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Echocardiography > Echo Principles > Flashcards

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
Q

PRF:
definition
example
clinical implication

A

Number of pulsed transmitted / sec
Limited by time needed to reach and return

Max velocity measure able with pulsed Doppler is1m/ sec@ 6cm depth

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25
Q

Nyquist Limit

A

Max freq shift measurable with pulsed Doppler
= PRF/2
The greater the depth, the Lower max velocity measurable

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26
Q

Velocity error

20 deg vs 60 deg

A

20 deg 6%

60 deg 50%

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27
Q

Ultrasound exposure

A

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

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28
Q

Contrast bubbles

A

About size of rbc

2-8 micron rbc 6-8 micron

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29
Q

Bubble behavior

Mi low, mid, high

A

Low- linear
Mid nonlinear back scatter
Disruptive - transient harmonic

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30
Q

Contrast echo apical dropout

A

Correct by decreasing MI

Focal misplacent

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31
Q

Contrast swirling

A

MI too high

Low volume contrast

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32
Q

Artifact types:

A

Distant: parallel : reverberation
Opposite motion : mirror image
Same distance: beam width, side lobe, refraction

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33
Q

Dissection v artifact

A

Independent motion
Attached
Flow divider

34
Q

4 chamber to 5 chamber

A

Transducer anterior

35
Q

Ohm law

A

P=Q x R

Laplace wall p x r / m

36
Q

RV measurements abl

A 
Basal > 4.2
Mid > 3.5
Rv long > 8.6
Rv place prox > 3.3
Rvot psax > 2.
37
Q

Qualitative RV size

A

No < 2/3 LV

38
Q

Pulmonary embolism

Echo Sens

A 
30-40%
Rv size incr, Rv ef depresses
New tr
Rv thrombus 
McConnell sign
39
Q

RA pressure est

A

3,8,15

0-5, 5-10,> 15

40
Q

TAPSE

Volume vs pressure

A

Increase with vol overload

Decrease with pressure overload

41
Q

IVC

A

0-5 if < 2.1 collapse > 50%

10-20 if > 2.1 with < 50 % collapse

42
Q

Flying W

A

Severe pul htn

No a wave

43
Q

RVOT accel time

A

Nl > 120 msec
Mean pap = 79-0.45 x accel time
< 90 msec then peak > 60 mmhg

44
Q

LVEDD

A

Measure LV axis at tip MV leaflet

45
Q

Relative wall thickness

A

2 x pwt/ lvedd

46
Q

Concentric hypertrophy:
Eccentric
Concentric remodeling

A

Conc increased mass, increase RWT
Eccentric - increased mass, decreased RWT

Conc remodeling- nil mass, increased RWT

47
Q

Echo lvsv error

A

Underestimates - don’t include trabeculations

48
Q 
EF:
Nl
Mild
Mod
Severe
A

> 55%
Mild:45-54%
Moderate: 31-44%
Severe: <30%

49
Q

LA volume

A

4 chamber area x length
2 chamber area x length

0.85 x A1 x A2/ L (shorter of two lengths)

50
Q

LA size

A

Mild 29-33
Mod 34-39
Severe> 40

51
Q

TGC

A

Evens brightness

Suppresses strong near field, boots weak farfield

52
Q

Decrease frequency

A

Increases depth

Decreases resolution

53
Q

McConnell sign

A

Rv dilated
Apex hyperdynamic
Mid RV akinetic

54
Q

Prosthetic MV mismatch

A

Eoa mild < 1.2cm/m2

Severe < 0.9 cm/ m2

55
Q

Follow up echo prosthetic valves

A

2-4 yrs after replacement
Bio prosthetic 5 yr
Mech - no routine check

56
Q

Pseudodyskinesis

A

Inferior

Diastolic flattening - associated ascites, diaphragm

57
Q

HCM dimension

A

15 mm LV wall

13-14 mm borderline

58
Q

Mid sys knotch

A

m mode with SAM vs early closure with membrane

59
Q

HCM gradient

A

Peak instantaneous gradient
Sig if > 30 mmhg
Intervention if > 50

60
Q

Pseudo SAM

A

SAM after posterior wall contraction

61
Q

Cyclic pressure changes for sound

A

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
Q

How to resolve aliasing in HCM with pulse wave in llvot?

A
  1. Continuous wave
  2. Increase prf scale
  3. Switch to high prf
  4. Use lower freq transducer
  5. Adjust baseline
63
Q

Def of ultrasound period

A

Time to complete one cycle

0.06. - 0.05 micro seconds 10 to -6

64
Q

Ultrasound beam that is narrowist in far field?

Crystal size and freq

A

Larger crystals diverge less in far fields

Higher frequency diverges less in far fields

65
Q

PRF of 15 KHz - what is max shift?

A

Nyquist Is prf/2 so 7.5

66
Q

Variance map vs velocity map

A

Variance - adds green to depict turbulence

67
Q

Artifact in gray scale 2 d- step to disprove

A

Change depth setting -range artifact

Color flow nest step

68
Q

Refraction artifact

A

Misplacent of object in image due to change in direction At non perpendicular boundaries with different impedance

69
Q

Artifact : hyper intense signal behind a low attenuating structure as I fluid filled

A

Enhancement :

70
Q

Artifact resulting in placement of echo genic lines equally space in fluid filled structure?

A

Reverberation
From multiple echos created by two structures close to each other- reflection of us between structures before next pulse generated

71
Q

Ghost images off axis

A

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
Q

Best lateral resolution

A

lateral resolution best where beam narrowest

73
Q

..?Wavelength of sound in soft tissue from 3 MHz transducer

A

Speed 1540 m/ sec

1.54/ 3. = 0.51 mm

74
Q

Duty factor

A

% of time echo machine actually transmitting pulse
Most of time spent listening
0.2% time transmitting and 99.8% listening

75
Q

If pulse duration is 1 microsec and prf 1 ms, what is duty factor ?

A

Pulse duration / prf x 100

0.0000001 / 0.001 (x100%)= 0.1%

76
Q

What is maximum duty factor?

A

100%

77
Q

Reverberation

A

Multiple echos created between 2 close structures - lines equally spaced from reflection of energy between before next pulse generated

78
Q

Accuracy

A

True positive + true neg/

All tests

79
Q

Harmonic imaging probs

A

Makes MV look thicker

80
Q

ROA from PISA

A

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
Q

Vegetaions

A

Upstream side of valve
Abnl irregular mass
Chaotic motion

82
Q

Near length zone

A

NLZ = diam sq x f /4 wavelength

83
Q

Truncus arteriosis av types

A

Tri and quadra cusp

Echocardiography (14 decks)

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