What does anechoic mean?

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Anechoic means there are no echoes returning from the structure on ultrasound. In grayscale imaging, fluids such as simple cysts appear completely black because the sound waves pass through them with minimal reflection. The interior of an anechoic structure produces no internal echoes, and you often see brighter tissue behind it due to posterior acoustic enhancement, since sound travels with less attenuation through fluid. This term is used to distinguish fluid-filled spaces from tissues that produce echoes (hypoechoic, hyperechoic, etc.).