1) Ward B, Baker AC, Humphrey VF:
Nonlinear propagation applied to the improvement of resolution in diagnostic medical ultrasound. J Acoust Soc Am 101: 143-154, 1997.

2) Muir TG, Carstensen EL: Prediction of nonlinear acoustic effects in biomedical frequencies and intensities. Ultrasound Med Biol 6: 345-357, 1980.

3) Cristopher T, Carstensen EL: Finite amplitude distortion and its relationship to linear derating formulae for diagnostic ultrasound systems. Ultrasound Med Biol. 22: 1103-1116, 1996.

4) Starritt HC, Perkins MA, Duck FA et al: Evidence for ultrasonic finite-amplitude distortion in muscle using medical equipment. J Acoust Soc Am 77: 302- 306, 1985.

5) Starritt HC, Duck FA, Hawkins AJ et al: The development of harmonic distortion in pulsed finite-amplitude ultrasound passing through liver. Phys Med Biol 31: 1401-1409, 1986.

6) Muir TG: Nonlinear effects in acoustic imaging. Acoust Imag 9: 93-109, 1980.

7) Fatemi M, Greenleaf JF: Real-time assessment of the parameter of nonlinearity in tissue using "nonlinear shadowing". Ultrasound Med Biol 22: 1215- 1228, 1996.

8) Liu DL,Waag RC: Harmonic amplitude distribution in a wideband ultrasonic wavefront after propagation through human abdominal wall and breast specimens. J Acoust Soc Am 101: 1172-1183, 1997.

9) Hann LE, Bach AM, Cramer LD et al: Hepatic sonography: comparison of tissue harmonic and standard sonography techniques. AJR 173: 201-206, 1999.

10) Shapiro RS,Wagreich J, Parsons RB et al: Tissue Harmonic imaging sonography: evaluation of image quality compared with conventional sonography. AJR 171: 1203-1206, 1998.

11) Choudhry S, Gorman B, Charboneau W et al: Comparison of tissue harmonic imaging with conventional US in abdominal disease. RadioGraphics 20: 1127- 1135, 2000.

12) Ortega D, Burns PN, Simpson DH et al: Tissue Harmonic imaging: is it a benefit for bile duct sonography?. AJR 176: 653-659, 2001.

13) Gibson RN,Yeung E, Thompson JN et al: Bile duct obstruction: radiologic evaluation of level, cause, and tumor resectability. Radiology 160: 43-47, 1986.

14) Laing FC, Jeffrey RB Jr, Wing VW et al: Biliary dilatation: defining the level and cause by real-time US. Radiology 160: 39-42, 1986.

15) Koenigsberg M,Wiener SN,Walzer A: The accuracy of sonography in the differential diagnosis of obstructive jaundice: a comparison with cholangiography. Radiology 133: 157-165, 1979.

16) Cronan JJ, Mueller PR, Simeone JF: Prospective diagnosis of choledocolithiasis. Radiology 146: 467-469, 1983.

17) Honickman SP, Mueller PR, Wittenberg J et al: Ultrasound in obstructive jaundice: prospective evaluation of site and cause. Radiology 147: 511-515, 1983.

18) Blackbourne LH, Earnhardt RC, Sistrom CL et al: The sensitivity and role of ultrasound in the evaluation of biliary obstruction. Am Surg 60: 683-690, 1994.

19) Rigauts H, Marchal G, Van Steenbergen W et al: Comparison of ultrasound and ERCP in the detection of the cause of obstructive biliary disease. Rofo Fortschr Geb Rontgenstr Neven Bildgeb Verfahr 156: 252-257, 1992.

20) Siegels: Nonparametric statistics for the behavioral sciences, pag. 68-75. McGraw-Hill, New York, NY, 1956.

21) Altman DG: Weighted Kappa. In: Practical statistics for medical research, pag. 406-407. Chapman & Hall: London, England, 1991.

22) Bland JM, Altman DG: Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1: 307-310, 1986.

23) Diagnosis and treatment of common bile duct stones (CBDS). Results of a consensus development conference. Scientific Committee of the European Association for Endoscopic Surgery (EAES). Surg Endosc 12: 856-864, 1998.

24) Franceschi D, Brandt C, Margolin D et al: The management of common bile duct stones in patients undergoing laparoscopic cholecystectomy. Am Surg 59: 525-532, 1993.

25) Sugiyama M, Atomi Y: Endoscopic ultrasonography for diagnosing choledocholithiasis: a prospective comparative study with ultrasonography and computed tomography. Gastrointest Endosc 45: 143-146, 1997.

26) Pavone P, Laghi A, Lomanto D et al: MR cholangiography (MRC) in the evaluation of CBD stones before laparoscopic cholecystectomy. Surg Endoscop 11: 982-985, 1997.

27) Pamos S, Rivera P, Cannelles P et al: Magnetic resonance cholangiopancreatography (MRCP) versus endoscopic retrograde cholangiopancreatography (ERCP): diagnostic usefulness. Gastroenterol Hepatol 21: 174-180, 1998.

28) Musella M, Barbalace G, Capparelli G et al: Magnetic resonance imaging in evaluation of the common bile duct. Br J Surg 85: 16-19, 1998.

29) Contractor QQ, Boujemla M, Contractor TQ et al: Abnormal common bile duct sonography. The best predictor of choledocholithiasis before laparoscopic cholecystectomy. J Clin Gastroenterol 25: 429-432, 1997.

30) Rothlin MA, Schob O, Schlumpf R et al: Laparoscopic ultrasonography during cholecystectomy. Br J Surg 83: 1512-1516, 1996.