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Phys 314 Physics 3 > Elastography > Flashcards

Elastography Flashcards

1
Q

Palpation of tissue has been used for centuries to do what?

A

To help characterized and diagnose lesions and tissue

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2
Q

Elastography has become a means of palpation though what?

A

Imaging

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3
Q

Elastography can be viewed to do what?

A

Perform a virtual biopsy tissue whereby the stiffness of tissue can be related to specific structures and the pathology of such tissue

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4
Q

Elastography evolved from what?

A

M-mode tissue motion tracking in 1982

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5
Q

What did M-mode tissue motion tracking progress to?

A

Doppler based tracking in 1987

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6
Q

Doppler based tracking progressed to what?

A

Static Elastography at University of Texas in 1991

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7
Q

Elastography is a sonographic tool made that can give what?

A

Both quantitative and qualitative information about the stiffness or hardness of tissue

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8
Q

Elastography can be divided into what applications?

A

Strain and dynamic applications

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9
Q

What is static application?

A

Static occurs when the operator repeatedly applies force to the area of interest

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10
Q

The force of static application could also be the result of what?

A

Breathing or vessel pulsations

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11
Q

Dynamic application is a measurement of what?

A

Shear waves

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12
Q

Young’s modulus of Elasticity (E) is the ratio of what?

A

Stress to the strain

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13
Q

What is the formula for Young’s modulus?

A
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14
Q

With static Elastography, the sonographer physical pushes the transducer and the machine measures what?

A

The change in the tissues length using doppler strength

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15
Q

With static Elastography, an estimate of tissues stiffness is provided how?

A

Since softer tissues compress more than harder ones

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16
Q

Why is getting quantitative information impossible to gather with static Elastography?

A

The amount of stress is unknown

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17
Q

With static Elastography, softer tissues will have high staring values due to what? What about harder tissue?

A
  1. The large amounts of deformation and therefore, lower E values
  2. Harder tissues are the opposite
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18
Q

A technique called “cross correlation” is used to do what?

A

Evaluate the displacement of tissue with applied force

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19
Q

What does this diagram show?

A

Cross correlation

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20
Q

With static Elastography, a 2D image of what can be obtained?

A

2D image of tissue where stiffer/harder tissue appear dark and softer tissue is bright

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21
Q

In terms of stress testing, which colour indicates what with static Elastography?

A

Blue green colour indicates stiffer/harder tissue and red is softer

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22
Q

Can colour map be changed with static Elastography?

A

Yes, Just like conventional doppler

23
Q

What does this image demonstrate?

A

Colour maps/ Contrast with static Elastography

24
Q

When performing static Elastography there is typically an indication of what?

A

The quality of the stress applied

25
Q

On many machines capable of Elastography, there is something like a bar, pie chart or number displays what?

A

Quality of the compression

26
Q

When compression with static Elastography, you want the lesions to do what?

A

Move up and down

27
Q

If the lesion is moving sideways with static Elastography, what happens?

A

The calculations of strain will be inaccurate

28
Q

Static Elastography is very good for what?

A

Focal pathology but is limited when the disease process are diffuse

29
Q

Since static Elastography uses relative stiffness, diffuse diseases do what? Why is this a problem? 2

A
  1. Show all the tissue as the same relative stiffness
  2. With no comparative tissue, you cannot qualify the stiffness
30
Q

What is the most dominate type of Elastography used?

A

Dynamic Elastography

31
Q

How does dynamic Elastography work?

A

The Introduction of a vibration to the tissue or detecting shear waves

32
Q

Does dynamic and static work the same, in terms of detection?

A

The detection of shear waves works differently

33
Q

With dynamic Elastography, how does it work?

A

A short intensity pulse of sound is sent out from the transducer, this will cause a shear wave to be produced which will travel perpendicular to the longitudinal wave

34
Q

What is ARFI used for?

A

Dynamic Elastography

35
Q

What does ARFI stand for?

A

Acoustic radiation force imaging

36
Q

What does this image demonstrate? 3

A
  1. Low scale type of scanning that can be performed by having a patient hum while using power doppler
  2. Humming causes the tissue to vibrate
  3. A stiffer/ harder tissue would vibrate less
37
Q

The shear wave velocity can be used to calculate the stiffness of the tissue using an alternative formula, what its it?

38
Q

During dynamic elastography, the short intensity pulse initiates what? 2

A
  1. The shear waves next to the region of interest (ROI)
  2. A second and third pulse in the ROI, to detect the shear wave as it travels and calculates its velocity
39
Q

The stiffness can be expressed in what value?

A

Sheer wave speed or in kPa as actual numbers and compared to normal values

40
Q

Shear waves speed travels in a range of what?

A

0.5-10 m/s

41
Q

Shear wave speeds move how in comparison to compressional waves?

A

Much slower and weaker

42
Q

Wave velocities increase as what increases?

43
Q

What is the KPa range in soft tissue and fibrotic liver?

A

1 for fat to 300 for fibrotic liver

44
Q

A typical liver study requires how many measurements from an intercostal window?

45
Q

For a typical liver study, a depth of how much is best with the probe perpendicular to the capsule and breath held

46
Q

The interquartile range to median ratio (IQR/M) of the shear velocities should be what?

A

<30% for kPA measurements

47
Q

For dynamic Elastography, a colour coded confidence map may be used if what?

A

If available to improve reliability of results

48
Q

What are some limitations and considerations when performing elastography? 5

A
  1. It’s Best to use an inter costal window
  2. Depth is limited (about 6 cm due to attenuation)
  3. Breathing and patient movement
  4. Ascites, inflammation and fatty infiltration can affect results
  5. Beware of lesions and vessels
49
Q

What are some artifacts to be aware of with dynamic elastography? 4

A
  1. Reverberation
  2. ARFI push artifacts
  3. Vessels
  4. Not parallel to capsule
50
Q

What artifact is seen here with dynamic elastography?

A

Reverberation and can occur from the liver capsule

51
Q

What does this artifact show?

A

ARFI push artifacts like attenuation due to body habitus can limit the ability to detect shear waves

52
Q

With ARFI push artifacts what must we watch out for?

A

Lung and ribs

53
Q

What does this image show?

A

Vessels or bile ducts can have stiffer walls and skew results. Measurements should be taken a minimum of 5mm from vessels

54
Q

When the sound is not parallel to the liver capsule, what happens with dynamic elastography?

A

Cause erroneous values

Phys 314 Physics 3 (11 decks)

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