SPI Flashcards
1
Q
billion
A
10^9
giga
G
2
Q
million
A
10^6
mega
M
3
Q
thousand
A
10^3
kilo
k
4
Q
hundred
A
10^2
hecto
h
5
Q
ten
A
10^1
deca
da
6
Q
tenth
A
10^-1
deci
d
7
Q
hundreth
A
10^-2
centi
c
8
Q
thousandth
A
10^-3
milli
m
9
Q
millionth
A
10^-6
micro
10
Q
billionth
A
10^-9
nano
n
11
Q
Sound is a ______, ________ wave.
A
mechanical, longitudinal
12
Q
Sound carries _____ from place to place.
A
Energy.
13
Q
What are the acoustic variables?
A
Pressure, Density, Distance.
14
Q
Define Pressure.
A
Concentration of force within an area.
(force/area)
units:Pascals (Pa)
15
Q
Define Density.
A
Concentration of mass within a volume.
units: kg/cm^3
16
Q
Define Distance.
A
Measure of particle motion
units: cm, ft, miles
17
Q
With a transverse wave, particles travel in which direction?
A
Travel in a perpendicular direction, perpendicular to the wave.
18
Q
With a longitudinal wave, particles travel in which direction?
A
Particles move in the same direction as the wave.
19
Q
Acoustic Variables vs. Acoustic Parameters
A
Acoustic Variables inform us of which waves are sound waves while Acoustic Parameters describe the features of a particular sound wave.
20
Q
7 parameters of continuous waves.
A
Period Frequency Amplitude Power Intensity Wavelength Propagation Speed
21
Q
Period
A
Time required to complete a single cycle.
Determined by: source
units: microseconds
nonadjustable
22
Q
Frequency
A
Number of certain events that occur in a particular time duration.
Determined by: source
units:hz
nonadjustable
23
Q
Amplitude
A
Difference between the average value and the maximum value of an acoustic variable.
Determined by: source (initially)
units:pascals, cm
adjustable
24
Q
Power
A
The rate that work is performed or rate of energy transfer. Determined by: source (initially) units:Watts adjustable Power=Amplitude^2
25
Intensity
Concentration on energy in a sound beam.
Determined by: source (initially)
units:watts/cm^2
adjustable
26
Wavelength
The length or distance of a single cycle.
Determined by: Both
units: meters, mm
nonadjustable
27
Propagation Speed
Rate that sound travels through a medium.
Determined by: Medium
units:m/s
nonadjustable
28
Equation for wavelength
wavelength = propagation speed (mm/microsec) / frequency (MHz)
29
Intensity is _________ related to power.
directly
30
Equation for intensity.
intensity = power(watts) / beam area(cm^2)
31
How to determine the wavelength in soft tissue.
divide 1.54 (mm/us) by the frequency (Mhz)
32
Density vs. Stiffness
increase in stiffness=increase in speed.
| increase in density=decrease in speed.
33
Parameters of pulsed sound
```
Pulse Duration
Pulse Repetition Frequency
Pulse Repetition Period
Duty Factor
Spatial Pulse Length
```
34
Pulse Duration
```
The time from the start of a pulse to the end of that pulse.
Determined by: source
units: microsec
Nonadjustable
PD= # of cycles in pulse x period
```
35
Spatial Pulse Length
```
The length or distance that an entire pulse occupies in space.
Determined by: Both
units:mm
Nonadjustable
SPL=# of cycles x wavelength (mm)
```
36
Pulse Repetition Period
the time from the start of one pulse to the start of the next pulse; 1 pulse duration + 1 listening time.
Determined by: source
units:msec
Adjustable
37
Pulse Repetition Frequency
number of pulses created by the system in one second.
determined by: source
units:Hz
Adjustable
38
Duty Factor
% or fraction of time that the system transmits sound.
Determined by: source
unitless
adjustable
39
Duty factor is _____ related to depth.
Inversely; with shallower depth there is a higher duty factor, with more depth there is lower duty factor.
40
PRF is ____ related to depth.
Inversely; shallower image = higher PRF
| deeper image = lower PRF
41
PRP is ____ related to depth.
Directly.
42
How are PRP and PRF related?
They are reciprocals.
43
Factors involved with deep imaging...
low PRF
low duty factor
long PRP
44
Factors involved with shallow imaging....
high PRF
high duty factor
short PRP
45
Definition of Intensity
The concentration of power in the beam
46
5 Key Words of Intensity
```
Peak- max value
Average- mean value
Spatial- refers to distance or space
Temporal- refers to all time
Pulsed- refers to transmit time only
```
47
The greatest intensity...
SPTP
48
The lowest intensity...
SATA
49
The intensity related to tissue heating...
SPTA
50
What is attenuation?
The decrease in intensity, power and amplitude of a sound wave as it travels.
units: dB
51
What are the three components of attenuation?
Absorption
Scattering
Reflection
52
With lower frequency and shorter path length there is ....
less attenuation
53
With higher frequency and longer path length there is....
more attenuation
54
Reflection occurs when...
propagating sound energy strikes a boundary between two media and some returns to the transducer
55
Specular reflection arises from a...
smooth reflector (they return in one direction)
56
Diffuse reflection or backscatter arises from...
rough boundary (sound is redirected in many directions)
57
When are specular reflections best seen?
When sound strikes the boundary at 90 degrees.
58
When does Rayleigh scattering occur?
When the reflector is much smaller than the wavelength of sound; sound is then uniformly distributed in all directions
59
Rayleigh scattering is related to...
Frequency^4
60
Higher frequency sound undergoes more...
Rayleigh scattering
61
What is the attenuation coefficient?
The amount of attenuation per centimeter.
| units:dB
62
In soft tissue the attenuation coefficient is approx...
1/2 the frequency
63
Total attenuation equals...
path length(cm) x attenuation coefficient (dB/cm)
64
A mathematical expression that means 'half the transducer frequency' is...
0.5 dB/cm/MHz
65
Reflection of an ultrasound waves depends upon different
impedances
66
What is the equation for impedance?
impedance (rayls)= density (kg/m^3) x prop speed (m/s)
67
PORNN (normal incidence)
perpendicular
orthogonal
right angle
ninety degrees
68
Oblique incidence means...
not at right angles, anything other than 90 degrees.
69
What are the other names for Round Trip?
Time of flight
| Go return time
70
What is the definition for time of flight?
The time needed for a pulse to travel to and from the transducer and the reflector
71
What is the average speed in soft tissue?
1.54 km/sec
72
In the 13 sec rule, what would the reflector depth and total distance traveled at 26 sec?
Reflector: 2cm
Total: 4cm
73
What is the relationship between time of flight and distance?
Directly related
74
What does speed equal?
Speed= distance/time
75
What is the definition of a transducers?
Any device that converts one form of energy into another
76
What is the Piezoelectric Effect?
Property of certain materials to create a voltage when pressure is applied or when material is mechanically deformed.
77
What are all of the Piezoelectric materials?
PZT
Ceramic
Active element
Crystal
78
What happens to the crystal when is exceeds the Curie Point?
Depolarizes
79
What is Sterilization?
Complete destructs of all living microorganisms by means of exposure to heat, chemical agents, or radiation
80
What is disinfection?
Application of chemical agent to reduce or eliminate infectious organisms on an object
81
What requires Sterilization?
Items that Penetrate skin or mucous membranes
82
What requires disinfection?
Things that come in contact with mucous membranes
83
What are transducers disinfected with?
Cider
| Gluteradehyde
84
On the transducer, what does the case do?
Protects the internal components from damage and insulates the patient from electrical shock
85
Why don't we use transducers with a cracked case or frayed wire?
Potential electric shock to patient
86
The matching layer is ___________ wavelength thick.
1/4
87
What are the impedances of the matching layer?
PZT>matching layer> gel> skin
88
What reduced the transducers ringing?
Damping element or Backing material
89
What is the "rule" for the backing material?
Short pulses create better images
90
What is the backing material made out of?
Epoxy resin impregnated with tungsten
91
With the damping material, what are the imaging transducer characteristics?
```
Damping is effective
Short pulse and duration
Low sensitivity*
Wide bandwidth*
Low Q
Decreased output power
```
92
How come Therapeutic and Continuous wave transducers don't use damping element?
They don't create images
93
What does bandwidth mean?
Range of frequencies between the highest and the lowest frequency emitted from the transducer
94
What is another name for wide bandwidth?
Broadband
95
What are all the names of the main frequency emitted by the transducer?
Center
Resonant
Primary
Natural frequency
96
What is Quality factor?
Unitless number representing the extent of damping
97
What are the two characteristics that determine frequency in a pulsed transducer?
1. Thickness
| 2. Propagation Speed
98
In pulsed transducers, what will have a high frequency?
Thin crystal and fast PZT
99
In pulsed transducers, what would have a low frequency?
Thick crystal
| Slow PZT
100
When a PZT crystal is _____ as thick, the sounds frequency is ______ as high.
Half
Twice
101
Chart in book....
Component Thickness
- PZT crystal= 1/2 wavelength thick
- Matching layer= 1/4 wavelength thick
Pg. 57 cheater book
102
What creates better images?
Narrow beams
103
What is the focal point (focus)?
Location where the beam reaches its minimum diameter
104
What is the focal depth?
Distance from the transducer face to the focus.
105
What are the other names for focal depth?
Focal length
Near zone length
106
What is the near zone length?
Region or zone in between the transducer and the focus
Sound beams converge
107
What is another name for near zone?
Fresnel zone
108
What is the far zone?
Region or zone deeper than the focus, beyond the near field
Sound beams diverge
109
What is the focal zone?
Region surrounding the focus where the bean is "sort of narrow" and the image is good
110
What is focal depth determined by?
Transducer diameter (aperture)
Frequency
111
What is sound beam divergence determined by?
Transducer diameter
Frequency
112
What kind of sound wave does a large diameter crystal with a high frequency produce?
Less divergence in far field
113
What kind of divergence would a smaller diameter crystals with a lower frequency produce?
Large divergence in far zone
114
What is a continuous wave frequency determined by?
Electronic frequency
115
What is a pulsed frequency determined by?
Thickness of ceramic
Speed of sound
116
What is focal length determined by?
Diameter of ceramic
Frequency
117
What is divergence determined by?
Diameter of ceramic
Frequency
118
What is another name for V shaped wave?
Huygens wavelet
119
What produces the Huygens wavelet?
When produced by a tiny source, with a size near the wavelength of the sound waves will diverge in this shape as they propagate
120
What is the Huygens Principle?
Hourglass shape of an imaging transducers sound beam
121
The overall hourglass shape of a sound beam is the result of the ____________________ of many sound wavelets emitted from these numerous sound sources.
Constructive and destructive interference
122
What is Resolution?
Ability to image accurately
123
What is Axial Resolution?
Ability to distinguish two structures that are close to each other front to back, parallel to, or along beams axis
124
What is the synonym for Axial Resolution?
LARRD
125
What does LARRD stand for?
```
LARRD:
Longitudinal
Axial
Range
Radial
Depth
```
126
What is the equation for Axial Resolution?
LARRD Resolution= Spatial Pulse Length/2
127
What does LARRD resolution improve with?
Less ringing
Higher frequency
128
When is Axial Resolution at its best?
Using transducers with the highest frequency and the fewest number per cycle
129
What is Lateral Resolution?
Minimum distance that two structures are separated by side-to-side or perpendicular to the sound beam that produces two distinct echoes
130
What is the synonym for Lateral Resolution?
LATA
131
What is the incident intensity?
intensity of the sound wave prior to striking a boundary.
132
What is the reflected intensity?
Portion of the incident intensity that, after striking a boundary, changes direction and returns back from where it came.
133
What is the transmitted intensity?
Portion of the incident intensity that, after striking a boundary, continues on in the same general direction that is was originally traveling.
134
What is the equation of incident intensity?
incident intensity = reflected intensity + transmitted intensity
135
What is the Intensity Reflection Coefficient?
The percentage of the US intensity that bounces back when the sound strikes a boundary.
136
What is the Intensity Transmission Coefficient?
The percentage of the incident intensity that after striking a boundary continues on in the same general direction that it was originally traveling.
137
Where does conservation of energy exists?
at a boundary.
138
IRC + ITC = ?
100%
139
When the reflected and transmitted intensities are added, what is the result?
The incident intensity
140
With greater impedance differences between the two media, the IRC ______, and the amount of reflection ____.
increases, increases
141
Whatever is not transmitted, must be ____.
reflected
142
What do we know about oblique incidence?
Nothing!
143
What is refraction?
Transmission with a bend.
144
Refraction requires what?
1. ) oblique incidence
| 2. ) different speeds
145
Refraction cannot occur with...
Normal incidence and the same speeds.
146
Snell's Law describes..
The physics of refraction
147
How are period and frequency related?
They're reciprocals.
148
Narrower sound beams create better____________
Images
149
What is another name for transducer diameter?
Aperture
150
What is the focus (focal point)?
Location where the beam reaches its minimum diameter
151
What is focal depth?
Distance from the transducer face to the focus.
152
What is another name for focal depth?
Focal length
Near zone length
153
What is the near zone?
Region or zone in between the transducer and the focus. Sound beams converge!
154
What is another name for the near zone?
Fresnel zone
155
What is the far zone?
Region or zone deeper than the focus, beyond the near field. Sound beams diverge
156
What is another name for the far zone?
Fraunhofer zone
157
What is the focal zone?
Region surrounding the focus where the beam is "sort of narrow" and picture is relatively good
158
What is focal depth determined by?
Transducer diameter (aperture)
Frequency
159
Hint....
Compared to beams with a shallow focus, beams with a deep focus have a lower intensity at the focus
160
What will cause a shallow focus?
Small diameter
Low frequency
161
What will cause a deep focus?
Large diameter
High frequency
162
Define sound beam divergence.
Spread of the sound beam in the deep far zone
163
What factors affect sound beam divergence?
Transducer diameter (aperture)
Frequency
164
What kind of transducer would produce the best lateral resolution?
Beam narrower in far field
Large diameter
High frequency
165
Transducer that would produce the worst lateral resolution?
Far field diameter is wide.
Small diameter with low frequency
166
What is continuous wave frequency determined by?
Electronic frequency
167
What is Pulsed wave frequency determined by?
Thickness of ceramic
Speed of sound
168
What is focal length determined by?
Aperture of ceramic
Frequency
169
What is divergence determined by?
Aperture of ceramic
Frequency
170
What is another name for diffraction pattern?
Huygens wavelet
171
What is the shape of the waves produced by diffraction pattern?
V shaped wave
172
What is the Huygens Principle?
Hourglass shape of an imaging transducers sound beam
173
The overall hourglass shape of a sound beam is the result of the ______________________ interference of the many sound wavelets emitted from these numerous sound sources.
Constructive and destructive interference
174
What is resolution?
Ability to image accurately
175
What is Axial resolution?
Ability to distinguish two structures that are close to each other
Front to back
Parallel to
Along the beams main axis.
176
What is the synonym for Axial resolution?
LARRD:
```
Longitudinal
Axial
Range
Radial
Depth
```
177
What creates better axial resolution?
Shorter pulses
- short pulse means short spatial length or short pulse duration
178
What are the units for Axial resolution?
Mm, cm - units of distance
179
Equation:
LARRD= Spatial Pulse Length/2
180
What does LARRD improve with?
Less ringing
Higher frequency
181
Note....
As frequency increases, the numerical value of LARRD resolution decreases. This means high frequency transducers have improved LARRD resolution and create more accurate images.
182
What is Axial Resolution best with?
Highest frequency
fewest number of cycles per pulse
183
Define Lateral Resolution
Minimum distance that two structures are separated by
Side by side
Or perpendicular to sound beam that produces two distinct echoes
184
What is the synonym for Lateral resolution?
LATA:
Lateral
Angular
Transverse
Azimuthal
185
Note....
Lateral resolution = beam diameter
186
What is point spread artifact?
When two side by side structures are closer together than the beam width, only one wide reflection is seen on image
187
What are the three ways focusing alters the sound beam?
1. Narrower "waist" in US beam
2. Shallower focus
3. Smaller focus zone
188
What are the general types of focusing?
1. Fixed (conventional)(mechanical)
| 2. Adjustable (phased array)
189
What are the three methods of focusing?
1. Lens- external focusing
2. Curved Pizeoelectric Crystal- internal focusing
3. Electronic focusing- adjustable
190
Note...
Single crystal transducers are always fixed focus
191
What are 2D images referred to as?
B-scans or "B-mode"
192
What is mechanical scanning?
Contains one disc, element
193
What is the steering for mechanical scanning?
Mechanical
194
What is the focusing for mechanical scanning?
Conventional or fixed
195
What is the image shape for mechanical scanning?
Sector
196
If the crystal is destroyed in mechanical scanning, what does the image look like?
No image.
197
Switched arrays are also known as what?
Sequential
198
What is the steering for linear switched?
No steering. Scan lines are parallel and remain equally spaced at depths
199
What is the focusing for a linear switched?
Fixed focusing or curved crystal
200
What is image shape for linear switched?
Rectangular
201
There is a defective Crystal in a linear switched, what will image look like?
Dropout from superficial to deep
| Top to bottom
202
What does a phased array mean?
Adjustable focus or multi-focus
203
What is the steering and focusing for a phased array?
Electronic
204
What is the image shape for a phased array?
Sector shaped
205
What is the time delay for a phased array?
10ns
206
What is a beam former?
Created electronic patterns. Delays are 10ns
207
Multidimensional arrays
2D create 3D or 4D images.
208
What resolution does a 1 1/2 dimensional array improve?
Elevational
209
Vector array, what is the image shape?
Trapezoidal imaging
210
What is contrast resolution?
visualizing a variety of gray shades in an image.
211
What is spatial resolution?
visualizing detail in an image.
212
What is real-time imaging
"motion picture" A series of frames displayed in a rapid fashion to give the impression of constant motion.
213
What is temporal resolution?
the ability to accurately locate moving structures at anyh particular instant in time.
214
What is temporal resolution determined by?
Frame rate only
215
What are the units of temporal resolution?
Hertz (20Hz-100Hz)
216
What is frame rate determined by?
1) Imaging depth
| 2) # of pulses per image
217
What is frame rate limited by?
1) speed of sound in the medium
| 2) imaging depth
218
What is the fundamental limitation of temporal resolution?
Speed
219
What 3 things change the number of pulses in an image?
| That are under sonographer control
1) # of pulses per scan line (multi-foucus)
2) sector size
3) line density
220
The 4th setting that the sonographer controls for temporal resolution, but dose not effect the number of pulses in an image?
maximum imaging depth
221
Temporal resolution improves with...
- shallower depth and fewer pulses
- less time to create am image (higher frame rate)
- more frames created each second
222
Temporal resolution degrades with...
- deeper and more pulses
- more time to create an image (lower frame rate)
- less frames created each second
223
If the imaging depth is doubled the frame rate will be..
halved
224
Improving image quality often degrades....
temporal resolution
225
Multi focus improves ....
Lateral resolution
226
Multi focus degrades..
temporal resolution
227
A narrow sector is better for..
temporal resolution
228
Line Density
the number of scan lines per degree of sector
229
Low line density degrades..
spatial resolution
230
With regard to line density, what will create a frame with fewer pulses?
Low Line density
231
The time required to make a frame is called?
Tf
232
Tf X FR=
1
233
When one frame is created in 1/10th of a second then the frame rate will be....
10/second or 10 Hz
234
What is an Ultrasound System?
a device that produces sound beams, retrieves the echoes and produces visual images and audio signals.
235
What are the 6 components of an Ultrasound system?
```
Master Synchronizer
Transducer
Pulser
Receiver
Display
Storage
```
236
What communicates with all of the individual components, and organizes and times their functions so as to operate as
a single integrated system?
Master Synchronizer
237
What converts electrical into acoustic energy during transmission and converts acoustic in to electrical energy during reception?
Transducer
238
What controls the electrical signals sent to the active elements for sound pulse generation?
Pulser
239
What determines the pulse repetition period and pulse amplitude?
Pulser
240
What creates a firing pattern for phased array systems (beam former)?
Pulser
241
What processes the electronic signal produced by the transducer during reception and producing a picture on a display device?
Receiver
242
What is associated with the presentation of processed data for interpretation, monitor, speakers, paper record?
Display
243
A device or media that are used to permanently archive the data...
Storage
244
This increases the sound intensity created by the transducer and sent into the patient....
When the sonographer increases the output power.
245
For a phased array system the pulser is also called the...
beam former
246
Other words for Transducer Output
```
output gain
acoustic power
pulser power
energy output
transmitter output
```
247
What is determined by the excitation voltage from the pulser?
Transducer output
248
The crystal vibrates with a magnitude related to the....
Transducer output
249
What results from a transducer output change?
All reflections change..the brightness of the entire image changes.
250
Signal
meaningful portion of the data
251
noise
inaccurate part of the data. Degrades the quality of information.
252
High signal to noise ratio
the meaningful part of data is stronger=high quality image
253
Low signal to noise ratio
the inaccurate part of the data is stronger=poor quality image
254
Receiver functions
```
Amplification
Compensation
Compression
Demodulation
Rejection
```
255
What increases the strength of all electrical signals in the receiver prior to further processing?
Amplification
256
Amplification is also called...
receiver gain
257
Amplification changes the brightness of...
the entire image.."uniform amplification"
258
Preamplifier
alters the signal before it is amplified
259
Compensation
makes all echoes from similar reflectors appear identical regardless of depth. "uniform brightness from top to bottom"
260
What is used to create uniform brightness from top to bottom?
Compensation
261
TGC is
compesation
262
The more attenuation...
the more TGC must be used
263
TCG curve
```
near gain
delay
slope
knee
far gain
```
264
What will you adjust if you cannot see reflectors in the near field?
TGC
265
Compression
reduces the total range of signals, from smallest to the largest
266
What keeps signals within the operating systems electronics and the gray scale within the range of what the human eye can see?
compression
267
What decreases the dynamic range of the signals?
compression
268
What allows us to see all gray shades?
compression
269
What changes the gray scale mapping?
compression
270
What changes the signals form to one more suitable for display?
Demodulation
271
What part of demodulation changes all of the negative voltages in to positive ones?
rectification
272
What part of demodulation puts and envelope around the "bumps" to even them out?
Enveloping or Smoothing
273
What eliminates low-level noise in our images?
Rejection
274
Does rejection effect bright echoes?
NO
275
Output Power vs Receiver gain
When the term suggests outgoing function it is output power.
| When the word indicates reception or incoming, the function is receiver gain
276
Harmonics
creates scans from sound reflections at 2x the transmitted frequency.
277
Where are harmonics created?
In the tissues
278
A transducer creates a sound pulse with a fundamental frequency of 2MHz. In the harmonic mode, an image is created from ?MHz sound reflections is displayed?
4
279
Non-linear behavior creates
harmonics
280
Sound moves slightly faster in regions of...
compression
281
Sound moves slightly slower in regions of
rarefaction (lower pressure)
282
Pulse inversion Harmonic Imaging
positive and negative pulses are transmitted down each scan line.
283
What is a disadvantage of pulse inversion imaging?
degrades temporal resolution, because the frame rate is half that of the fundamental imaging
284
Brightness
related to the brilliance of the image
285
contrast
determines the range of brilliancies that are displayed.
286
bistable
high contrast
287
Analog
real world
| a variable attains a continuum of values
288
digital
computer world
| a variable attains only discrete values
289
Scan converter
changes the data format.
| Gray scale not possible with out it
290
Digital scan converter
converts the image into numbers . the numbers can be processed and translated for display as an image
291
The smallest element of a digital picture
pixel
292
pixel density
pixels per sq inch
low pixel density= poor spatial resolution
high pixel density= good spatial resoluion
293
spatial resolution on a digital display is determined by...
pixel density
294
spatial resolution is related to
the number of lines per frame
295
the smallest number of digital storage is
Binary Digit
296
a bit is
bistable, either 0 or 1
297
a group of bits is assigned to
each pixel
298
the more bits per pixel the
more shades of gray and the better the contrast resolution
299
Byte
8 bits
300
2 bytes
16 bits is a Word
301
If you have 10 bits per pixel how many shades of gray can be represented per pixel?
2 to the 10th power = 1024 shades of gray
302
How many bits are needed to represent 10 shades of gray?
4 . 4 bits can display up to 16 shades of gray.
| 2x2x2x2=16
303
Preprocessing
manipulating the data before the storage. Can not be reversed.
304
Post processing
manipulating the data after it has been stored. Performed on frozen images.
305
Electrical signals created by the PZT are
analog
306
Analog-Digital Conversion
```
Analog signal from transducer
A to D converter
Digital scan converter
D to A converter
Analog Signal dislpay
```
307
Read Magnification
number of pixels is unchanged and pixel size increases
308
Write Magnification
the size of the pixels stays the same and the number of pixels increases
309
Fill-In Interpolation
improves images by filling in the gaps between lines. Preprocessing.
Improves image detail (spatial resolution)
310
What artifact causes a granular appearance in tissues that are really homogenous? Created by interference effects.
Speckle
311
When are scan lines steered by the transducer in different directions or views, so structures are interrogated by multiple pulses from several different angles?
Spatial Compounding
312
What type of transducers can use Spatial Compounding?
Phased array
313
What provides a history of past frames that are overlaid or added on top of the current frame?
Temporal Compounding or Persistence
314
What divides the reflection into sub-bands of smaller frequency ranges and creates images from each of theses sub-bands?
Frequency Compounding
315
Dynamic Aperture
a from of electronic receive focusing
| Uses a varying number of elements to receive a reflected signal.
316
Edge enhancement
increases the contrast at a boundary
317
What uses long sound pulses that contain a complex pattern of frequencies and cycles, called a code?
coded excitation
318
coded excitation takes place in the ...
pulser
319
coded excitation improves...
```
signal to noise ratio
penetration
axial resolution
spatial resolution
contrast resolution
```
320
What technique produces images based on a change in shape when a force is applied to a tissue?
elsastography
321
What is rendering?
creates images with shadow, color, texture and optical effects.
322
dynamic range
the ratio of the largest to the smallest signal strength.
323
PACS
Picture Archiving and Communications System
324
DICOM
Digital Imaging and Communications in Medicine
325
NAS
network storage device used in PACS
326
What is flow?
the movement of a fluid from one location to another
327
Steady flow
fluid movement at a constant speed or velocity.
328
Pulsatile flow
arterial
cardiac contraction
high pressure
329
Phasic flow
venous
respiration
low pressure
330
What is Laminar flow?
streamlines are layered, may be "plug" or "parabloic"
| Parallel and aligned
331
What is Turbulent Flow?
chaotic flow in many directions and speeds.
332
What is a swirling pattern of rotational flow?
vortex
333
What are small regions of turbulent flow that have vastly different velocities?
Doppler spectral broadening
334
When flow energy is lost, what does it convert to?
sound (murmurs, bruits)
| vibration (thrill)
335
What is Energy Gradient?
When the total fluid energy at one location differs from the total fluid energy at another location.
336
What is another name for "motion energy"?
Kinetic Energy
337
What is a form of potential or stored energy that has the ability to perform work?
Pressure energy
338
What is the conversion of other forms of energy into heat?
Friciton
339
Viscosity
describes the thickness of a fluid (poise)
340
What increases the viscosity of blood?
Increased hematocrit or hemoglobin
341
What is a narrowing or irregularity in a lumen?
Stenosis
342
Units of resistance?
Ohms
343
What are the resistance vessels in circulation?
Arterioles
344
What is Bernoulli's Principle?
In a stenosis, the highest velocity, lowest pressure and kinetic energy is highest at the maximum narrowing.
345
During Inspiration
```
Diaphragm desends
pressure in the abd increases
venous flow to legs decreases
pressure in the thorax decreases
venous return to heart increases
```
346
During Exhalation
```
Diaphragm ascends
pressure in the abd decreases
venous flow to legs increases
pressure in the thorax increases
venous return to heart decreases
```
347
What is the valsalva maneuver?
a bearing down or forceful attempt at expiration, when nose and mouth are closed. It increases pressure in the thorax and reduces all venous flow.
348
What is a doppler shift?
a change or variation in the frequency of the sound as a result of motion between the sound source and the receiver. or difference between received and transmitted frequencies.
349
positive doppler shift
when source and receiver are approaching each other, so the reflected frequency is higher than the transmitted.
350
negative doppler shift
when the source and receiver are moving apart, so the reflected frequency is lower than the transmitted.
351
Does doppler measure frequency or amplitude?
frequency
352
if emitted frequency is FE and reflected frequency is FR then...
FD (doppler frequency)=FR-FE
353
doppler shift is directly related to...
blood cell speed
frequency of the transducer
cosine of the angle
354
doppler shift is inversely related to...
speed of sound in the medium
355
doppler shift =
2x reflector speed x incident frequency x cos (angle) / propagation speed
356
What requires magnitude and direction?
velocity
357
How many crystals are in a continuous wave doppler?
2
1 always transmitting
1 always receiving
358
What is the advantage to continuous wave doppler?
high velocities are accurately measured
359
What are the disadvantages to continuous wave doppler?
range ambiguity
360
How many crystals are in a pulsed wave doppler?
1
361
What is the advantage to pulsed wave doppler?
since we have a gate we know where the flow is being measured, this is called range resolution or specificity
362
Aliasing is an disadvantage of what?
pulsed wave doppler
363
What is it called when you are imaging and using doppler at the same time?
duplex
364
What does x axis represent for doppler?
time
365
What does y axis represent for doppler?
velocity
366
What is it called when high velocities appear negative on doppler?
aliasing
367
Nyquist limit=
PRF/2
368
What king of doppler does not create aliasing?
continuous wave
369
Ways to reduce aliasing are...
```
use continuous wave
use a lower frequency
select a new view with a shallower sample volume
increase the scale
baseline shift
```
370
Do smaller or larger sample volumes (gates) produce a doppler spectra with a cleaner window?
smaller
371
What are gray shade on a doppler spectrum related to?
amplitude of the reflected signal
| number of red blood cells creating the reflection
372
What doses color doppler report?
average velocities
373
When using color doppler in velocity mode what does the color on the top represent?
blood cells flowing towards the transducer
therefore bottom color represents flow away from transducer
374
When using color doppler in variance mode, what does the appearance of colors on the right side of the color bar mean?
turbulent flow
therefore left side represents laminar flow
375
What are multiple ultrasound pulses needed to accurately determine red blood cell velocities by Doppler called?
doppler packets
can be large or small
376
what are the advantages to large doppler packets?
greater accuracy
| sensitivity to low flow
377
What are the disadvantages to large doppler packets?
more time required
| frame rate and temporal resolution are reduced
378
What are the limitations of color power doppler?
no measurement of velocity or direction
lower frame rates
flash artifact
379
What are the advantages of color power doppler?
increase sensitivity to low flows
not affected by angle , except 90 degrees
no aliasing
380
When is spectral analysis used?
to identify the individual frequencies making up the complex signal
381
What are the current methods of spectral analysis?
fast fourier transform (FFT)
| autocorrelation (less accurate but faster)
