Gallstones

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Nonshadowing stones

• Less than 3 mm may not cast detectable shadow
• Higher frequency can convert nonshadowing stones to shadowing (because sound absorption increases at higher frequency)
• Focal zone should be set at the depth of the zone so it absorbs a greater percentage of the sound beam (as the beam profile is narrowest here)
• Real-time compounding diminishes shadowing

Wall-echo-shadow (WES) complex

• Helps differentiate stone-filled GB from gas-filled bowel
• Three arc-shaped lines followed by a shadow
  • 1st line is echogenic and usually represents pericholecystic fat, the interface between GB wall and liver, and the outer surface of the GB wall
  • 2nd line is hypoechoic and represents muscularis of GB wall
  • 3rd line is echogenic and arises from the stones

Cholesterol stones

• More likely to float to the antedependent surface as they may be less dense than the bile
• [[Vicarious excretion]] of contrast in the GB can increase the specific gravity of bile