Final Flashcards
1
Q
what are the 7 parameters of a pulsed wave
A
period, frequency, amplitude, power, intensity, wavelength, propagation speed
2
Q
what is period determined by
A
sound source
3
Q
what is frequency determined by
A
sound source
4
Q
what is amplitude determined by
A
sound source
5
Q
what is power determined by
A
sound source
6
Q
what is intensity determiend by
A
sound source
7
Q
what is wavelength determined by
A
sound source and medium
8
Q
what is propagation speed determined by
A
medium
9
Q
what are the units for period
A
seconds, microseconds
10
Q
what are the units for frequency
A
Hz, MHz
11
Q
what are the units for amplitude
A
dB
12
Q
what are the units for power
A
watts
13
Q
what are the units for intensity
A
watts/cm^2
14
Q
what are the units for wavelength
A
mm, cm, m
15
Q
what are the units for propagation speed
A
m/s, cm/s
16
Q
what is period
A
the amount of time it takes a wave to complete one cycle
17
Q
is period adjustable
A
no
18
Q
what is frequency
A
number of cycles per second
19
Q
is frequency adjustable
A
no
20
Q
what is amplitude
A
the bigness of a sound wave
21
Q
is amplitude adjustable
A
yes
22
Q
what is power
A
the rate that energy is transferred
23
Q
is power adjustable
A
yes
24
Q
what is intensity
A
concentration of energy in a sound beam
25
is intensity adjustable
yes
26
what is a wavelength
distance of one cycle
27
is wavelength adjustable
no
28
what is propagation speed
rate at which a sound travels through a medium
29
is propagation speed adjustable
no
30
what is the relationship between power and amplitude
P ∝ A^2
31
what is the relationship between intensity and amplitude
I∝A^2
32
what is the relationship between intensity and power
I∝ P
33
what is the formula for intensity
Intensity=power/area
34
what is the wavelength formula
wavelength = velocity/frequency
35
what does an increase in density do to speed
decreases speed
36
what does an increase of stiffness do to speed
increases speed
37
what is stiffness also known as
bulk modulus
38
what are the five parameters of a pulsed wave
PRP, PRF, PD, DF, SPL
39
what is PRP determined by
sound source
40
what is PRF determined by
sound source
41
what is PD determined by
sound source
42
what is SPL determined by
sound source and medium
43
what is DF determined by
sound source
44
is PD adjustable
no
45
is SPL adjustable
no
46
is PRP adjustable
yes
47
is PRF adjustable
yes
48
is DF adjustable
yes
49
what is PD
the actual time of a pulse from start to end
50
what is the unit for PD
microseconds (us)
51
what is the formula for PD
PD=#cycles x period or #cycles/frequency
52
what is the SPL unit
mm
53
what is SPL
length that a pulse occupies
54
what is the SPL formula
#cycles x wavelength
55
what is PRP
time from the start of one pulse to the start of the next pulse
56
what is PRP related to
both transmit and receive time
57
what is the PRP formula
PRP=1/PRF, or depth x 13 us/cm
58
what is PRF
number of pulses transmitted each second
59
what is the PRF formula
PRF (Hz) = 1/PRP, or 77,000 cm/s / imaging depth
60
what is the PRP unit
ms
61
what is the PRF unit
Hz
62
what is DF
the fraction of time that the system is "on"/transmitting a pulse
63
what is the DF formula
DF=(PD/PRP) x 100
64
what is attenuation determined by
distance and frequency
65
what is the unit for attenuation
dB
66
what are the 3 contributors to attenuation
reflection, scattering, absorption
67
what are the two forms of reflection
specular and diffuse (non-specular)
68
what is specular reflection
smooth, large boundaries. sound is reflected in 1 direction
69
what are the limitations of specular reflection
waves that are slightly off axis won't return to the transducer
70
what is diffuse reflection
irregular surfaces. sound is reflected in a few directions
71
what are the advantages of diffuse reflection
interfaces at suboptimal angles can still produce reflections that will return to the transducer
72
what are the disadvantages of diffuse reflection
backscattered signals have lower strength than specular reflections
73
what is scattering
random re-direction of sound in many directions
74
what is needed for scattering
tissue interfaces are small-equal or less than the wavelength of the incident beam
75
what is rayleigh scattering
redirects sound equally in all directions
76
what is rayleigh scattering caused by
interaction with RBCs
77
what is the rayleigh formula
Rayleigh ∝ frequency^4
78
what is absorption
conversion of ultrasound energy to heat
79
when frequency increases, absorption will....
increase
80
what is the attenuation co-efficient formula
frequency/2
81
what is the total attenuation formula
attenuation coefficient x distance
82
what is the attenuation co-efficient
number of decibels of attenuation that occurs when sound travels 1 cm
83
what are the two conditions needed for refraction
different acoustic impedances, oblique incidence
84
what does snell's law quantify
refraction
85
what is the time of flight formula
TOF= depth x 13 microseconds
86
how do you find the depth of a reflector in soft tissue given the time of flight?
depth= (1.54mm/s x TOF)/2
87
what is axial resolution determined by
SPL
88
what is axial resolution
measures the ability of a system to display two close structures that are parallel to sound beam's main axis
89
what are the synonyms for axial resolution
Longitudinal resolution, Axial resolution, Range resolution, Radial resolution, Depth resolution
90
is axial resolution adjustable
no
91
what is the axial resolution formula
=SPL/2
=(wavelength x #cycles in pulse)/2
=(.77 x #cycles in pulse)/frequency
92
what is lateral resolution
ability of the system to display two close structures that are perpendicular to the sound beam's main axis
93
what is lateral resolution determined by
width of the sound beam
94
what are the synonyms for lateral resolution
Lateral resolution, Angular resolution, transverse resolution, azimuthal resolution
95
what is axial resolution best with
short SPL
96
what is lateral resolution best with
small diameter in near field, large diameter in far field
97
how many elements does a mechanical transducer have
one
98
what is the image shape of a mechanical transducer
sector shape
99
what kind of steering does a mechanical transducer have
mechanical
100
what kind of focusing does a mechanical transducer have
mechanical/fixed
101
what effect does a damaged PZT in a mechanical transducer have on the image
loss of entire image
102
what shape is the element of a mechanical transducer
circular, disc-shaped
103
what are pre-processing functions
compression, write magnification, TGC, interpolation, spatial compounding, edge enhancement
104
what are post-processing functions
black/white inversion, read magnification, contrast variation, 3-D rendering
105
what is a low mechanical index associated with
no harmonics, backscatter, linear behavior, little microbubble expansion
106
does low MI have high or low frequency
high
107
does low MI have high or low beam strength
low
108
what is a low MI number
less than 0.1
109
what is high MI associated with
some harmonics, resonance, non-linear behavior, moderate microbubble expansion
110
does high MI have low or high frequency
low
111
does high MI have low or high beam strength
high
112
what is a high MI number
between 0.1-1.0
113
what is an extremely high MI number
above 1.0
114
what is an extremely high MI associated with
strong harmonics, extremely non-linear behavior, bubble disruption, big bubble expansion
115
what is the MI formula
MI= peak rarefaction pressure/sq. root of frequency
116
what is the relationship between MI and frequency
inverse
117
what is the relationship between MI and sound wave strength
direct
118
what is hemodynamics
study of blood moving through the circulatory system
119
what is flow
volume of blood moving during a particular time
120
what are the units for flow
liters/minute
121
what are the flow types
pulsatile, phasic, steady
122
what is pulsatile flow
occurs when blood moves with variable velocities ex. cardiac contractions
123
where does pulsatile flow most commonly appear
in arterial circulation
124
what is phasic flow
occurs when blood moves with variable velocities that changes with respiration
125
where is phasic flow most commonly found
venous circulation
126
what is steady flow
occurs when blood moves at a constant speed
127
where is steady flow found
in venous circulation when the pt stops breathing
128
what is laminar flow
layers of blood are moving at independents speeds. Flow streams are aligned and parallel
129
what are the types of laminar flow
plug and parabolic
130
what is plug flow
all layers are traveling at the same velocity
131
what is parabolic flow
velocity is highest at the center of the lumen. bullet shaped profile
132
what is turbulent flow
chaotic flow patterns in many different directions and speeds
133
what is turbulent flow often associated with
cardiovascular pathology
134
what is the reynold's number for laminar and turbulent flow
laminar: <1500
turbulent: >2000
135
in a stenotic vessel, where is pressure the highest and lowest
highest right before the stenosis, lowest at the stenosis
136
in a stenotic vessel, where is velocity the highest
at the stenosis
137
what happens downstream from a stenosis
turbulent flow
138
What is Bernoulli's principle?
describes the relationship between velocity and pressure.
139
what is Bernoulli's principle derived from
principle of conservation of energy
140
What does Bernoulli's principle state?
as the speed of a moving fluid increases, the pressure within the fluid decreases
141
what is hydrostatic pressure
pressure related to the weight of blood pressing on a vessel
142
what is the unit for hydrostatic pressure
mmHg
143
what is the hydrostatic pressure when a pt is supine
0 mmHg
144
what is the hydrostatic pressure at the head, heart, and legs when a pt is standing
head= negative number
heart=0
legs=positive number
145
what is the formula for hydrostatic pressure
measured pressure-circulatory pressure
146
what happens to venous blood flow in the legs during inspiration
decreases because diaphragm compresses IVC
147
what happens to venous flow to the heart during inspiration
increases because of a negative thoracic pressure
148
what is a doppler shift
change in frequency
149
what is the doppler shift formula
reflected frequency-transmitted frequency
150
what is a positive doppler shift
reflected frequency is higher than transmitted frequency. blood is moving towards the transducer
151
what is a negative doppler shift
blood is moving away from the transducer. transmitted frequency is higher than reflected frequency
152
what is the doppler equation
(2 x velocity x transducer frequency x cos θ)/ propagation speed
153
what is the cos θ when the angle is perpendicular to the vessel
0
154
what is the relationship between doppler shift and cos θ
direct
155
what is cos θ
the cos of the angle between the direction of the ultrasound beam and the direction of blood flow
156
what is the cos θ formula
measured velocity/true velocity
157
what is continuous wave doppler
two crystals one transmit one received
158
what is an advantage of continuous wave doppler
high ability to accurately measure high velocities
159
what is a disadvantage of continuous wave doppler
the exact location of moving blood cannot be determined
160
what is pulsed wave doppler
uses short pulsed to measure blood flow and velocity
161
what is an advantage of pulsed wave doppler
can see exact location where the velocities are measured
162
what are disadvantages of using pulsed wave doppler
aliasing, inaccurate measurements of high velocities
163
what is bidirectional doppler
distinguishes the direction of flow towards or away from transducer
164
what is color flow doppler
identifies blood flow velocities and direction. has range resolution
165
what is power doppler
sensitive to slow flow. non directional
166
what is spectral doppler
Doppler shifts are detected along a single line and used to produce a graphic representation of the blood velocity
167
what are the advantages of power doppler
1. increased sensitivity
2. unaffected by angle unless it =90 degrees
3. no aliasing since velocity isn't processed
168
what are the disadvantages of power doppler
1) no measurement of velocity or direction
2) lower frame rate (reduced temp. res)
3) susceptible to motion of transducer, pt, or soft tissue which can cause burst of color or flash artifact
169
what conditions create aliasing
occurs only with pulsed doppler. occurs when the doppler sampling rate is too low in comparison to the measured blood velocities
170
what is exceeded for aliasing to occur
nyquist limit
171
what is the nyquist limit formula
PRF/2
172
what increases the nyquist limit
raising the PRF. Allows the velocity to be sampled many times per second
173
what kind of transducers create more aliasing
higher frequency
174
how do you avoid aliasing
adjust scale to its maximum
change windows
use lower frequency
use baseline shift
use CW transducer
175
what are the advantages of increasing the scale to avoid aliasing
increases the nyquist limit. velocities are able to be sampled more frequently, raising the nyquist limit
176
what are the disadvantages of increasing the scale to avoid aliasing
1) higher PRF causes reduced sensitivity to low velocities.
2) aliasing can still exist with very high velocities
177
what are the advantages of switching windows to avoid aliasing
when switching to a new view with a shallower sample gate, the PRF is increased, thus increasing nyquist limit.
178
what are the disadvantages of switching windows to avoid aliasing
none
179
what are the advantages of using a lower frequency transducer to avoid aliasing
Doppler shift is directly related to frequency. Lower transducer= lower shifts=less likely to exceed nyquist limit
180
what are the disadvantages of using a lower frequency transducer to avoid aliasing
no significant disadvantages
181
what are the advantages of using a base line shift to avoid aliasing
high velocity flows are displayed in proper direction instead of wrapping around
182
what are the disadvantages of using a base line shift to avoid aliasing
baseline shift will be ineffective when the doppler shift is extremely high
183
what are the advantages of using a continuous wave transducer to avoid aliasing
CW transducers never have aliasing
184
what are the disadvantages of using a continuous wave transducer to avoid aliasing
has range ambiguity. velocities along the entire region blend together
185
what are the two types of color maps
velocity mode and variance mode
186
what is velocity mode color map
only shows flow direction and velocity
187
what is variance mode color map
shows flow direction, velocities and if flow is laminar or turbulent.
188
what does the left side of a variance color map indicate
laminar flow
189
what does the right side of a variance color map indicate
turbulent flow
190
what is a wall filter used for
eliminates low frequency doppler shifts (eliminates color from slow velocity)
191
do wall filters affect high doppler shift
no
192
what are common doppler artifacts
ghosting/clutter
cross talk
193
what is the difference between ghosting and clutter
ghosting happens with color doppler, clutter happens with spectral displays
194
what is ghosting
slow moving anatomy (heart muscle, pulsating vessel walls) can create very low frequency doppler shifts, creating color outside the vessel
195
what is cross talk
type of "mirror image" but for spectral analysis doppler
196
what causes cross talk
spectral doppler gain is too high
incident angle is near 90 degrees
197
what is spectral analysis
identifies the individual velocities which make up the reflected Doppler signal
198
what are the two forms of spectral analysis
Fast Fourier Transform (FFT) and Autocorrelation
199
what is fast fourier transform
Digital technique used to process both pulsed and continuous wave Doppler signals
200
what are the advantages of fast fourier transform
very accurate
displays all individual velocity components that make up a complex reflected signal
201
what is the significance of fast fourier transforms techniques
can distinguish between laminar flow and turbulent flow
202
what is autocorrelation
digital technique used to analyze color flow doppler
203
what are artifacts caused by
violation of assumptions
equipment malfunction
ultrasound physics
operator error
204
what is reverberation
multiple, equally spaced echoes parallel to the sound beam's main axis
205
what is reverberation caused by
the bouncing of the sound wave between two strong reflectors positioned parallel to the ultrasound beam
206
what is a comet tail artifact
solid hyperechoic line directed downward. located parallel to the sound beam's main axis
207
what is comet tail also known as
ring down artifact
208
what is a comet tail artifact caused by
created when closely spaced reverberations merge.
209
when is a comet tail more likely to appear
in a medium with very high propagation speed (mechanical heart valve)
210
when does shadowing appear
when the attenuation is higher in the tissue above the shadow than in the surrounding tissue
211
what are the characteristics of shadowing
hypo-/anechoic, result of too much attenuation
212
what is an edge shadow caused by
refracting at the edge of a curved reflector, and the drop of intensity as the beam diverges around the edges of the reflector
213
what is focal enhancement
horizontal hyperechoic region
214
what is focal enhancement also known as
focal banding
215
what causes focal enhancement
increased intensity at the focus
216
what is a mirror image caused by
sound reflects off a strong reflector and is redirected towards another structure
| deeper, not side by side
217
what is speed error artifact
when sound propagates at a speed other than soft tissue
218
how does a speed error artifact appear
as a step-off
219
how does speed error artifact appear when the sound travels slower than the system expects
reflectors are too deep
220
how does speed error artifact appear when the sound travels faster than the system expects
reflectors are too shallow
221
what is the difference between side lobes and grating lobes
side lobes are created by mechanical transducers. grating lobes are created by array transducers
222
how do you reduce grating lobes
subdicing and apodization
223
what is refraction artifact
sound pulse changes direction during transmission
224
how does refraction appear on an ultrasound
second copy of the reflector is side by side the true reflector
225
how does a mirror image artifact appear on an ultrasound
second copy is deeper than the true reflector
226
what is slice thickness artifact
reflectors from above or below the assumed imaging plane may appear in the image. This is because of the flare of the beam shape
227
how is slice thickness artifact reduced
thinner imaging planes
228
what is multipath artifact
sound pulses glance off a second structure on the way to or from the primary reflector. Transmit length differs from the return path length
229
what is the curved or oblique reflector artifact
when a sound beam strikes a curved/oblique reflector, some of the reflected sound is directed away from the transducer. This causes reflectors to be absent, too weak, or appear different from other similar reflecting boundaries
230
what is a tissue equivalent phantom
have ultrasonic features similar to soft tissue
231
what are tissue equivalent phantoms used to evaluate
gray scale and tissue texture, muti-focus, adjustable-focus transducers
232
how are tissue equivalent phantoms similar to soft tissue
have the same speed of sound, has attenuation, scattering characteristics, and echogenicity
233
what is a doppler phantom
include vibrating strings, moving belt and flow phantom to evaluate doppler systems
234
what is a slice thickness phantom
assess slice thickness and its effect upon image accuracy
235
what is an AIUM 100 mm test object
fluid filled tank that has the speed of soft tissue and does not attenuate. contains steel pins and cannot evaluate gray scale
236
what is a calorimeter
converts sound beam energy to heat and measures total power in the sound beam
237
what is a thermocouple
tiny electronic thermometer. converts sound beam energy to heat and measures temperature
238
what are liquid crystals
converts sound beam energy into heat and changes color based on temperature
239
what does in vivo mean
in the body
240
what does in vitro mean
outside the body
241
what is dosimetry
measures the potential of a sound beam to produce bioeffects
242
what are the two techniques used to study bioeffects
mechanistic and empirical
243
what is the mechanistic approach of studying bioeffects
searches for a relationship between cause and effect
244
what is the empirical approach of studying bioeffects
searches for a relationship between exposure and response
245
what are the two important bioeffect mechanism
thermal and cavitation
246
what is thermal index
useful predictor of maximum temperature increase under most clinically relevant conditions
247
what are the three types that TI is reported in
TIS, TIB, and TIC
248
what are the two types of cavitation
stable (not bursting) and transient (bursting)
249
does transient cavitation have high or low MI
high
