Elastography Flashcards
What does elastography measure?
Stiffness of the liver
What is used to measure the stiffness of a material?
(hint: the units)
Youngs Modulus in kPa
What unit is Young’s modulus measured in?
kPa
What is true of materials with a SMALL young’s modulus?
Softer material and a larger strain as it can compress more easily
What is true of materials with a LARGE young’s modulus?
Stiffer material and a small strain as it cannot compress very easily
What type of ultrasound technology is used for shear wave imaging?
Elastography
In shear wave imaging, how is the stiffness of liver quantified?
It is measured in kPa and a HIGHER score indicates a greater stiffness
What is the range in kPa for soft tissue?
1-300 kPa
What is the value in kPa for fat vs. fibrotic liver?
Fat = 1
Fibrotic liver = 300
What is the formula for Young’s modulus?
Force/strain
What is the ratio of the applied stress to the resulting strain a result of?
A stress that either compresses or stretches tissue - measured with Young’s modulus
Elastography provides an imaging means of?
Palpation
What method in elastography involves initiating a MANUAL force to the tissue?
STATIC
In using what method can Young’s modulus not be quantified and only uses qualitative information?
Static method
Applications of static elastography?
- Cancer detection of small parts (breast, thyroid, prostate)
- Myocardium viability
- Monitoring of therapies that alter tissue composition such as ablation
Dynamic methods use what kind of force?
Short transient force or time-varying repetitive force
What force is INITIALLY produced in a dynamic method?
Compressional strain
What is another term for compressional strain?
Transient or oscillatory
Does compressional strain travel at a high or low propagation speed? What is the speed?
High: 1440-1640 m/s
Through what kind of force is a compressional strain converted to shear waves?
Radiation force
Do shear waves travel at a high or low propagation speed? What is the speed?
Low: 0.5-10 m/s
In what direction do shear waves propagate in tissue during shear wave elastography?
Perpendicular to the direction of tissue compression
How can shear displacements of propagating shear waves be tracked?
Ultrafast by using high frame rates to determine their propagation speed
What does ARFI stand for?
Acoustic Radiation Force Impulse Imaging
What is the function of ARFI?
Determining propagation speed of tissue to determine the stiffness
How do we determine propagation speeds in shear wave imaging?
Using high frame rates
What units is shear wave reported in?
m/s
What kind of method is used to determine quantitative information?
Dynamic
Where do we scan for shear wave?
Intercostally
What segments of the liver are shear wave measurements taken from?
7 or 8
Take elastography measurements using what kind of breath on a patient?
Suspended breath hold
Where should the shear wave box be located?
1-2 cm below liver capsule
T or F? We should always increase the gain in shear wave imaging
FALSE: Do not attempt to increase the gain as it will likely lead to an inaccurate measurement
To have a good shear wave measurement, how much colour must be filled in?
> 50%
F1 Normal to mild fibrosis staging in kPa?
5.48-8.29
F2 mild to moderate fibrosis staging in kPa?
8.29-9.4
F3 moderate to severe fibrosis staging in kPa?
9.4-11.9
F4 Cirrhosis
> 11.9
What position is the patient usually in during elastrography?
Supine or LLD with R arm above head
What method uses both qualitative and quantitative assessment of liver stiffness?
Dynamic - no force applied
T or F? Radiation force is most intense at the focal zone?
TRUE
Radiation force is a result of a change in wave?
Momentum due to scattering at an obstacle
What is measured to equal radiation force?
Rate of momentum change, averaged over the period of the wave
