Elastography Flashcards
Palpation of tissue has been used for centuries to do what?
To help characterized and diagnose lesions and tissue
Elastography has become a means of palpation though what?
Imaging
Elastography can be viewed to do what?
Perform a virtual biopsy tissue whereby the stiffness of tissue can be related to specific structures and the pathology of such tissue
Elastography evolved from what?
M-mode tissue motion tracking in 1982
What did M-mode tissue motion tracking progress to?
Doppler based tracking in 1987
Doppler based tracking progressed to what?
Static Elastography at University of Texas in 1991
Elastography is a sonographic tool made that can give what?
Both quantitative and qualitative information about the stiffness or hardness of tissue
Elastography can be divided into what applications?
Strain and dynamic applications
What is static application?
Static occurs when the operator repeatedly applies force to the area of interest
The force of static application could also be the result of what?
Breathing or vessel pulsations
Dynamic application is a measurement of what?
Shear waves
Young’s modulus of Elasticity (E) is the ratio of what?
Stress to the strain
What is the formula for Young’s modulus?
With static Elastography, the sonographer physical pushes the transducer and the machine measures what?
The change in the tissues length using doppler strength
With static Elastography, an estimate of tissues stiffness is provided how?
Since softer tissues compress more than harder ones
Why is getting quantitative information impossible to gather with static Elastography?
The amount of stress is unknown
With static Elastography, softer tissues will have high staring values due to what? What about harder tissue?
- The large amounts of deformation and therefore, lower E values
- Harder tissues are the opposite
A technique called “cross correlation” is used to do what?
Evaluate the displacement of tissue with applied force
What does this diagram show?
Cross correlation
With static Elastography, a 2D image of what can be obtained?
2D image of tissue where stiffer/harder tissue appear dark and softer tissue is bright
In terms of stress testing, which colour indicates what with static Elastography?
Blue green colour indicates stiffer/harder tissue and red is softer
Can colour map be changed with static Elastography?
Yes, Just like conventional doppler
What does this image demonstrate?
Colour maps/ Contrast with static Elastography
When performing static Elastography there is typically an indication of what?
The quality of the stress applied
On many machines capable of Elastography, there is something like a bar, pie chart or number displays what?
Quality of the compression
When compression with static Elastography, you want the lesions to do what?
Move up and down
If the lesion is moving sideways with static Elastography, what happens?
The calculations of strain will be inaccurate
Static Elastography is very good for what?
Focal pathology but is limited when the disease process are diffuse
Since static Elastography uses relative stiffness, diffuse diseases do what? Why is this a problem? 2
- Show all the tissue as the same relative stiffness
- With no comparative tissue, you cannot qualify the stiffness
What is the most dominate type of Elastography used?
Dynamic Elastography
How does dynamic Elastography work?
The Introduction of a vibration to the tissue or detecting shear waves
Does dynamic and static work the same, in terms of detection?
The detection of shear waves works differently
With dynamic Elastography, how does it work?
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
What is ARFI used for?
Dynamic Elastography
What does ARFI stand for?
Acoustic radiation force imaging
What does this image demonstrate? 3
- Low scale type of scanning that can be performed by having a patient hum while using power doppler
- Humming causes the tissue to vibrate
- A stiffer/ harder tissue would vibrate less
The shear wave velocity can be used to calculate the stiffness of the tissue using an alternative formula, what its it?
During dynamic elastography, the short intensity pulse initiates what? 2
- The shear waves next to the region of interest (ROI)
- A second and third pulse in the ROI, to detect the shear wave as it travels and calculates its velocity
The stiffness can be expressed in what value?
Sheer wave speed or in kPa as actual numbers and compared to normal values
Shear waves speed travels in a range of what?
0.5-10 m/s
Shear wave speeds move how in comparison to compressional waves?
Much slower and weaker
Wave velocities increase as what increases?
Stiffness
What is the KPa range in soft tissue and fibrotic liver?
1 for fat to 300 for fibrotic liver
A typical liver study requires how many measurements from an intercostal window?
10
For a typical liver study, a depth of how much is best with the probe perpendicular to the capsule and breath held
1.5-3 cm
The interquartile range to median ratio (IQR/M) of the shear velocities should be what?
<30% for kPA measurements
For dynamic Elastography, a colour coded confidence map may be used if what?
If available to improve reliability of results
What are some limitations and considerations when performing elastography? 5
- It’s Best to use an inter costal window
- Depth is limited (about 6 cm due to attenuation)
- Breathing and patient movement
- Ascites, inflammation and fatty infiltration can affect results
- Beware of lesions and vessels
What are some artifacts to be aware of with dynamic elastography? 4
- Reverberation
- ARFI push artifacts
- Vessels
- Not parallel to capsule
What artifact is seen here with dynamic elastography?
Reverberation and can occur from the liver capsule
What does this artifact show?
ARFI push artifacts like attenuation due to body habitus can limit the ability to detect shear waves
With ARFI push artifacts what must we watch out for?
Lung and ribs
What does this image show?
Vessels or bile ducts can have stiffer walls and skew results. Measurements should be taken a minimum of 5mm from vessels
When the sound is not parallel to the liver capsule, what happens with dynamic elastography?
Cause erroneous values
