Let us have a close look at the comparison between elasticity imaging and measurement in terms of several dierent characteristics including requirements for resolution, computational complexity and parameters. e resolution required for imaging is higher than that for measurement, because the former deals with mapping of the elasticity at each point. e purpose of elasticity mapping is to nd any abnormal lesion embedded in a possibly homogeneous background, so the resolution of imaging should be at least able to discriminate the lesion from its surroundings (Figure 7.1). Regarding the computational complexity, that of imaging is generally higher than of measurement because multiple point measurement is involved in elasticity imaging. Concerning the parameters used, intrinsic material properties are always used in the measurement because their values may be compared

with those of experiments conducted at dierent times, on dierent body parts or in dierent places. erefore, the parameters adopted should not vary with the time and place. Only intrinsic material properties meet these specic requirements. However, when the same instruments and the same test protocols are used, these requirements can be relaxed and non-intrinsic parameters can also be used for relative comparison purposes. For elasticity imaging, both intrinsic and phenomenological parameters can be used because the local contrast is the most important factor in the case of detecting focal lesion in elasticity imaging. For example, strain is not an intrinsic parameter, but strain imaging is broadly adopted in ultrasound elastography to detect hard inclusions because it can clearly show the contrast necessary for diagnosis. In the following section, a brief introduction of dierent elasticity imaging methods and their state-of-the-art development is given.