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Formulas For US Physics > Boards > Flashcards

Boards Flashcards

1
Q

Axial resolution

A

SPL/2

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2
Q

Axial resolution in soft tissue

A

.77 x #of cycles in pulse/ frequency

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3
Q

Axial resolution is best with

A

Short SPL
Short PD
High frequency
Fewer cycles/pulse
Lower numerical values

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4
Q

Intensity

A

Power/beam area

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5
Q

If amplitude doubles, intensity increases

A

By factor of 4

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6
Q

Focal length

A

Transducer diameter squared x frequency/6

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7
Q

CW beam diameter

A

2NZL

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8
Q

Frequency in PW

A

Prop speed/2x thickness

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9
Q

With oblique incidence, angle of reflection

A

Equals incident angle

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10
Q

Time of Flight

A

1.54/2

13 per cm reflector depth w/total distance 2 cm

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11
Q

Focal depth

A

Diameter squared x frequency/6

Or

Diameter squared/4 x wavelength

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12
Q

Aperture

A

Beam width/beam diameter

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13
Q

Two things that determine frequency in PW

A

Speed of sound in PZT
Thickness of PZT

INVERSELY RELATED

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14
Q

Frequency

A

Sound speed in PZT/2 x thickness

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15
Q

QF

A

Resonant frequency/bandwidth

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16
Q

Imaging probes have

A
  1. Pulses w/short length and duration
  2. Backing material
  3. Reduced sensitivity
  4. Wide bandwidth
  5. Lower QF
  6. Improved axial resolution
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17
Q

Dampening Material

A
  1. Decreases sensitivity
  2. Wide bandwidth
  3. Low QF

1/4 wavelength thick

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18
Q

PRF in soft tissue

A

77,000/imaging depth

As depth increases PRF decreases

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19
Q

Snell’s law

A

Refraction
1. If media 1 speed = media 2, no refraction
2. If media 1 is less than media 2 transmission angle is greater than incident
3. If media 2 is faster than media 1, transmission angle is less than incident angle

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20
Q

Transmission w/oblique incidence and different prop speeds

A

Refraction

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21
Q

Incident intensity

A

Reflected intensity + transmitted intensity

Sound waves initial intensity before it strikes a boundary

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22
Q

How much gets reflected at soft tissue

A

1%

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23
Q

How much gets reflected at air-tissue

A

99%

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24
Q

How much gets reflected at bone- tissue

A

50%

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25
Q

ITC

A

Transmitted intensity/incident intensity

X 100

99% transmitted at soft tissue

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26
Q

In clinical imaging what percent of incident sound wave is reflected?

A

1% or less

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27
Q

Normal incidence

A

Strikes at 90°
Perpendicular
Right angle
Orthogonal

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28
Q

IRC

A

% of intensity that bounces back when sound hits boundary between media

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29
Q

Transmitted intensity

A

Incident intensity x ITC

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30
Q

Matching layer

A

1/4 wavelength thick

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31
Q

PZT

A

Active element

1/2 wavelength thick

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32
Q

Distance to boundary

A

Go-return x speed/ 2

In soft tissue distance=time x .77

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33
Q

Pressure

A

Force/area

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34
Q

Power

A

Amplitude squared

If amp is tripled, power increases by 9

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35
Q

Duty factor

A

PD/PRP

In imaging DF = .2% (small time transmitting, long time receiving)

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36
Q

SPTA

A

most related to tissue heating

If CW and PW have same intensity SPTP - CW has higher SPTA

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37
Q

Attenuation coefficient

A

Frequency/2

In soft tissue .5dB/cm/MHzh

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38
Q

Attenuation

A

Requires 2 intensities

*more attenuation, longer distance, higher frequency

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39
Q

Reflection

A

Specular - smooth

Diffuse - irregular

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40
Q

Half value layer thickness

A

Distance sound travels in tissue that reduces intensity to 1/2 its original value

Thin 1/2 layer = high frequency

Depends on media and frequency

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41
Q

Reflection Angle aka

A

Incident angle

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42
Q

Incident angle

A

Angle at which wave strikes boundary

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43
Q

Pixel size

A

Total length of picture edge/ # of pixels in that length.

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44
Q

Byte

A

8 bits or 2x2x2x2x2x2x2x2 or 256 shades

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45
Q

Word

A

2 bytes

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46
Q

Huygen’s principle

A

The minimum distance that two structures positioned front to back can be apart and show 2 images

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47
Q

Total attenuation

A

Path length x attenuation coefficient

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48
Q

Impedance

A

Density x speed Rayls

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49
Q

Noise

A

Increasing output power is most common way to get rid of noise

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50
Q

Rayleigh Scattering

A

RBC
Hitting much smaller than beam’s wavelength

Increases with increasing frequency

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51
Q

Scattering

A

Random direction of sound in different directions

High frequency, more scattering

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52
Q

W/fixed focus transducer focal depth depends on

A
  1. Transducer diameter
  2. Frequency of sound

Shallow w/smaller PZT diameter and lower frequency

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53
Q

Adjustable focus

A

Phased array

54
Q

Pulse duration

A

of cycles in pulse/frequency

Determined by source NOT adjustable

Shorter PD - better image

55
Q

Focusing techniques

A
  1. Lens (external) fixed, conventional, mechanical
  2. Curved active element - (internal) - fixed
  3. Electronic (phased array) - adjustable
56
Q

Lateral resolution

A

1/2 transducer diameter

Best at 1 NZL (at focus)

Changes with depth

The smaller the number the better

57
Q

Slice thickness or elevational resolution

A

Deals with 3D shape
1. Shallow to deep
2. Side to side
3. Above and below imaging plane

Thick slice structures above and below create reflections

58
Q

Side lobes

A

Created by single element transducer

Degrades lateral resolution

59
Q

Grating lobes

A

Array transducers

Degrade lateral resolution which can be fixed by apodization (alters electrical spike voltages and reduces lobe strength

Reduced by subdicing

60
Q

Temporal resolution

A

of pulses x PRP

Best with high FR
Impacted by speed of sound in medium and imaging depth

61
Q

Frame rate

A

Decreased by multi focus

Inversely related to depth

62
Q

Pulsed & beam former

A

Pulser - determines amplitude, PRP, PRF

Former - responsible for firing delay patterns

63
Q

Receiver

A

Analog to digital

64
Q

Display

A

Presents processed data

65
Q

Storage

A

Archives

66
Q

Master Synchronizer

A

Maintains and organizes proper timing

67
Q

Pulser Voltage

A

Output gain, acoustic power, Pulser power, energy output, transmitter output, power, gain

*changes brightness of entire image

68
Q

PRP

A

Determines maximum imaging depth

As depth increases, PRP increases

Depth x 13usec

69
Q

Shallow imaging

A
  • less listening time
  • shorter PRP
  • higher PRF
  • higher DF
70
Q

Channel

A

A single PZT element, the electronics in the beam former/Pulser and connecting wire

*most systems between 32 and 256 channels

71
Q

Receiver

A
  1. Amplification
  2. Compensation
  3. Compression
  4. Demodulation
  5. Reject

Adjustable

72
Q

Amplification

A

Receiver gain, image becomes brighter

73
Q

Compensation

A

TGC, corrects attenuation

74
Q

Compression

A

Modifies gray scale mapping 20 shades

75
Q

Demodulation

A

Rectification and smoothing

76
Q

Reject

A

Controls low level gray scale info aka threshold or suppression

77
Q

Dynamic frequency tuning

A

Only uses high freq part of pulse to create superficial image and lower freq to create deeper parts

78
Q

Analog

A

Best for spatial resolution
Limits are image fade, image flicker, instability, deterioration

79
Q

Digital

A

Benefit - uniformity, stability, durability, speed, accuracy

80
Q

Pixel and bit (digital)

A

Low pixel density means less detail, larger pixels, lower spatial resolution

81
Q

Calculating shades of gray

A

If 5 bits of memory 2x2x2x2x2=32

82
Q

Bit versus pixel

A

Bit - shades of gray, computer memory and contrast resolution.
Pixel - image element, image detail, spatial resolution

83
Q

Preprocessing

A
  1. TGC
  2. Log compression
  3. Write magnification
  4. Persistence
  5. Spatial compounding
  6. Edge enhancement
  7. Fill in interpolation
84
Q

Write magnification

A

Rescans ROI creates new image w/increased spatial resolution

85
Q

Post processing

A
  1. Any change after freeze frame
  2. Black/white inversion
  3. Read magnification
  4. Contrast variation
  5. 3D rendering
86
Q

Read magnification

A

Creates larger pixels from info already in scan converter

87
Q

Coded excitation

A

Higher signal to noise ratio
Improved axial, spatial, and contrast resolution
Deeper penetration

*uses a series of pulses to create wider range of frequencies

88
Q

Spatial compounding

A

*reduces shadowing artifact

Method of using sono info from several different imaging angles to produce a single image

89
Q

Frequency compounding

A

Reduces speckle artifact and noise in images

90
Q

Temporal compounding

A

Persistence
*reduces temporal resolution, used to better fill a vessel with color

Less effective w/slow flow

91
Q

Fill in interpolation

A

*improves spatial resolution by increasing line density, improves ability to precisely visualize boarders of round structures

92
Q

MI

A

Peak rarefaction pressure/square root of frequency

*low MI - small pressure variation and higher frequency

93
Q

Reynolds’s number

A

Predicts if flow is laminar or turbulent

Less than 1,500 laminar
2,300 or more turbulent

94
Q

Stenosis effects

A
  1. Changes direction as blood flows in and out
  2. Increased velocity in stenosis
  3. Post stenotic turbulence
  4. Pressure gradient across stenosis (pressure downstream less than upstream)
  5. Conversion of pulsatilla flow patterns to steady flow
95
Q

Bernoulli’s principle

A

Describes relationship between velocity and pressure in moving fluid

96
Q

Pressure gradient

A

Flow x resistance

97
Q

Hydrostatic pressure

A

Related to weight of blood above or below heart

Supine pressure is 0mm/Hg

98
Q

With inspiration flow to legs

A

Decreases

*flow to heart increases

99
Q

With expiration

A

Reduces venous return to heart and increases flow to legs

100
Q

Doppler Shift

A

=reflected freq - transmitted freq

Directly related to velocity and frequency of transmitted sound

101
Q

Angles and Cosin

A

0°. 1
60° .5
90° 0

Doppler performed w/a 2MHz transducer and the Doppler shift is 3 kHz. Same study with 4 MHz transducer - shift becomes 6kHz

102
Q

Nyquist limit

A

PRF/2

Highest frequency or velocity that can be measured w/o aliasing

103
Q

Aliasing happens

A

When sample volume is deep, PRF is low, and Nyquist limit is low

104
Q

Avoid Aliasing by

A
  1. Adjust scale to maximum
  2. Select a new shallower view
  3. Lower frequency transducer
  4. Baseline shift
  5. Use CW Doppler
105
Q

Increasing Nyquist limit

A

Adjust scale to max
Select shallower view

106
Q

Doppler artifacts

A

Ghosting (color bleed out of vessel)
Clutter

107
Q

Eliminate Doppler artifacts

A

With wall filter - eliminate low frequency Doppler shifts around baseline (color from slow velocity reflectors - ie, movement)

108
Q

Crosstalk

A

Special form of mirror image but w/spectral Doppler

Happens when
1. Doppler gain is set too high
2. Incidence angle is near 90° between sound beam and flow direction

109
Q

Spectral Analysis

A

2 forms
1. FFT
2. Autocorrection

Spectral measures peak velocity

110
Q

FFT

A

Digital processing, very accurate, displays all individual velocities

111
Q

Autocorrection

A

Digital technique used to analyze color flow Doppler

112
Q

Color Flow Doppler

A
  • PW
  • range resolution
  • subject to aliasing
  1. Presence of flow
  2. Direction
  3. Average velocity
  4. Character of flow

Measures average

113
Q

Power Doppler

A

Non directional
- picks up low flow
- unaffected by angles
- no aliasing
BUT
- no measurement of velocity or direction
- lower frame rate
- susceptible to motion of transducer/patient (flash artifact)

114
Q

Flash artifact

A

Caused by motion of patient or transducer

115
Q

Enhancement

A

W/abnormally low attenuation

Hyperechoic line between tissues with abnormally low attenuation

116
Q

Focal enhancement

A

Side by side, most prominent at focud

117
Q

Reverberation

A

Multiple equally spaced echoes

118
Q

Shadowing

A

Too much attenuation

119
Q

Edge shadow

A

Created as sound beams refract and diverge along the edge of a curved structure

120
Q

Comet tail

A

Polyps
Created by gas bubble that resonates and produces its own sound wave

121
Q

Attenuation coefficient

A

Frequency/2

.5 dB/cm/MHz
In soft tissue

122
Q

2D imaging Mechanical Transducer

A

Single, circular active element
- fan or sector
- fixed focal depth
1. Internal focus (active element)
2. External focus (lens)

Entire image lost when crystal malfunctions

123
Q

Array transducer

A
  1. Linear ——
  2. Annular (circles in circles)
  3. Convex
124
Q

Linear Array

A

Steered and focused by phasing
- fan or sector
- electronic steering
- if element damaged, inconsistent steering and focusing

125
Q

Annular Phased array

A

Mechanical steering
- multi focal zones
- fan or sector shaped like spokes on bike wheel
- when one ring malfunctions only portion of image lost

126
Q

Linear Sequential Array

A
  • sector shaped images, large acoustic footprint, rectangle shaped

120-250 strips of PZT

Steering - small group fired simultaneously

127
Q

Convex or Curvilinear array

A

120-250 elements
Focus is electronic
Shape is blunted sector

128
Q

Dynamic receive focusing

A

In convex/curvilinear is achieved by phase delays in signals returning to transducer

129
Q

Vector Array

A

Small footprint
Focusing is electronic
Trapezoidal image

130
Q

PD

A

Period x # cycles in pulse

Formulas For US Physics (1 decks)

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