an artifact that appears on a spectral doppler display

266
Q

what happens with speed error artifact?

A

it’s created when a sound wave propagates through a medium at a speed other than that of soft tissue, the correct number of reflectors are displayed, but appear at incorrect depths; assump # 3

267
Q

what do lobe artifacts degrade?

A

lateral resolution

268
Q

how can side lobes artifacts be reduced?

A

subdizing and apodization

269
Q

what do we get with refraction artifact?

A

a second copy of a true reflector incorrectly appears on the image; the artifact is at the same depth as the true reflector; assum #1

270
Q

what is slice thickness artifact aka section thickness artifact or partial volume artifact?

A

the thickness of an imaging plane varies, the portions of the slice have inferior elevational resolution when compared to thinner portions; assump #5

271
Q

what is lateral resolution artifact, aka point spread artifact?

A

it may create one reflection on the image from two reflectors, it may also create a horizontal reflection from a smaller reflector

272
Q

what is axial resolution artifact?

A

it may create one reflection from multiple small reflectors

SPI (3 decks)

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