In vitro sonographic evaluation of common bile duct stones and fragments with a high-frequency microprobe

This study was conducted to evaluate the sonographic characteristics of common bile duct (CBD) stones and stone fragments scanned in vitro with a high-frequency (20-MHz) microprobe.

We sonographically examined 4 whole CBD stones (1 cholesterol stone with radiant cross section, 1 cholesterol stone with lamellar cross section, 1 black pigment stone, and 1 brown pigment stone), 44 fragments of a cholesterol stone (diameter range, 1.1-3.0 mm; mean diameter, 2.0 mm), and 75 fragments of a black pigment stone (diameter range, 1.1-3.0 mm; mean diameter, 2.0 mm). The chemical composition of all stones was analyzed by infrared absorption spectroscopy. All stones and fragments were placed in a plastic box filled with physiologic saline solution for scanning with a 20-MHz microprobe and a 5-MHz probe. Echogenic foci and acoustic shadows revealed at each frequency were compared.

At 5 MHz, the 4 CBD stones showed different sonographic characteristics. The cholesterol stone with radiant cross section showed an echogenic focus but no definite acoustic shadow, whereas the cholesterol stone with lamellar cross section showed an echogenic line, several echogenic spots, and a definite acoustic shadow. The black pigment stone showed an echogenic line with a vague acoustic shadow, and the brown pigment stone showed echogenicity of the whole stone and a definite acoustic shadow. At 20 MHz, the 4 stones showed an echogenic line with a definite acoustic shadow. All fragments appeared as echogenic foci at 20 and 5 MHz. Seventy-seven percent (34) and 5% (2) of 44 cholesterol stone fragments cast a definite acoustic shadow at 20 and 5 MHz, respectively. Sixty-nine percent (52) and 15% (11) of 75 black pigment stone fragments cast a definite acoustic shadow at 20 and 5 MHz, respectively. Among fragments 1.5 mm in diameter and smaller, only 45% (5 of 11) from a cholesterol stone and 30% (6 of 20) from a black pigment stone showed a definite acoustic shadow at 20 MHz.

High-frequency (20-MHz) sonography demonstrates a definite acoustic shadow more frequently among CBD stones and fragments 1.6 mm in diameter or larger than does low-frequency (5-MHz) sonography, but it does not discriminate the chemical composition.