Elastography Imaging Changes The Mechanical Properties Of Tissue

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CHAPTER 1 INTRODUCTION
In olden days, palpation was the basis of diagnosis for various diseases as it was known that some diseases change the mechanical properties of the tissues. This change results in increase in stiffness or elastic modulus of the tissue. Hence this phenomenon is the basis of Elastography imaging which depends on the mechanical properties of the tissue [1, 2].
There are three types of elastic modulus namely
1. Young’s Modulus denoted by E - It is the tendency of the object to deform along the axis when the opposing forces are applying along that axis. It characterises the stiffness of the tissue.
2. The shear Modulus denoted by G - It is the ratio of transverse or shear strain to transverse stress and it is related to shear
…show more content…
In strain imaging, ultrasound is used to image the response of the tissue to an externally applied force (stress). The tissue response is in the form of displacement and can indicate the stiffness of the tissue. There are certain limitations for this method, one of the most important limitations and sources of inconsistency in literature, is the dependency of strain images on the amount of force applied to tissue by the sonographer. If sonographers use different force to compress the tissue, the tissue have different response since the strain-stress behaviour of the tissue is linear only within a certain range of compressions. Therefore, it is very important to have a precise control on the amount of compression force (and consequently the strain) of the tissue to achieve reliable strain Elastography images. Recently, it is shown that the temporal profile of the compression force (stress) can also affect the measurements and in fact by controlling the temporal profile of the force, it is possible to extract more accurate information about the viscoelastic properties of the tissue. Researchers have recently demonstrated that the combination of strain and ARF Elastography can reveal nonlinear elasticity parameters of the tissue that could better help characterization of soft tissues. Previous studies using mechanical tests showed that nonlinear response …show more content…
sonographers). Ideally, such measurements have to be done when the probe is levelled (i.e. same pressure to both ends of the linear array transducer) and a minimum compression force is being applied to the patient body. However, often in practice these conditions are not satisfied and therefore the measurements of tissue elasticity are biased and even inconsistent from one measurement to another measurement. Therefore, there is a need for a force-controlled device that can assure the balanced alignment of the ultrasound probe on patient body as well as minimizing the applied compression

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