Lack of an acoustic shadow on scans of gallstones: a possible artifact.

摘要: The high attenuation of gallstones results in the formation an acoustic shadow on ultrasound scan. Such shadows are best seen when stone lies within focal zone transducer and is large comparison to beam width or wavelength employed. Inadequecies dynamic range available TV display units necessitate use compression-amplification signal processing which may preclude perception such a seriously interfere with diagnostic accuracy.