Final Exam Review Flashcards
(140 cards)
1
Q
What is sound?
A
Mechanical, travels in a straight line, longitudinal, can’t travel through a vacuum
2
Q
What variables distinguish sound from other waves
A
Three acoustic variables: pressure, density, distance
3
Q
What are the parameters that decribe a sound wave?
A
Period, Frequency, Wavelength, Intensity, Power, Amplitude, Velocity
4
Q
Does a wave with differing frequency throughout have constructive or destructive interferrence?
A
Both occur at different times. some parts of the wave are in phase and others are out-of phase at the same time
5
Q
What is period? Is it adjustable and what is it determined by?
A
time of one cycle, not adjustable, determined by source
6
Q
What is frequency? Is it adjustable and what is it determined by?
A
cycles per second, not adjustable, determined by source
7
Q
What is wavelength? Is it adjustable and what is it determined by?
A
distance of one cycle, not adjustable, determined by source AND medium
8
Q
What is amplitude? Is it adjustable and what is it determined by?
A
difference between average and either min or max value, is adjustable, determined by source
9
Q
What is intensity? Is it adjustable and what is it determined by?
A
concentration of energy (watts) over area in a beam, is adjustable, determined by source
10
Q
What is power? Is it adjustable and what is it determined by?
A
rate (watts) work is performed, is adjustable, determined by source
11
Q
What is propagation speed? Is it adjustable and what is it determined by?
A
the rate at which sound travels through a medium, not adjustable, determined by medium’s density and stiffness
12
Q
What is the frequency of ultrasound?
A
Greater than 20 K HZ
13
Q
What is the equation for wavelength
A
1.54/Hz
14
Q
What is the equation for amplitude
A
intensity or power = amplitude ^ 2
15
Q
What is the equation for propagation speed
A
C= Hz x Wavelength
16
Q
What is the equation for intensity
A
Power/area
17
Q
What is pulse duration? Is it adjustable and what is it determined by?
A
The length of a pulse’s “on” time. Determined by source and not adjustable
18
Q
What is Spatial pulse length? Is it adjustable and what is it determined by?
A
The distance of a pulse’s “on” time. Determined by source and medium, not adjustable
19
Q
What is Pulse Rep Period? Is it adjustable and what is it determined by?
A
The length of whole pulse plus listening time. Determined by source and depth and is adjustable
20
Q
What is Pulse Rep Frequency? Is it adjustable and what is it determined by?
A
Pulses per second in Hz. Determined by source and depth and is adjustable
21
Q
What is Duty Factor? Is it adjustable and what is it determined by?
A
percentage of time the pulse is “on”. Determined by source and is adjustable
22
Q
How are PRP directly and PRF inversely related to depth
A
Depth increases listening time because a second pulse cannot be sent until the first returns. When listening time increases, so does PRP. This decreases the frequency that the pulses will occur.
23
Q
What is the equation for Pulse Duration
A
PD= cycles/Hz or cycles x period
24
Q
What is the equation for spatial pulse length
A
cycles x wavelength
25
What is the equation for duty factor
DF% = PD/PRP
26
How could you change SPL or PD
Add cycles or change frequency
27
How do you change intensity with a 3 or -3 dB change? What about 10 or -10 dB?
for a change of 3 or -3 dB, multiply intensity by 2 or 1/2. For a change of 10 or -10, multiply instensity by 10 or 1/10
28
What do decibles require?
2 intensities: a starting level and a level at the time of measurement
29
What is attenuation determined by?
path length and frequency
30
What does it mean if a wave attenuated 10 dB?
it is -10 dB
31
What processes are associated with attenuation?
Reflection, absorption, scattering
32
What are components of specular reflection?
1 directional and organized, large and smooth boundary, must be 90 degrees or will not return.
33
What are components of diffuse reflection?
multiple directions and disorganized creating backscatter, large and irregular boundary, non-90 degree angles will create reflection but the signal will be weaker.
34
What are components of scattering?
random reflection of sound in multiple directions, small interface (less than or equal to 1 wavelength)
35
What are components of Rayleigh scattering
organized, RBCs, frequency^4
36
What is absorption?
energy converted to another form (such as heat)
37
What are scattering and absorption directly related to?
frequency
38
What is an attenuation coefficient?
the amount of decibles of attenuation in 1 cm
39
What is the attenuation coefficient equation?
frequency / 2
40
What is the equation that measures total attenuation?
Coefficient x distance
41
What is half value layer?
Half value layer is the distance sound travels that reduces the intensity to 1/2 its original value or when it attenuates by 50%.
42
What is half value layer determined by? When would it be thick vs thin?
medium and frequency. It is thick in highly attenuating tissue like lung/bone and thin with low-attenuating fluid.
43
what is impedence
resistance of sound in a medium. it is calculated not measured
44
what is the impedence equation
rayls = density x speed
45
what is normal incidence?
striking a boundary at exactly 90 degrees.
46
What are ITC and IRC? What is their equation?
intensity transmission coefficient and intensity reflected coefficient. When added they equal 100%
47
If striking a boundary at a 90 degree angle, how does conservation of energy occur?
whatever sound is not reflected must be transmitted.
48
What will the reflected angle always equal
the incident angle
49
With two identical impedences, how much is reflected? How much is transmitted?
Nothing would reflect, it would all be transmitted.
50
What is refraction
bending of the transmitted angle when traveling from one medium to another
51
What is required for refraction to occur?
velocity mismatch and an oblique angle
52
What happens with refraction if the speeds are equal? Which speed should be greater to have a greater transmission angle?
If speeds are equal, no refraction will occur. The speed of medium 2 should be greater to have a greater transmission angle?
53
What is pulse average
the average intensity during a pulse
54
what is temporal average
the average intensity over the pulse and listening time
55
what is the difference between spatial peak and spatial average
spatial peak is the intensity at the greatest point of the beam and average is over the width of the beam.
56
What is greater in continuous wave? Pulse average or Temporal average?
They are the same in cont wave because there is no listening time. They would be equal.
57
What is the most relevant intensity measurement in regards to DMS
SPTA
58
What is dosimetry
the study of identifying bioeffects
59
what is cavitation
interaction of sound waves with microbubbles in tissues. These bubbles are either transient or stable
60
What are the forms of thermal index?
Thermal Index of Soft tissue, bone, and cranial bone. TIS, TIB, and TIC.
61
What is stable cavitation associated with?
swinging bubbles and low mechanical index- meaning less harmful effects.
62
What is transient cavitation associated with?
bursting bubbles, high temperature, high mechanical index
63
What is a mechanical index? what is a high MI associated with?
MI is the likelihood of harmful bioeffects effects. High MI is associated with more pressure, cavitation, and less frequency.
64
What are the assumptions of sound
reflection strength is related to tissue's characteristics, imaging plane is thin, only the main axis will reflect, it travels in a straight line, to reflector and back, at 1,540 m/s
65
What is reverberation?
equally spaced bouncing of soundwaves. the first and second are real and the rest are artifacts
66
What is the difference between comet tail and ring down artifacts?
comet tail is usually off a solid object like a stone whereas ring down is from gas bubbles or infection
67
what causes shadowing in an image.
100% reflection and 0% transmission. this is due to too much attenuation not speed
68
what causes edge shadow
the beam diverging and changing intensity
69
which mirror image is false?
the bottom artifact is false
70
With a speed error artifact, what happens when the speed of sound is too fast?
too fast tissue is shown too shallow on the screen
71
what is subdicing
splitting a PZT into several smaller pieces to improve resolution
72
what is apodization
exciting elements with different voltages
73
What is a side lobe created by?
a single element transducer
74
what is a grating lobe created by?
array transducers.
75
What determines axial resolution
pulse length (PD and SPL)
76
what determines lateral resolution
the width of the beam
77
What is LARRD
Longitudinal, Axial, Radial, Range, Depth
78
What is LATA
Lateral, Angular, Transverse, Azimuthal
79
What is the equation for Axial resolution
SPL/2
80
What factors improve axial resolution?
dampened pulse to shorten pulse length, high frequency, fewer cycles
81
What factors improve lateral resolution in the near field?
small diameter crystal
82
What factors improve lateral resolution in the far field and why?
large diameter crystal and high frequency. this has the least divergence.
83
how is SPL and AR value related?
directly related
84
What is the equation for lateral resolution?
Lateral resolution = beam diameter
85
what types of focusing are fixed?
external focusing with a lens and internal focusing with curved PZT. These are creaetd when the beam is manufactured
86
What kind of focusing is adjustable?
electronic phased array focusing by the ultrasound system
87
What are both the focal length and beam divergence determined by?
diameter of crystal and frequency
88
What determines frequency in pulsed wave?
in pulsed wave the thickness and speed of sound in PZT
89
Is axial resolution adjustable? Why or why not?
no. it is related to SPL which is a non adjustable value.
90
What is the width of the focal zone
1/2 the beam width
91
How does a large diameter transducer with high frequency relate to scanning depth
A large diameter scans deeper and a higher frequency has longer depth
92
Do thicker crystals diverge more or less
less. PZT is inversely related to divergence
93
How many crystals does a mechanical transducer have? What shape is the image?
1 crystal, sector shaped
94
How many crystals does a linear sqequential transducer have? What shape is the image?
120-250 PZT, rectangular shaped
95
How many crystals does a linear phased array transducer have? What shape is the image?
100-300 PZT, sector shaped
96
How many crystals does a annular phased transducer have? What shape is the image?
multiple disc shaped PZT, sector shaped
97
How many crystals does a curvilinear transducer have? What shape is the image?
120-250 PZT, blunted sector shaped
98
How many crystals does a vector transducer have? What shape is the image?
120-250 PZT, trapezoid shaped
99
What transducer types are not electrically steered and focused?
Mechanical transducers are mechanically steered and focused. Annular phased transducers are mechanical steering but electronically focused
100
What benefit do disc shaped crystals have?
better lateral and elevational resolution
101
What is a side lobe and what creates it
extra areas of sound outside far zone that are created by single element transducers with worsened lateral resolution
102
What is a grating lobe and how is it created
extra sound beams along the beam's course. This is created by array transducers.
103
What does a transducer do
transforms electric energy into acoustic and vice versa
104
What does a pulser do?
Creates a signal and determines the time between each voltage strike (PRP)
105
What happens to the image during the increase in voltage that occurs when the pulser strikes the PZT?
When voltage increases so does image brightness.
106
What does the beam former do
receives the pulser's spike and distributes it among the crystals. it also adjusts the voltage as needed (apodization etc.).
107
What does the switch do?
protects components and directs electrical signals to components in the transducer
108
What does the receiver do?
prepares information to be displayed.
109
What are the steps of receiving a pulse?
amplification- makes pulse bigger, gain
compression- accurate grey scale
compensation- battles attenuation, TGC
demodulation- converts - to + and smooths
reject- eliminates low-level echos as needed
110
What is frame rate determined by?
sound speed and depth
111
What is Temporal resolution
the ability to display real-time changes
112
What is T Frame? How is it related to frame rate?
the time it takes to display one frame. It is inversely related to frame rate.
113
What is the T Frame equation
number of pulses x PRP
114
greyscale is made possible with what type of transducers?
analog
115
what are the benefits of a digital scan converter?
Speed Uniformity Stability Durability Accuracy
116
What is associated with high pixel density
more pixels per inch, smaller pixels, better spatial resolution
117
what is a word of memory
16 bits or 2 bytes of computer memory
118
Is contrast resolution related to more or fewer shades of grey
more shades of grey
119
What is the echo ranging theory equation?
for every 13 us, the reflector is 1 cm deep
120
What is coded excitation
using a long sound pulse with a large range of frequency to minimize intensity's bioeffects
121
What is spatial compounding
using multiple angles to improve image quality
122
What is frequency compounding
Reducing noise by splitting frequencies into sub bands.
123
What is temporal compounding
Overlapping a previous image of the same view with new information to improve quality
124
What is Fill-In interpolation
A computer prorgam predicts the greyscale based on surrounding tissue to fill in the gaps from low line density
125
is transmission piezoelectric or reverse piezoelectric?
Transmission is reverse piezoelectric.
126
Why do we use backing material?
to shorten the pulse which improves axial resolution
127
What is PZT used for? What is the equation for PZT Thickness?
The characteristics of PZT determine the sound's. thickness = 1/2 the wavelength
128
What is a matching layer used for? How thick is it?
it protects the PZT and increases the efficiency of the sound/energy transfer. it is 1/4 the wavelength
129
What does the acoustic insulator do?
prevents case vibrations from exciting PZT
130
what does the electrical shield do
prevents signals from the air from entering and contaminating the desired signals
131
What does it mean when the backing layer decreases sensitivity? What does this improve?
It means the transducer is less sensitive to low level echoes whcih are undesireable. this improves axial resolution
132
What does it mean when the backing layer has a wide bandwidth? Do transducers usuallly have wide or narrow?
A wide bandwidth means it receives a wide variety of frequencies. A transducer is usually wide
133
What does Q value mean? How does this relate to bandwidth?
Q value is the ring time of a transducer as a result of dampening the pulse. Low Q value means wide bandwidth, they are inversely related.
134
What is the equation for Q factor?
frequency/ bandwidth
135
How are crystal thickness, frequency, and divergence related?
Crystal thickness and frequency are both inverselt related to divergence. A thick crystal and high frequency diverge less.
136
how are speed of sound, PZT thickness, and frequency related?
Thickness is inversely and speed is directly related to frequency
137
what is the equation for frequency in PZT
speed / (2 x thickness)
138
are period, wavelength, and SPL related to Duty Factor?
Yes, directly related.
139
Is frequency related to scattering?
Yes, directly related
140
What does "array transducer" mean?
Array means multiple crystals that fire to make a pulse
