Chapter 1: Physical Principles Flashcards
1
Q
Sound is a pressure wave, created by a mechanical action, and is therefore called a ________
A
mechanical wave
2
Q
produced when a vibrating source causes the molecules of a medium to move back and forth
A
sound wave
3
Q
any form of matter: solid, liquid, or gas
A
medium
4
Q
Sound requires a _____ to propagate; therefore it cannot travel in a vacuum
A
medium
5
Q
When sound energy propagates through a medium, it does so in _____ waves, meaning that the molecules of the medium vibrate back and forth in the same direction that the wave is traveling.
A
longitudinal
6
Q
Sound is a _______, _______ wave.
A
mechanical
longitudinal
7
Q
molecules in a medium vibrate at 90 degrees to the direction of the traveling wave
A
transverse waves
8
Q
changes that occur within a medium as a result of sound traveling through that medium
A
acoustic variables
9
Q
The three primary acoustic variables are _____, ______, and ______.
A
pressure
density
particle motion
10
Q
Each back and forth movement of molecules completes one _____ or one cycle of movement
A
wave
11
Q
Each cycle consists of two parts: _______ and ______
A
compression
rarefaction
12
Q
molecules are pushed closer together
A
compression
13
Q
molecules are spread wider apart
A
rarefaction
14
Q
mass per unit of volume
A
density
15
Q
the back and forth motion of the molecules in the medium, and its units are that of distance
A
particle motion
16
Q
how far apart objects are, and it is the measurement of particle motion
A
distance
17
Q
may also be referred to as vibration or displacement
A
distance
18
Q
if one variable increases the other increases
A
directly related
19
Q
if one variable increases the other decreases
A
indirectly related
20
Q
Parameters of sound
A
period
frequency
amplitude
power
intensity
propagation speed wavelength
21
Q
the time it takes for one cycle to occur
A
Period
22
Q
units of Period
A
us
23
Q
the number of cycles per seond
A
frequency
24
Q
Frequency units
A
Hs, kHz, MHz
25
Frequency and period are _____ related
inversely
26
When two reciprocals are multiplied together the result is
1
27
the speed at which a sound wave travels through a medium
propagation speed
28
Propagation speed is faster in _____
solids
29
Units for propagation speed
m/s or mm/us
30
average speed of sound in all soft tissue
1540 m/s
1.54 mm/us
31
Propagation speed is influenced by two properties
stiffness
density
32
the ability of an object to resist compression and related to hardness of the medium
stiffness
33
Stiffness and propagation speed are _____ related
directly
34
Density is _____ related to propagation speed
inversely
35
the length of a single cycle of sound
wavelength
36
distance from the beginning of a cycle to the end of that cycle
wavelength
37
In clinical imaging, the wavelengths measures between ___ and __ mm
0.1
0.8
38
Wavelength and frequency are _____ related
inversely
39
propagation speed divided by the frequency
wavelength
40
____, _____, and _____ all relate to size of strength of a sound wave.
amplitude
power
intensity
41
maximum or minimum deviation of an acoustic variable from the average value of that variable
amplitude
42
Ultrasound physics = _______ amplitude
pressure
43
units of amplitude
pascals
44
defined as the rate at which work is performed or energy is transmitted
Power
45
units of power
Watts or milliwatts
46
Power is proportional to ______
amplitude squared
47
If the amplitude doubles, the power ______
quadruples
48
defined as the power of the wave divided by the area over which it is spread, or the energy per unit area
intensity
49
_______ is proportional to both power and to amplitude squared
intensity
50
Intensity range in diagnostic ultrasound
0.01 to 100 mW/cm^2
51
Resistance to the propagation of sound through a medium
impedance
52
The amount of ______ depends on the density and the propagation speed of the medium
impedance
53
______ and ______ are controlling factors of propagation speed
density
stiffness
54
impedance units
Rayls
55
the product of the density of the medium and the propagation speed of sound in the medium
impedance
56
average speed of sound in soft tissue
1540 m/s
57
Assuming the beam strikes the interface at a 90 degree angle and there exists a large impedance difference between two tissues, there will be a _______
strong reflection
58
If the impedance between two tissues is the same there will be ______ reflection.
no
59
sound that is continuously transmitted
continuous wave ultrasound
60
material within transducers that when electronically stimulate, produce ultrasound waves
piezoelectric materials
61
pressure is created when voltage is applied to the material and electricity is created when a pressure is applied to the material
principle of piezoelectricity
62
Parameters of pulsed sound
PRF
PRP
PD
DF
SPL
63
number of pulses of sound produced in 1 second
PRF
64
Diagnostic imaging typical values PRF
1-10 kHz
65
The PRF changes when the sonographer changes the ______ control.
depth
66
If imaging depth increases, PRF ______
decreases
67
The time taken for a pulse to occur
PRP
68
the time from the start of one pulse to the start of the next pulse, and therefore, it includes the "on" and "off" times.
PRP
69
If PRP increases, PRF ______
decreases
70
the time during which the sound is actually being transmitted, the "on" time
Pulse Duration
71
The duration of "on" time depends on:
how many cycles there are in each pulse
period of each cycle
72
equal to the number of cycles in the pulse multiple by how long each cycle lasts
pulse duration
73
A ____ PD is preferred for imaging
short
74
The _____ or _____ layer reduces the long "ring" of a vibrating crystal to two or three cycles per pulse.
backing
damping
75
The backing layer helps improve _____ resolution.
axial
76
the percentage of time that sound is actually being produced
duty factor
77
PD/PRP =
duty factor
78
If the PRP is short, the DF will be _____
greater
79
In continuous wave, the DF is:
100%
80
In clinical imaging with pulsed wave, the DF will be:
1% or less
81
the length of a pulse
spatial pulse length
82
depends on the wavelength of each cycle and the number of cycles in each pulse
SPL
83
equals the number of cycles in the pulse multiplied by the wavelength
SPL
84
If the wavelength increases, the SPL ______
increases
85
If the number of cycles in the pulse increases, then SPL ______
increases
86
Shorter SPLS mean ______ pulse durations
shorter
87
Parameters determined by the sound source
period
frequency
amplitude
power
intensity
pulse duration
duty factor
pulse repetition period
pulse repetition frequency
88
Parameters determined by the medium
propagation speed
impedance
89
Parameters determined by the sound source and the medium
wavelength
spatial pulse length
90
decrease in the amplitude, power, and intensity of the sound beam as sound travels through tissue
attenuation
91
3 mechanisms of attenuation
absorption
reflection
scattering
92
used when evaluating two intensities, such as powers or amplitudes
decibels
93
If intensity or power doubles = change by ___ dB
3
94
If intensity or power decreases by half = change by ___ dB
-3
95
conversion of sound energy to heat
absorption
96
greatest contributor to attenation
absorption
97
The amount of attenuation that occurs as sound travels is related to the ____ of the beam
frequency
98
rate at which sound is attenuated per unit depth
attenuation coefficient
99
equal to 1/2 of the frequency in soft tissue
attenuation coefficient
100
total amount of sound in dB that has been attenuated at a given depth
total attenuation
101
If length increases, attenuation ____
increases
102
Average rate of attenuation in soft tissue is
0.7 dB/cm/Mhz
103
describes the depth at which sound has lost half, or -3dB of its intensity
half-intensity depth
104
Soft tissue half intensity depth is equal to:
6/f
105
dividing line between two different media
interface
106
occur when sound impinges upon a large, smooth reflector at a 90 degree angle
specular reflections
107
one in which the size of the reflector is larger than the wavelength of the incident beam
large specular reflector
108
Which reflectors are highly angle dependent?
specular reflectors
109
If the sound strikes the transducer at an _____ angle, the reflection will not return to the transducer.
oblique
110
one in which their size is smaller than the wavelength of the incident beam
nonspecular reflector
111
scattered sound in many different directions
backscatter
112
_______ reflectors are not angle dependent
nonspecular
113
constructive and destructive interactions
acoustic speckle
114
Higher frequency transducers = ______ intensity of scatter
intensity
115
very small reflectors; scatter sound equally in all directions
Rayleigh scatterers
116
As the frequency increases, intensity of the scatter increases proportional to:
the fourth power of frequency
117
When is reflection formed?
normal incidence
two media have two different impedances
118
synonyms for normal incidence
orthogonal
right angle
perpendicular
90 degrees
119
No change in impedance =
no reflection
120
Angle of reflection =
angle of incidence
121
Two types of oblique angles
obtuse
acute
122
percentage of sound transmitted at an interface
intensity transmission coefficient
123
equal to 1 minus the IRC
intensity transmission coefficient
124
the percentage of sound reflected at an interface
intensity reflection coefficient (IRC)
125
IRC + ITC
1
126
If impedances are the same, then there is no reflection, and ITC =
100%
127
The transmitted beam angle is equal to ______
incident angle
128
When sound strikes an interface with an oblique angle of incidence, the transmitted beam angle will equal the incident angle only if the ______ are identical
propagation speeds
129
If there is oblique incidence and a propagation speed mismatch, the transmitted angle will be different from the _____ angle
incident
130
If the propagation speed of medium 2 is less than the propagation speed of medium 1, then the angle of transmission will be ____ than the angle of incidence
less
131
describes the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media
Snells law
132
______ and _____ refer to where the beam was measured.
Spatial average
Spatial peak
133
SP intensity is measured where?
at the center of the beam
134
SA intensity is average intensity across ______
face of entire beam
135
SP/SA factor
beam uniformity ratio
136
ratio of center intensity to average spatial intensity
Beam Uniformity Ratio
137
intensity measured at the highest intensity, or peak, of the pulse
Temporal peak
138
highest of all temporal intensities
Temporal peak
139
average of all of the intensities during both transmission and the listening period
Temporal average
140
lowest of all temporal intensities
Temporal average
141
measured only during beam transmission
Pulse average
142
PA x DF
TA
143
lowest of intensities
SATA
144
highest of intensities
SPTP
145
used to measure output intensity
hydrophone, or microprobe
146
