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Echo Physics 101 Flashcards

(75 cards)

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1
Q

Fundamental Imaging

A

Based on the reflection of transmitted frequency. US waves pass through tissue twice

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2
Q

Harmonic Imaging

A

harmonic frequency is generated as the US signal propagates through the tissue. It is single-pass imaging and therefore reduces artifacts. Useful for imaging deeper structures

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3
Q

Reverberation - define
how to fix

A

more distant to true object
comet/ring down
straight line through probe center
fix: decrease gain
alternate imaging plane

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4
Q

Acoustic shadowing
how to fix

A

alternative imaging
increase gain or adjust TGC

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5
Q

mirror artifact

A

more distant than true object
decrease gain

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6
Q

refraction artifact

A

at same distance from probe
decrease gain
use alternative imaging planes/avoid refracting structure

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7
Q

side lobe artifact

A

linear, symmetric at both sides of object
same direction from probe (arc-like in radial direction)

apply color doppler
decrease gain

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8
Q

beam width artifact

A

at same distance from probe
true object/doppler signal outside imaging plane

adjust focal zone
alternative imaging plane

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9
Q

near field clutter

A

apply color doppler, reducing scale
alternative imaging plane

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10
Q

doppler shift equation

A

[2xreflector speed x incident freq x cos(theta)]/propagation speed

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11
Q

doppler shift is directly related to _

A

blood cell speed
freq of transducer
cos of angle bet. flow and sound beam

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12
Q

doppler shift is inversely related to _

A

speed of sound in medium

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13
Q

what does the 2 in doppler equation represent

A

double doppler shift : 1st is when sound strikes cell, 2nd is from moving cell reflecting wave back to transducer

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14
Q

in order to accurately determine velocity…

A

the angle between direction of flow and sound beam must be known

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15
Q

velocity (measured) is as related to Doppler shift…

A

= true velocity x cos (theta)

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16
Q

Doppler shift definition

A

a change or variation in the frequency of sound as a result of motion bet. sound source and the receiver

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17
Q

Doppler frequency

A

difference between received and transmitted frequencies

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18
Q

Positive doppler shift

A

when source and receiver are approaching each other
reflected freq > transmitted freq

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19
Q

Negative doppler shift

A

when source and receiver are moving apart
reflected freq < transmitted freq

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20
Q

typical values for audible sound

A

20 Hz to 20 kHz

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21
Q

doppler US uses these transducers

A

2 to 10 MHz

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22
Q

Demodulation

A

extracts Doppler freq from transducer freq and is performed by a demodulator

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23
Q

bi-directional doppler is analyzed with

A

phase quadrature processing

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24
Q

doppler shift alternate equation

A

received - transmitted freq

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25
relation bet. velocity and doppler shift
direct
26
duplex US
simultaneous imaging and Doppler
27
disadvantage of CW Doppler
range ambiguity - echoes arise from entire length of overlap between transmit and receive beams range = depth
28
Nyquist limit
prf/2 (in kHz)
29
aliasing appears when
doppler shift exceeds the Nyquist limit
30
5 ways to Eliminate Aliasing
use CW use lower freq transducer (reduces doppler shift and shrinks spectrum) select new view with shallower sample vol (increases PRF and Nyquist limit) increase scale baseline shift
31
PW Type of Transducer
minimum 1 crystal range resolution limit of max velocity uses damped, low Q, wide bandwidth transducer
32
CW Type of Transducer
minimum of 2 crystals range ambiguity unlimited max velocity uses UNdampled, high Q, low bandwidth transducer (allows for higher sensitivity to small Doppler shifts)
33
Color Doppler is based on PULSED US and is subject to...
range resolution/specificity aliasing
34
Color doppler provides
info on direction of flow and is semi-quantitative knowledge of angle not really important
35
what kind of velocities does Color Doppler report?
average velocities ie. mean velocities
36
relationship bet. color Flow and doppler shift
doppler shifts are coded into colors and superimposed on a 2D image
37
Packet
multiple pulses Multiple ultrasound pulses are needed to accurately determine red blood cell velocities by hDoppler
38
small packet
less accurate Doppler less sensitive to low velocity flow higher frame rate and improve temporal resolution
39
LARGE packet
more accurate doppler more sensitive to low velocity flow lower frame rate, reduced temporal resolution
40
packet size must balance between
accurate velocity measurements and temporal resolution
41
Spectral Analysis
is performed to extract or identify the individual frequencies making up the complex signal. It is used to interpret individual velocities in the signal.
42
methods of spectral analysis for cw pw vs. color Doppler
FFT for PW and CW Autocorrelation for color (less accurate but faster than FFT)
43
Lateral Resolution determined by... best with...
LATA determined by Beam Width best with narrowest beam
44
Lateral Resolution changes with
depth best at focus
45
Lateral resolution In Near Field, best with
smallest diameter crystal
46
Lateral resolution In Far Field, best with
largest diameter crystal and highest frequency (largest divergence)
47
Axial Resolution determined by... best with...
determined by pulse length best with shortest pulse highest freq and fewest cycles
48
Axial Resolution changes with
same at all depths does not change
49
Axial Resolution In Near Field, best with
shortest pulse
50
Axial Resolution In Far Field, best with
shortest pulse
51
Duty Factor definition
percentage of time that an echo machine is actually transmitting a pulse into the body
52
approximate time transmitting vs. listening in average US machine
0.2% of the time transmitting and 99.8% of the time “listening” for returning signals
53
Duty Factor formula
[Pulse Duration/PRP] x100
54
TDI vs. Blood flow Doppler
TDI signals - high amplitude (power output and gain are low), low velocities Blood flow Doppler - high velocity and high frequency, low amplitude in TDI, low amp, high freq signals filtered out
55
frequency determined by
sound source
56
wavelength determined by
sound source and medium
57
relationship of stiffness and density to speed
stiffness directly related to speed density indirectly related to speed
58
pulse duration formula
#cycles in pulse x period
59
pulse duration definition
time from start of pulse to the end of that pulse actual time the pulse is "ON" time usec
59
relationship between pulse duration and sonographer
cannot be altered by sonographer does not change with depth determined by transducer
60
SPL
length or distance the entire pulse occupies in space distance from start to end of one pulse
61
SPL determined by...
source and medium
62
SPL relationship to sonographer
cannot be changed by sonographer
63
SPL formula
#cycles x wavelength mm
64
PRP definition
from start of one pulse to the start of the next one one pulse duration + one listening time
65
PRP determined by
imaging depth directly related
66
PRP relationship to sonographer
changed by sonographer adjusting depth of view changes listening time the deeper, the longer the PRP
67
PRF definition
number of pulses created by the system in one second
68
PRF determined by
imaging depth inverse relationship
69
PRF relationship to sonographer
can be changed by sonographer by adjusting the PRP, PRF is changed
70
Duty Factor relationship to sonographer
changed by sonographer when imaging depth is changed
71
shallow vs. deep image and Duty Factor
shallow - high DF deep - low DF
72
very low MI imaging...
minimizes microbubble destruction in the near field (permits detection of apical abnormalities)
73
relationship spatial resolution and frequency
higher frequency means better spatial resolution and shorter wavelength
74
Short pulses are seen with... Shorter pulses result in better...
seen with higher frequency or with transducers that dampen the pulse signal so that there is less ringing result in better axial resolution

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