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Physics > Echo Physics 101 > Flashcards

Echo Physics 101 Flashcards

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
Q

relation bet. velocity and doppler shift

A

direct

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26
Q

duplex US

A

simultaneous imaging and Doppler

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27
Q

disadvantage of CW Doppler

A

range ambiguity - echoes arise from entire length of overlap between transmit and receive beams

range = depth

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28
Q

Nyquist limit

A

prf/2 (in kHz)

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29
Q

aliasing appears when

A

doppler shift exceeds the Nyquist limit

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30
Q

5 ways to Eliminate Aliasing

A

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

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31
Q

PW Type of Transducer

A

minimum 1 crystal
range resolution
limit of max velocity
uses damped, low Q, wide bandwidth transducer

32
Q

CW Type of Transducer

A

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
Q

Color Doppler is based on PULSED US and is subject to…

A

range resolution/specificity
aliasing

34
Q

Color doppler provides

A

info on direction of flow and is semi-quantitative
knowledge of angle not really important

35
Q

what kind of velocities does Color Doppler report?

A

average velocities ie. mean velocities

36
Q

relationship bet. color Flow and doppler shift

A

doppler shifts are coded into colors and superimposed on a 2D image

37
Q

Packet

A

multiple pulses
Multiple ultrasound pulses are needed to accurately
determine red blood cell velocities by hDoppler

38
Q

small packet

A

less accurate Doppler
less sensitive to low velocity flow
higher frame rate and improve temporal resolution

39
Q

LARGE packet

A

more accurate doppler
more sensitive to low velocity flow
lower frame rate, reduced temporal resolution

40
Q

packet size must balance between

A

accurate velocity measurements and temporal resolution

41
Q

Spectral Analysis

A

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
Q

methods of spectral analysis for cw pw vs. color Doppler

A

FFT for PW and CW
Autocorrelation for color (less accurate but faster than FFT)

43
Q

Lateral Resolution
determined by…
best with…

A

LATA
determined by Beam Width
best with narrowest beam

44
Q

Lateral Resolution changes with

A

depth
best at focus

45
Q

Lateral resolution
In Near Field, best with

A

smallest diameter crystal

46
Q

Lateral resolution
In Far Field, best with

A

largest diameter crystal and highest frequency (largest divergence)

47
Q

Axial Resolution
determined by…
best with…

A

determined by pulse length
best with shortest pulse
highest freq and fewest cycles

48
Q

Axial Resolution
changes with

A

same at all depths
does not change

49
Q

Axial Resolution
In Near Field, best with

A

shortest pulse

50
Q

Axial Resolution
In Far Field, best with

A

shortest pulse

51
Q

Duty Factor definition

A

percentage of time that an echo machine is actually transmitting a pulse into the body

52
Q

approximate time transmitting vs. listening in average US machine

A

0.2% of the time transmitting and 99.8% of the time “listening” for returning signals

53
Q

Duty Factor formula

A

[Pulse Duration/PRP] x100

54
Q

TDI vs. Blood flow Doppler

A

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
Q

frequency determined by

A

sound source

56
Q

wavelength determined by

A

sound source and medium

57
Q

relationship of stiffness and density to speed

A

stiffness directly related to speed

density indirectly related to speed

58
Q

pulse duration formula

A

cycles in pulse x period

59
Q

pulse duration definition

A

time from start of pulse to the end of that pulse

actual time the pulse is “ON”

time usec

59
Q

relationship between pulse duration and sonographer

A

cannot be altered by sonographer
does not change with depth
determined by transducer

60
Q

SPL

A

length or distance the entire pulse occupies in space
distance from start to end of one pulse

61
Q

SPL determined by…

A

source and medium

62
Q

SPL relationship to sonographer

A

cannot be changed by sonographer

63
Q

SPL formula

A

cycles x wavelength

mm

64
Q

PRP definition

A

from start of one pulse to the start of the next one

one pulse duration + one listening time

65
Q

PRP determined by

A

imaging depth

directly related

66
Q

PRP relationship to sonographer

A

changed by sonographer

adjusting depth of view changes listening time

the deeper, the longer the PRP

67
Q

PRF definition

A

number of pulses created by the system in one second

68
Q

PRF determined by

A

imaging depth

inverse relationship

69
Q

PRF relationship to sonographer

A

can be changed by sonographer

by adjusting the PRP, PRF is changed

70
Q

Duty Factor relationship to sonographer

A

changed by sonographer when imaging depth is changed

71
Q

shallow vs. deep image and Duty Factor

A

shallow - high DF
deep - low DF

72
Q

very low MI imaging…

A

minimizes microbubble destruction in the near field

(permits detection of apical abnormalities)

73
Q

relationship spatial resolution and frequency

A

higher frequency means better spatial resolution and shorter wavelength

74
Q

Short pulses are seen with…
Shorter pulses result in better…

A

seen with higher frequency or with transducers that dampen the pulse signal so that there is less ringing

result in better axial resolution

Physics (1 decks)

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