How can gallstones be identified on ultrasound?

Gallstones can be identified on ultrasound primarily as echogenic, shadowing foci within the gallbladder. This is due to the high acoustic reflectivity of the stones, which make them appear bright (echogenic) on the ultrasound image. The term "shadowing" refers to the effect that occurs behind the gallstone where the ultrasound waves are unable to penetrate due to the high density of the stone, creating a dark area or "shadow" behind it. This characteristic is crucial in differentiating gallstones from other structures or conditions within the gallbladder.

The presence of these echogenic spots, along with the shadowing effect, enables radiologists to confidently diagnose gallstones during an abdominal ultrasound. This method of imaging is favored because it is non-invasive and does not involve radiation exposure, making it a safe option for diagnosing gallbladder issues.