Helpful Notes Flashcards
(162 cards)
1
Q
What does propagation speed depend on?
A
medium, not frequency
2
Q
As stiffness increases, what happens to the propagation speed?
A
Propagation speed increases
3
Q
As density increases, what happens to the propagation speed?
A
Propagation speed decreases
4
Q
What is a typical wavelength in U/S?
A
0.1-0.8 mm
5
Q
What is the typical intensity in U/S?
A
0.01-100 mW/cm2
6
Q
What is the unit of impedence?
A
rayls
7
Q
What occurs if impedence between 2 media are the same?
A
all transmission, no reflection
8
Q
what happens to PRF if depth increases?
A
decrease PRF
9
Q
What is DF in U/S typically?
A
1% or less
10
Q
What are determined by the medium?
A
- propagation speed
- impedence
11
Q
What is determined by both propagation speed and the medium?
A
- wavelength
- SPL
12
Q
What does one need to know to determne attenutation?
A
rate (Ac) and path length (L)
13
Q
what is the average rate of attenuation in U/S?
A
0.7 dB/cm
14
Q
is specular or non specular angle dependant?
A
specular
15
Q
In rayleigh scatter, what happens to intensity if frequency increases?
A
intensity increases 4x
16
Q
How is temporal average determined?
A
pulse average x DF
17
Q
What is the typical thermal bioeffects setting?
A
SPTA
18
Q
What can a hydrophone measure?
A
- PD
- PRP
- T
19
Q
what are scan lines?
A
pulses that RETURN from tissues
20
Q
What is sensitivity?
A
the ability of a system to display low level or weak echoes.
21
Q
What does spatial resolution refer to?
A
- Lateral res
- Axial res
- Elevational res
- Contrast res
22
Q
What material is used for backing material?
A
resin, Tungsten
23
Q
What material is used for elements/crystals?
A
PZT
24
Q
What does resonating frequency depend on?
A
thickness of the element and propagation speed of the element
25
How many volts does a ultrasound machine produce to drive piezoelectric elements?
10-500 V
26
How many individual elements do modern scanheads contain?
more than 100
27
Is a higher or lower Quality Factor better?
lower
28
Do CW have high or low Q Factors?
high becuase they do not have damping
29
What is quality factor?
How near to the actual operating frequency is the bandwidth
30
What is another name for lateral resolution?
Azimuthal resolution
31
Do most transducer have better axial or lateral resolution?
Axial
32
How is elevational resolution most commonly focused?
with a lens
33
What is the minimum FR that needs to be maintained or the image will flicker?
15 Hz
34
what are 3 adjustments that alter FR?
- image depth (PRF)
- number of focal zones
- number of scan lines per frame (line density)
35
How is PRF related to FR?
directly
36
binary
0's and 1's
37
Bistable
black and white image
38
Bit
smallest unit of memory in a digital device
39
Byte
8 bits if memory
40
Pixel
smallest component of a 2D digital image
41
voxel
smallest component of a 3D image
42
what does the scan converter consisit of?
- A-D converter
- computer memory
- D-A converter
43
what is subdicing?
dividing the peizoelectric elements into very small pieces to reduce grading lobes
44
Analog
dimmer switch, infinite
45
Digital
On/Off switch, finite
46
Is it better to have more pixels or more shades of gray?
more pixels=better spatial resolution
47
What transducers produce grating lobes?
linear transducers
48
Where is flash artifact seen?
movement of tissue in POWER doppler
49
What is inertia?
Newton's principle that states an object in motion stays in motion unless acted on by an outside force.
50
What is Ohm's law?
A law used in electronics in which flow is equal to the pressure divided by the resistance.
51
What is an oscillator?
the component of a CW doppler device that produces the voltage that drives the transducer
52
What is persistence?
the averaging of colour frames in order to display blood flow with a low signal-noise ratio.
53
What is poiseuilles law?
law that describes the relationship of resistance, pressure, and flow.
54
How is power doppler determined?
amplitude mode, brightness is determined by amount of RBC.
55
What cross sectional area percentage is considered to be hemodynamically significant?
75%
56
What diameter reduction percentage is considered to be hemodynamically significant?
50%
57
What are the advantages of PW over CW for spectral?
- ability to select a specific depth to sample by utilizing range gate
- ability to angle correct to calculate velocity
58
Are autocorrelation or FFT's more accurate?
FFT
59
Does more white make a color more or less saturated?
less saturated.
60
What type of signal does flowing blood typically produce?
low amplitude, high velocity signal.
61
what is mechanical index?
the calculation used to identifty the liklihood that caviation will occur.
MI<0.4
62
What is thermal index?
the calculation used to predict the maximum temperature elevation in tissues as a result of attenuation of sound
TI<2
63
What documentation of U/S images should it include?
- pt's name
- facilty info
- date of exam
- image orientation
64
What should the post examination worksheet include?
- pt's name
- date of exam
- type of exam
- relevant clinical info
- ICS 9 code (ACC)
- name of patients healthcare provider and contact info.
65
What is the definition of communication?
transfer of information from one person to another.
66
What is anaphylactic shock?
allergic reaction leading to vasodilation and pooling in peripheral blood vessels.
67
What is cardiogenic shock?
failure of the heart to pump the proper amount of blood to vital organs.
68
What is distributive shock?
When blood vessels lack the ability to constrict and assist in the return of blood to the heart, leading to pooling in the periphery.
69
What is hypovolemic shock?
when the amount of intravascular fluid decreases by 15-25%
70
What is neurogenic shock?
loss of the sympathetic pathologic conditions that interfere with the normal pumping action of the heart.
71
What is obstructive shock?
results from pathologic conditions that interfere with the normal pumping of the heart.
72
What is septic shock?
There is an immune responce of thre body that leads to capillary permeability and vasodilation.
73
What are the 3 categories of distributive shock?
- anaphalytic
- septic
- neurogenic
74
Are frequencies higher in Doppler or B-mode imaging?
frequency for doppler is lower than for B-mode imaging.
This is because sound attenuates when looking at color compared to just tissue.
75
What receiver function is responsible for decreasing the difference between the smallest and largest received signal amplitudes?
Compression
76
Is gray scale map assessment pre or postprocessing?
postprocessing
77
The technique of frame averaging (persistence) during real-time acquisition is designed to:
Reduce random noise
Persistence reduces speckle
78
What is one of the main advantages of harmonics?
improves contrast resolution
79
How is contrast resolution always improved?
increasing frequency
80
Interpolation is used to fill in the missing data between scan lines in what?
both grayscale and color doppler
81
To generate a sonographic image, what is the order in which the following system components are activated?
- Pulser
- Beam Former
- Reciever
- Memory
- Display
82
What is a typical frame rate for B-mode real-time imaging?
10-50 Hz
83
What control could you adjust to improve the signal-to-noise ratio on the image?
Frame averaging (persistence)
84
Define Duty Factor
the fraction of time that the transducer is activly transmitting sound
85
If you increase the pulse repetition frequency and leave all other controls unchanged, what will happen to frame rate?
frame rate will increase
86
What does increasing dynamic range do to contrast resolution?
decreases contrast resolution
87
Does increasing PRF decrease frame rate?
no
88
What is compression opposite of?
dynamic range
89
What is the difference between compression and dynamic range?
compression-decreases the range of signal amplitudes present
Dynamic range-the series of echo amplitudes present within the signal
90
Increasing the number of acoustic scan lines in one frame improves what?
lateral resolution
91
What component is necessary for a real-time B-mode scanner but is not present in an A-mode scanner?
scan converter
92
A digital scan converter is another name for what system component?
Image memory
93
Where are images stored in the ultrasound system?
scan converter
94
What three colors are used on a color monitor to produce the range of available colors?
red
green
blue
95
When you “freeze” the ultrasound image, where is the echo information stored?
scan converter
96
What type of resolution is determined by the number of pixels in the scan converter?
spatial resolution
97
What is the order in which the signal travels in the ultrasound system?
Transducer
Reciever
Scan converter
Display
98
You are imaging a 3D data set that has anisotropic resolution. What does this mean?
Unequal resolution is present between imaging planes.
99
What is another name for spatial compounding?
compound imaging
100
While scanning a curved structure, you notice shadowing at the lateral edges of the structure. What is required for this artifact to occur?
Different media propagation speeds
101
What are the artifacts of reverberation?
- comet tail
- ring down
- ?
102
When you select spatial compound imaging which artifacts will it eliminate?
- refraction
- shadowing
- enhancement
- acoustic speckle
103
What results in banding?
incorrect TGC
| when there are areas of brightness and darkness in different depths of the image
104
Which artifact is associated with resonance of a gas bubble?
ring down
105
Which of the following helps to improve the lateral resolution in a B-mode image?
increase aperature
106
What technique reduces grating lobes?
tissue harmonic imaging
107
What technique would be most likely to produce grating lobes in your image?
Beam steering
108
A standard for handling and transferring images and medical information between computers is:
DICOM
109
Which artifact is related to the sound beam traveling through a structure with low attenuation?
Enhancement
110
What type of focusing is performed by delay circuitry upon reception?
dynamic recieve focusing
111
When you select one focal zone, how many pulse/listen cycles are required for each acoustic scan line in one image frame?
one
112
define esemble length/packet size?
For color doppler, each line of sight must be pulsed multiple times. The number of pulses per line is termed esemble length or packet size.
113
What is velocity estimation in doppler based on?
measurement of doppler angle of incidence.
114
What are varience color maps?
green color shows turbulence
115
Flash artifact is typically what type of signal?
high amplitude, low frequency
116
What does interial losses of fluid energy depend on?
changes in flow direction and and changes in blood velocity.
117
When does reynolds number increase?
Reynolds number increases with increasing flow speed and enlarging tube diameter.
118
how may a bruit appear on spectral doppler?
Seen in an area of post stenotic turbulence. It appears as bright echoes near the baseline located undernath the systolic peak.
119
What two controls affect the spatial resolution of the color image?
Frequency and line density
120
What are another names for lateral resolution?
- Angular
- Transverse
- Azimuthal
121
What are another names for axial resoltuion?
- longitudinal
- axial
- Radial
- Range
- Depth
122
What is doppler shift frequency proportional to?
velocity of the reflector
123
What is doppler shift frequency dependant on?
doppler angle and transducer frequency
124
Transmission of the sound wave from one medium to the next is determined by the media’s _________
impedance
125
what is the thickness of the matching layer equal to according to the wavelength?
1/4 of the wavelength
126
What pulse wave transducer displays a trapezoidal image?
Vector
127
The greater the impedance difference between two structures, the greater the:
reflection
128
The speed at which a wave travels through a medium is determined by
what?
stiffness and density of the medium
129
What will happen to pressure at a stenosis?
preasure will decrease
130
Where is uniform intensity of the sound beam located?
In the far field
131
The amplitude of the transmitted and recieved signals is the the responsibility of what?
system output
132
The mechanical index is inversely proportional to the:
operating frequency
133
How do you fix range ambuigity?
PRF should be reduced
134
What is apodization only good for?
grade lobes
135
What are doppler shift frequencies in the range of? (infra, audible, ultra)?
audible
136
What are the frequency ranges for ultrasound?
20 KHz
| 2-20 MHz
137
The display will generally have a DR smaller or larger than other portions of the ultrasound instrument?
smaller
138
Analog voltages occur at the output of the:
beam former
| transducer
139
Digital signals occur at the output of the:
beam former
| signal processor
140
Another name for analog
proportional
141
Another name for digital
discrete
142
What is a tuned amplifier?
is simply an amplifier with an electronic filter called the bandpass filter.
143
What is another name for detection?
demodulation
144
What is the typical DR of an amplifier?
100-120 dB
145
What is the typical DR of a display?
30 dB
146
List the lowest to highest intensity values:
- SPTA gray scale
- M-mode
- pulsed wave
- color doppler
147
What is mechanical index inversely related to?
operating frequency
148
What is the thickness of the element equal to according to wavelength?
1/2 wavelength
149
What are types of transducer construction?
- linear
- convex
- annular
150
What are types of transducer operations?
- sequenced
- phased
- vector
151
What does focal length also mean?
near zone length
152
To improve contrast resoltion what would we do to dynamic range?
increase DR (compression)
153
When we decrease DR what happens?
more contrast, granier
154
When we increase DR, what happens?
less contrast, smoother
155
The impedance of the matching layer is
less than that of the crystal and greater than the impedance of the skin
156
What is section thickness related to?
beam width
157
What is frame rate determined by?
penetration depth and propagation speed of the medium
158
What constitutes a transmission
| channel?
an independant pulse delay and an element
159
Is contrast resolution or spatial resolution most likely related to pixel density?
spatial resolution
160
What is the size of the sample volume determined by?
- beam diamter
- length of US pulse
- reciever gate length
161
According to pressure, which direction does blood flow?
from higher pressure to lower pressure
162
What does the vertical axis of spectral analysis represent?
frequency
