Boards Flashcards
1
Q
Axial resolution
A
SPL/2
2
Q
Axial resolution in soft tissue
A
.77 x #of cycles in pulse/ frequency
3
Q
Axial resolution is best with
A
Short SPL
Short PD
High frequency
Fewer cycles/pulse
Lower numerical values
4
Q
Intensity
A
Power/beam area
5
Q
If amplitude doubles, intensity increases
A
By factor of 4
6
Q
Focal length
A
Transducer diameter squared x frequency/6
7
Q
CW beam diameter
A
2NZL
8
Q
Frequency in PW
A
Prop speed/2x thickness
9
Q
With oblique incidence, angle of reflection
A
Equals incident angle
10
Q
Time of Flight
A
1.54/2
13 per cm reflector depth w/total distance 2 cm
11
Q
Focal depth
A
Diameter squared x frequency/6
Or
Diameter squared/4 x wavelength
12
Q
Aperture
A
Beam width/beam diameter
13
Q
Two things that determine frequency in PW
A
Speed of sound in PZT
Thickness of PZT
INVERSELY RELATED
14
Q
Frequency
A
Sound speed in PZT/2 x thickness
15
Q
QF
A
Resonant frequency/bandwidth
16
Q
Imaging probes have
A
- Pulses w/short length and duration
- Backing material
- Reduced sensitivity
- Wide bandwidth
- Lower QF
- Improved axial resolution
17
Q
Dampening Material
A
- Decreases sensitivity
- Wide bandwidth
- Low QF
1/4 wavelength thick
18
Q
PRF in soft tissue
A
77,000/imaging depth
As depth increases PRF decreases
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
20
Q
Transmission w/oblique incidence and different prop speeds
A
Refraction
21
Q
Incident intensity
A
Reflected intensity + transmitted intensity
Sound waves initial intensity before it strikes a boundary
22
Q
How much gets reflected at soft tissue
A
1%
23
Q
How much gets reflected at air-tissue
A
99%
24
Q
How much gets reflected at bone- tissue
A
50%
25
ITC
Transmitted intensity/incident intensity
X 100
99% transmitted at soft tissue
26
In clinical imaging what percent of incident sound wave is reflected?
1% or less
27
Normal incidence
Strikes at 90°
Perpendicular
Right angle
Orthogonal
28
IRC
% of intensity that bounces back when sound hits boundary between media
29
Transmitted intensity
Incident intensity x ITC
30
Matching layer
1/4 wavelength thick
31
PZT
Active element
1/2 wavelength thick
32
Distance to boundary
Go-return x speed/ 2
In soft tissue distance=time x .77
33
Pressure
Force/area
34
Power
Amplitude squared
If amp is tripled, power increases by 9
35
Duty factor
PD/PRP
In imaging DF = .2% (small time transmitting, long time receiving)
36
SPTA
most related to tissue heating
If CW and PW have same intensity SPTP - CW has higher SPTA
37
Attenuation coefficient
Frequency/2
In soft tissue .5dB/cm/MHzh
38
Attenuation
Requires 2 intensities
*more attenuation, longer distance, higher frequency
39
Reflection
Specular - smooth
Diffuse - irregular
40
Half value layer thickness
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
41
Reflection Angle aka
Incident angle
42
Incident angle
Angle at which wave strikes boundary
43
Pixel size
Total length of picture edge/ # of pixels in that length.
44
Byte
8 bits or 2x2x2x2x2x2x2x2 or 256 shades
45
Word
2 bytes
46
Huygen’s principle
The minimum distance that two structures positioned front to back can be apart and show 2 images
47
Total attenuation
Path length x attenuation coefficient
48
Impedance
Density x speed Rayls
49
Noise
Increasing output power is most common way to get rid of noise
50
Rayleigh Scattering
RBC
Hitting much smaller than beam’s wavelength
Increases with increasing frequency
51
Scattering
Random direction of sound in different directions
High frequency, more scattering
52
W/fixed focus transducer focal depth depends on
1. Transducer diameter
2. Frequency of sound
Shallow w/smaller PZT diameter and lower frequency
53
Adjustable focus
Phased array
54
Pulse duration
# of cycles in pulse/frequency
Determined by source NOT adjustable
Shorter PD - better image
55
Focusing techniques
1. Lens (external) fixed, conventional, mechanical
2. Curved active element - (internal) - fixed
3. Electronic (phased array) - adjustable
56
Lateral resolution
1/2 transducer diameter
Best at 1 NZL (at focus)
Changes with depth
The smaller the number the better
57
Slice thickness or elevational resolution
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
Side lobes
Created by single element transducer
Degrades lateral resolution
59
Grating lobes
Array transducers
Degrade lateral resolution which can be fixed by apodization (alters electrical spike voltages and reduces lobe strength
Reduced by subdicing
60
Temporal resolution
Best with high FR
Impacted by speed of sound in medium and imaging depth
#of pulses x PRP
61
Frame rate
Decreased by multi focus
Inversely related to depth
62
Pulsed & beam former
Pulser - determines amplitude, PRP, PRF
Former - responsible for firing delay patterns
63
Receiver
Analog to digital
64
Display
Presents processed data
65
Storage
Archives
66
Master Synchronizer
Maintains and organizes proper timing
67
Pulser Voltage
Output gain, acoustic power, Pulser power, energy output, transmitter output, power, gain
*changes brightness of entire image
68
PRP
Determines maximum imaging depth
As depth increases, PRP increases
Depth x 13usec
69
Shallow imaging
- less listening time
- shorter PRP
- higher PRF
- higher DF
70
Channel
A single PZT element, the electronics in the beam former/Pulser and connecting wire
*most systems between 32 and 256 channels
71
Receiver
1. Amplification
2. Compensation
3. Compression
4. Demodulation
5. Reject
Adjustable
72
Amplification
Receiver gain, image becomes brighter
73
Compensation
TGC, corrects attenuation
74
Compression
Modifies gray scale mapping 20 shades
75
Demodulation
Rectification and smoothing
76
Reject
Controls low level gray scale info aka threshold or suppression
77
Dynamic frequency tuning
Only uses high freq part of pulse to create superficial image and lower freq to create deeper parts
78
Analog
Best for spatial resolution
Limits are image fade, image flicker, instability, deterioration
79
Digital
Benefit - uniformity, stability, durability, speed, accuracy
80
Pixel and bit (digital)
Low pixel density means less detail, larger pixels, lower spatial resolution
81
Calculating shades of gray
If 5 bits of memory 2x2x2x2x2=32
82
Bit versus pixel
Bit - shades of gray, computer memory and contrast resolution.
Pixel - image element, image detail, spatial resolution
83
Preprocessing
1. TGC
2. Log compression
3. Write magnification
4. Persistence
5. Spatial compounding
6. Edge enhancement
7. Fill in interpolation
84
Write magnification
Rescans ROI creates new image w/increased spatial resolution
85
Post processing
1. Any change after freeze frame
2. Black/white inversion
3. Read magnification
4. Contrast variation
5. 3D rendering
86
Read magnification
Creates larger pixels from info already in scan converter
87
Coded excitation
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
Spatial compounding
*reduces shadowing artifact
Method of using sono info from several different imaging angles to produce a single image
89
Frequency compounding
Reduces speckle artifact and noise in images
90
Temporal compounding
Persistence
*reduces temporal resolution, used to better fill a vessel with color
Less effective w/slow flow
91
Fill in interpolation
*improves spatial resolution by increasing line density, improves ability to precisely visualize boarders of round structures
92
MI
Peak rarefaction pressure/square root of frequency
*low MI - small pressure variation and higher frequency
93
Reynolds’s number
Predicts if flow is laminar or turbulent
Less than 1,500 laminar
2,300 or more turbulent
94
Stenosis effects
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
Bernoulli’s principle
Describes relationship between velocity and pressure in moving fluid
96
Pressure gradient
Flow x resistance
97
Hydrostatic pressure
Related to weight of blood above or below heart
Supine pressure is 0mm/Hg
98
With inspiration flow to legs
Decreases
*flow to heart increases
99
With expiration
Reduces venous return to heart and increases flow to legs
100
Doppler Shift
=reflected freq - transmitted freq
Directly related to velocity and frequency of transmitted sound
101
Angles and Cosin
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
Nyquist limit
PRF/2
Highest frequency or velocity that can be measured w/o aliasing
103
Aliasing happens
When sample volume is deep, PRF is low, and Nyquist limit is low
104
Avoid Aliasing by
1. Adjust scale to maximum
2. Select a new shallower view
3. Lower frequency transducer
4. Baseline shift
5. Use CW Doppler
105
Increasing Nyquist limit
Adjust scale to max
Select shallower view
106
Doppler artifacts
Ghosting (color bleed out of vessel)
Clutter
107
Eliminate Doppler artifacts
With wall filter - eliminate low frequency Doppler shifts around baseline (color from slow velocity reflectors - ie, movement)
108
Crosstalk
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
Spectral Analysis
2 forms
1. FFT
2. Autocorrection
Spectral measures peak velocity
110
FFT
Digital processing, very accurate, displays all individual velocities
111
Autocorrection
Digital technique used to analyze color flow Doppler
112
Color Flow Doppler
- PW
- range resolution
- subject to aliasing
1. Presence of flow
2. Direction
3. Average velocity
4. Character of flow
Measures average
113
Power Doppler
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
Flash artifact
Caused by motion of patient or transducer
115
Enhancement
W/abnormally low attenuation
Hyperechoic line between tissues with abnormally low attenuation
116
Focal enhancement
Side by side, most prominent at focud
117
Reverberation
Multiple equally spaced echoes
118
Shadowing
Too much attenuation
119
Edge shadow
Created as sound beams refract and diverge along the edge of a curved structure
120
Comet tail
Polyps
Created by gas bubble that resonates and produces its own sound wave
121
Attenuation coefficient
Frequency/2
.5 dB/cm/MHz
In soft tissue
122
2D imaging Mechanical Transducer
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
Array transducer
1. Linear ——
2. Annular (circles in circles)
3. Convex
124
Linear Array
Steered and focused by phasing
- fan or sector
- electronic steering
- if element damaged, inconsistent steering and focusing
125
Annular Phased array
Mechanical steering
- multi focal zones
- fan or sector shaped like spokes on bike wheel
- when one ring malfunctions only portion of image lost
126
Linear Sequential Array
- sector shaped images, large acoustic footprint, rectangle shaped
120-250 strips of PZT
Steering - small group fired simultaneously
127
Convex or Curvilinear array
120-250 elements
Focus is electronic
Shape is blunted sector
128
Dynamic receive focusing
In convex/curvilinear is achieved by phase delays in signals returning to transducer
129
Vector Array
Small footprint
Focusing is electronic
Trapezoidal image
130
PD
Period x # cycles in pulse
