**2. Principle of elastography imaging**

The two major categories of non-invasive hepatic elasticity imaging are dynamic elastogra‐ phy techniques, such as Fibroscan, and static elastography techniques, such as RTE. At present the dynamic elastography techniques have the advantage of allowing a quantitative imaging and better resolution than the static elastography techniques. These techniques re‐ quire more complex equipment for the generation mode and imaging modalities. Ultra‐ sound and magnetic resonance imaging are the major imaging modalities. The dynamic elastography techniques may be devided into two groups, based on the method of generat‐ ing the shear wave: remote generation using radiation force and mechanical vibration. Of the static elastography techniques, real time tissue elastography developed by Hitachi Medi‐ cal is most advanced ultrasound technique and can reveal tissue distortion using the hart beat and pulsing of the aorta. Several elastography techniques are summarized in Table 1.


**Table 1.** Elastography techniques for measurement of liver stiffness.
