Learning about the echogenicity of tissues began in the 1940s with Dr. George Ludwig and John Wild. Dr. Ludwig worked at the Naval Medical Research Institute, Bethesda, Maryland. He was the first to use the medical application of ultrasound on a person. In 1949, John Wild used ultrasound to measure bowel tissue to see how thick it was.
A transducer---a handheld device that changes one type of energy to another type---generates high frequency sounds (ultrasounds). The transducer sends the ultrasounds to a selected tissue; a pause in sending a signal allows the transducer to receive a signal reflected from the tissue.
The echogenicity of an internal body tissue is not predetermined. To analyze the reflections from the ultrasound, compare them with tissue that has nothing wrong with it.
The amount of echogenicity of a structure or tissue depends upon what it is composed of. Hypoechoic refers to very little reflection of the ultrasound by fluids. The other end of the spectrum is hyperechoic, where bone and gas reflect a large portion of the ultrasound waves.
The ultrasound waves can also be scattered, refracted (a portion of the signal sent in another direction) or absorbed, and any combination of these tissue reactions can occur.
The images produced based upon the echogenicity of tissues are not limited to a one dimensional view. The technology can also produce three dimensional images and show movement, such as blood through vessels.
Placing a substance within the tissue can change its echogenicity.