Echogenicity describes how bright or dark a structure appears on a B-Mode ultrasound image. Tissues that reflect many echoes back to the transducer appear bright (hyperechoic), while tissues that reflect few echoes appear dark (hypoechoic). Structures with no internal echoes — such as fluid-filled cysts — appear black (anechoic). Echogenicity is always described relative to a reference tissue; for example, a liver lesion may be described as hyperechoic relative to the surrounding liver parenchyma.