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Echo Class > Physics Boards > Flashcards

Physics Boards Flashcards

0
Q

Nyquist limit?

A

1/2 prf

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1
Q

Near zone length?

A 
6
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2
Q

What determines the range of brilliancies within a displayed image?

A

Contrast

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3
Q

A television image is made up of how many closely spaced horizantal lines?

A

525

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4
Q

Bistable images , which only appear in black and white have what kind of contrast?

A

High

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5
Q

What determines the brilliance of the displayed image?

A

Brightness = brilliance

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6
Q

Greyscale imaging was first made possible with the use of what?

A

Scan Converters

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7
Q

What does the scan converter do?

A

Ultrasound info is obtained from pulses emitted by a transducer that penetrates into the body. Multiple penetrations, or spokes, are needed for each two dimensional image. However television displays video infromation as 525 interlaced , horizantal lines divided into two fields. THE SCAN CONVERTER TRANSLATES THE INFORMATION FROM THE SPOKE FORMAT INTO VIDEO FORMAT.

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8
Q

The process of storage of information into the scan converter is called what ?

A

Writing. Image is then read from the scan converter for display on the CRT

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9
Q

What are analog #’s?

A

Real world numbers that are found in our everyday lives

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10
Q

What are digital numbers?

A

associated with a computer device

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11
Q

What is Spacial Resolution?

A

Image detail

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12
Q

What are the four limitations of analog scan converters?

A

image fade

image flicker

instability

deterioration

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13
Q

Digital scan converters use computer technology to convert images into numbers using a process called?

A

digitizing

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14
Q

What is a pixel?

A

The smallest building block of a digital picture?

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15
Q

What is the number of picture elements per inch?

A

Pixel density

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16
Q

Higher pixel density is achieved what?

A

smaller pixels

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17
Q

Spacial resolution is improved with high or low pixel density?

A

High

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18
Q

Low pixel density = ?

A

Larger pixels

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19
Q

What is the smallest amount of computer memory?

A

Bit 0’s and 1’s

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20
Q

What is a byte?

A

A group of 8 bits of computer memory
10011111
A word of computer memory is made up of 2 bytes or 16 bits

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21
Q

More shades of grey appear on an image with more what?

A

More bits per pixel.

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22
Q

Images that have many shades of grey have superior what?

A

Contrast resolution

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23
Q

More shades of grey = ?

A

IMPROVED CONTRAST RESOLUTION

MORE BITS PER PIXEL

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24
Q

How do you determine the number of shades of grey there are in an image?

A

Multiply 2 by itself the same number of times as there are bits

2 to the (number of bits) power)

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25
Q

How many possible shades of grey are displayed with 5 bits of memory?

A

32
mulitpling 2 by itself 5 times yield 32
2x2x2x2x2 = 32

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26
Q

Any processing of the reflected signals before storage is called what?

A

pre-processing.Pre processing alters the image data forever and cannot be reversed or “un-done”.

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27
Q

What is the manipulation of an image after storage in the scan converter, a process that can be reversed or applied to a frozen image?

A

Post Processing

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28
Q

Read magnification occurs during what stage of processing?

A

Post processing. It can be catorigized by the number of pixels or scan lines in the magnified image is the same as the original image. MAGGING AFTER YOU HAVE ALREADY AQUIRED.

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29
Q

Write magnification occurs during what processing stage?

A

pre processing. It is applied during data aquisition. Mag’ing DURING SCANNING

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30
Q

Harmonic imaging = ?

A

2 x fundamental frequency

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31
Q

Contrast harmonics are created because of uneven changes in the size of the bubble when exposed to a sound beam of adequate strength. What is this called?

A

resonance

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32
Q

The amount of contrast harmonics produced may be estimated by a number called what?

A

Mechanical Index

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33
Q

The mechanical index depends on what ?

A

frequency of transmitted sound

pressure of the sound wave

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34
Q

Harmonic production (as well as the mechanical index) increases with :

A

more pressure

lower frequency

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35
Q

what is the frequency used in ultrasound?

A

2 to 4mz

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36
Q

low MI =

A

less than .1
high frequency sound
low beam strength

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37
Q

medium mi(high mi)=?

A

.1 - 1.0 mi
resonance
low frequency

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38
Q

highest mi =

A

greater than 1
bubble disruption
lowest frequency

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39
Q

What are the 2 characteristics of contrast agents?

A

the nature of the outer shell

the gas that fills the microbubble

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40
Q

When are tissue harmonics created?

A

During transmission

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41
Q

Beams that are least likely to create artifacts are most likely to create what?

A

harmonics

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42
Q

What causes the strongest harmonic signal?

A

Contrast harmonics because bubble diruption creates the strongest harmonic signal.

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43
Q

sound in compression travels ______ than sound in rarefaction

A

faster

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44
Q

Volume of blood moving at a particular time?

A

flow

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45
Q

When exposed to the high pressure component of a sound wave, a microbubble will ________.

A

shrink

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46
Q

In phasic flow, blood accelerates and decelerates from what?

A

Respiration

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47
Q

Phasic flow appears in _________ circulation.

A

venous

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48
Q

Pulsitile flow occurs in _________ circulation.

A

arterial

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49
Q

Steady flow occurs when?

A

In venous circulation when an individual stops breathing for a moment. (decrease in venous return)

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50
Q

What exist when the flow streamlines are aligned and parallel and blood travels at individual speeds?

A

Laminar Flow

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51
Q

What are the 2 forms of laminar flow?

A

Plug Flow

Parabolic Flow

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52
Q

What occurs when all of the layers and blood cells travel at the same velocity?

A

plug flow

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53
Q

What kind of flow is it when the velocity is highest in the center of the lumen and gradually decreases to its minimum at the vessle wall? Has a bullet shaped profile?

A

Parabolic Flow

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54
Q

What predicts whether flow is laminar or turbulant?

A

Reynold’s number

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55
Q

What is characterized by chaotic flow patterns in many different directions and at many different speeds?

A

turbulent flow

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56
Q

Sound associated with a turbulent flow is called what?

A

murmur or a bruit

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57
Q

Tissue vibration associated with turbulence is called what? It can also be described as a palpable murmer?

A

a thrill

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58
Q

How does blood flow from one location to another?

A

energy gradient

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59
Q

A form of potential or stored energy. It has the ability to perform work

A

pressure energy

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60
Q

THis type of energy is a form of stored;potential energy and is associated with an elevated object

A

Gravitational energy

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61
Q

A narrowing of the lumen of the vessel

A

Stenosis

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62
Q

Pressure Gradient = ?

A

Flow x Resistnace

Pressure gradient increases when either the flow increases or resistance increases

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63
Q

Voltage = ?

A

current x resistance

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64
Q

What is the typical resistance of veins?

A

low resistance

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65
Q

The shape of a vein during normal function is:

A

flattened or hourglass shaped

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66
Q

As more pressure occurs within the vein, what happens to the shape?(during excercise when venous flow increases)

A

Becomes more circular

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67
Q

The pressure acting to expand the veins is known as what?

A

transmural pressure

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68
Q

What is related to the weight of blood pressing on a vessel measured at a height above or below the heart?

A

hydrostatic pressure

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69
Q

The significance of hydrostatic pressure in clinical medicine is demonstrated when?

A

When taking a patients blood pressure.

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70
Q

Blood pressure is accurately assessed when the measurement is made at what location?

A

at the same level of the heart. Blood pressure will obviosley be WAY too high at levels below the heart and WAY to low at levels above the heart.

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71
Q

When a patient is supine, what is the hydrostatic pressure?

A
  1. All parts are at the same level of the heart
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72
Q

During inspiration, the diaphragm moves downward, the chest cavity expands. This creates what kind of pressure in the chest?

A

negative

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73
Q

Negative thoracic pressure (inspiration), produces a suction that does what to the venous return towards the heart?

A

Increases

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74
Q

During expiration, the diaphram moves upward which increases the thoracic pressure in the chest. Expiration does what to the venous return to the heart?

A

Decreases

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75
Q

During inspiration, the abdominal compression increases abdominal pressure which does what to the venous flow in the legs?

A

Decrease.

It increases with expiration(flow to the legs)

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76
Q

Doppler shift is also called what?

A

doppler frequency

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77
Q

The frequency does not change when the distance between the sound source and the receiver remains _______.

A

constant

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78
Q

Frequency changes as a result of what?

A

Relative motion between the source and the reciever

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79
Q

What principle is used to measure red blood cell velocities?

A

Doppler principle

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80
Q

What is the doppler shift?

A

The low frequency that rides on top of the much higher transducer’s transmitted frequency

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81
Q

The process of extracting the low doppler frequency from the higher transducer frequency.

A

demodulation

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82
Q

What is the formula for doppler shift?

A

Doppler Shift = reflected frequency - transmitted frequency
If the doppler shift is a positive number, that obviously means there is a positive shift.
Transmitted frequency - 5,000,000
Reflected Frequency - 5,003,000
shift = + 3,000

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83
Q

When RBC’s move toward the transducer, the doppler shift is _____, that is , the reflected frequency is _______ than the transmitted frequency.

A

positive; higher

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84
Q

What is the equation for Doppler Shift?(elongated)

A

Doppler shift= 2 x speed of blood x transducer frequency x Cos 0
_______________________________________

                                     propagation speed of blood
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85
Q

My grandsons bag of marbles contain 30 marbles, If he decrease his bag by a factor of three, how many marbles does he have?

A 
10.
30/3 = 3
# at first divided by the factor
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86
Q

Simplify the expression 10 to the -3 power?

A

.001
-3 is milli which is thousandths

.1 = tenths
.01= hundreths
.001= thousanths
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87
Q

Simplify the expression 10 to the 3rd power

A 
1000
\+3 is thousands
10=1     take 1 and move it three to the right and you get thousand
\+1 = tens
\+2= hundreds
\+3 = thousands
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88
Q

What is the reciprocal for the prefix milli? 10 to the -3?

A

kilo

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89
Q

.00875 equals what in notation?

A

8.75 x 10 -3 power

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90
Q

Density is defined as ?

A

mass per unit volume

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91
Q

What are the acoustic variables?

A

density
motion/distance
pressure
temperature

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92
Q

A sound wave is a traveling variation in quantities called:

A

acoustic variables

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93
Q

With longitudinal waves , particles oscillate ______ to the direction of the sound beam?

A

parallel

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94
Q

If the amplitude is doubled, what happens to the intensity?

A

Increased by a factor of 4

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95
Q

Bulk modulus refers to which of the following quantities?

A

stiffness

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96
Q

Arrange the following media in order in terms of propogation speed from lowest to highest

bone, muscle, air , fat

A

air - fat - muscle - bone

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97
Q

What is the formula for wave lenght?

A

Propogation speed / frequency

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98
Q

Pulse duration =?

A 
# of cycles x period
0r

of cycles / frequency

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99
Q

Spacial pulse length= ?

A

of cycles x wavelength

or

of cycles / frequency

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100
Q

Common SPTA intensities are greater or less than 720 mW/cm?

A

less than 720 mW/cm 2

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101
Q

If the intensity transmission coefficent is .74, what is the reflection coefficient?

A

.26

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102
Q

The advantage of a 256x256 image format compared to a 64x64 image format is = ?

A

more pixels = greater spatial res/detail

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103
Q

Elastography is an ultrasound imaging mode that depicts tissue _______.

A

stiffness

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104
Q

A bistable picture is represented by only two shades , black and white, and requires _________bits.

A

1
2 to the x power(number of bits) = 2 shades(black and white)

2 to the 1 power will give you 2

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105
Q

The ability of grey scale display to distinguish between echoes of slightly different intensities is called _________

A

contrast resolution

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106
Q

PACS?

A

Picture Archiving and Communications System

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107
Q

The averaging of sequential frames together to provide a smoother image appearance is called __________.

A

persistence

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108
Q

In which excitation technique do ensembles or trains of pulses drive the transducer to generate a single scan line?

A

coded excitation

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109
Q

What is the purpose of write zoom?

A

Improve spacial resolution of the displayed image

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110
Q

How many pixels compose an image in which the matrix is described as 500 rows and 500 columns?

A

250,000

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111
Q

What is the Reynolds number that predicts when turbulence will occur?

A

2000

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112
Q

What is the auscultatory consequence of turbulent flow?

A

bruit

113
Q

What is neccesary in order for blood to flow?

A

pressure gradient

114
Q

What of flow is occurring when the average flow velocity is 1/2 the maximum velocity in the center of the vessel?

A

parabolic flow

115
Q

What is another term for gravitational potential energy?

A

hydrostatic pressure

116
Q

What is the definition of volumetric flow?

A

amount of fluid moving past a reference point in time

117
Q

What type of arterial flow demonstrates a constant velocity across an entire vessel?

A

plug flow

118
Q

The pressure difference between the inside of the vein and the tissue outside is known as:

A

transmural flow

119
Q

In order to maintain flow, if the area of a vessel increases, what must happen to the velocity of the flow?

A

it must decrease

120
Q

What indicates turbulent flow?

A

Reynolds number

121
Q

When sound travels faster through compressed tissue than it does through expanded tissue, the type of propagation speed present is __________.

A

non - linear

122
Q

Where is harmonic energy located?

A

near field or center of the beam

123
Q

What is the ability of a test to predict disease?

A

sensitivity

124
Q

Test objects evaluate?

A

detail resolution

125
Q

What does development of a quality assurance program ensure?

A

image consistency

126
Q

What assessment does a quality assurance provide?

A

image quality

127
Q

The ability to place reflections in their proper position no matter the imaging orientation describes :

A

registration

128
Q

The ability of a test to predict absence of disease?

A

specificty

129
Q

What describes the mechanistic approach to the study of bioeffects?

A

cause-effect

130
Q

What does 3 db mean?

A

1/2 the original intensity

131
Q

What is the formula for duty factor?

A

Pulse duration/ PRP

132
Q

What is intensity?(formula?)

A

amplitude squared

133
Q

If the amplitude of a sound wave is increased threefold, the intensity will:

A

increase 9 fold

134
Q

An echo from which reflector is most dependent on the angle of incidence?

A

specular reflector

135
Q

If the propagation speed through the second medium is less than the first medium, the transmission angle is ______ than the incident angle.

A

less

136
Q

What is normal incidence?

A

= to 90 degrees

137
Q

What is the Reynolds number for laminar flow?

A

less than 1500

138
Q

What is the Reynolds number for Turbulent flow?

A

Greater than 2000

139
Q

What is inertia?

A

tendency of fluid to resist changes in its velocity

140
Q

Inertial energy loss occurs during three events:

A
  1. pulsatile
  2. phasic
  3. stenotic
141
Q

If resistance increases, volumetric flow will _______.

A

increase

142
Q

Energy is neither created nor destroyed as it flows through a vessel. This is known as:

A

continuity rule

143
Q

When venous flow in the legs decreases, venous flow to the heart _______.

A

increases

144
Q

Another name for RBC’s is :

A

erythrocytes

145
Q

Hydrostatic pressure is related to the weight of blood measured where?

A

At a height above or below the right atrium

146
Q

What determines the shape of a vein?

A

transmural pressure

147
Q

The typical hematocrit % is

A

45%

148
Q

What is the simplified law of hemodynamics?

A

Pressure Gradient= volumetric flow * Resistance

149
Q

What causes an increase in pressure gradient?

A

Flow increase and resistance increase

150
Q

Hydrostatic Pressure = pgh
p=density
g=?
h=?

A 
g = gravitational pressure
h= height of column of blood
151
Q

Where is hydrostatic pressure most accurate?

A

right atrium

152
Q

At locations below the heart, hydrostatic pressure is:

A

positive

153
Q

What is the cardiac flow rate?

A

5000ml/min

154
Q

What is the formula for doppler shift?

A

F dop = F (recieved) - Frequency (transmitted)

155
Q

What is the doppler equation?

A

Fdop = 2 ( V rbc’s * Frequency * Cos 0
__________________________

                                 c(propoagtion speed of tissue-1.54)
156
Q

Doppler frequencies indicate speed or velocity?

A

velocity
velocity is defined by magnitude and direction
speed is strictly magnitude

157
Q

When an angle exist between the direction of flow and the sound beam, the neasured velocity is ________ than the true velocity.

A

less

158
Q

measured velocity = true velocity * ________.

A

cos0

159
Q

Phasic flow appears in _________ circulation.

A

venous

160
Q

Pulsitile flow occurs in _________ circulation.

A

arterial

161
Q

Steady flow occurs when?

A

In venous circulation when an individual stops breathing for a moment. (decrease in venous return)

162
Q

What exist when the flow streamlines are aligned and parallel and blood travels at individual speeds?

A

Laminar Flow

163
Q

What are the 2 forms of laminar flow?

A

Plug Flow

Parabolic Flow

164
Q

What is the cosine of 0 degrees?

A

+1

164
Q

What is the cosine of 180 degrees?

A

-1

165
Q

What is the cosine of 60 degrees?

A

.5

The cosine of 60 degrees is .5 ; therefore the measured velocity at 60 degrees is 1/2 the actual velocity

166
Q

If red blood cells travel at 2m/s and at a 60 degree angle to the sound beam, what will the doppler report?

A

1 m/s

167
Q

What is the cosine of a 30 and 45 degree angle?

A

.87 and .71

168
Q

What dose non directional doppler or non coherent predict?

A

The pressence of blood velocity and NOT the direction

169
Q

What does Bidirectional doppler detect?

A

Distinguishes the direction of flow toward or away from the transducer

170
Q

What is phase quadrature or quadrature detection?

A

A signal processing technique for bidirectional doppler

171
Q

What is the main disadvantage of CW?

A

range ambiguity-NO SPECIFICITY

172
Q

How many crystals does a PW doppler take?

A 
1 crystal
dampened PZT
low Qfactor
Wide BW
Lower sensitivity
173
Q

How many crystals for a CW doppler?

A 
2 
undampened PZT
High Q factor
Narrow Bandwidth
High sensitivity
174
Q

What creates aliasing?

A

HIGH FREQUENCY TRANSDUCERS
HIGHER BLOOD VELOCITIES
DEEP GATE - DEEPER IMAGING = LOW PRF

175
Q

What are the 5 techniques that are used to avoid aliasing artifact?

A
  1. Adjust the scale to its maximum
  2. Select a lower frequency transducer
  3. Select a new ultrasonic view with a shallower sample volume.
  4. Use continuous wave doppler
  5. adjust the baseline
176
Q

Simultaneous anatomic imaging as seen in CW(one crystal listens and one recieves) is called:

A

duplex imaging

177
Q

What is the greatest advantage of pulse doppler?

A

range resolution aka
range specificty
freedom from range ambiguity artifact

178
Q

What is variance mode on a color map?

A

distinguishes laminar flow from turbulent flow
laminar flow is on the (L) Left -and-
turbulent flow is on the right

179
Q

What does the black area in the center of a color doppler represent?

A

0 doppler shift

180
Q

What is power doppler?

A

Determines the presence of flow only

181
Q

With color doppler, multiple pulses are used to accuratley determine blood cell velocities. Theses multiple pulses are called:

A

packets or ensemble

182
Q

Low frequency doppler shifts that are usually located at the baseline are called

A

clutter

with color its called ghosting artifact

183
Q

What is a special form of mirror image artifact that appears as an identical image both above and below the baseline?

A

crosstalk

184
Q

What is performed to assess the mean velocity of color doppler?

A

autocorrelation

185
Q

What tool breaks complex signals into its basic building blocks and identifies individual velocities which make up the reflected doppler signal?

A

Spectral analysis
2 forms:

  1. FFT - cw and pw
  2. Autocorrelation - color doppler
186
Q

THe region between the baseline and the spectrum is:

A

the spectral window

187
Q

A wider range of velocities and doppler shifts within the sample volume is a situation known as :

A

spectral broadening

188
Q

What is a quantitive , doppler derived measurement of the vascular resistance of a segment of the arterial system?

A

Resistive index

189
Q

which is the horizontal axis?

A

x axis

190
Q

what does the z axis represent?

A

brightness

191
Q

What does it mean to INCREASE by a factor of two or three?

A

To multiply by 2 or multiply by 3

192
Q

What does it mean to decrease by a factor of 2 or 3?

A

divide by 2 or divide by 3

193
Q

What is the formula for perimeter of a circle(circumfrence)?

A

c= pie x diameter
or
c = pie(2 x Radius)

194
Q

What is the formula for area of a square or rectangle?

A

area = lenght x width

195
Q

What are the units for perimeter?e

A

meter

196
Q

What are the units for area?

A

meters squared

197
Q

What are the units for volume?

A

The units for volume are meters cubed

198
Q

What is the formula for area of a circle?

A

A= pie x radius squared

199
Q

What is the formula for volume of a square or a rectangle?

A

volume = length x height x width

200
Q

Sound waves are what kind of waves?

A

mechanical

201
Q

Longitudinal waves propogate by a series of particle ________ and __________

A

compression and rarefaction

202
Q

What are acoustic variables?

A 
physical quantities that change as sound travels through the medium:
pressure
density 
temerature
distance - particle motion
203
Q

What is pressure?

A

pressure is the concentration of force or force per area

204
Q

What is density and what is the formula?

A

Density is the concentration of mass per volume

density = mass/volume

205
Q

What are the 7 acoustic parameters?

A 
Wavelenght
Amplitude
Power
Propogation Speed
Period
Intensity
Frequency
206
Q

What is interference?

A

Waves that are at the same location at the same time.

207
Q

What is constructive interference?

A

Constructive interference occurs between in phase waves and results in a LARGER amplitude of a new wave.

208
Q

What is the definition of period?

A

Time to complete one cycle

Time from the start of one cycle to the next

209
Q

What is the definition of frequency?

A

The frequency is known as the number of events for a specified duration of time

210
Q

What is the diagnostic ultrasound range ?

A

1 MHZ - 15 MHZ

211
Q

What are the frequencies for therapeutic ultrasound?

A

.5 MHZ - 3 MHZ

212
Q

What are the 3 bigness parameters?

A

Amplitude
Power
Intensity

213
Q

What is the definition of Amplitude?

A

Max variation that occurs in an acoustic variable.

The difference between the mean and the maxima or the the mean and the minima

214
Q

What determines Amplitude? Amplitude can be measured in ANY of the acoustic variables-
volts - pascals - decibels - distance

A 
Initially, its the sound source. As the beam transmits through tissue, the amplitude will decrease and this is known as attenuation.
Other names for amplitude include:
acoustic amplitue
acoustic intensity
output power
215
Q

What is the definition of power?

A

Power is known as the rate at which work is performed. It is measured in units of watts.
Determined by the sound source initially , and then by the medium through attenuation.

216
Q

What happens to power if the amplitude is decreased by a factor of 3?

A

~Power = amplitude squared

amplitude = 1/3
since its squared: 1/3 x 1/3 = 1/9!

217
Q

What happens to power if the amplitude is tripled?

A

power = amplitude squared
amplitude = 3
3 x 3 = 9 fold

218
Q

What is the formula for intensity?

A

intensity = power/area

intensity is porportional to the amplitude squared

219
Q

What is the definition of wavelenght?

A

length or distance of one cycle

Determined initially by the sound source, then the medium through attenuation

220
Q

What is the definition of intensity?

A

Concentration of energy in a sound beam.
Determined initially by the sound source only , then affected
by the medium through a process called attenuation

221
Q

What is the formula for wavelenght?

A

WL = prop speed/ frequency

222
Q

What is elasticity?

A

Ability of a solid object to return to its original shape after distortion by a force

223
Q

What is compressibility?

A

Measure of how much the volume of a material changes for a given distorting force

224
Q

What is stiffness?

A

Ability of an object to resist compression.(inverse to compressibility and elasticity).

225
Q

Sound travels faster in _______ and slower in _________.

A 
faster in solids and slower in gasses
.3  air
.5  lung
1.54 soft tissue
3.5 - 4 bone
226
Q

What does a high bulk modulus mean?

A

Not compressible or Stiff / inelastic

227
Q

An increase in stiffness = an increase in ________.(hint s = s)

A

Speed.

An increase in density = a decrease in speed

228
Q

What has the greatest affect on propagation speed of a medium?

A

stiffness or compressibility

229
Q

What determines the three bigness parameters and are they adjustable by the sonographer?

A

Initially determined by the sound source and then decreased by attenuation. They are ALL adjustable by the sonographer.

230
Q

Wavelength is the only parameter that is determined by the _________ and the _______.

A

sound source

medium

231
Q

What is the main advantage of Pulsed Wave ultrasound?

A

range resolution

232
Q

What is the formula for pulse duration? What is pulse duration?

A

of cylces x period

# of cycles / frequency
 Pulse duration is the TIME from the start of one pulse to the end of the same pulse. It is the actual time that a pulse is on.
233
Q

What is the equation for duty factor?

A

PD/ PRP x 100

Duty factor is a percentage

234
Q

What is duty factor?

A

% of time that sound is transmitting. -

determined by the sonographer by adjusting the depth of view

235
Q

Is Pulse duration and Spacial Pulse length adjustable by the sonographer?

A

NO!!!!

236
Q

What does shorter SPL give you as far as resolution?

A

Better axial resolution/detail resolution

237
Q

How does the sonographer adjust the duty factor?

A

adjusting the imaging depth. Since duty factor= pd/prp,

increasing the imaging depth, which would mean an increase in prp, would essentialy decrease the duty factor

Duty Factor = PRF
when prf increases, the duty factor increases

238
Q

What is the definition of PRF?

A

The number of pulses that are sent into the body in one second

239
Q

What does the term temporal mean?

A

Refers to all time; transmit and recieve

240
Q

What does the term pulsed refer to?

A

refers TO THE AVERAGE INTENSITY FOR THE PULSE DURATION ONLY

241
Q

What is spacial peak intensity?

A

The beams intensity at the location where it is maximum.

242
Q

What is the spatial avg intensity? hint: cross sectional area.

A

The average intensity across the beam’s entire cross sectional area. Think of spacial as “in space” or “ area”.

243
Q

What is the temporal peak intensity?

A

The point in time where the beam is at its maximum intensity

244
Q

What is I max?

A

The average intensity during the most intense half cycle. The half cycle is “half” of one full cycle in a wave. Basically it is the avg of the max amplitude.

245
Q

What is the Pulse Average?

A

The average of intensities during the pulse duration or TRANSMIT TIME

246
Q

What is the temporal avg?

A

The average intensity during the entire pulse repetition period; which is from the beginning of one pulse to the beginning of the next pulse. This is the only intensity measured at BOTH THRANSMIT AND RECEIVE TIMES!

247
Q

What is the duty factor of pulsed ultrasound? The percentage of time an actual pulse is being sent out?

A

.2%

99.8% of the time is when the system is listening and silent and the intensity is 0

248
Q

What are the units for intensity? hint: formula for intensity

A

Watts/ cm squared

intensity = power/area
or
watts / cm squared

249
Q

The different measurment of intensities is important in the study of ___________. Why do we care about how intense a beam is?

A

bioeffects

250
Q

Which intensity is the most relevant with respect to tissue heating?

A

SPTA
Spacial Peak Temporal Average
The average of the TRANSMIT AND RECIEVE TIME

251
Q

What does the beam uniformity coefficient or the SP/SA factor describe?

A

The spread of a beam in space. The SP/SA factor is unitless with a value of 1 or greater

252
Q

When are the ALL the pulse average’s and temporal averages the SAME?
So everything ending with PA or TA equal the same?
SPTA= SPPA AND SATA = SAPA?

A

During CW because the beam is always on

253
Q

What is the logarithm of 1000? hint: count the numbers of zero for log

A

3

254
Q

What quantifies relative change of the strength of a sound beam?

A

decibel or decibel notation

“the signal strength has doubled” or is “now 1/10”

255
Q

What is the meaning of a 6db change?

A

3db means the intensity doubled so a 6db change = INTENSITY QUADRUPLED

256
Q

When a waves intensity doubles, what is the relative change in decibel notation?

A

+3 db

257
Q

When the intensity increases 10 fold, what is the relative change in decibel notation?

A

+10 db

258
Q

A sound beam had increased from its initial intensity by a factor of 100. How is this described in decimal notation?

A

Well,
10 x 10 = 100
an increase 10 fold = +10db
10db + 10db = 20db

20db

259
Q

A sound beam has decreased to 1/100 of its initial intensity. How is this described in decimal notation?

A

1/100 = 1/10 x 1/10

1/10 in decimal notation = -10db

  • 10db + -10db = -20db
  • 20db
260
Q

What is the method of describing the extent to which a signal can vary and still be processed acuratley?

A

dynamic range

261
Q

What is the formula for volumetric flow rate?

A

Q(flow) = P(pressure) x pie x radius to the 4th
___________________________

                8 x lenght of vessel x viscosity
262
Q

When does steady flow occur?

A

in the venous system when the individual stops breathing for a moment

263
Q

What does path lenght and frequency of sound determine?

A

attenuation

  1. the further sound travels, the greater the attenuation and the weaker the beam becomes
  2. the HIGHER the frequency, the greater the attenuation
264
Q

Reflection,scattering and absorbtion contribute to:

A

attenuation

265
Q

Most interfaces are not smooth, but have some irregularities. When a wave reflects off an irregular surface, it radiates in more than one direction. This is called what?

A

diffuse reflection

266
Q

What has more scatter, more attenuation, and does not create harmonic imaging?

A

high frequency sound

267
Q

What is the form of scattering when the structure’s dimensions are much smaller than the beam’s wavelength and the scattering is redirected equally in all directions?

A

Rayleigh scattering

268
Q

When the boundry is smooth, the sound is reflected in only one direction in an organized manner?

A

specular

269
Q

Scattering is directly related to what?

A

frequency

270
Q

What is the formula for TOTAL attenuation?

A

total attenuation = attenuation coefficient x distance

271
Q

What is the formula for the ATTENUATION COEFFICIENT?

A

atten coef = 1/2 the frequency in soft tissue

272
Q

What is impedance and what is the formula?

A

Impedence is the acoustic resistance to sound in a tissue. The formula is:

density of medium x speed

273
Q

Define sensitivity of a diagnostic test?

How is it calculated?

A

Sensitivity measures how sensitive the test is in identifying the presence of disease or the probability that a test will be positive when the patient actually has the disease.

True Positive
__________
true positive + false negative

274
Q

Define specificity?

A

Specificity measures “how specific” the test is in RULING OUT disease.
true negative
___________
true negative + false positive

275
Q

Define the positive predictive value

A

Positive predictive value test is defined as the probability that the disease is present when the result of the diagnostic test is positive.
This is different than sensitivity, because it has to do with “testing” and EVERYTHING IS POSITIVE

TRue positive
__________
true positive + false positive

276
Q

Define the negative predicitve value.

A

Negative predictive value is defined as the probability that the disease is not present when the result of the diagnostic test is negative. EVERYTHING IS NEGATIVE:

true neg
________
true negative + false negative

277
Q

Define accuracy

A

porportion of test that yielded the correct results

278
Q

While performing an ultrasound exam with a 3-MHZ transducer,the sonographer activates the harmonic mode. What is the fundamental frequency?

A

3 MHZ.

The fundamental frequency is defined as the frequency of sound wave transmitted by the transducer.

279
Q

Which intensity is best used with respect to bioeffects?

A

SPTA

Spacial Peak Temporal Average

280
Q

What is the mechanical index?

A

number related to the possibility that cavitation will occur.

Echo Class (6 decks)

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