physics principles Flashcards
1
Q
what is sound
A
a mechanical, longitudinal wave.
2
Q
what does longitudinal mean?
A
parallel from the sound source.
3
Q
what does 1 complete cycle mean?
A
it means 1 compression & 1 rarefaction
4
Q
λ
A
wavelength
5
Q
c
A
propagation speed
6
Q
f
A
frequency
7
Q
what does wavelength depend on?
A
frequency & propagation speed
8
Q
what is propagation speed determined by?
A
a medium
9
Q
what is frequency determined by?
A
a sound source
10
Q
mediums with fast propagation speed = ______
A
longer wavelength
11
Q
mediums with slower propagation speed = ______
A
shorter wavelength
12
Q
infrasound
A
<less than 20Hz
13
Q
audible sound
A
20 - 20,000Hz
14
Q
ultrasound
A
> greater than 20,000Hz
15
Q
diagnostic ultrasound
A
2 - 20MHz
16
Q
power
A
rate of flow of energy
17
Q
intensity
A
power/area
18
Q
amplitude
A
height of pressure wave
19
Q
why do we use decibels?
A
to describe how much our intensity has changed
20
Q
a reduction of 6dB means the intensity is reduced by how much?
A
1/4. 25%
21
Q
adjusting overall gain from 25dB to 28dB will cause what affect to the intensity of the echoes?
A
there was an increase of 3dB which means the intensity was doubled.
22
Q
in soft tissue..
A
1.54 mm/ms or 1540 m/s
23
Q
bulk modulus
A
stiffness
24
Q
is propagation speed affected by frequency or wavelength?
A
NO
25
impedance
obstruct or hinder
26
each medium has it's own _______.
impedance
27
what is impedance dependent on?
the medium
28
Z
impedance
29
p
density
30
Z = pc means...
impedance = density & propagation speed
31
interface
tissue change
32
when sound encounters interface what can happen?
some sound can be reflected (bounce back) & the rest continues traveling or is transmitted.
33
attenuation
weakening of sound
34
what does attenuation depend on?
a medium
35
what is the average rate of attenuation in soft tissue?
1/2 dB/cm/MHz
36
decibels change in ..
intensity
37
frequency & attenuation are ______ related.
directly
38
increase in frequency = _____________
increase attenuation
39
how much is the frequency going to attenuate per cm?
half the frequency
40
4 MHz will attenuate ___
2 dB/cm
41
8 MHz will attenuate _______
4 dB/cm
42
What are Pulsed Ultrasound Parameters?
PRF, PRP, SPL, PD, DF
43
PRF
Pulsed Repetition Frequency
44
PRP
Pulsed Repetition Period
45
SPL
Spatial Pulse Length
46
PD
Pulse Duration
47
DF
Duty Factor
48
what does Pulsed US Parameters do?
generate 2-3 cycles only
49
what does PRF depend on
depends on depth since the machine as to wait for the echo before sends it to next pulse.
50
if PRF is too high the machine will...
the machine will not know the location or depth.
51
PRF is ______ related to depth.
inversely ↑Depth ↓PRF
52
pulse repetition frequency =
number of uses in 1s
53
pulse repetition period=
time between beginning of 1 pulse to beginning of next pulse
54
PRP is _______ related to PRF
inversely ↑PRF ↓PRP
55
PRP is _____ related to depth
directly ↑PRP ↑PRF
56
spatial pulse length=
length of one pulse
57
what does SPL depend on
frequency
58
pulse duration=
time for one pulse to occur
59
what does PD depend on?
SPL
60
in diagnostic US, PRF is in ___
kHz
61
what is DF?
the fraction or % of time that an imaging system is transmitting
62
is DF used often?
no, only 0.1 - 1.0%
63
what is resolution?
the machines ability to detect & display accurately
64
what are the 2 main types of resolution?
spatial resolution & temporal resolution
65
what is spatial resolution?
the machines ability to distinguish between 2 closely spaced objects & display them separately.
66
what is spatial resolution measured in?
space or distance (mm)
67
axial
vertical
68
lateral
horizontal
69
1/2 SPL is ____
axial
70
LARRD
longitudinal, axial, radial, range, depth
71
what is the axial res from a SPL of 1.8mm
0.9mm
72
how do you find the axial resolution of a SPL?
1/2 SPL
73
the 2 objects have to be separated by ____ in order to be resolved.
1mm max
74
an SPL of 1.8mm = axial resolution of 0.9mm. Is it resolved?
yes!
75
an SPL of 2.2mm = axial resolution of 1.1mm. Is it resolved?
no, its more than 1.0mm so they are blurred together vertically
76
what is the goal of axial resolution?
shorten the pulse
77
when you decrease frequency what happens?
decreases wavelength=decreases pulse
78
what is damping/backing material do?
reduces ringing of crystal = shortens the pulse
79
what does a wide bandwidth do?
shorter pulse (low Q-factor)
80
what is a trade off?
when you gain something by giving something else up
81
what has trade offs?
resolutions
82
what is the main way to improve axial resolution?
increase frequency
83
do you always chose the highest frequency you have?
no, because you will not be able to scan deeper
84
what is axial resolution?
the ability to see the two structures that are side by side as separate and distinct when parallel to the beam.
85
lateral = _______
beam width
86
LATA
lateral, azimuthal, transverse, angular
87
what is lateral resolution?
the image generated when the two structures lying side by side are perpendicular to the beam
88
what does temporal mean?
time
89
in order for the 2 objects to be seen what has to happen?
the 2 objects have to be hit by their own beam, then they will produce separate echoes & the machine will display both go them.
90
what is the goal in lateral resolution?
narrow the beam
91
what are some ways to narrow the beam?
1. focusing:
multiple focal zones=overall beam narrowing
2. # scan lines/scan line intensity
sea lines=beams. increase line density=smaller beam size
3. sector angle
decreasing sector size=increase line density
4. transducer choice
sector FOV(field of view)=lower line density in far field, lat res worsens
92
temporal
frame rate
93
what is frame rate determined by?
the amount of work the machine has to do or time it needs to produce the frame.
94
what happens if you have poor frame rate?
the images will be blurred together giving it a slow motion effect
95
what is frame rate?
it helps the machine keep up with whatever is going on in the body
96
high PRF =
faster frame rate
97
piezoelectric
pressure-electric
98
PZT
lead ziconate titanate (man made ceramic crystal)
99
what are the 2 crystal materials?
PZT & Quartz
100
what is operating frequency determined by?
the thickness of the crystal (typically 0.2 - 1.0mm)
101
crystal thickness = _____
1/2 wavelength
102
crystal thickness & frequency are _____ related
inversely
103
the thinner the crystal ________
the higher the frequency
104
fixed
we cannot control
105
what do the lens do?
focuses ultrasound beams on a target
106
what is the impedance matching layer?
a layer at the transducer face that matches the impedances.
107
why do you need to match the impedances?
so that most of the beam can be transmitted easily into the body
108
what does the matching layer do?
reduces reflection. similar to gel
109
what is backing/damping material do?
reduce the ringing of the crystal & shortens the pulse
110
for pulsed US how many cycles do you want?
2-3 cycles only
111
bandwidth
the range of frequencies
112
what determines bandwidth
the size of the pulse
113
short pulse = _____ bandwidth
wide
114
long pulse = ______ bandwidth
narrow
115
do we want high Q transducers ?
no, high Q means narrow bandwidth which means long pulses which means poor axial resolution. we want lower Q Factor.
116
Q-Factor
quality of frequency off the transducer
117
what are the 3 beam characteristics?
1. Fresnel Zone
2. Fraunhofer Zone
3.Focal zone/point
