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Echo Boards > Physics/knobs/doppler > Flashcards

Physics/knobs/doppler Flashcards

1
Q

Class 1 indications for TEE from 1996

A

1 Rescue tool
2 surgical repair of valves, HCM, dissection
3 eval complex valve replacements
4 congenital lesions requiring cpb
5 surgical intervention for endocarditis
6 placement of intracardiac devices and monitoring position
7 evaluation of pericardial window procedures

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2
Q

2010 update on indications

A

1 Cardiac and Thoracic surgery
2 Noncardiac rescue and monitoring
3 Critical care

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3
Q

absolute contraindications to TEE

A

esophageal stricture
transesophageal fistula
esophageal trauma
esophagectomy/esophagogastrectomy

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4
Q

relative contraindications to TEE

A

barretts
hiatal hernia
large escending aortic aneurysm
unilateral vocal cord paralysis

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5
Q

Precautions for TEE in high risk patients

A

consider other imaging
obtain GI consult
use smaller probe
limit exam and unnecessary probe manipulation

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6
Q

Piezoelctric and reverse piezoelectric effect

A

piezoelectric- sound waves strike crystal which is converted into electricity
reverse effect- voltage applied to crystal which is converted to sound waves

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7
Q

Imaging modes

A

A mode= amplitude mode (strength = amplitude)
b mode= brightness mode
m mode = motion mode
2d = multiple m mode lines
3d = pyramid of m mode lines

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8
Q

M mode frame rate and brightness

A

frame rate = 1000
brighness = strength of signal

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9
Q

HOCM M mode

A

premature systolic closure of aortic valve, and fluttering

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10
Q

sound waves

A

mechanical longitudinal waves but often talked about as transverse wave

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11
Q

wave properties

A

period
frequency
pulse duration
pulse repetition period
pulse repetition frequency= 2x nyquist limit and determines temporal resolution

wavelength
spatial pulse length=

amplitude= max acoustic variable- avg acoustic variable. Higher amp is stronger pulse
power = amount of work/time
intensity = power/area and determines bioeffects

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12
Q

spatial resolution

A

Axial>lateral>elevational
axial- longitudinal, range, depth, determined by 1/2 spatial pulse length
lateral- determined by beam witdth, known as transverse, angular, azimuthal
elevational- determined by beam heighth

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13
Q

audible sound frequency and ultrasound frequency

A

20-20KHz audible
above 20KHz ultrasound

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14
Q

Determinants of temporal resolution

A

how much something moves
frame rate ( # pulses, line density, image depth, sector width)

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15
Q

Pulse repetition frequency

A

proportional to frame rate and temporal resolution
2x Nyquist limit

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16
Q

Optimize image tips

A

decrease depth
narrow sector width
place focal point at ROI

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17
Q

Gain

A

no bioeffects, no power change
amplifies returning signals

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18
Q

time gain compensation

A

compensates for attenuation with depth

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19
Q

lateral gain compensation

A

compensates for attentuation in lateral position, corrects enhancement artifact

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20
Q

compression

A

reduces dynamic range of ultrasound signals-> leads to brighter brights, darker darks, less shades of gray, highly contrasted image

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21
Q

dynamic range

A

inverse of compression, and more shades of gray with increase

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22
Q

Doppler shift

A

simply a change in frequency. Frequency received - frequency transmitted

blood flow in parallel with ultrasound beam will cause change in frequency

VCos(theta)2Ft/C is dopper shift equation

significant error when theta greater than 20-30

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23
Q

continuous wave doppler

A

one crystal always sending
one crystal always listening

PRF = infinity and therefore high nyquist limit and no aliasing

measures high velocities but range ambiguity , duty factor 100%

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24
Q

Pulsed wave doppler

A

emits pulse , waits, listens for echo from sample gate/sample volume

time = distance

used to calculate SV, AVA, dimensionless index (independent of patient size), diastolic function

advantages = range resolution
limitations=aliasing/limited max velocity

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25
Q

nyquist limit

A

same as max doppler shift
= 1/2 PRF

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26
Q

reduce aliasing

A

lower transmitted frequency
decrease depth of gates (increase PRF)
shift baseline
use continuous wave
Increase PRF (NL=1/2PRF)

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27
Q

color flow doppler

A

form of pulsed wave doppler
Blue away , red towards
Variance map looks at laminar vs turbulent (left laminar , right turbulent)

decreasing box size will increase frame rate by making machine do less work

rapid precise visualization and assessment of flow and regurgitation

limitations= aliasing, decreased temporal resolution and velocity measurements are estimates

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28
Q

cos of 30 , 45, 60, 90

A

0 =1
30=sqrt(3)/2
45=sqrt(2)/2
60=sqrt(1)/2
90 = 0

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29
Q

high pass wall filter

A

filters out low velocities
used for blood flow velocities
200-800 Hz
can affect mean and peak velocities and prevent detection of onset and determination of blood flow

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30
Q

low pass wall filter

A

filters out high velocities/frequencies
used for Tissue doppler
allows low velocity , high amplitude signals

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31
Q

Reject filter

A

used in 2d imaging, filters low amplitude signals indicative of ‘noise’

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32
Q

5 functions of receiver

A

amplification
compensation
compression
demodulation
rejection (AKA suppression, threshold)

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33
Q

Power Doppler

A

Energy mode or color angio
shows flow but no direction or velocity
low frame rate and susceptible to flash artifact

unaffected by angle unless 90, aliasing, and its sensitive to low flow

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34
Q

parameters determined by ultrasound source and medium

A

anything with length like wavelength

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35
Q

parameters determined by sound source only

A

Anything with time units (seconds) and strength

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36
Q

Only parameter determined by medium

A

velocity

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37
Q

Parameters determining velocity

A

Increased stiffness and decreased density

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38
Q

PWD changes to peak E and decel time from atria into ventricle

A

Peak E increases as it goes through valve into ventricle
E wave decel time decreases as it goes into ventricle through valve

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39
Q

wave between E and A wave on MV inflow

A

L wave - indicates impaired relaxation and elevated LAP

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40
Q

simplified bernoulli for pressure gradient

A

= 4v^2

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41
Q

what percentage of peak velocity is the velocity at which pressure half time occurs

A

71%

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42
Q

Pressure half time definition

A

time it takes to go from max pressure gradient to half max pressure gradient

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43
Q

Lesions for PHT, utility and limitations

A

Aortic regurgitation
Mitral stenosis

used to determine size of hole
Formula is 220/PHT for MS

limitations: debate it shouldn’t be used when not rheumatic valves

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44
Q

AI effect on mitral PHT

A

decreases pressure half time causing underestimation of MS

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45
Q

lv compliance effect on PHT

A

stiffer ventricle shortens PHT and underestimates MS

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46
Q

Impaired relaxation on PHT

A

increases PHT, overestimates MS

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47
Q

AI PHT cutoff

A

> 500 ms mild
200-500 ms moderate (slope>2m/s?
<200 ms severe (slope >3 m/s)

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48
Q

Uses for tissue doppler

A

diastolic function- use lateral e’ -> E/e’
systolic function- s’ should be greater than 8 cm/s, <5 cm/s is bad
ischemia, constrictive pericarditis
RV function - measure TA velocity

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49
Q

what is post systolic shortening

A

seen in ischemia on TDI
velocities occurring during isovolumic relaxation time

50
Q

What is annular reversus

A

seen in constrictive pericarditis when lateral e’ < septal e’

51
Q

Limitations of tissue doppler

A

angle dependent (should be <20)
average over 3 cycles to reduce error
MAC / MV tethering

52
Q

myocardial performance index

A

= IVCT + IVRT / ET
usually less than 0.39
measure of both systolic and diastolic function
DIlated CM usually >0.59

53
Q

a’ and e’/a’ values

A

a’ <10 good
e’/a’ <1 bad

54
Q

isovolumic acceleration (IVA)

A

max isovolumic velocity/ IVCT and is used for systolic function
Usually 1-2 m/s2 normal

55
Q

Te’

A

time for onset of e’ wave. prolonged in diastolic dysfunction

56
Q

TE

A

Time from R on QRS to E inflow
Te’-TE is prolonged with diastolic dysfunction

57
Q

TDI for ischemia

A

S’ decreases, e’/a’ <1
PSS, e’ decrease, prolong Q to peak s’

58
Q

TDI in CP and tamponade vs RICM

A

Normal in both, annular reversus in CP

decreased in RICM

59
Q

Best view for RV TDI

A

transgastric RV I/O or RV inflow
RVs’ less than 10 is abnormal in young healthy person

60
Q

tricuspid closure opening time (TCO)

A

Same as IVCT + ET + IVRT and used to get RV MPI
MPI above 0.5 is predictave of instability and mortality

61
Q

Tissue doppler for strain

A

Strain and strain rate can be calculated

(V2-V1)/distance between the two = strain rate

62
Q

Determinants of frame rate

A

line density
# pulses per line
image depth
sector width

63
Q

amplitude

A

Difference between avg value and max value of an acoustic variable.
POwer and intensity are proportional to amplitude squared

64
Q

power

A

rate at which work is performed or energy is transferred
measured in watts or j/sec

65
Q

intensity

A

power/area
determines bioeffects

66
Q

mechanisms of bioeffects

A

thermal- limit to max of 1C rise in local tissue temp
cavitation
vibration

67
Q

max SPTA for focused and unfocused beam

A

unfocused <1W/cm2
focused<100 mW/cm2

68
Q

What causes most heating of all US modes

A

PWD

69
Q

mechanical index

A

measure of US to produce cavitation

70
Q

harmonic frequencies

A

caused by shrinking and expanding of bubbles
allows for better imaging of areas that werent imaged well before
arise from non linear behavior

71
Q

Mechanical index depends on frequency and pressure

A

Increases with lower frequency and stronger pressure

72
Q

Mechanical index

A

strongest harmonics and resonance leading to cavitation seen when MI > 1
harmonics and resonance with MI 0.1-1
no harmonics with MI <0.1 - only backscatter and linear behavior

73
Q

Harmonics

A

tissue harmonics- US travels through tissue and frequency changes into harmonic frequency. strength grows as it goes deeper

contrast harmonics- echo contrast with microbubbles. Harmonic imaging causes bubbles to shrink and then expand leading to cavitation

74
Q

Resonance

A

uneven shrinking and expanding of microbubbles

75
Q

Time- wave properties

A

period
frequency
pulse duration
PRP
PRF- higher frame rate and better temporal resolution

Determined by the sound source

76
Q

wave properties determined by medium

A

velocity. Increased with increased stiffness and decreased density

sound travels faster in dense materials because of its stiffness not density

Impedance

77
Q

attenuation

A

increases with increasing depth and increasing frequency

over 80% of attenuation is from absorption in tissues

78
Q

Impedance

A

resistance to sound traveling through medium
Z = density (p) x velocity (v)

pzt > matching layer > gel > mucosa

79
Q

incident intensity

A

= reflected + transmitted intensity

80
Q

Curie temp

A

temp that can change crystal to no longer produce ultrasound waves

81
Q

damping material

A

also called backing material
decreases ringing
decreases SPL and improves axial resolution
decreases sensitivity to reflected echoes
decreases pulse duration
increases bandwidth
decreases Q factor ( RF/ bandwidth)

82
Q

Frequency determination for PWD

A

V/2T

83
Q

frequency determination for CWD

A

electrical frequency of voltage applied to crystal

84
Q

q factor

A

ability of trasnducer to emit a clean pulse with narrow bandwidth
damping decreases q factor

85
Q

matching layer

A

layer between crystal and skin/tissue

86
Q

anatomy of a sound beam

A

focus is at the minimum diameter of the beam and is where best lateral resolution is

near field ( fresnel) = r (crystal)^2/ wavelength

far field ( fraunhofer)

focal zone is near the focus

87
Q

focusing ultrasound

A

lens
curved crystal
focusing mirror
electronic (used by TEE)

88
Q

range resolution

A

describes axial resolution
but also describes object at specific depth as with PWD

89
Q

ultrasound system

A

master synch
pulser
transducer
receiver and processor
storage

90
Q

functions of receiver

A

amplification- enlargement of returning signal (gain)
compensation- makes all echoes from similar objects appear with similar brightness (tgc, lgc)
compression - reduces range of signals from smallest to largest
demodulation- rectification and smoothing
rejection - filters low amplitude signals

91
Q

artifacts

A

due to US assumptions (sound travels in straight line, reflections are along main axis, intensity of reflection corresponds to reflectors scattering strenth)

92
Q

reverberation

A

rungs on ladder or blurred comet tail / ringdown

93
Q

refraction artifact

A

assumes that us travels in straight line. Places object that is off to side in straight line and deeper

94
Q

side and grating lobes

A

assumes us only travels in main axis.
Strong reflectors in side lobe path will place it in main axis

95
Q

acoustic shadowing/echo dropout

A

strong reflectors that do not allow penetration of US beam

96
Q

mirror artifact

A

similar to reflection artifact
pericardium can act as strong reflector

97
Q

raleigh scattering

A

occurs when the reflectors dimensions are much smaller than the wavelength of the US

sound wave equally redirected in all directions

98
Q

backscatter

A

AKA diffuse reflection in which the object has irregular surface and allows for imaging at suboptimal angle, but its weak.

99
Q

snells law

A

determines refraction
sin transmission / sin incidence = v2/v1

if velocity transmitted is less then angle is smaller than incident angle

100
Q

refraction

A

requires angle that is not 90
requires v2 does not equal v1

101
Q

oblique reflection

A

reflection angle the same as incident angle when it does occur

102
Q

shallow focal length

A

high density, low impedance, thickest crystal, lowest diameter

103
Q

temporal resolution depends on 2 things

A

how much the object moves
the frame rate which depends on several things

104
Q

frame rate depends on several factors

A

line density = # of scan lines/ image ( as line density increases , frame rate goes down)
# foci / line = pulses per scan line (increase pulse per scan will decrease frame rate)
imaging depth (less depth = increase frame rate)

105
Q

1540 m/s in mm/microsec

A

1.54 mm/microsec

106
Q

backing material

A

decreases transducer sensitivity to reflected echoes
improves axial res by decreasing SPL
Decreases Q factor = RF/BW (increases BW)

107
Q

Pulse effect on bandwidth

A

shorter pulses = larger bandwidth

108
Q

velocity of wave formula

A

v=frequency x wavelength

109
Q

primary form of attention in tissue

A

absorption

110
Q

intensity reflection coefficient

A

determined by acoustic impedance
=reflected intensity/ incident intesity
affected by stiffness, density, velocity of two media

111
Q

largest to smallest impedance

A

pzt = matching layer > matching layer > gel > skin

112
Q

q factor for imaging transducer

A

lower number better quality. Imaging transducers have short pulses that contain a broad range of requencies and lead to a low q factor

113
Q

propagation speed artifact

A

assumes us travels exactly at 1540. If it travels too fast or too slow then the structure will be placed at improper depth

114
Q

most transducers have what frequency

A

2-15 MHz

115
Q

range ambiguity

A

results when emission of pulse happens before all previous pulses have been received back.

116
Q

lowest to highest velocity in media

A

air<lung<fat<soft tissue< bone

117
Q

Formulas for pressure , intensity, amplitude, power

A

pressure dB=20 Log p2/p1
Intensity dB= 10 Log I2/I1
Amplitude dB = 20 Log A2/A1
Power dB= 10 Log P2/P1

118
Q

Continuous mode unfocused transducer focus size

A

Focus = transducer diameter / 2

119
Q

Spectral doppler change from LA to mitral leaflet tips

A

peak E increases and decel time shortens (steeper decel)

120
Q

Curie temp changes to crystal

A

causes it to become depolarized and lose piezoelectric properties

Echo Boards (11 decks)

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