Chapter 6 Artifacts notes

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1

Artifact

anything that is not properly indicative of the structures or events

2

Benefits to artifacts

shadowing
enhancement

- tell the difference between solid and fluid
- characterize masses

3

Negative attributes of artifacts

improper location
wrong size
wrong shape
wrong acoustical properties
absent
present
absuring

4

Artifacts can be due to improper equipment settings

receiver gain
compensation settings
pre/post processing
range ambiguity

5

Artifacts can be due to ultrasound pysics

ring down
enhancement
edge shadowing
shadowing
reverberation
mirroring

6

Artifacts occur from assumptions

straight line
along the beam axis
amplitude related to the object struck
speed of sound in soft tissue

7

Doppler artifacts

incorrect spectral flow
aliasing
range ambiguity
mirror imaging
speckle

8

Slice thickness artifact

when 3D is flattened to convert to 2D external echoes show up in the image

9

Cause of slice thickness artifact

beam is not razor thin

10

AKA slice thickness artifact

section thickness
elevational resolution
partial volume artifact

11

What transducers are prone to slice thickness artifacts?

linear array

due to poor elevational resolution

12

why are machines good at axial resolution?

axial resolution does not change with depth

13

what artifacts is similar to multipath?

mirror

14

What causes multipath?

returning echoes do not return in a direct line

15

Multipath

gives wrong depth

16

cause of acoustic speckle

small amplitudes of sound waves interfering with each other

17

Acoustic speckle

card image

liver

specular reflections

incorrect texture

18

How to improve acoustic speckle?

THI

19

What are the problems associated with acoustic speckle?

if too bad you will not be able to see (fat encompassing)

liver - pathological degrees of fatty filtration

20

Reverberation

card image

bouncy ball

multiple echos (strong reflectors) that appear on the screen

multiple bounces between two or more surfaces

always equal distance

normal declining intensity

21

Ring down artifact

ring down occurs with gas filled loops of bowel

tends to occur with dirty shadowing

22

Comet trails

squeezed out reverberation

reflectors close

23

mirror image

card image

and improper location caused by a change in propagation speed

caused by an adjacent strong reflector

24

What frequently causes mirror image?

diaphragm

25

Spectral mirroring

when spectral doppler appears in both sides of the baseline

26

what is a common cause of spectral doppler?

receiver gain too high

27

How do you fix spectral mirroring?

change angle
turn down receiver gain
change to higher frequency

28

What type of transducer produces side lobes?

single element

29

What type of transducer produces grating lobes?

array transducers

30

What causes lobes?

weak beams that might otherwise be ignored hit a strong reflector.

the reflected echoes become misplaced.

31

How do you get rid of lobes?

subdicing the element

using dynamic apodization

32

apodization

weakening of the outside elements

listening is decreased on the side

33

How do speed errors occur?

system works on the assumption that sound will make a round trip through soft tissue in 13 μs/cm

34

Where is the object placed if the speed is faster than 13 μs/cm?

closer

35

Where is the object placed if the speed is slower than 13 μs/cm?

farther

36

Split off artifact

object in front of another object causes the sound to travel faster or slower only on a portion of the second object. Part of the object usually the diaphragm is placed incorrectly and the object appears cut

37

step off artifact

aka split off artifact

38

cut artifact

aka split off artifact

39

What causes Range ambiguity?

caused by deep echoes from a previous pulse

40

what is range ambiguity?

object is placed closer and near the scan plane

41

How can you correct range ambiguity?

Change frequency

change depth

change PRF

most systems will adjust PRF

42

What is shadowing

shadows distal to strong attenuator

43

What causes shadowing?

strong reflector bouncing all sound back imediately

strong absorber - no echoes left to return

44

What causes edge shadowing?

reflections bouncing away when hitting a curved object - none return

45

Dirty shadowing

usually occurs with bowels

shadowing when internal echoes are present

46

What is enhancement

hyperechoic areas distal to a a weak attenuator

cysts

47

What causes enhancement

an unexpected increase in amplitude

48

focal enhancement

increased enhancement at the focus

49

What can you do to correct focal enhancement?

spacial compounding

50

what is thru transmission?

aka enhancement

51

Aliasing

peaks cut off and place on bottom

speeding ticket

blood travels faster than the nyquist limit

52

What can cause aliasing?

insufficient spatial sampling

insufficient temporal sampling

53

What can correct aliasing?

raise PRF - chance of range ambiguity

increase doppler shift

shift baseline - cosmetic

switch to continuous wave

54

What is the nyquist limit?

1/2 PRF

55

PRF

pulses per second

56

Artifact cause

axial resolution

pulse length

57

Artifact cause

lateral resolution

pulse width

58

Artifact cause

section thickness

pulse width

59

Artifact cause

speckle

interference

60

Artifact cause

reverberation

multiple reflections

61

Artifact cause

refraction

refraction

62

Artifact cause

multipath

multiple reflections

63

Artifact cause

mirror image

multiple reflections

64

Artifact cause

side lobes

side lobes

65

Artifact cause

grating lobes

grating lobes

66

Artifact cause

comet trail

reverberation

67

Artifact cause

ring down

resonance

68

Artifact cause

speed error

speed error

69

Artifact cause

range ambiguity

high PRF

70

Artifact cause

shadowing

high attenuation

71

Artifact cause

enhancement

low attenuation

72

Artifact cause

edge shadowing

refraction

73

Artifact cause

focal enhancement

focusing

74

Artifact cause

aliasing

low PRF

75

Artifact cause

spectral mirroring

high doppler gain

76

Which testing is the most challenging?

Doppler

77

What part of the system is most likely to break down?

transducer

electric shock

78

Why do we perform performance testing?

to prevent degradation of image

79

What do acoustic output testers evaluate?

beam former and transducer acting together as a source of ultrasound

80

what do flow testers evaluate?

Doppler

81

What do detail testers evaluate?

lateral and axial resolution

82

What so output testers evaluate?

sound output

83

What is the goal of system testers?

detect gradual changes in system performance

84

Who does the responsibility of quality assurance rest?

sonographer

85

How often should equipment be tested?

one a month

86

Perfecting these methods is _____ but must be done & must be ______.

difficult

repeatable

87

What do AIUM test objects test for?

slice thickness

beam width

detail resolution\depth accuaracy

measurement accuracy

dead zone

88

What is the main problem with AIUM test objects?

no attenuation properties

89

What is the AIUM test object usually filled with?

water

but sometimes no water

90

What is the main advantage of the AIUM test object

price

91

What does the tissue/cyst phantum test for?

detail resolution

dynamic range

time gain compensation

contrast resolution

92

What does the cyst phantom contain

columns of simulated cysts

93

How do you fix lateral smearing?

decrease depth (increases frame rate - improves temporal resolution)

94

Describe the constructions of the tissue phantum

rubber face & sides

plexiglass base

cosists of cystic, nylon other materials

95

What is the test phantom filled with?

gel - 1.54

rubber - 1.45

96
card image

How would you test the dead zone?

card image
97
card image

How do you evaluate cysts

card image
98
card image

What does the cyst evaluation show?

size and depth variation

99
card image

How would you evaluate axial resolution?

card image
100
card image

What does this test for?

axial resolution

smallest distance two pins can be seen as two separate pins

101
card image

How would you evaluate vertical registration?

card image
102
card image

What does this test for?

vertical registration / range accuracy

ability to display echoes at the proper depth or top line

103
card image

How would you evaluate Horizontal registration?

card image
104

What does this test for?

Horizontal registration

the ability to position echoes in the their correct position along a line that is perpendicular to the ultrasound beam

105
card image

How would you evaluate lateral resolution?

card image
106
card image

What does this test for?

lateral resolution

minimum distance two pins can be seen as two separate pins at a specific depth

107
card image

How would you evaluate grey scale?

card image
108
card image

What does this test for?

grayscale / contrast resolution

the ability to discriminate between 2 different objects that have different shades of grey

109
card image

What is the difference between these two test for contrast resolution?

the first one has size variation

the second one has depth variation

110

Minimum sensitivity

start by making TGC flat then increase gain from minimum value

the point the echo appears on screen is minimum sensitivity

111

Normal sensitivity

is the point in which all the pins on an AIUM test object are displayed

112

Sensitivity

is the range that echoes are barely visible to fully sensitivity

113

lateral resolution

the minimum distance that two rods are displayed as two separate images at a specific depth

114

Focal zone

the depth at which the intensity is the highest and beam is the narrowest

this may be found using beam profiler or hydrophone

115

Dynamic range / greyscale

change in gain should result in a change in greyscale

116

vertical registration / range accuracy

the machines ability to display echoes at the proper depth

117

depth calibration

the accuracy of B mode, m mode and A mode on displaying the depth of reflectors

118

horisontal calibration

the machines ability to position echoes in the correct postiion perpendicular to the U/S beam

119

longitudinal resolution

smallest distance at which two pins are displayed as two separate echoes in their position parallel to the beam

120

What do the Doppler performance tools evaluate?

the effective position of the Doppler beam (penetration)

accuracy of measured flow

accuracy volume and flow speed

121

What do we use for Doppler testing?

Blood tissue phantom

Doppler testing object

122

What is a Blood tissue phantom

Doppler testing the mimicks blood

  • sephadex in water
  • polystyrene microspheres in water/glycerol
  • water + machine cutting oil
  • starch suspensions
123

What is a Doppler testing object?

Doppler test object uses controlled movement of strings

  • moving solid object
  • usually a string ultrasound
    • pulsatile motions
    • reverse motion
124

What are the disadvantages of the Doppler string phantom?

  1. over estimates peak velocities
  2. causes artifactual spectral broadening
125

What does a Blood tissue phantom contain?

an image face

medium

a flow conduit

pump

blood mimick

reservoir

126

How does a Blood tissue phantom work?

complex

tube connects to a pump

pumps an echogenic fluid through out a known velocity simulates a stenosis.

127

What is a microprobe?

small transducer on a hollow needle

128

What is a hydrophone?

large piezoelectric membrane with electrodes on both sides

129

What are microprobe and hydrophone used for?

Measure intensity

produce a waveform on an oscilloscope

130

What do microprobe and hydrophone use as a piezoelectric material?

PVDF

131

How do microprobe and hydrophone work?

receive sound from all directions measure pressure at a given point within the beam in response to the varying pressure

the hydrophone produces a varying voltage

132

What is the voltage produced by a hydrophone displayed on?

oscilloscope

133

What does an oscilloscope display?

bandwidth

134

What do hydrophones measure?

frequency

PRF

duty factor

pressure amplitude

wavelength

SPL

intensity

135

Which type of U/S produces the greatest acoustic output?

Pulsed Spectral Doppler

Color Doppler

M mode

B mode

136

Intensity and output indexes have already been copulated using a ______.

hydrophone

137

What is the #1 assumption of risk?

U/S is energy and any energy applied to human cells can cause change

138

What is the rule of U/S?

risk benefit ratio

any possible benefit must outweigh possible risks

  • whenever possible
    • increase benefit
    • decrease risk
139

How do we increase benefit?

Better equipment

  • choose best greatest depth higher resolution - output gain will not need to be increased
  • harmonic imaging
  • appropriate transducer

Better operator

  • knowledgable
    • formal
    • informal learning
  • experience
140

How do we decrease risk?

decrease output/exposure

  • use only when indicated
  • minimize length of exam

decrease bioeffects

  • lower exposure intensity
  • decrease length of exam
  • use low output imaging methods
141

Do you need a Doctors orders for an ultrasound exam?

Yes

medical device regulates by the FDA

142

What are the two types of mechanical bioeffects?

cavitation

radiation

143

What is radiation?

the amount of force that a beam exerts on an absorber or reflector

144

What are the two types of bioeffects?

heating - attenuation of U/S is primary by heat

cavitation - motion of microbubbles

145

What is heating primarily due to?

absorption

146

Why does absorption cause heating?

absorption involves conversion of U/S to heat

147

U/S produce a temp. rise as it propagates through tissue

...

148

What happens to heat when intensity goes up?

rises

149

What happens to heat when frequency goes up?

rises

150

What can Rayleighs scattering cause?

Thermal injury

151

Where are temperature elevations more likely to occur?

tissue-bone interface

152

What area is of great concern to thermal injury?

soft tissue adjacent to bone in a fetus

153

What is SPTA associated with?

tissue heating

154

What exam can be used without fear?

any exam that causes elevation in temperature of less than 2 degrees Celcius

155

What exam may cause harm in a fetus?

an exam that causes an elevation of temperature of greater than 41 degrees Celcius

156

What does Rayleigh scattering cause?

RBC to scatter

157

What is Rayleigh scattering?

when the wavelength of the incident sound beam is smaller than the size of the RBC

158

Which causes higher Temperature elevation Pulsed wave or Continuous wave?

CW causes higher temperature elevation

159

Which causes higher Temperature elevation Focused or unfocused?

unfocused causes higher temperature elevation

* focused has a narrow beam and heat is easily dispersed

160

What is cavitation?

the production and behavior of bubbles in a liquid medium

161

Where would a sound wave may cause cavitation?

Nucleation sites

tissue with gas bubbles

162

What are the two types of cavitation?

stable cavitation

transient cavitation

163

What is stable cavitation?

expand and contract

bubbles that oscillate in diameter with the passing pressure of a sound wave

bubbles don't burst

causes shear stress - cutting force

164

What does shear force cause?

microstreaming

165

What is microstreaming?

rapid rotational flow that occurs in intact blood vessels

166

What is shear stress?

cutting force

167

What is transient cavitation?

bubbles expand and collapse violently

bubbles burst

168

What is another name for transient cavitation?

Collapse / inertial cavitation

169

What does transient cavitation cause?

destructive effects

shockwaves

light emissions

high temperature

170

What is Thermal index?

heat production index -

deals with bioeffects caused by heating

171

If a machine can exceed thermal or mechanical indexes what must be?

acoustic output displayed

172

What is Mechanical index

Motion production index -

deals with bioeffects caused by cavitation

173

What is the thermal index measured in?

degrees celcius

174

Which display is preferred SPTA or Thermal index?

Thermal index - more accurate

175

What should SPTA be below?

720 mw/cm2

176

TIS

Thermal index soft tissue

177

TIB

Thermal index bone

178

TIC

Thermal index cranial

179

TI of 2 or less =

expected heating of 2 degrees or less

180

Mechanical index formula

MI = derated peak rarefractional pressure / sqrt (U/S center frequency

181

What is threshold for MI?

.3 or less

182

What is normal body temperature?

37 degrees C

183

What is the max body temp rise?

39 degrees C

184

C to F

37°C x 9/5 + 32 = 98.6°F

185

F to C

(98.6°F - 32) x 1.8 = 37°C

(98.6°F - 32) x 5/9 = 37°C