Non-invasive method of exploration through materials or substances that allow the passage of sound waves, and that by the rebounds of the echo allow to find and trace the location of elements that have a different density. It consists of the Greek voices 951; 967; 969; ( echoed " ) 947; 961; 945; 966; 949; 953; 957; ( grafein "write, draw") . See ecoic, hyperechoic, ecolucent, hypoechoic, ecogenic, echodense, prefix eco- and suffix-grafía.