Purpose: The ultrasonographic study of the common bile duct in cholecystectomized patients is very often hampered by the presence of meteorism, scarring tissue, and internal adhesions. The aim of this study was to assess the usefulness of Tissue Harmonic Imaging (THI) in these clinical circumstances. In this technique, the image is formed by using not only the fundamental echo but also its harmonics, which improves the signal-to-noise ratio and considerably reduces the artefacts found in conventional US images.
Materials and methods: Seventy-six consecutive cholecystecomized patients (53 F, 23 M, average age 56.9+/-14.5 SD, range 20-81) were assessed. Patients were examined on an empty stomach. The examinations were performed with conventional ultrasonography and with THI. Based on the capability to visualise the distal portion of the common bile duct and in particular to assess the intraluminal content, the study results were rated by three radiologists blinded to each other's evaluation as insufficient (1), sufficient (2), good (3) ad excellent (4).
Results: The average diameter of the common bile duct was 4.74+/-2.3 mm (range 1.6-13 mm); at conventional ultrasonography, the visualisation was insufficient in 30% of the cases, sufficient in 52%, good in 18%. With THI the visualisation was sufficient in 17% of the cases, good in 59% and excellent in 24%. Ten out of 76 patients (13%) had stones in the common bile duct. In these cases, conventional ultrasonography was insufficient for diagnosis in 5 patients. All three radiologist (A, B and C) rated THI better than fundamental ultrasonographic imaging (ETG) (p-value <0.0001, Wilcoxon signed rank test). The mean (SD) of the differences between THI and ETG rating were for radiologist A, B and C respectively: 1.25 (0.57), 1.22 (0.51), 1.09 (0.57). Differences for all the radiologists did not significantly vary between older (over 74 years) and younger patients (p-value = 0.35, Wilcoxon rank-sum test). With Cohen's Kw evaluation we obtained better inter-observer agreement (0.71 and 0.80 A and B; 0.7 and 0.79 A and C; 0.71 and 0.81 B and C by conventional ultrasonography and THI).
Conclusions: THI proved to be superior to conventional ultrasonography in the study of the common bile duct in cholecystecomized patients and in particular in the identification of choledocholithiasis.