SPI Review Flashcards
(175 cards)
1
Q
The thickness of the matching layer is ________ the wavelength
A
1/4
2
Q
What do the piezoelectric crystals do?
A
Convert electrical signals to acoustic pulses
3
Q
The thickness of the PE is ________ the wavelength
A
1/2
4
Q
What does frequency depend on in the transducer?
A
element thickness
5
Q
Thicker element = _______ frequency
A
lower
6
Q
Wider element diameter = ___________ beam intensity
A
low
7
Q
Higher frequency = ___________ axial/lateral resolution and ________ penetration
A
improved / less
8
Q
What does the damping/backing layer do?
A
reduces the ringing
9
Q
Damping _________ axial resolution and decreases the ________
A
improves / SPL
10
Q
What is the footprint?
A
The portion of the transducer that touches the skin
11
Q
When is a therapeutic ultrasound transducer used?
A
Usually with physical therapy
12
Q
What are 1-D arrays?
A
Elements arranged side by side oriented with the long axis and fired along the parallel axis
13
Q
What are 1.5-D arrays?
A
arranged side by side oriented with the long axis but are etched parallel to the long axis to create multiple elements in the short axis.
14
Q
What are 2-D arrays?
A
Typically have a few thousand elements. Used in 3D imaging and with linear, sector, and curvilinear transducers.
15
Q
What is propagation speed in soft tissue?
A
1.54 mm/ms
16
Q
Detail resolution is _________ and _________
A
axial and lateral
17
Q
Axial resolution is determined by
A
the length of the pulse (1/2 the SPL) and pulse duration
18
Q
Axial resolution is for structures ____________ to the beam?
A
parallel
19
Q
Lateral resolution is for structures _______ to the beam?
A
perpendicular
20
Q
Lateral resolution has to do with _______________
A
beam width
21
Q
Contrast resolution has to do with
A
number of shades of grey
22
Q
Temporal resolution has to do with
A
frame rate. The number of focuses, the number of scan lines
23
Q
Which resolution is controlled by depth?
A
temporal
24
Q
Deeper = _______ PRF
A
longer
25
Spatial resolution = __________ resolution
detail
26
Other names for axial resolution
depth, longitudinal, radial, range, linear
27
If frequency increases, axial's numbers ________, and indicates _________ axial resolution
decrease / better
28
Other names for lateral resolution
transverse, angular, azimuthal
29
What is temporal resolution?
the ability to accurately display moving structures over time
30
_______ has the best temporal resolution and _______ has the worst
M-mode / color Doppler
31
Temporal resolution increases with
shallow depth
single focal zone
decreased pulses per scan line
narrow sector angle
decreased line density
interpolation
32
What is frame time?
the amount of time required to produce a single frame
33
________ frame time leads to ________ frame rate and _______ resolution
increased / decreased / temporal
34
What is slice thickness resolution? (Elevational resolution)
A measure of the beam width perpendicular to the image plane. Set by the manufacturer
35
The ______ the element diameter, the _____ the near zone
wider / longer
36
The ________ the frequency of the beam, the _______ the near zone
higher / longer
37
Linear array have about how many elements?
about 200
38
Linear arrays use _______ focusing and beam steering
electronic
39
What specialties use linear arrays?
abdominal, OB, small parts, vascular, and musculoskeletal
40
About how many elements are in curvilinear arrays?
120-250
41
Curvilinear arrays have _________ focusing and beam steering?
electronic
42
Curvilinear arrays are used in what specialties?
abdominal, OB, gynecological, small parts
43
About how many elements are used in phased arrays?
100-200
44
Phased array has _______ steering and steered
electronic
45
Phased arrays are used in what specialties?
cardiac, abdominal, pelvic, vascular, transcranial, and neonatal brain imaging
46
Vector array is used in what specialties?
pelvic, echocardiography, abdominal, transcranial, neonatal brain imaging
47
What is laminar flow?
Concentric layers of flow each with a slight difference in velocity. (fastest in the center, slower at the edges due to friction)
48
What is plug flow?
When all layers of flow are moving at relatively the same velocity (like the aorta)
49
What is parabolic flow?
When there is more of a difference in the velocity between layers.
50
What is Poiseuille's equation about?
The relationship between pressure, flow volume, and resistance
51
When is Poiseuille's equation used?
to describe how much fluid (blood) moves through a pathway (artery)
52
Vessel length and viscosity are relatively _________. Increases in either one will cause __________ resistance
constant / increased
53
What is resistance?
the rate of flow in the arteries and is regulated by the arterioles
54
In a resting patient, the highest resistance in the arterial system is
the arterioles
55
Extremities/muscles have a much ________ resistance to blood flow than the organs
higher
56
increased viscosity and vessel length lead to ______ resistance
increased
57
increased vessel radius leads to _________ resistance
decreased
58
As resistance increases, blood flow __________ with ____________ in pressure
decreases / no change
59
Stenosis causes resistance to increase ___________ to a stenosis and decreases ________ to the stenosis
proximal / distal
60
Pressure is defined as
the concentration of force within an area
61
When does pressure increase?
systole
62
Average pressure in the veins is _______ and in the arteries _______
2 mmHg / 100 mmHg
63
Arterial stenosis leads to _________ pressure as the velocity __________ with stenosis
decreased / increases
64
Volumetric flow rate is always _________ to blood pressure
proportional
65
resistance and flow rate are _________ related
inversely
66
What is the Bernoulli effect?
The decrease in pressure at a stenosis due to increased velocity at the site
67
What is antegrade?
moving forward in the direction of blood flow
68
what is retrograde?
backward flow or filling, or against the normal direction of flow
69
what is turbulence?
disrupted flow cause by a stenosis, tortuosity, or bifurcation, appears at the exit point of a stenosis
70
what is bruit?
abnormal blood flow sound in a blood vessel, can be due to stenosis; also seen with vessel branching or tortuosity
71
what is thrill?
abnormal flow sensation in a blood vessel (vibration), can be due to stenosis; also seen with pseudo aneurysm and hemodialysis grafts
72
What is pulsatility?
continuous throbbing or beating, flow in the arteries pulsates due to continuous cardiac contractions, venous flow is not pulsatile because it is not moved by cardiac contraction
73
What is capacitance?
the ability of veins to store blood
74
Why are veins considered the capacitive vessels?
because of their increased compliance and ability to store larger volumes of blood than arteries
75
What is hydrostatic pressure?
weight of the column of blood inside the vessels
76
What is transmural pressure?
pressure within the veins pushing outward. (normally low)
77
______ and _____ are responsible for moving flow through the venous system
respiration / muscle contraction
78
Which increases venous return to the heart from the upper body, inspiration or expiration?
inspiration
79
What is the Doppler shift?
the mathematical difference between the transmitted and received frequencies, occurs when structures are moving towards or away form the listener
80
Doppler shift is directly related to ____________, __________ of red blood cells being sampled, and the ___________ between the US beam and blood flow
transducer frequency / velocity / cosine of the angle
81
The angle between the ________ and the ________ must be known to determine an accurate Doppler shift
US beam / blood flow
82
Doppler shift is inversely related to the _________
speed of sound in the medium
83
Doppler measures ______ not _________
velocity / speed
84
A low pass filter does what?
Eliminates the signal from the blood and only shows color information representing wall motion (color Doppler)
85
Larger packet size causes ___________ frame rates but produce more __________ flow velocity information
decreased / accurate
86
Larger packet sizes are better able to identify ________ flow more accurately
low velocity
87
What is autocorrelation?
automatically correlates data from multiple sampling sites. assesses the data from multiple sampling sites and produces a display representing mean flow velocities
88
What is packet size?
the number of pulses per scan line within the color gate.
89
Flow needs to be __________ to the beam. Never _________
parallel / 90 degrees
90
What is power Doppler?
Doppler mode in which the signal is determined by the amplitude of the shift, not the shift itself. Amplitude is directly proportional to the number of red blood cells.
91
How is power doppler imaging different than color doppler imaging?
Power doppler measures the energy variance not the frequency shift. It is not angle dependent
92
Power doppler is very __________, it is ideal for ______________, but also makes it more susceptible to __________
sensitive / slow, small vessels / patient or organ motion
93
For CD, PD, PW, and CW signals, ___________ are customarily used to eliminate the small doppler shift caused by movements of other tissues
high-pass wall filters
94
What is spectral doppler?
Doppler shifts are detected along a single line and used to produce a graphic representation of the blood velocities
95
How does PW Doppler work?
Using controlled time intervals between transmitted and received sounds to collect information using a single PZT element
96
Aliasing is the biggest disadvantage of PW Doppler because...
it limits the velocities that can be evaluated
97
Doppler shift is _______________ related to the transducer frequency
directly
98
The best incident angle to produce the most accurate Doppler shift information is
0 degrees (or 180 degrees)
99
The best obtainable incident angle that is most commonly used to provide Doppler shift information is
60 degrees
100
A 90 degree Doppler incident angle will demonstrate ________
no flow in either direction
101
An insonation angle less than 90 degrees will result in _________ shift
positive
102
an insonation angle greater than 90 degrees will result in _______ shift
negative
103
What does adjusting the color gain do?
adjusts the displayed amplitude of the reflected frequency shift from the flowing blood.
104
Setting the macine to a proper color gain involves what?
increasing the gain until blossoming is noted and then decreasing to just below that level
105
What is the optimum color angle sample between the sample box and the blood flow
0 degrees or parallel to flow
106
What happens as the incident angle moves closer to 90 degrees?
color Doppler display will decrease until it is absent
107
More _______ structures provide better color display with _____ frame rates and ______ temporal resolution
superficial / faster / improved
108
What is the color packet size?
also known as the ensemble length. The packet size refers to the number of samples taken during evaluation
109
What does the wall filter do?
Eliminates low frequency Doppler shifts from display. Used to reduce clutter/flash/ghosting artifacts. Will not eliminate aliasing
110
What is color priority/threshold?
determines wheter color pixels should be displayed preferentially over grayscale pixels
111
Lower threshold means _____
Higher threshold means _____
less color / more color
112
What is persistence?
temporal compounding. color sensitivity. uses the average of previous frames to create the displayed image. improves signal to noise ratio on color image
113
Higher persistence levels allow
prolonged display of color on the image. It is preferred for slow moving flow.
114
Increased persistence and sensitivity levels can aid in
the evaluation of heavily calcified arteries
115
For spectral Doppler, what is displayed on the graph?
Doppler shifts along a single line, used to produce a graphic representation of the blood velocities
116
What does the horizontal axis on the spectral graph represent?
Time
117
What does the vertical axis on the spectral graph represent?
Doppler shift/Velocity
118
What degree of angle will flow velocity be miscalculated?
20 degrees off axis
119
Usually a ________ cursor angle is necessary to obtain accurate Doppler information (especially in vascular)
60 degrees
120
What is the average size of the sample volume for arterial evaluations?
1 - 1.5 mm
121
What is the standard sweep speed setting for spectral Doppler display?
50 mm/s
122
Anytime a monophasic waveform is seen in an _____ it is abnormal
extremity
123
anytime a biphasic/triphasic waveform is seen in an _______ it is abnormal
organ
124
What is resistive index?
Doppler measurment used to quantitate the resistiveness of the distal bed.
125
When is resistive index used?
to evaluate arterial stenosis
126
What is pulsatility index?
Doppler measurement used to determine how pulsatile a vessel is over time.
127
How many planes/views are required to determine if it's artifact or something more?
at least two
128
What is range ambiguity?
Shallow reflectors reflect sound energy that arrives at the transducer before the rest of the original pulse finishes transmitting.
129
What does noise/speckle degrade?
contrast and spatial resolution
130
What is volume averaging artifact?
also known as slice thickness or beam width artifact. The echo information from the 3rd dimension is overlapped with the echoes from the center of the beam on the image. Happens the most in deep imaging where the beam is widest.
131
How to correct for slice thickness artifact?
narrowing the thickness of the beam, short axis focusing, using a standoff pad, or repositioning the focal zone
132
What is clutter (Doppler artifacts)
Also known as color flash, color bleeding, color ghosting. Unwanted Doppler display patterns typically caused by structure motion or breathing
133
What is blooming or blossoming (Doppler artifact)?
Color obscures the gray scale display of soft plaque because the resolution of color Doppler is lower than the gray scale. Causes the pixel to be displayed as color instead of grey scale.
134
What does the x and y axis represent in M-mode?
x = time / y = depth
135
What does the x and z axis represent in B-mode?
x = reflector depth / z = reflector brightness (amplitude)
136
What does the beam former do?
Controls the timing of the signals sent to the individual elements for steering and focusing the beam
137
What are grating lobes?
artifacts caused by extraneous sound that lies outside of the primary path of the beam
138
What is apodization?
controlled by the beam former by decreasing the strength of the voltage pulse sent to the outermost elements.
139
What is the pulser?
part of the beam former that controls the strength, or amplitude, of the electricity striking the elements, as well as the PRF and PRP.
140
What does the pulser control?
The amount of power entering the patient.
141
What other terms mean power?
output, output gain, output power, acoustic power...
142
The _______ the output power, the ______ the return echo
higher / stronger
143
What are the benefits of increased power output?
1) higher amplitude return echoes for a better signal-to-noise ratio.
2) improved depth penetration
144
How can the sonographer adjust the output power?
adjust the control stating output, power, or transmit.
145
What is frequency compounding?
Soft tissue is imaged at various frequencies and averaged. The displayed image is the result of all the frequencies and is another way to produce the image with improved contrast resolution and reduction in noise and acoustic speckle.
146
What is the master synchronizer?
The part of the machine responsible for controlling the timing of the echoes. It tells the pulser to send out a pulse and pays attention to when the echoes come back to determine their range.
147
What is harmonics?
harmonic signal produced by the patient's tissue that is a multiple of the fundamental frequency. Harmonics are only generated as the beam travels deeper. (2F is used)
148
If a 2 MHz beam is sent into the patient, with harmonic imaging, what signal is sent back?
4 MHz
149
What type of resolution is improved with harmonic imaging?
lateral resolution
150
What is the receiver?
Where the return signal is processed. (preampfication, amplification, compensation, compression, demodulation, and rejection)
151
What is amplification?
overall gain. increases or decreases the strength of all the returning echoes equally
152
What is compensation?
time-gain compensation. compensates for the fact that attenuation occurs, and the more distant echoes are increased in brightness to achieve a uniform level of brightness.
153
What is compression?
the function of the receiver that decreases the range of signal amplitudes present within the machines receiver.
154
What is dynamic range?
The series of echo amplitudes present within the signal. Inversely related to compression.
155
What is demodulation?
processes the signal to make it easier for the machine to handle. (Rectification and smoothing)
156
What is rectification?
Turning negative voltages into positive voltages
157
What is smoothing?
wrapping an envelope around the signal to make it less bumpy or remove the humps.
158
What is rejection?
discards signal amplitudes below a certain threshold to reduce image noise
159
What is the transmit/receive switch?
Ensures the electrical signals travel in the correct direction. It ensures the pulser voltages go to the transducer, and the received voltages from the transducer go to the signal processor (receiver)
160
What is the scan converter?
part of the machine that makes grayscale imaging possible and is responsible for storage of the image data.
161
Signals travel from the receiver to the __________ and then to the scan converter/image memory, and then to the _______
analog to digital converter / digital to analog converter
162
What is preprocessing?
where incoming signals are assigned shades of gray based on their amplitudes. Happens before the scan converter. Images are still live at this point.
163
A ______ is the smallest amount of computer memory possible.
Bit
164
_____ bits make 1 ______
8 / byte
165
The more pixels on display, the better the ______ resolution
spatial
166
What is write zoom?
a pre-processing function, enlarges the image by redrawing it. High quality zoomed image
167
What is read zoom?
a post-processing function, enlarges the image by magnifying the pixels. Offers a coarser, less optimal type of zoom.
168
What is spatial compounding?
Eliminates edge shadowing because the object is imaged at different angles.
169
What does spatial compounding reduce?
speckle artifact and reverberation
170
What is the purpose of the damping material?
to shorten the length of the pulse by decreasing the number of cycles in the pulse
171
What is sensitivity of the transducer?
the ability of the system to display low-level or weak echoes.
172
What is bandwidth?
the range of frequencies present within the beam
173
The more damping there is, the _______ the pulse, the ______ the bandwidth, the _____ the QF
shorter / wider / lower
174
What is the quality factor?
the measure of the beam purity. the operating frequency of the transducer divided by the bandwidth
175
What is elevational resolution?
the resolution in the third dimension of the beam. the slice-thickness plane
