Wednesday, November 5, 2008

Elasticity Imaging

To all,

There have been several questions about elasticity imaging and the advantages of strain versus stress imaging. I have asked Jae to share his insights and thoughts on the concepts behind Elasticity Imaging.

Many thanks to Jae.

Denis


ELASTICITY IMAGING

Elasticity Imaging has been gaining some attention in the field of Breast Cancer beyond the research community due to positive clinical results1. The reason behind the success of elasticity imaging is due to the fact that the elasticities of cancerous lesions are hundreds of times greater than other breast tissue2. This phenomenon has been used by clinicians for thousands of years with their sense of touch to diagnose breast cancer (click on image to enlarge).

Wellman PS, PhD Thesis - Tactile Imaging - Harvard University 1999

Here is a simplified technical definition of elasticity. When you take any object and apply enough force to it, it will compress as shown by the diagrams below (click on image to enlarge).

Stress is defined as the amount of force applied over a given area and Strain is defined as the amount of change in length divided by the original length.

Modulus of elasticity or Young's modulus, E, is the ratio of stress, to strain and can be calculated by dividing the stress by the strain: (click on image to enlarge).

where

E is the Young's modulus (modulus of elasticity)

F is the force applied to the object;

A0 is the original cross-sectional area through which the force is applied;

ΔL is the amount by which the length of the object changes;

L0 is the original length of the object.


Siemens and Hitachi have commercialized strain imaging on their high end ultrasound machines for $150,000. There are two approaches. One method is for the operator to compress the tissue and the software looks at the compressed and uncompressed images to determine the amount of strain (or compression of tissue) associated with that cross section. Another method uses very brief high energy pulses from the MRI or ultrasound that virtually push the tissue rather than relying on the operator to compress the tissue.

The other component of elasticity is Stress. SureTouch measures the reactive pressures generated by the lesion in the same manner that clinicians have done for thousands of years, that is by stressing the tissue. By using hundreds of individual sensors, a stress image of the lesion can be generated as shown in the figure on the left (click on image to enlarge).


Is one method superior to the other? Not really, they are two components of elasticity used to determine the same result – the stiffness of tissue. When asked about the effectiveness difference between strain and stress imaging, expert scientist in this field, Armen Sarvazyan stated, “There is no dramatic difference between this machine ( ultrasound device) and SureTouch regarding the inclusion imaging efficacy. The major difference is the price: the machine costs $150k.”


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18 comments:

  1. Hi Denis and Aristotle

    Great overview and useful - thank you!

    Troels

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