SPI Flashcards
1
Q
Sound is
A
A type of wave that carries ENERGY from place to place
2
Q
Sound is made up of
A
A series of compressions and rare fractions
3
Q
Compressions are
A
Areas of increased pressure and density
4
Q
Rarefactions are
A
Areas of decreased pressure and density
5
Q
Sound must travel thru
A
A medium
Cannot travel thru a vacuum
6
Q
A sound wave is
A
Mechanical and longitudinal
7
Q
Sound travels in
A
A straight line
8
Q
Acoustic propagation properties are
A
The effects of the medium on the sound wave
9
Q
Biological effects are
A
The effects of a sound wave on biologic tissue
10
Q
Acoustic Variables
A
Pressure
Density
Distance
(Help identify which are sound waves)
11
Q
Pressure is
A
The concentration of force within an area
Units= pascals (Pa)
12
Q
Density is
A
Concentration of mass within volume
Units= kg/cm^3
13
Q
Distance is
A
Measure of particle motion
Units= cm, ft, miles
14
Q
Transverse waves
A
Particles move perpendicular (right angle or 90 degrees) to the direction of the wave
15
Q
Longitudinal wave
A
Particles move back and forth in the same direction as the wave
16
Q
Acoustic Parameters
A
Describe the features of a particular sound wave
Period Frequency Amplitude Power Intensity Wavelength Propagation speed
17
Q
Period
A
Time required to complete a single cycle
Units= microseconds
Determined by source
Not adjustable
18
Q
Frequency
A
of events that occur in a particular time frame
Units= Hz
Determined by sound source
Not adjustable
19
Q
Period and frequency relationship
A
Reciprocals
Inverse relationship
(Period decreases, frequency increases)
(Shorter period, higher frequency)
(Longer period, lower frequency)
20
Q
Bigness parameters
A
Describe beam’s strength
All behave the same way
Amplitude
Power
Intensity
21
Q
Amplitude
A
Difference between average and max value of an acoustic variable
Units= Pa, g/cm^3, cm, dB
Can be adjusted
Decreases as sound propagates thru body
22
Q
Power
A
Rate of work is preformed
Units Watts
Determined by source (initially)
Can be adjusted
Decreases as sound propagates thru body
23
Q
Relationship between power and amplitude
A
Power is proportional to amplitude^2
Examples
If amplitude is tripled the power is increased by a power of 9
If the amplitude is halved the power is decreased by a factor of 4
If the amplitude is doubled the power is increased by a power of 4 (quadrupled)
24
Q
Intensity
A
Concentration of energy in a sound beam
Units W/cm^2
Determined by source (initially)
Can be adjusted
25
Equation for intensity
Intensity (W/cm^2)= power(W)/beam area (cm^2)
Intensity=power
Intensity=amplitude^2
26
Wavelength
Length or distance of a single cycle
Units= m, mm
Determined by source and medium
Not adjustable
27
Equation for wavelength
Wavelength(mm)= prop speed/frequency
In soft tissue= 1.54/frequency
28
Propagation speed
Rate that sound travels thru medium
Aka velocity or speed
Units= m/s, mm/s
Determined by medium
Not adjustable
29
All sound travels at
The same speed thru any specific medium
30
Speed and wavelength relationship
Directly related
Sound in a slow medium has a short wavelength
Sound in a fast medium has a long wavelength
31
General Rule of average speed of all sound in soft tissue
1540 m/s
Lung(air)<
32
Rules of thumb
Density and stiffness
Stiffness and speed= same direction
Density and speed = opposite direction
33
Compressibility and elasticity are opposites of?
Stiffness
34
Bulk modulus is
The same as stiffness
35
Changes in stiffness have the greatest effect on?
Speed
36
Stiffness is related to
Change in shape (squishability)
37
Density is related to
Weight
38
Audible, Infra, and Ultrasound
Audible =frequencies between 20 Hz - 20,000 Hz (20kHz)
Ultrasound = greater than 20kHz
Infrasound= less than 20 Hz
39
Phase relationships
Constructive interference = in phase waves
Deconstructive interference = out of phase waves
Pg. 22
40
Pulsed sound parameters
```
Pulse duration
PRP
PRF
Duty Dactor
Spatial Pulse Length
```
41
Pulse Duration
Time from start of pulse to end of that pulse (actual time pulse is “on”)
Units= microseconds
Determined by source
Not adjustable
Equation Pulse duration = # of cycles in pulse x period
42
PRP
Pulse repetition period
Time from start of one pulse to the start of the next Pulse
Units= msec or any unit of time
Determined by source
Can be adjusted (only changes listening time)
43
PRP is determined by
Imaging depth
As PRP increases depth increases
As PRP decreases depth decreases
44
PRF
Pulse Repetition Frequency
of pulses created by system in one second
Units Hz (per sec)
Determined by source
Can be adjusted
45
PRF and depth have what kind of relationship?
Inverse
Shallow image = higher PRF
Deep image = lower PRF
46
PRP and PRF have what kind of relationship
Reciprocals
Equation PRP (sec) x PRF (Hz) = 1
47
Duty Factor
% of time that system transmits sound
Unitless
Determined by source
Can be adjusted when imaging depth is changed
Shallow image higher duty factor
Deep image lower duty factor
48
Spatial Pulse Length
Length/ distance from start to end of one pulse
Units=mm
Determined by source and medium
Not adjustable
Determines axial resolution
49
Equation for Spatial Pulse Length
SPL (mm)= #cycles x wavelength (mm)
50
Intensity
The concentration of the power in a beam
51
Intensity is a key parameter for
Bioeffects
52
5 key words for intensity
```
Peak-max value
Average
Spatial
Temporal (transmit and receive)
Pulsed (transmits only)
```
53
Units for intensity
W/cm^2 (all intensities)
54
SPTP
Spatial Peak Temporal Peak
Highest Value
55
SATA
Spatial Average Temporal Average
Lowest Value
56
SPTA
Spatial Peak Temporal Average
Most important for thermal bioeffects
57
Three Commandments if Intensity
* Intensities May be reported in various ways with respect to time and space
* Intensity is the key parameter with regard to bioeffects
* Peak is greater than average so SPTP is the highest intensity and SATA is the lowest
58
Decibels are
A RELATIVE comparison or ratio between the final of the initial two strengths
(See the word relative think dB)
59
Decibel is what kind of scale?
Logarithmic
60
Positive decibels
Means getting bigger or increasing
3dB - two times bigger than original intensity
10 dB - ten times bigger than original
6dB- four times bigger than original
9dB- eight times bigger than original
Pg. 39
61
Negative decibels
Getting smaller intensity decreasing
- 3dB means one half original value
- 10 dB means one tenth original value
Hint: for negative dB calculate positive dB then invert
62
Attenuation
Decrease in intensity, power and amplitude of a sound wave as it travels
Hint: unrelated to speed
63
Units of attenuation
dB
64
Less attenuation means
Lower frequency and shorter path length
65
More attenuation means
Higher frequency and longer path length
66
Three components of attenuation
Absorption
Scattering
Reflection
67
Absorption
Primary, sound converted to heat
68
Scattering
Redirection of sound in many directions
Two types
Diffuse and Rayleigh
69
Diffuse scattering
Backscatter
| Rough boundary
70
Rayleigh scattering
Reflector much smaller than wavelength of sound
Higher frequency undergoes this
RBC is an example of this
71
Rayleigh scattering is related to
Frequency^4
72
Attenuation in different media
Air has much more attenuation than in soft tissue (gel used to remove air from path of US)
Lung and Bone have more attenuation than soft tissue. Bone absorbs lung scatter
Water is much less than soft tissue
Attenuation in blood is less than soft tissue
73
Attenuation and penetration
In soft tissue lower frequency results in less attenuation
Attenuation ultimately limits max imaging depth where meaningful reflections are obtained
74
Reflection
When propagating sound energy strikes a boundary between 2 media and some returns to the transducer
75
Specular reflection
Reflections from a smooth reflector (mirror) and return in one direction.
Well seen when sound strikes boundary at 90 degrees
76
Strongest reflections are produced?
With normal incidence 90 degrees
77
Attenuation coefficient
Amount of attenuation per cm
Units dB/cm
78
Attenuation coefficient relationship to frequency
Direct relationship
As frequency increases, attenuation coefficient increases
79
Attenuation coefficient in soft tissue
0.5dB/cm/MHz
One-half if the transducers frequency
80
Equation
Attenuation
Total attenuation (dB) =path length (cm) x attenuation coefficient(dB/cm)
81
For numerical questions on board remember
Always make sure units are perfect from question to answer
82
Impedance
associated with a medium
Units Rayls (Z)
83
Reflection depends on
Different acoustic impedances
84
Equation for impedance
Impedance (rayls Z) = density (kg/m^3) x propagation speed (m/s)
85
Incidence
Normal = 90 degrees
PORNN
```
Perpendicular
Orthogonal
Right Angle
Ninety Degrees
Normal
```
86
Oblique incidence
Anything other than 90 degrees
Acute- less than 90
Obtuse- more than 90
We know nothing
Reflected angle= incident angle
87
Incident intensity
Intensity of sound wave at instant prior to striking a boundary
W/cm^2
88
Reflected intensity
The intensity that after striking a boundary changes direction and returns back from where it came
W/cm^2
89
Transmitted intensity
Intensity that after striking a boundary continues on in the same general direction that it was originally traveling
W/cm^2
90
Equation for incident intensity
Incident intensity= reflected intensity+transmitted intensity
91
Conservation of energy exists where?
At a boundary
92
Intensity Reflection Coefficient (IRC)
The percentage of the US intensity that bounces back when the sound strikes a boundary
Usually less than 1%
93
Intensity Transmission Coefficient (ITC)
The percentage of the incident intensity that after striking a boundary continues on in the general direction that it was originally traveling
ITC more than 99%
94
In biologic media
% of reflection
Soft tissue - air = 99% reflection
Soft tissue - bone= 50% reflection
Soft tissue - Soft tissue = <1%
95
Normal incidence
Reflection occurs only if the two media at the boundary have different acoustic impedances
When impedance is the same no reflection
If no reflection 100% transmission
96
PORNN
For normal incidence
```
Perpendicular
Orthogonal
Right Angle
Ninety degrees
Normal
```
97
Oblique incidence
Anything other than 90%
Acute less than 90
Obtuse more than 90
98
Refraction
Transmission with a bend
Requires oblique incidence and different speeds
99
Snell's Law
Describes physics of refraction
sin(transmission angle)/ sin(incident angle) = prop speed 1 / prop speed 2
Chart bottom of pg 53
100
Time of flight is what?
Aka go return time, round trip time
Time needed for a pulse to travel to and from the transducer to the reflector
1.54 km/sec in soft tissue
101
How are time of flight and distance related?
Directly
102
When time of flight is measured we can determine what?
Reflector depth
103
13 microsecond rule
Pg 57.
104
Speed equation
Speed =distance/time
105
What is a transducer?
Any device that converts one form of energy into another.
106
Piezioelectric effect
A property of certain materials to create a voltage when pressure is applied or when the material is mechanically deformed
107
Reverse piezioelectric effect
Materials deform or change shape when a voltage is applied to them.
108
Piezioelectric materials
Aka Ferroelectric
Lead zicornate titanate
PZT
Ceramic
Active element
Crystal
109
Curie Point
When PZT is heated above this temp. And loses it's piezioelectric properties, PZT is depolorized
360°C or 680°F
110
Sterilization
Complete destruction of all living microorganisms by means of exposure to heat, chemical agents, or radiation.
111
Most critical objects that require sterilization
Those that penetrate mucous membranes or skin
112
Disinfection
Application of chemical agent to reduce or eliminate infectious organisms on an object.
113
Objects that require disinfection
Insturments that only come in contact with skin such as a transducer.
114
When disinfecting transducers what should you use?
Cold germacides such as gluteradehyde or cidex
DO NOT USE HEAT
115
Transducer components
```
Case
Electric shield
Acoustic insulator
PZT ( 1/2 wavelength thick)
Wire
Matching layer
Backing material
```
116
Case
Protects internal components from damage and insulates patient from electric shock
117
Acoustic insulator
Thin barrier of cork/rubber "uncouples" internal components; prevents vibration in case.
118
Matching Layer
One quarter wavelength thick.
Has an impedance between those of the skin and active element to increase the percentage of transmitted US between the active element and skin.
119
Gel's impedance is in between?
Those of the matching layer and skin to further increase the efficiency of sound transmission.
120
Matching layer impedances
PZT>MATCHING LAYER>GEL>SKIN
121
Damping element/ backing material
Reduces ringing of PZT
commonly made of epoxy resin impregnated with metal powder
RULE: short pulses create more accurate images.
122
Damping material imaging transducer characteristics
```
Damping is effective (backing material)
Short pulse length and duration
Low sensitivity
Wide bandwidth
Low Q factor
Decreased output power
```
123
Bandwidth
Range of frequencies between highest and lowest frequency emitted from transducer
124
Imaging transducers have what kind of bandwidth?
Wide or broadband because of backing material
125
Q factor
Unitless number representing extent of damping
Imaging transducers are low Q
126
Continuous Wave Transducers have what frequencies?
Sound waves frequency equals the frequency of the voltage applied to the PZT by the machine's electronics
Electrical freq=acoustic freq.
127
Pulsed transducers have what kind of frequency?
Determined by thickness of PZT and speed of sound in PZT.
128
High frequency pulsed transducer has what?
Thin crystal
| Fast PZT
129
Low frequency transducer has what?
Thick Crystal and slow PZT
130
When PZT crystal is half as thick the sound frequency is?
Twice as high
