Module 7 Flashcards
1
Q
Sound waves are transmitted by
A
Piezoelectric material
2
Q
A rapidly alternating electrical voltage applied to material will cause it to
A
Expand & contract
3
Q
What determines the range of sound wave frequencies that are generated?
A
The mechanical properties of the piezoelectric material
4
Q
Sound waves propagate (spread) by
A
Creating compression & refraction
5
Q
What is refraction
A
Change in direction of a wave passing from one medium to another
6
Q
What is reverse piezoelectric effect
A
When an electrical signal creates a mechanical strain (converts electrical energy into mechanical)
7
Q
When a mechanical strain generates a voltage, this is the
A
Piezoelectric effect
8
Q
Transducers create sound waves by the
A
Reverse piezoelectric effect
9
Q
What are important parameters in signal analysis?
A
Frequency, Wavelength, velocity, power & intensity
10
Q
Ultrasound ranges from
A
1-5megahertz
11
Q
What is inversely proportional to the wavelength
A
Frequency
11
Q
What is frequency
A
The number of sound waves per second (Hertz)
12
Q
Frequency is directly proportional to
A
The propagation speed of a sound through a given tissue
13
Q
Frequency is determined by the
A
Piezoelectric crystals
14
Q
Propagation speed is determined by the
A
Density of the tissue
15
Q
Propagation of ultrasound through tissue is
A
1540 meters a second
16
Q
The resolution or sharpness of the image is measured by the
A
Wavelength that is used
17
Q
Shorter wavelengths have a
A
Higher frequency & produce a higher resolution, but penetrate more shallowly
18
Q
Longer wavelengths have a
A
Lower frequency & a longer wavelength, producing a lower resolution but can penetrate deeper
19
Q
Curvilinear probes provide what kind of freqency
A
Low & can visualize deeper structures
19
Q
What is key to the best ultrasound image
A
Maintaining adequate penetration & maximum resolution
20
Q
What is axial resolution
A
The ability to differentiate objects along the axis of the ultrasound beam (vertical resolution on the screen)
21
Q
Lateral resolution is
A
A horizontal resolution or objects perpendicular to the ultrasound beam
22
Q
Collateral resolution will
A
Decrease as the depth increases due to scattering & divergence of the ultrasound beam
23
Image resolution can be affected by the
Number of piezoelectric crystals that emit & receive ultrasound waves, as well as their sensitivity
24
What is a fixed property of the transducer
Image resolution
25
The focal zone is the
Narrowest portion of the sound beam (in the middle)
Gives the highest beam intensity & best resolution
26
What is reflection
When a wave passes between tissues with different impedances (opposition to altering current) & part of the wave bounces back
27
What is refraction
The wave is refracted in a different direction due to the incidence
28
Scattering occurs when a
Sound wave is turned into heat
29
Depth of structures is determined by the
Time delay for echoes to return to the transducer
30
What is propagation speed
The velocity of sound & tissue & varies depending on the physical properties of the tissue
31
What is Acoustic impedance
The resistance to propagation of sound waves, a fixed property of the tissues
32
Acoustic impedance is determined by the product of its
density & the speed of sound within that medium
33
In reference to acoustic impedance, what determines the reflectivity of sound waves
The difference; The greater the difference in impedance, the greater the reflection of the sound waves
34
What is attenuation?
The loss of energy as the sound wave travels through tissue
35
Energy loss is dependent on the
Attenuation coefficient of the tissues; the frequency of sound waves & the distance traveled
36
Energy loss is due to
Absorption
Deflection
Divergence
37
What is the most important cause of attenuation
Absorption because it causes heat in the tissue
38
Absorption determines
The depth of ultrasound
39
Deflection can be either
Reflection, Refraction or Scattering, leading to a reduction of ultrasound echoes
40
What can be utilized to overcome attenuation
Gain, which will adjust the generated image, NOT improve signal quality
41
What is the most common type of ultrasound used
2D; B-mode or brightness mode
42
Anechoic
No sound waves returning
43
Hypoechoic
Less sound waves are returning & surrounding structures & objects appear darker
44
Isoechoic
Same color
45
What is Motion Mode
M-Mode; used to analyze movement over time
45
Hyperechoic
Appears bright; can be calcified or dense structures
46
The Doppler effect is a
Shift in the frequency of sound waves due to the relative motion between the source & the observer
47
Blood flow moving away
Blue; Negative; Low frequency
48
Blood flow moving the transducer will be
Red; Positive; High frequency
49
When is there no Doppler shift
When probe is perpendicular to blood flow
50
Color Doppler only shows
Flow, not structure
51
What prevents external interference
Electric shield that lines the transducer
51
What dampens vibrations from the case
Acoustic insulator
52
Axial resolution is the ability to differentiate
Objects on the same trajectory as the ultrasound beam
53
What dampens ongoing vibrations
Backing material; sound waves are absorbed by the backing material to prevent continued transmissions
53
Axial resolution is determined by
Sound wave frequency
Higher-better axial resolution
54
Lateral resolutions is determined by the
Width of the ultrasound beam, which is influenced by the diameter & frequency of the 2D piezoelectric crystals
55
Lateral resolution is the ability to differentiate objects that are
Perpendicular to the sound beam
55
Elevation resolution is determined by the
Thickness of the ultrasound beam in the image depth of the signals
56
Elevation is like looking into a
Swimming pool; objects appear on same plane
56
Temporal resolution is the visualization of
Moving structures
High-indicates a high frame rate & better capture of movement
57
Pulse frequency is the
Rate at which transducers emit sound
57
What are the 4 types of transducers
Linear, Curvilinear, Phased Array & Intracavity
57
Linear transducers are arranges in a
Flat matrix; Paralell beam; Rectangular image; High frequency, shorter wavelength; Excellent axial & lateral resolution; Superficial structures
58
Intracavity transducers combine a small
Convex footprint with high frequency range; Wider field of view; high resolution image; not ideal of deep structures
58
A higher pulse frequency & shallow depth increases
Temporal resolution because they are reflected sound waves that can be received by the transducer in more rapid succession
59
Phased array transducers produce
Diverging low frequency; pie shape image; differential excitation of piezoelectric elements creates rapid beam sweeping (pulsing multiple crystals); more efficient 2D
59
Rocking is moving the transducer
Side to side
59
Curvilinear transducer produces
Trapezoidal ultrasound beam; wide view; lower resolution; deeper structures, low frequency; longer wavelengths; greater slice thickness
60
Rotating the probe is
Twisting on its central axis
Used to align beam with long/short axis
60
Tilting the probe is
Changing the angle of plane
Obtain several cross sections
60
Sliding is moving the transducer
On the skin surface/up & down
61
What is the advantage of real time ultrasound
Ability to visualize structures in multiple planes
62
When looking at the screen, understand that
3D images are being displayed on a 2D ultrasound screen
63
Screen orientation markers in the upper corners means
Superficial structures are viewed at the top of the screen
63
The body is divided into what 3 primary planes
Sagittal
Transverse/Axial
Coronal
64
Which planes are long axis
Sagittal & Coronal
65
Which plane is the short axis
Transverse/Axial
66
The sagittal plan divides the body into
Left & Right
67
In standard convention, the transducer marker is directed
Superiorly towards the patient head so that superior structures are seen on the left side of the screen
68
The coronal plane divides the body into
Ventral & Dorsal/Front & Back
69
The transverse/axial plane divides the body into
Superior & Inferior/Upper & Lower
70
In the short axis/Transverse/Axial plane, how is the needle inserted
Perpendicular
71
If the depth is too shallow
Structures may be missed
72
If the depth is too deep
Structures are seen but with a lower resolution
73
Ultrasound waves are attenuated or weakend as they
Travel away from the transducer, reducing the number of returning echoes from deep structures
74
How do machines compensate for attenuation
By automatically increasing gain as depth increases= Time gain compensation
74
High zoom resolution will
Increase the resolution as the zoom is increased
75
The focal zone has the best
Lateral resolution
76
Increasing the depth of focus is to improve
Lateral resolution of the deeper structures
77
Spectral Doppler is useful to measure
Velocity of blood flow & calculate pressure gradients and flow rates
Specific area is measures
78
What is the main advantage of motion mode
Have high sampling rate, which provides good temporal resolution of rapidly moving structures
79
What are the forms of artifacts?
Artifact of wave propagation
Gain characteristics
Velocity Errors
Attenuation
79
Artifacts originate from
Erroneous ultrasound signaling due to a violation of rules
80
Sound waves reflect at tissue interfaces where
There's a large difference in the speed of sound between 2 tissues= Acoustic Impedance
81
The amount of reflected sound waves at tissue interfaces is directly proportional to the
Difference in acoustic impedance between the 2 adjacent tissues
82
Reverberation artifact occurs when 2 tissues
Interfaces with large acoustic impedance are parallel to each other & the sound beams path is perpendicular to the structures
Will see bright parallel lines
83
Reverberation artifact is most pronounces when the ultrasound beam is
Perpendicular to the highly reflective structures, so tilting & changing the angle of isonations may lessen them
84
Mirroring is created by the
Reflection of sound waves between a transducer, a strong reflector & a target structure
85
How can you decrease mirror image artifacts
Changing the angle of isonation & decreasing the gain
86
Refraction results from the
Differences in the speed of sound in the different tissues because of their different acoustic properties
86
What is refraction
Is a change in the direction of the sound waves as the wave passes between tissues
87
The degree of the deflection is proportional to
Speed of sound differences & the angle of incidence of the ultrasound beam
88
As the difference in speed & the angle of incidence increases,
The magnitude of refraction increases
89
Beam when artifact is due to
Lateral resolution & is most common distal to the focal zone where the beam is wider
89
Refraction is most pronounced in
Fat, soft tissue & high oblique interfaces
90
How can you reduce secondary lobe artifacts
Decreasing the gain & using tissue harmonic imaging (THI)
91
Slice thickness artifact is due to
Limitations of elevational resolution
Adjust the depth of the focal zone
92
Acoustic shadowing is seen
Distal to highly attenuated structures that either reflect, scatter or absorb the majority of ultrasound waves
93
Sound travels through fluid
Unimpeded
93
Lateral resolution is determined by
Ultrasound frequency & beam width
94
The higher the frequency, the narrower the focus & the
Better axial & lateral resolution
95
What outside element can reduce refraction
Ultrasound gel
96
What is the oldest ultrasound technique
A-mode, which used 1D imaging with a series of vertical peaks
97
The curved probe produces
Curvilinear scan & arc shape image
98
A linear transducer produces
Parallel lines & a rectangular display
99
The echoes exhibit a
Steady decline in amplitude with increasing depth
100
Gain is the ratio of
Output to input & electrical power
101
Gain can be used to increase the
Amplitude of incoming signals from various tissue depths
102
A peripheral nerve is always located in the
Vicinity of an artery between fascicular layers
103
What 5 functions allow you to achieve an optimal image
Depth
Frequency
Focusing
Gain
Doppler
104
Lateral resolution can be improved by utilizing
High frequency & focusing the ultrasound beam
105
Focusing will
Narrow the ultrasound beam to improve the lateral resolution & sensitivity
106
Inserting a needle in plane means
Placing in the plane of the ultrasound beam, resulting in the needle shaft & tip being observed in the longitudinal view
Typically used
107
Inserting a needle out of plane means
Inserting the needle perpendicular to the transducer
Used for vascular access
108
Enhancement is
Overly intense echogenicity behind a fluid filled structure
109
Nerve stimulator below 0.2 milliamps indicates
That the needle tip is within the nerve
110
Circumferential spread around the nerve will provide
Quicker onset & better anesthesia
111
Impedance is where
Waves stop
112
Gain does not change the
Resolution
113
Mechanical properties of piezoelectric material determine the
Range of sound wave frequencies that are generated
114
Elevation resolution is a
Fixed property
115
Reflection & propagation of sound waves depends on
Acoustic impedance & attenuation
116
Attenuation, which is energy lost is due to
Absorption, Deflection & divergence
117
Divergence refers to
A loss of ultrasound beam intensity as the beam widens & a fixed amount of acoustic energy is spread over a wider area
118
What 3 things determine Doppler Shift
Frequency
Velocity
Angle of Insonation
139
Sound waves are transmitted by
Piezoelectric crystals
140
