How does fluid appear on an ultrasound image?

Fluid appears on an ultrasound image as an anechoic (dark) area due to its properties and the way ultrasound waves interact with fluids. Anechoic means that the substance does not produce echoes that contribute to the ultrasound image, resulting in very low echogenicity. This is because fluid, such as blood or other bodily fluids, allows most of the ultrasound sound waves to pass through without reflecting them back to the transducer. The absence of significant echoes from the fluid leads to a darker appearance on the ultrasound image.

In contrast, different tissue types such as fat, muscle, or solid organs produce varying levels of echoes, leading to brighter or more echogenic areas on the image. Understanding this differentiation is important for interpreting ultrasound findings accurately.