Chapters 1-24 Flashcards
(272 cards)
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
2
Q
increase by a factor means
A
multiply by that number
3
Q
decrease by a factor means
A
divide by that number
4
Q
10^9 means…..
A
giga, G, billion
5
Q
10^6 means…..
A
mega, M, million
6
Q
10^-3 means….
A
milli, m, thousandth
7
Q
10^-6 means…
A
micro, u, millionth
8
Q
10^-9 means….
A
nano, n, billionth
9
Q
10^3 means….
A
kilo, k, thousand
10
Q
sound is …..
A
- a mechanical wave
- travels in a straight line
- sound waves are longitudinal
11
Q
acoustic propagation properties are…
A
the effects of the medium upon the sound wave
12
Q
Biologic effects are….
A
the effects of the sound wave upon the biologic tissue through which it passes
13
Q
acoustic variables
A
the way sound waves are identified
- pressure - pascals (Pa)
- density - kg/cm^3
- distance - cm, mm
14
Q
acoustic parameters
A
a waves features or characteristics
15
Q
Decibels are what?
A
-a relative measurement, a comparisson, a ratio, logarithmic
16
Q
Negative decibels describe what?
A
Signals that are decreasing in strenght or are getting smaller
17
Q
Attenuation is determined by what two factors?
A
Path length and frequency of sound
18
Q
How are frequency and attenuation related?
A
Directly
19
Q
What 3 processes contribute to attenuation?
A
Reflection, scattering & absorption
20
Q
Specular reflection is?
A
When the beam reflected hits a smooth boundary
21
Q
Diffuse reflection (rough boundary) is aka?
A
Backscatter
22
Q
intensity =
A
power (w) / area (cm^2)
23
Q
Power is related to?
A
amplitude squared
24
Q
Intensity is related to?
A
amplitude squared
25
Power is related to?
intensity
26
Wavelength (mm) =
1.54 mm/us /frequency (MHz)
27
speed (m/s) =
frequency (Hz) x wavelenght (m)
28
as stiffness increases.....
speed increases
29
as denstiy increases....
speed decreases
30
bulk modulus is the same as?
stiffness
31
which 5 parameters describe pulsed sound?
- pulse duration
- pulse repetition period
- pulse repetition frequency
- duty factor
- spatial pulse length
32
what is duty factor?
the percentage of time that the system transmits a pulse
33
With shallow imaging we have....
- less listening
- shorter PRP
- higher RRF
- higher duty factor
34
With deep imaging we have....
-more listening
-longer PRP
-lower PRF
lower duty factor
35
what is the duty factor for continuous wave sound?
1.0 (100%)
36
what is the typical value for duty factor for pulsed wave sound?
0.2 -0 .5%
37
what are the intensity measurement methods?
- SPTP
- SATP
- SPTA (tissue heating & bioeffects)
- SATA
- SPPA
- SAPA
38
all intensities have units of ?
W/cm^2
39
What are the temporal intensities from largest to smallest?
Itp, Imax, Ipa, Ita
40
What is the rank of intensities from largest to smallest?
SPTP, Im, SPPA, SPTA, SATA
41
What happened to sound as he travels in the body?
It attenuates
42
What are the units of attenuation?
dB
43
Decibels require what?
2 intensities
44
Positive decibels report signals that or what?
Increasing and strength or getting larger
45
Decibel notation is?
A relative measurement, a comparison, a ratio,logarithmic
46
Negative decibels describe signals that are what?
Decreasing and strength are getting smaller
47
Attenuation is determined by what two factors?
Path length and frequency of sound
48
More attenuation happens with?
Longer distances and higher frequencies
49
Less attenuation happens with?
Shorter distances and lower frequencies
50
What the processes contribute to attenuation?
Reflection, scattering, and absorption
51
What are the two forms of reflection?
Specular and diffuse
52
Diffuse reflection a.k.a.?
Backscatter
53
What is scattering?
Random redirection of sound in many directions
54
What is the relation between frequency and Rayleigh scattering?
Proportional to frequency to the fourth power
55
What is the attenuation Coefficient?
Is the number of decibels of attenuation that occurs when sound travels 1 cm
56
What are the units of attenuation coefficient?
dB/cm
57
What is the half-value layer thickness?
Is the distance sound travels in a tissue that reduces intensity of sound to one half its original value
58
What are the bases for ultrasonic imaging?
Reflection and transmission
59
What are the units of impedance?
Rayls
60
What is normal incidence also called?
Perpendicular, Orthogonal, right angle, 90°
61
What is incident intensity?
Is the sound wave's intensity immediately before it strikes a boundary
62
What percentage of a sound waves intensity is reflected at a boundary between two Soft tissues?
Very little 1% or less
63
What percentage of a sound wave's intensity is transmitted at a boundary between two soft tissues?
Most 99% or more
64
When we have normal incidence reflection occurs only if?
The media on either side of the boundary have different impedances
65
What to physical principles always apply to reflection with oblique incidence?
Conservation of energy and reflection equals incident angle
66
Refraction occurs only you?
Oblique incidence and different propagation speeds of the two media
67
What is Snell's law?
It's quantifies the physics of refraction
68
If speed 1 equals speed 2....
No refraction, transmission angle equals incident angle
69
Speed 2 greater than speed 1.....
Transmission angle greater the incident angle
70
Speed 2 less than speed 1...
Transmission angle less than incident angle
71
What is the go return time?
The elapsed time from pulse creation to pulse reception
72
What is the 13 µs rule?
For every 13 µs of go return time the object creating the reflection is 1 cm deeper in the body
73
What does the backing material enhance?
Axial resolution
74
In decreasing order of impedance....
PZT>Matching layer>gel>skin
75
What are 3 consequences of backing material?
Decrease sensitivity, wide bandwidth,and low-quality factor
76
What are the characteristics of damping material?
High degree of sound absorption and acoustic impedance similar to PZT
77
What is bandwidth?
The range frequency found in a pulse
78
With continuous wave transducers, electrical frequency equals......
Acoustic frequency
79
What 2 characteristics of the active element combine to determine the frequency of sound?
Speed of sound in the PZT and thickness of the PZT
80
What are the characteristics of high frequency waves imaging transducers?
Thinner PZT crystals & PZT with higher speeds
81
What are the characteristics of low. Frequency pulsed wave imaging transducers?
Thicker PZT crystals and PZT with lower speeds
82
What gives us a shallow focus?
Small diameter PZT & lower frequency
83
What gives us a deep focus?
Large diameter PZT and higher frequency
84
What gives us less divergence?
A larger diameter and higher frequency
85
What gives us more divergence?
Smaller diameter and lower frequency
86
What are HUYGEn's wavelets aka?
Spherical waves, or diffraction patterns (v shaped waves)
87
What is axial
| resolution?
It deals with structures that are parallel to the sound beam
88
LARRD stands for?
Longitudinal, axial, range, radial and depth
89
What is better axial resolution associated with?
Shorter spatial pulse lenght, shorter pulse duration, higher frequencies (shorter wavelength), fewer cycles per pulse (less ringing) and lower numerical values
90
What is lateral resolution?
It relates to structures that are positioned perpendicular to the sound beam
91
What does LATA stand for?
Lateral, angular, transverse, and azimuthal
92
Where is lateral resolution Best at?
At the focus
93
What does focusing do?
It concentrates the sound energy into a narrower beam and thus improve lateral resolution
94
Fixed focusing is aka?
Conventional or mechanical focusing
95
What are the effects of focusing?
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.
96
What are the three basic modes oh viewing ultrasound information?
Amplitude mode, brightness mode, and motion mode
97
With M-mode....
X-axis displays time
| Y-axis displays depth
98
With B-mode....
X-axis displays depth
| Z-axis displays amplitude
99
With A-mode....
X-axis displays depth
| Y-axis displays amplitude
100
What are the US system's main components?
Transducer, pulser and beam former, receiver, display, storage, and master synchronizer
101
What is the pulser's function?
It creates electrical signals that excite the transducers PZT crystals and create sound beams
102
what are array transducers?
they contain multiple active elements; an array comprises a single slab of PZT cut into a collection of separate pieces called elements
103
3 types of array transducers are:
linear, annular and convex
104
phased array always means what?
adjustable or multi-focus
105
What creates electronic steering?
slope
106
slice thickness or elevational resolution is what?
it deals with shallow to deep
| side to side and above to below the imaging plane
107
side and grating lobes degrade what?
lateral resolution
108
side lobes are created by what?
mechanical transducers
109
grating lobes are created by what?
array transducers
110
What is apodization?
when stronger electrical signals are used to excite the inner crystals and progressively weaker electrical spikes excite the outer crystals. Lobes are diminished
111
What is subdizing?
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
what is dynamic aperture aka variable aperture?
it can be used to make a sound beam narrow over a greater range of depths and thus optimize lateral resolution
113
frame rate is determined by what 2 factors?
- sound's speed in the medium
| - the depth of imaging
114
Tframe and frame rate are?
inversely related
115
what system settings affect frame rate?
imaging depth (deeper, lower FR) and number of pulses per frame (less pulses, higher FR)
116
what factors determine the number of pulses per frame?
- number of focal points
- sector size
- line density
117
multifocusing does what to FR?
it decreases FR and disminishes temporal resolution
118
multifocus improves what?
lateral resolution
119
Sector size aka FOV, does what to FR?
if narrow this means less pulses, so it increases FR
120
What does line density do to FR?
If we increase line density, we decrease FR
121
What does high line density do?
it increases spatial resolution, but decreases temporal resolution
122
what type of resolution does multi-focusing improve?
lateral resolution
123
To have higher FR, we need to have?
- shallower imaging
- single focus
- narrow sector
- low line density
124
To have lower FR, we need to have?
- deeper imaging
- multiple focal points
- wide sector
- high line density
125
What is the transducer output aka?
Output gain, acoustic power, pulser power, energy output, transmitter output power or gain.
126
what are the six components of an US system?
- Transducer
- Pulser and beam former
- receiver
- display
- storage
- master sychronizer
127
what is the function of the pulser?
it determines amplitude, PRP, and PRF
128
what is the function of the beam former?
determines the firing delay patterns for phased array systems
129
output power increases what?
signal to noise ratio
130
what are the receiver operations?
- amplification (remember alphabetical order)
- compensation
- compression
- demodulation
- rejects
131
what happens with amplification (dB)?
all electrical signals in the receiver are affected identically by amplification
132
what is compression?
it alters the gray scale mapping of an us image; aka log compression or dynamic range
133
what does demodulation do?
a 2 part process that changes the electrical signal into a form more suitable for display; rectification and smoothing (or enveloping)
134
what does reject affect?
only weak signals affected; strong signals remain unchanged
135
what is contrast?
a control that determines the range of brilliances within the displayed image. Bistable images are high contrast
136
what are some limitations of analog scan converters?
image fade, image flicker, instability, deterioration
137
what are some advantages of digital scan converters?
uniformity, stability, durability speed, and accuracy
138
what is pixel density?
the number of picture elements per inch
139
what's a bit?
the smallest amount of computer memory
140
what is a byte?
a group of 8 bits such as 10011111
141
what do get with fewer bits per pixel?
fewers shades of gray and degraded contrast resolution
142
what do we get with more bits per pixel?
more shades of gray and improved contrast resolution
143
EX: how many possible shades of gray are displayed with 5 bits of memory?
multiplying 2 by itself 5 times yields = 32
144
coded excitation provides what?
- higher signal to noise ratio
- improved axial resolution
- improved spatial resolution
- improved contrast resolution
- deeper penetration
145
what is coded excitation?
creates very long sound pulses containing a wide range of frequencies; it occurs in the pulser
146
what does PACS stand for?
picture archiving and communications system
147
what does DICOM stand for?
digital imaging and computers in medicine
148
what is dynamic range?
a method of reporting the extent to which a signal can vary and still be accurately measured; units dB
149
what are the mathematics of compression?
add or subtract
150
with fewer shades of gray we have....
- few choces
- black and white (bistable)
- narrow dynamic range
- high contrast
151
with more shades of gray we have....
- many choices
- gray scale
- wide dynamic range
- low contrast
152
tissue harmonics are
- created in tissues
- created during transmission
- created by non-linear behavior
- primarily created along the beams main axis
153
what is pulse inversion harmonics?
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
modulation harmonics is what?
another imaging technique specifically disigned to augment harmonic reflections, while eliminating distorted fundamental reflections.
155
contrast agents must must meet what requirements?
- safe
- metabolically inert
- long lasting
- strong reflector of ultrasound
- small enough to pass through capillaries
156
What is contrast harmonics?
they are created because microbubbles act in a non-linear manner when struck by sound waves; they are created during reflection
157
what are contrast agents (aka microbubbles)?
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
Contrast bubbles.....
expand to a greater extent than they shrink
159
what is the Mechanical Index?
the amount of contrast harmonics produce may be estimated by this number
160
higher MI increases with?
large pressure variation and lower frequency
161
lower MI increases with?
small pressure variation and higher frequency
162
With the highest MI, greater than 1, we get?
- strongest harmonics
- bubble disruption
- extreme nonlinear behavior
- lowest frequency sound
- highest beam strength
- bubbles expands greatly
163
flow aka volume flow rate indicates what?
the volume of blood moving during a particular time; units are volume divided by time, ex: 5L/min
164
what is velocity?
speed that indicates direction
165
what is pulsatile flow?
when blood moves in variable velocity, blood accelerates and decelerates as a result of cardiac contraction; associated with arterial circulation
166
what is phasic flow?
when blood moves in variable velocity, blood accelerates and decelerates as a result of respiration; associated with venous circulation
167
what is steady flow
when fluid moves at a constant speed or veloctiy
168
what is laminar flow
when the flow streamlines are aligned and parallel; associated with normal physiologic states
169
what are the 2 types of laminar flow?
plug and parabolic (bullet shaped)
170
what is the Reynold's number?
it predicts whether flow is laminar or turbulent
171
what is turbulence?
chaotic flow patterns in different directions and speeds; (eddie current or a vortex); associated with pathology
172
what is a murmur or a bruit?
sound associated with turbulence
173
what is a thrill?
tissue vibration associated with turbulence
174
what is the Reynold's number for turbulence flow?
greater than 2000
175
what are the 3 forms of energy?
- kinetic (moving object)
- pressure(stored or potential energy)
- gravitational(stored or potential energy associated with elevated objects)
176
what are the 3 energy losses in the circulation?
- viscous loss (units of Poise)
- frictional loss
- inertial loss
177
what are the effects of a stenosis?
- change in flow direction
- increased velocity as vessel narrows
- turbulence downstream from the stenosis
- pressure gradient across the stenosis
- loss of pulsatility
178
Where is pressure lowest at a stenosis?
at the vessel's narrowest point (stenosis)
179
where is velocity of blood the highest?
at the stenosis
180
what is Bernoulli's principle?
describes the relationship between velocity and pressure in moving fluid
181
pressure gradient increases when either what?
- flow increases
| - resistance increases
182
flow increases when either what?
- pressure gradient increases, or
| - resistance decreases
183
in the circulatory system, what are the resistance vessels called?
arterioles
184
electrical resistance is reported in units of?
ohms
185
what is the shape of a vein as pressure increases?
hourglass shape(lower pressure), oval shape (intermediate pressure) and round shape(higher pressure)
186
what is hydrostatic pressure?`
it's related to the weight of blood pressing on a vessel measured at the height above or below heart level
187
in a supine individual, what is the hydrostatic pressure ?
in this case, all parts of the body are at the same level of the heart, hydrostatic pressure is zero everywhere
188
in a standing individua, what is the hydrostatic pressure? depends upon whether the measurement is made above or below heart level
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
what happens with inspiration?
- diaphragm moves downward the abd
- thoracic pressure decreases
- abd pressure increases
- venous return to the heart increases
- venous flow in legs decreases
190
what happens with expiration?
- diaphragm moves upward into the thorax
- thoracic pressure increases
- abdominal pressure decreases
- venous return to the heart decreases
- venous flow in leg increases
191
Doppler shift, aka doppler frequency is what?
a change in frequency, the frequency of sound changes when the sound source and the receiver move closer together or farther apart
192
what is a positive doppler shift?
when blood cells move toward the transducer, they reflect sound with a higher frequency
193
what is negative doppler shift?
when blood cells move away from the transducer, they reflect sound with a lower frequency
194
Doppler shift?
2 x velocity of blood x transducer frequency x cos / propagation speed
195
Doppler shift is directly related to what?
velocity
196
when does the first shift occur?
when the sound wave from the transducer strikes moving blood cells
197
when does the second doppler shift occur?
it results from the transducer's reception of the sound wave from moving red blood cells
198
what do the x and y axis of a doppler spectrum represent?
- x-axis = time
| - y-axis = doppler shift or velocity
199
Doppler shift is directly related to what?
frequency of the transmitted sound
200
when does the doppler shift represent 100% of the true velocity?
when blood flow is is parallel to the sound beam
201
what happens when an angle exists between the direction of flow and the sound beam?
the measured velocity is less than the true velocity
202
what determines how much of the velocity is measured, when the sound beam and flow direction are not parallel?
it depends on the cosine of the angle between the sound beam and the direction of motion
203
How is doppler shift related to cosine?
directly related, when the cosine doubles, the doppler frequency doubles; the cosine increases as angles approach zero degrees
204
doppler shift and velocites cannot be measured when?
with a perpendicular incidence, 90 degrees
205
when is flow parallel to the sound beam?
when the angle between the direction of motion and sound is 0 or 180 degrees
206
cosine 0 degrees is 1, this indicates?
flow toward the the transducer
207
cosine 180 degrees is -1 indicates?
flow away from the transducer
208
Since the cosine of 60 degrees is 0.5, the measure velocity at 60 degrees is what
one half the actual velocity
209
what is bidirectional doppler?
spectral doppler tracing flow toward and away from the tranducer (above and below the baseline)
210
what is phase quadrature aka quadrature detection?
a commonly used signal processing technique for bidirectional doppler
211
a pulsed doppler transducer is characterized by?
- at least one crystal
- damped PZT
- low Q-factor
- wide bandwidth
- lower sensitivity
212
a CW doppler transducer is characterized by?
- at least 2 crystals
- undamped PZT
- high Q-factor
- narrow bandwidth
- higher sensitivity
213
pulsed doppler gives us?
- range resolution
- sample volume
- limited maximum velocity- Nyquist limit
- aliasing
214
CW doppler gives us?
- range ambiguity
- region of overlap
- unlimited maximum velocity
- no asiasing
215
with imaging we have?
- normal incidence- 90 degrees
- higher frequency, improves resolution
- pulsed wave only
- minimum of 1 crystal
216
with doppler we have?
- 0 or 180 degrees
- lower frequency-avoids aliasing
- pulsed or CW
- min. of 1 (pulsed ) or 2 (CW) crystals
217
what is aliasing?
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
what is the Nyquist limit aka Nyquist frequency?
is the highest Doppler frequency or velocity that can be measured without the appearance of aliasing
219
we get less aliasing with?
- slower blood velocity
- lower frequency transducer
- shallow gate (high PRF)
220
we get more aliasing with?
- faster blood velocity
- higher frequency transducer
- dep gate (low PRF)
221
what two methods to eliminate aliasing, increase PRF?
increasing the scale and moving to a new view with a shallower sample volume (increase the Nyquist limit
222
what do the following techniques to eliminate aliasing do?
1. lower transducer frequency
2. zero baseline shift
3. CW doppler
1. decreases Doppler shift
2. aliasing remains but display more appealing
3. never aliases, but range ambiguity
223
what does eliminating aliasing improve?
the ability to measure the maximum velocity with Doppler
224
what does color doppler measure?
mean or average velocity
225
what does spectral doppler measure (pulsed and CW) measure?
peak velocity
226
what are the two mot commonly used doppler color maps used?
velocity mode and variance mode
227
with a variance mode, what do colors on the Lt represent?
laminar flow
228
with variance mode, what do colors on the Rt represent?
turbulent flow
229
with any color flow image that is sector-shaped, the horizontal vessel will display what?
both the toward and away colors, the center of the lument will be black
230
with any color flow image that has a rectangular shape, the horizontal vessel will display what?
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
what are doppler packets aka ensemble?
multiple ultrasound pulses used to accurately determine blood velocities
232
packets composed of a larger number of pulses have what 2 advantages?
- more accurate velocity measurements
| - increased sensitivity to low flow
233
what disadvantages are there with packets with more pulses?
- more time needed to acquire data
- reduced frame rate
- decreased temporal resolution
234
what is power doppler aka energy mode or color angio?
it identifies the presence of a doppler shift, but does not evaluate speed or direction
235
what are 3 advantages of power mode?
- 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
what are 3 disadvantages of power mode?
- no measurement of velocity or direction
- lower frame rates
- suscepitble to motion of the transducer, pt, or soft tissues
237
what does a wall filter aka high pass filter do?
eliminates low frequency doppler signals near the baseline (ghosting and clutter)
238
what is crosstalk?
a mirror image artifact
239
what is spectral analysis?
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
what does Fast Fourier Transform used for?
to process both pulsed and continous wave doppler signals
241
what are the advantages of FFT?
exceedingly accurate and displays all individual velocity components that make up the complex reflected signal
242
what is autocorrelation aka correlation function used for?
to analyze color flow doppler
243
for color to appear in a vessel, what must be created?
an angle other than 90 degrees must be created between the direction of flow and the direction of the sound beam
244
when will color NEVER appear in a vessel?
when the directions of flow and sound are perpendicular
245
what happens when we have a color flow images and our color gain level is too high?
color appears throughout the box, color confetti
246
what happens when our color gain is too low?
all color disappears from the image
247
what happens when we have a spectral display, and our pulsed doppler gain is too high?
gray scale noise appears throughout the spectrum
248
what happens when we have a spectral display, and our pulsed doppler gain is too low?
all gray scale will disppear
249
when should aliasing be considered?
when we have peculiar color variation
250
how can we distinguish bidirectional flow from aliasing with color flow doppler?
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
how can we eliminate or reduce aliasing from a color doppler image?
the most effective way is to increase the velocity scale
252
what other effect does increasing the scale have on a color doppler image?
it decreases the sensitivity to slow flows
253
what happens when we increase the walter filter in a color flow image?
ghosting artifact disappears and removal of color from the slow flow states; increasing the wall filter leaves the high velocity flows inchanged
254
in a doppler spectrum, what happens when we increase the wall filter?
the wall filter, selectively eliminates low frequency doppler shifts near the baseline; this does not affect the appearance of higher velocity flows
255
if we have a color flow image and increase the wall filter, what happens?
it eliminates low frequency doppler shifts; is does not get rid of aliasing
256
what happens when we increase the scale in a color flow image?
aliasing disappears and so does the low frequency flows
257
what are the 6 assumptions of imaging systems?
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
when are reverberations created?
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
when does comet tail aka ring down artifact appear?
when a sound wave bounces back and forth between two very closely spaced objects; assum #2
260
when does shadowing artifact happen?
when sound hits a highly attenuating object such as bone; assum #6
261
when are edge shadows created?
as sound beams refract and diverge along the edge of a curved structure; assump #6
262
what is enhancement artifact?
a hyperechoic region that extends beneath structures with abnormally low attenuation; assum # 6
263
what is focal enhancement aka focal banding?
is a hyperechoic horizontal region at the depth of the focus; assum #6
264
when does mirror image artifact appear?
when sound reflects off a strong reflector (mirror), and is redirected toward a second structure; assum # 1 and 2
265
what is crosstalk?
it's an artifact that appears on a spectral doppler display
266
what happens with speed error artifact?
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
what do lobe artifacts degrade?
lateral resolution
268
how can side lobes artifacts be reduced?
subdizing and apodization
269
what do we get with refraction artifact?
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
what is slice thickness artifact aka section thickness artifact or partial volume artifact?
the thickness of an imaging plane varies, the portions of the slice have inferior elevational resolution when compared to thinner portions; assump #5
271
what is lateral resolution artifact, aka point spread artifact?
it may create one reflection on the image from two reflectors, it may also create a horizontal reflection from a smaller reflector
272
what is axial resolution artifact?
it may create one reflection from multiple small reflectors
