Elastography

Elastography is a non-invasive method in which stiffness or strain images of soft tissue are used to detect or classify tumors. A tumor or a suspicious cancerous growth is normally 5-28 times stiffer than the background of normal soft tissue. When a mechanical compression or vibration is applied, the tumor deforms less than the surrounding tissue. i.e. the strain in the tumor is less than the surrounding tissue.

Medical Imaging
Ultrasonic imaging is the most common medical imaging technique for producting elastograms. However, some research has been conducted using MRI (magnetic resonance elastography) and computed tomography.

Transient elastography is used for example to measure the stiffness of the liver in vivo (FibroScan, Echosens, France). It is an alternative noninvasive method to liver biopsy. A correlation between liver elasticity and the fibrosis score (or cirrhosis) has been shown.

Mathematical Description
Pre-compression images are correlated to post-compression images, resulting in regions of large and small change in position. This is called the shift-diagram. The derivative of the shift will produce the strain diagram.