[Effects of depth on the display of color Doppler flow imaging with transesophageal and transthoracic transducers: an experimental study].

Transesophageal color Doppler flow imaging has proved to provide an accurate and sensitive information for diagnosis of valvular regurgitation. However, it is necessary to understand the difference in the display of color Doppler image between transesophageal and conventional transthoracic transducers for quantitative assessment of valvular regurgitation. In this study, the effects of the depth between transducer and jet flow on color Doppler flow imaging were evaluated with the transesophageal (3.75 MHz) and conventional (2.5 MHz) transducers by using a flow phantom. A flow circuit was filled with saline in which nylon corpuscles (average diameter; 5 microns) were suspended to enhance the Doppler effects. A turbulent jet with constant flow velocity (Reynolds number; 3500) stimulating valvular regurgitant flow was produced in a water bath through a small orifice (2 mm) by constant driving pressure (100 mmHg). Color jet imaging in the long- and short-axis views were observed at each depth with both transducers. The measurement was made every 1 cm in depth from 3 to 12 cm. The color gain setting was fixed at the optimal point so as to get the maximal flow image with the minimal static background noise. We obtained larger image of the color jet signal with the conventional than the transesophageal transducer. Although a mosaic pattern was displayed more distinctly with the transesophageal transducer compared with that of the conventional transducer, the transesophageal image tended to become indistinct in the depth deeper than 8 cm. On the other hand, the transthoracic image was maintained relatively constant at any depth.(ABSTRACT TRUNCATED AT 250 WORDS)