What characteristic of gallstones can be observed during an ultrasound?

During an ultrasound, gallstones are typically observed as echogenic (bright) lesions within the gallbladder. One of the key characteristics that can be seen is shadowing caused by the density of the stones. This occurs because gallstones are denser than the surrounding bile and gallbladder wall. The ultrasound waves encounter the dense stone, and instead of passing through, they are reflected back, creating a shadow posterior to the stone on the image.

This shadowing phenomenon is crucial for diagnosing gallstones, as it helps distinguish them from other structures and confirms their presence. Additionally, the artifacts created by the shadowing can provide further insight into the size and number of stones present.

In contrast, the other characteristics listed do not typically apply to the ultrasound findings for gallstones. Fluid-filled spaces can indicate other conditions, signs of inflammation might be seen in relation to associated complications but are not direct characteristics of the stones themselves, and changes in stone color are not applicable in ultrasound imaging, which relies on sound waves rather than visible light.