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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
nyquist limit
same as max doppler shift = 1/2 PRF
26
reduce aliasing
lower transmitted frequency decrease depth of gates (increase PRF) shift baseline use continuous wave Increase PRF (NL=1/2PRF)
27
color flow doppler
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
28
cos of 30 , 45, 60, 90
0 =1 30=sqrt(3)/2 45=sqrt(2)/2 60=sqrt(1)/2 90 = 0
29
high pass wall filter
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
30
low pass wall filter
filters out high velocities/frequencies used for Tissue doppler allows low velocity , high amplitude signals
31
Reject filter
used in 2d imaging, filters low amplitude signals indicative of 'noise'
32
5 functions of receiver
amplification compensation compression demodulation rejection (AKA suppression, threshold)
33
Power Doppler
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
34
parameters determined by ultrasound source and medium
anything with length like wavelength
35
parameters determined by sound source only
Anything with time units (seconds) and strength
36
Only parameter determined by medium
velocity
37
Parameters determining velocity
Increased stiffness and decreased density
38
PWD changes to peak E and decel time from atria into ventricle
Peak E increases as it goes through valve into ventricle E wave decel time decreases as it goes into ventricle through valve
39
wave between E and A wave on MV inflow
L wave - indicates impaired relaxation and elevated LAP
40
simplified bernoulli for pressure gradient
= 4v^2
41
what percentage of peak velocity is the velocity at which pressure half time occurs
71%
42
Pressure half time definition
time it takes to go from max pressure gradient to half max pressure gradient
43
Lesions for PHT, utility and limitations
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
44
AI effect on mitral PHT
decreases pressure half time causing underestimation of MS
45
lv compliance effect on PHT
stiffer ventricle shortens PHT and underestimates MS
46
Impaired relaxation on PHT
increases PHT, overestimates MS
47
AI PHT cutoff
>500 ms mild 200-500 ms moderate (slope>2m/s? <200 ms severe (slope >3 m/s)
48
Uses for tissue doppler
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
49
what is post systolic shortening
seen in ischemia on TDI velocities occurring during isovolumic relaxation time
50
What is annular reversus
seen in constrictive pericarditis when lateral e' < septal e'
51
Limitations of tissue doppler
angle dependent (should be <20) average over 3 cycles to reduce error MAC / MV tethering
52
myocardial performance index
= IVCT + IVRT / ET usually less than 0.39 measure of both systolic and diastolic function DIlated CM usually >0.59
53
a' and e'/a' values
a' <10 good e'/a' <1 bad
54
isovolumic acceleration (IVA)
max isovolumic velocity/ IVCT and is used for systolic function Usually 1-2 m/s2 normal
55
Te'
time for onset of e' wave. prolonged in diastolic dysfunction
56
TE
Time from R on QRS to E inflow Te'-TE is prolonged with diastolic dysfunction
57
TDI for ischemia
S' decreases, e'/a' <1 PSS, e' decrease, prolong Q to peak s'
58
TDI in CP and tamponade vs RICM
Normal in both, annular reversus in CP decreased in RICM
59
Best view for RV TDI
transgastric RV I/O or RV inflow RVs' less than 10 is abnormal in young healthy person
60
tricuspid closure opening time (TCO)
Same as IVCT + ET + IVRT and used to get RV MPI MPI above 0.5 is predictave of instability and mortality
61
Tissue doppler for strain
Strain and strain rate can be calculated (V2-V1)/distance between the two = strain rate
62
Determinants of frame rate
line density # pulses per line image depth sector width
63
amplitude
Difference between avg value and max value of an acoustic variable. POwer and intensity are proportional to amplitude squared
64
power
rate at which work is performed or energy is transferred measured in watts or j/sec
65
intensity
power/area determines bioeffects
66
mechanisms of bioeffects
thermal- limit to max of 1C rise in local tissue temp cavitation vibration
67
max SPTA for focused and unfocused beam
unfocused <1W/cm2 focused<100 mW/cm2
68
What causes most heating of all US modes
PWD
69
mechanical index
measure of US to produce cavitation
70
harmonic frequencies
caused by shrinking and expanding of bubbles allows for better imaging of areas that werent imaged well before arise from non linear behavior
71
Mechanical index depends on frequency and pressure
Increases with lower frequency and stronger pressure
72
Mechanical index
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
Harmonics
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
Resonance
uneven shrinking and expanding of microbubbles
75
Time- wave properties
period frequency pulse duration PRP PRF- higher frame rate and better temporal resolution Determined by the sound source
76
wave properties determined by medium
velocity. Increased with increased stiffness and decreased density sound travels faster in dense materials because of its stiffness not density Impedance
77
attenuation
increases with increasing depth and increasing frequency over 80% of attenuation is from absorption in tissues
78
Impedance
resistance to sound traveling through medium Z = density (p) x velocity (v) pzt > matching layer > gel > mucosa
79
incident intensity
= reflected + transmitted intensity
80
Curie temp
temp that can change crystal to no longer produce ultrasound waves
81
damping material
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
Frequency determination for PWD
V/2T
83
frequency determination for CWD
electrical frequency of voltage applied to crystal
84
q factor
ability of trasnducer to emit a clean pulse with narrow bandwidth damping decreases q factor
85
matching layer
layer between crystal and skin/tissue
86
anatomy of a sound beam
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
focusing ultrasound
lens curved crystal focusing mirror electronic (used by TEE)
88
range resolution
describes axial resolution but also describes object at specific depth as with PWD
89
ultrasound system
master synch pulser transducer receiver and processor storage
90
functions of receiver
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
artifacts
due to US assumptions (sound travels in straight line, reflections are along main axis, intensity of reflection corresponds to reflectors scattering strenth)
92
reverberation
rungs on ladder or blurred comet tail / ringdown
93
refraction artifact
assumes that us travels in straight line. Places object that is off to side in straight line and deeper
94
side and grating lobes
assumes us only travels in main axis. Strong reflectors in side lobe path will place it in main axis
95
acoustic shadowing/echo dropout
strong reflectors that do not allow penetration of US beam
96
mirror artifact
similar to reflection artifact pericardium can act as strong reflector
97
raleigh scattering
occurs when the reflectors dimensions are much smaller than the wavelength of the US sound wave equally redirected in all directions
98
backscatter
AKA diffuse reflection in which the object has irregular surface and allows for imaging at suboptimal angle, but its weak.
99
snells law
determines refraction sin transmission / sin incidence = v2/v1 if velocity transmitted is less then angle is smaller than incident angle
100
refraction
requires angle that is not 90 requires v2 does not equal v1
101
oblique reflection
reflection angle the same as incident angle when it does occur
102
shallow focal length
high density, low impedance, thickest crystal, lowest diameter
103
temporal resolution depends on 2 things
how much the object moves the frame rate which depends on several things
104
frame rate depends on several factors
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
1540 m/s in mm/microsec
1.54 mm/microsec
106
backing material
decreases transducer sensitivity to reflected echoes improves axial res by decreasing SPL Decreases Q factor = RF/BW (increases BW)
107
Pulse effect on bandwidth
shorter pulses = larger bandwidth
108
velocity of wave formula
v=frequency x wavelength
109
primary form of attention in tissue
absorption
110
intensity reflection coefficient
determined by acoustic impedance =reflected intensity/ incident intesity affected by stiffness, density, velocity of two media
111
largest to smallest impedance
pzt = matching layer > matching layer > gel > skin
112
q factor for imaging transducer
lower number better quality. Imaging transducers have short pulses that contain a broad range of requencies and lead to a low q factor
113
propagation speed artifact
assumes us travels exactly at 1540. If it travels too fast or too slow then the structure will be placed at improper depth
114
most transducers have what frequency
2-15 MHz
115
range ambiguity
results when emission of pulse happens before all previous pulses have been received back.
116
lowest to highest velocity in media
air
117
Formulas for pressure , intensity, amplitude, power
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
Continuous mode unfocused transducer focus size
Focus = transducer diameter / 2
119
Spectral doppler change from LA to mitral leaflet tips
peak E increases and decel time shortens (steeper decel)
120
Curie temp changes to crystal
causes it to become depolarized and lose piezoelectric properties

Echo Boards (11 decks)

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