Real-time compound imaging:: Improved visibility of biopsy needles and localization wires as compared to single-line ultrasonography

Aim: To compare the visibility of biopsy needles and localization wires using real-time compound imaging (SonoCT (TM)) and single-line ultrasound (SLU). Methods: 14-18G biopsy needles and 5 different localization wires with and without puncture needle were placed into cadaverous muscle in 4 different angulations (0, 12, 18 and 25 degrees). Sonography was performed with an ATL HDI 5000 sonography device with a 5-12 MHz linear array using single-line ultrasound and compound imaging with 3 and 9 frames (Comp3 and Comp9) from different viewing angles. Images of the needles were obtained in the longitudinal plane without changing depth, focus position, and gain settings between the measurements. The mean grey values of the needle (gv_n) and of the background (gv_b) were obtained from histograms. Contrast was calculated using the equation (gv_n-gv_b)/gv_b + gv_n). Mean contrast in single-line and compound images was compared for each angulation using a Student t-test. Results: The mean contrast at 0 was 0.686 in single-line ultrasound. This was significantly higher than in Comp3 (0.62) and Comp9 (0.633) (p<0.05) images. At 12 no significant differences could be observed. At 18<degrees> image contrast was significantly higher in compound images with 0.493 (Comp3) and 0.498 (Comp9), compared to SLU (0.433) (p<0.05). At 25<degrees> the difference between compound images (Comp3: 0.394; Comp9: 0.402) and SLU (0.306) was greatest (p < 0.0001). Conclusion: At 0<degrees> and 12 degrees visibility is very good For all tested materials. For steeper angulations contrast was partly critical in SLU and significantly enhanced with compound imaging. Thus, SonoCT (TM) may be useful to increase precision of ultrasound-guided percutaneous interventions.