Normally there is no or merely few lipid droplet in parenchyma cells except for fat cells. If there is an increase of lipid droplets, it is called fatty degeneration or fatty change. Density of lipid droplet varies with liver cells at different levels of fatty change. Ultrasound waves will scatter and reflect on the interface of lipid droplet when they are propagated in liver tissues. In liver tissues with denser lipid droplet, ultrasound waves reflect strongly on the propagation path. For this reason, attenuation of sound energy and measured sound attenuation parameter become higher than those tissues with thinner lipid droplet when the travel of ultrasound waves is same. So, the sound attenuation parameter of FibroTouch is directly related to density of lipid droplet in liver tissues and reflects the fatty change level.