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Registry Review Class > SPI > Flashcards

SPI Flashcards

1
Q

Sound is

A

A type of wave that carries ENERGY from place to place

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2
Q

Sound is made up of

A

A series of compressions and rare fractions

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3
Q

Compressions are

A

Areas of increased pressure and density

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4
Q

Rarefactions are

A

Areas of decreased pressure and density

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5
Q

Sound must travel thru

A

A medium

Cannot travel thru a vacuum

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6
Q

A sound wave is

A

Mechanical and longitudinal

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7
Q

Sound travels in

A

A straight line

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8
Q

Acoustic propagation properties are

A

The effects of the medium on the sound wave

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9
Q

Biological effects are

A

The effects of a sound wave on biologic tissue

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10
Q

Acoustic Variables

A

Pressure

Density

Distance

(Help identify which are sound waves)

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11
Q

Pressure is

A

The concentration of force within an area

Units= pascals (Pa)

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12
Q

Density is

A

Concentration of mass within volume

Units= kg/cm^3

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13
Q

Distance is

A

Measure of particle motion

Units= cm, ft, miles

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14
Q

Transverse waves

A

Particles move perpendicular (right angle or 90 degrees) to the direction of the wave

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15
Q

Longitudinal wave

A

Particles move back and forth in the same direction as the wave

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16
Q

Acoustic Parameters

A

Describe the features of a particular sound wave

Period 
Frequency
Amplitude
Power 
Intensity
Wavelength
Propagation speed
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17
Q

Period

A

Time required to complete a single cycle

Units= microseconds
Determined by source
Not adjustable

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18
Q

Frequency

A

of events that occur in a particular time frame

Units= Hz
Determined by sound source
Not adjustable

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19
Q

Period and frequency relationship

A

Reciprocals
Inverse relationship

(Period decreases, frequency increases)
(Shorter period, higher frequency)
(Longer period, lower frequency)

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20
Q

Bigness parameters

A

Describe beam’s strength
All behave the same way

Amplitude
Power
Intensity

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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

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22
Q

Power

A

Rate of work is preformed

Units Watts
Determined by source (initially)

Can be adjusted

Decreases as sound propagates thru body

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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)

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24
Q

Intensity

A

Concentration of energy in a sound beam

Units W/cm^2

Determined by source (initially)

Can be adjusted

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25
Q

Equation for intensity

A

Intensity (W/cm^2)= power(W)/beam area (cm^2)

Intensity=power

Intensity=amplitude^2

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26
Q

Wavelength

A

Length or distance of a single cycle

Units= m, mm

Determined by source and medium

Not adjustable

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27
Q

Equation for wavelength

A

Wavelength(mm)= prop speed/frequency

In soft tissue= 1.54/frequency

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28
Q

Propagation speed

A

Rate that sound travels thru medium

Aka velocity or speed

Units= m/s, mm/s

Determined by medium

Not adjustable

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29
Q

All sound travels at

A

The same speed thru any specific medium

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30
Q

Speed and wavelength relationship

A

Directly related

Sound in a slow medium has a short wavelength

Sound in a fast medium has a long wavelength

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31
Q

General Rule of average speed of all sound in soft tissue

A

1540 m/s

Lung(air)<

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32
Q

Rules of thumb

Density and stiffness

A

Stiffness and speed= same direction

Density and speed = opposite direction

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33
Q

Compressibility and elasticity are opposites of?

A

Stiffness

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34
Q

Bulk modulus is

A

The same as stiffness

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35
Q

Changes in stiffness have the greatest effect on?

A

Speed

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36
Q

Stiffness is related to

A

Change in shape (squishability)

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37
Q

Density is related to

A

Weight

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38
Q

Audible, Infra, and Ultrasound

A

Audible =frequencies between 20 Hz - 20,000 Hz (20kHz)

Ultrasound = greater than 20kHz

Infrasound= less than 20 Hz

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39
Q

Phase relationships

A

Constructive interference = in phase waves

Deconstructive interference = out of phase waves

Pg. 22

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40
Q

Pulsed sound parameters

A 
Pulse duration
PRP
PRF
Duty Dactor
Spatial Pulse Length
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41
Q

Pulse Duration

A

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

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42
Q

PRP

Pulse repetition period

A

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)

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43
Q

PRP is determined by

A

Imaging depth

As PRP increases depth increases

As PRP decreases depth decreases

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44
Q

PRF

Pulse Repetition Frequency

A

of pulses created by system in one second

Units Hz (per sec)

Determined by source

Can be adjusted

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45
Q

PRF and depth have what kind of relationship?

A

Inverse

Shallow image = higher PRF

Deep image = lower PRF

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46
Q

PRP and PRF have what kind of relationship

A

Reciprocals

Equation PRP (sec) x PRF (Hz) = 1

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47
Q

Duty Factor

A

% 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

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48
Q

Spatial Pulse Length

A

Length/ distance from start to end of one pulse

Units=mm

Determined by source and medium

Not adjustable

Determines axial resolution

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49
Q

Equation for Spatial Pulse Length

A

SPL (mm)= #cycles x wavelength (mm)

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50
Q

Intensity

A

The concentration of the power in a beam

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51
Q

Intensity is a key parameter for

A

Bioeffects

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52
Q

5 key words for intensity

A 
Peak-max value
Average
Spatial
Temporal (transmit and receive)
Pulsed (transmits only)
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53
Q

Units for intensity

A

W/cm^2 (all intensities)

54
Q

SPTP

A

Spatial Peak Temporal Peak

Highest Value

55
Q

SATA

A

Spatial Average Temporal Average

Lowest Value

56
Q

SPTA

A

Spatial Peak Temporal Average

Most important for thermal bioeffects

57
Q

Three Commandments if Intensity

A
  • 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
Q

Decibels are

A

A RELATIVE comparison or ratio between the final of the initial two strengths

(See the word relative think dB)

59
Q

Decibel is what kind of scale?

A

Logarithmic

60
Q

Positive decibels

A

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
Q

Negative decibels

A

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
Q

Attenuation

A

Decrease in intensity, power and amplitude of a sound wave as it travels

Hint: unrelated to speed

63
Q

Units of attenuation

A

dB

64
Q

Less attenuation means

A

Lower frequency and shorter path length

65
Q

More attenuation means

A

Higher frequency and longer path length

66
Q

Three components of attenuation

A

Absorption
Scattering
Reflection

67
Q

Absorption

A

Primary, sound converted to heat

68
Q

Scattering

A

Redirection of sound in many directions

Two types

Diffuse and Rayleigh

69
Q

Diffuse scattering

A

Backscatter

Rough boundary

70
Q

Rayleigh scattering

A

Reflector much smaller than wavelength of sound

Higher frequency undergoes this

RBC is an example of this

71
Q

Rayleigh scattering is related to

A

Frequency^4

72
Q

Attenuation in different media

A

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
Q

Attenuation and penetration

A

In soft tissue lower frequency results in less attenuation

Attenuation ultimately limits max imaging depth where meaningful reflections are obtained

74
Q

Reflection

A

When propagating sound energy strikes a boundary between 2 media and some returns to the transducer

75
Q

Specular reflection

A

Reflections from a smooth reflector (mirror) and return in one direction.

Well seen when sound strikes boundary at 90 degrees

76
Q

Strongest reflections are produced?

A

With normal incidence 90 degrees

77
Q

Attenuation coefficient

A

Amount of attenuation per cm

Units dB/cm

78
Q

Attenuation coefficient relationship to frequency

A

Direct relationship

As frequency increases, attenuation coefficient increases

79
Q

Attenuation coefficient in soft tissue

A

0.5dB/cm/MHz

One-half if the transducers frequency

80
Q

Equation

Attenuation

A

Total attenuation (dB) =path length (cm) x attenuation coefficient(dB/cm)

81
Q

For numerical questions on board remember

A

Always make sure units are perfect from question to answer

82
Q

Impedance

A

associated with a medium

Units Rayls (Z)

83
Q

Reflection depends on

A

Different acoustic impedances

84
Q

Equation for impedance

A

Impedance (rayls Z) = density (kg/m^3) x propagation speed (m/s)

85
Q

Incidence

A

Normal = 90 degrees

PORNN

Perpendicular 
Orthogonal
Right Angle
Ninety Degrees
Normal
86
Q

Oblique incidence

A

Anything other than 90 degrees

Acute- less than 90

Obtuse- more than 90

We know nothing

Reflected angle= incident angle

87
Q

Incident intensity

A

Intensity of sound wave at instant prior to striking a boundary

W/cm^2

88
Q

Reflected intensity

A

The intensity that after striking a boundary changes direction and returns back from where it came

W/cm^2

89
Q

Transmitted intensity

A

Intensity that after striking a boundary continues on in the same general direction that it was originally traveling

W/cm^2

90
Q

Equation for incident intensity

A

Incident intensity= reflected intensity+transmitted intensity

91
Q

Conservation of energy exists where?

A

At a boundary

92
Q

Intensity Reflection Coefficient (IRC)

A

The percentage of the US intensity that bounces back when the sound strikes a boundary

Usually less than 1%

93
Q

Intensity Transmission Coefficient (ITC)

A

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
Q

In biologic media

% of reflection

A

Soft tissue - air = 99% reflection

Soft tissue - bone= 50% reflection

Soft tissue - Soft tissue = <1%

95
Q

Normal incidence

A

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
Q

PORNN

A

For normal incidence

Perpendicular
Orthogonal
Right Angle
Ninety degrees
Normal
97
Q

Oblique incidence

A

Anything other than 90%

Acute less than 90
Obtuse more than 90

98
Q

Refraction

A

Transmission with a bend

Requires oblique incidence and different speeds

99
Q

Snell’s Law

A

Describes physics of refraction

sin(transmission angle)/ sin(incident angle) = prop speed 1 / prop speed 2

Chart bottom of pg 53

100
Q

Time of flight is what?

A

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
Q

How are time of flight and distance related?

A

Directly

102
Q

When time of flight is measured we can determine what?

A

Reflector depth

103
Q

13 microsecond rule

A

Pg 57.

104
Q

Speed equation

A

Speed =distance/time

105
Q

What is a transducer?

A

Any device that converts one form of energy into another.

106
Q

Piezioelectric effect

A

A property of certain materials to create a voltage when pressure is applied or when the material is mechanically deformed

107
Q

Reverse piezioelectric effect

A

Materials deform or change shape when a voltage is applied to them.

108
Q

Piezioelectric materials

A

Aka Ferroelectric

Lead zicornate titanate

PZT

Ceramic

Active element

Crystal

109
Q

Curie Point

A

When PZT is heated above this temp. And loses it’s piezioelectric properties, PZT is depolorized

360°C or 680°F

110
Q

Sterilization

A

Complete destruction of all living microorganisms by means of exposure to heat, chemical agents, or radiation.

111
Q

Most critical objects that require sterilization

A

Those that penetrate mucous membranes or skin

112
Q

Disinfection

A

Application of chemical agent to reduce or eliminate infectious organisms on an object.

113
Q

Objects that require disinfection

A

Insturments that only come in contact with skin such as a transducer.

114
Q

When disinfecting transducers what should you use?

A

Cold germacides such as gluteradehyde or cidex

DO NOT USE HEAT

115
Q

Transducer components

A 
Case
Electric shield
Acoustic insulator
PZT ( 1/2 wavelength thick)
Wire
Matching layer
Backing material
116
Q

Case

A

Protects internal components from damage and insulates patient from electric shock

117
Q

Acoustic insulator

A

Thin barrier of cork/rubber “uncouples” internal components; prevents vibration in case.

118
Q

Matching Layer

A

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
Q

Gel’s impedance is in between?

A

Those of the matching layer and skin to further increase the efficiency of sound transmission.

120
Q

Matching layer impedances

A

PZT>MATCHING LAYER>GEL>SKIN

121
Q

Damping element/ backing material

A

Reduces ringing of PZT
commonly made of epoxy resin impregnated with metal powder

RULE: short pulses create more accurate images.

122
Q

Damping material imaging transducer characteristics

A 
Damping is effective (backing material)
Short pulse length and duration
Low sensitivity
Wide bandwidth
Low Q factor
Decreased output power
123
Q

Bandwidth

A

Range of frequencies between highest and lowest frequency emitted from transducer

124
Q

Imaging transducers have what kind of bandwidth?

A

Wide or broadband because of backing material

125
Q

Q factor

A

Unitless number representing extent of damping

Imaging transducers are low Q

126
Q

Continuous Wave Transducers have what frequencies?

A

Sound waves frequency equals the frequency of the voltage applied to the PZT by the machine’s electronics

Electrical freq=acoustic freq.

127
Q

Pulsed transducers have what kind of frequency?

A

Determined by thickness of PZT and speed of sound in PZT.

128
Q

High frequency pulsed transducer has what?

A

Thin crystal

Fast PZT

129
Q

Low frequency transducer has what?

A

Thick Crystal and slow PZT

130
Q

When PZT crystal is half as thick the sound frequency is?

A

Twice as high

Registry Review Class (6 decks)

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