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Echo Principles Flashcards

0
Q

Ultrasound interaction with tissues (4 types)

A

Reflection: creates ultrasound images
Scattering: basis of Doppler ultrasound
Refraction: used to focus us waves
Attenuation: loss of signal strength in tissues

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1
Q

Ultrasound descriptors (4 characteristics)

A

Frequency : cycles per sec= Hz, 1000 cycles/sec = 1 MHz
Propagation velocity: 1540 m/sec in blood
Wavelength: propagation velocity/frequency
Amplitude: decibels or dB

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2
Q

Tissue penetration and frequency

A

Greatest with lower frequency transducer (2-3 MHz)

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3
Q

Frequency and resolution

A

Greatest (about 1 mm) with higher frequency transducer (5-7.5 MHz)

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4
Q

6 dB change

A

Amplitude logarithmic : 6 dB change doubling or halving of signal amplitude

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5
Q

Acoustic impedance factors (2)

A

Tissue density

Propagation velocity

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6
Q

Ultrasound reflection factors (3)

A

Greatest with smooth tissue boundaries with different impedences and perpendicular to tissue interface

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7
Q

Scattering best characteristics

A

Doppler occurring with small structures scatters generating Doppler signals- velocities best when parallel to flow

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8
Q

Frequency:
Definition
Example
Clinical implication

A

Number of cycles per second in wave
Eg: transducer frequencies MHz 1,000,000c/sec
Doppler KHz 1,000 cycle/sec
Clinical implication: different transducer freq for specific application- affects tissue penetration, image res and Doppler signal

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9
Q

Velocity of propagation:
Definition
Example
Clinical implication

A

Ultrasound speed thru tissue
Average velocity in soft tissue about 1540m/sec
Velocity similar in soft tissue myocardium,liver,fat, but lower in lung and much higher in bone

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10
Q

Wavelength:
Definition
Example
Clinical implication

A 
Distance between ultrasound waves
Wavelength =prop vel/ freq
Ex: shorter with higher freq and longer with lower freq
Resolution best with shorter wavelength 
Depth is greatest with lover wavelength
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11
Q

Amplitude:
Definition
Examples
Clinical implication

A

Height of ultrasound wave or loudness dB
Log scale: 80 dB 10,000 fold and 40dB 100 fold increase
Wide range of amplitude can be displayed using greyscale for imaging and spectral Doppler

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12
Q

Acoustic impedence:
Definition
Examples
Clinical implication

A

Tissue specific defined by density (p) and prop velocity (c) z = p x c
Eg: lung low density, slow prop velocity, bone high density fast prop velocity
US reflected by boundaries of acoustic impedence- blood vs myocardium

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13
Q

Reflection:
Definition
Examples
Clinical implication

A

Return of ultrasound signal to transducer from smooth tissue boundary
Reflection used for 2D images
Greatest when perpendicular to surface

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14
Q

Scattering:
Definition
Example
Clinical implication

A

Radiation of ultrasound in multiple directions from small structures such blood cells
Eg: change in freq of signals scattered from moving blood cells basis for Doppler ultrasound
Clinical implication : amplitude is 100-1000 less than reflected

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15
Q

Refraction:
Definition
Example
Clinical implication

A

Deflection of ultrasound waves from straight path due to different acoustic impedence
Eg: used in transducer design to focus us beam
Causes double image artifacts

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16
Q

Attenuation:
Definition
Examples
Clinical implication

A

Loss in signal strength due to absorption of ultrasound energy by tissues
Higher frequencies have more attenuation (less penetration)
Lower freq transducer needed for apical views in larger patients

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17
Q

Resolution:
Definition
Examples
Clinical implication

A

The smallest resolvable distance between two specular reflectors on ultrasound image
Resolution has 3 dimensions:
1. Along length of beam (axial) 2. Lateral across the image (azimuthal) 3. Elevation plane
Eg: axial most precise, therefore measurements best along length of beam

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18
Q

Bandwidth

A

Transducer design

Wider gives better axial resolution

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19
Q

Pulse length

A

Burst length
Higher freq signal can be transmitted in short pulse length
Short pulse length improves axial resolution

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20
Q

Pulse rep freq

A

Number of transmission-receive /sec
PRF decreases with depth due to time needed for sig to get to transducer
Affects resolution and frame rate

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21
Q

M mode sample time

A

1800/sec

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22
Q

Doppler modalities

A

Pulsed: sample velocities timed for depth- limited velocities
Color flow imaging:
Continuous wave: can measure high velocities- cannot localize depth

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23
Q

Doppler effect:
definition
example
clinical implication

A

Freq change of ultrasound scattered from moving target
V=c x delta F/ 2F (cos theta)
Shift from 1 - 20 kHz
Assumes theta cos = 1

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24
PRF: definition example clinical implication
Number of pulsed transmitted / sec Limited by time needed to reach and return Max velocity measure able with pulsed Doppler is1m/ sec@ 6cm depth
25
Nyquist Limit
Max freq shift measurable with pulsed Doppler = PRF/2 The greater the depth, the Lower max velocity measurable
26
Velocity error | 20 deg vs 60 deg
20 deg 6% | 60 deg 50%
27
Ultrasound exposure
Thermal index: ratio of transmitted power to power needed to increase temp 1 deg C Mechanical index: Ratio of peak rarefaction pressure to square root of transducer frequency
28
Contrast bubbles
About size of rbc | 2-8 micron rbc 6-8 micron
29
Bubble behavior | Mi low, mid, high
Low- linear Mid nonlinear back scatter Disruptive - transient harmonic
30
Contrast echo apical dropout
Correct by decreasing MI | Focal misplacent
31
Contrast swirling
MI too high | Low volume contrast
32
Artifact types:
Distant: parallel : reverberation Opposite motion : mirror image Same distance: beam width, side lobe, refraction
33
Dissection v artifact
Independent motion Attached Flow divider
34
4 chamber to 5 chamber
Transducer anterior
35
Ohm law
P=Q x R | Laplace wall p x r / m
36
RV measurements abl
``` Basal > 4.2 Mid > 3.5 Rv long > 8.6 Rv place prox > 3.3 Rvot psax > 2. ```
37
Qualitative RV size
No < 2/3 LV
38
Pulmonary embolism | Echo Sens
``` 30-40% Rv size incr, Rv ef depresses New tr Rv thrombus McConnell sign ```
39
RA pressure est
3,8,15 | 0-5, 5-10,> 15
40
TAPSE | Volume vs pressure
Increase with vol overload | Decrease with pressure overload
41
IVC
0-5 if < 2.1 collapse > 50% | 10-20 if > 2.1 with < 50 % collapse
42
Flying W
Severe pul htn | No a wave
43
RVOT accel time
Nl > 120 msec Mean pap = 79-0.45 x accel time < 90 msec then peak > 60 mmhg
44
LVEDD
Measure LV axis at tip MV leaflet
45
Relative wall thickness
2 x pwt/ lvedd
46
Concentric hypertrophy: Eccentric Concentric remodeling
Conc increased mass, increase RWT Eccentric - increased mass, decreased RWT Conc remodeling- nil mass, increased RWT
47
Echo lvsv error
Underestimates - don't include trabeculations
48
``` EF: Nl Mild Mod Severe ```
>55% Mild:45-54% Moderate: 31-44% Severe: <30%
49
LA volume
4 chamber area x length 2 chamber area x length 0.85 x A1 x A2/ L (shorter of two lengths)
50
LA size
Mild 29-33 Mod 34-39 Severe> 40
51
TGC
Evens brightness | Suppresses strong near field, boots weak farfield
52
Decrease frequency
Increases depth | Decreases resolution
53
McConnell sign
Rv dilated Apex hyperdynamic Mid RV akinetic
54
Prosthetic MV mismatch
Eoa mild < 1.2cm/m2 | Severe < 0.9 cm/ m2
55
Follow up echo prosthetic valves
2-4 yrs after replacement Bio prosthetic 5 yr Mech - no routine check
56
Pseudodyskinesis
Inferior | Diastolic flattening - associated ascites, diaphragm
57
HCM dimension
15 mm LV wall | 13-14 mm borderline
58
Mid sys knotch
m mode with SAM vs early closure with membrane
59
HCM gradient
Peak instantaneous gradient Sig if > 30 mmhg Intervention if > 50
60
Pseudo SAM
SAM after posterior wall contraction
61
Cyclic pressure changes for sound
Rarefaction and compressions In longitudinal wave particles move parellel to direction of wave Perpendicular to direction is how articles move in transverse wave Crest and trough describes transverse wave-sound waves are longitudinal
62
How to resolve aliasing in HCM with pulse wave in llvot?
1. Continuous wave 2. Increase prf scale 3. Switch to high prf 4. Use lower freq transducer 5. Adjust baseline
63
Def of ultrasound period
Time to complete one cycle | 0.06. - 0.05 micro seconds 10 to -6
64
Ultrasound beam that is narrowist in far field? | Crystal size and freq
Larger crystals diverge less in far fields | Higher frequency diverges less in far fields
65
PRF of 15 KHz - what is max shift?
Nyquist Is prf/2 so 7.5
66
Variance map vs velocity map
Variance - adds green to depict turbulence
67
Artifact in gray scale 2 d- step to disprove
Change depth setting -range artifact | Color flow nest step
68
Refraction artifact
Misplacent of object in image due to change in direction At non perpendicular boundaries with different impedance
69
Artifact : hyper intense signal behind a low attenuating structure as I fluid filled
Enhancement :
70
Artifact resulting in placement of echo genic lines equally space in fluid filled structure?
Reverberation From multiple echos created by two structures close to each other- reflection of us between structures before next pulse generated
71
Ghost images off axis
Grating lobe artifact Dues to division of small transducer face into large number of small elements- the small elements produce us energy at high singles compared to main beam
72
Best lateral resolution
lateral resolution best where beam narrowest
73
..?Wavelength of sound in soft tissue from 3 MHz transducer
Speed 1540 m/ sec | 1.54/ 3. = 0.51 mm
74
Duty factor
% of time echo machine actually transmitting pulse Most of time spent listening 0.2% time transmitting and 99.8% listening
75
If pulse duration is 1 microsec and prf 1 ms, what is duty factor ?
Pulse duration / prf x 100 | 0.0000001 / 0.001 (x100%)= 0.1%
76
What is maximum duty factor?
100%
77
Reverberation
Multiple echos created between 2 close structures - lines equally spaced from reflection of energy between before next pulse generated
78
Accuracy
True positive + true neg/ | All tests
79
Harmonic imaging probs
Makes MV look thicker
80
ROA from PISA
Pisa = 2 x 3.14 x rsq Pisa x vel alias = roa x vel MR Rv = roa x VTI SV = 3.14 x r sq x VTI
81
Vegetaions
Upstream side of valve Abnl irregular mass Chaotic motion
82
Near length zone
NLZ = diam sq x f /4 wavelength
83
Truncus arteriosis av types
Tri and quadra cusp

Echocardiography (14 decks)

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