Echo Contrast Agents Improve Flow Display of Color Doppler: In Vitro Studies

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Abstract
Flow detection by color Doppler is impaired by low velocity of flow and increasing attenuation and depth of ultrasound penetration. The effects of increased echogenicity on flow detection, (Toshiba SSH 65A) were thus studied in a flow model, which yielded similar strengths of Doppler signals as seen in the clinical routine, by adding microbubble solutions to the blood analog fluid (45% aqueous glycerin) arid comparing signal strength (score 0–5) prior to and after contrast. The flow within the plexiglass tube with < 3° angle of coincidence for Doppler interrogation was laminar with a parabolic velocity profile at physiological velocities and pressures. In comparison with various contrast agents at a flow velocity of 18 cm/sec and 19 dB attenuation, flow was not detectable in control color Doppler, after 4 mL of the blood analog fluid, and after 4 mL of an agitated saline solution 9 mg/mL, but visible after 4 mL ofEchovist, a polysaccharide solution with reproducible bubble size and concentration and after 4 mL of an agitatedpolygelatin solution. Increasing concentration ofEchovist (50–400 mg/mL) improved flow detection. Echovist 200 mg/mL enhanced the score by 1.1 + -0.6 for velocities 5–20 cm/sec (P < 0.01), by 1.6 + - 0.8 for 40–100 cm/sec (P < 0.001), and by 1.1 + - 0.6 for velocities > 150 cm/sec (P < 0.001). Echovist also caused significant (P < 0.01) increase of signal strength with increasing attenuation (10,19, 29 dB) and in < 8 cm versus > 8 cm penetration depth (P < 0.001). Echo contrast agents improve display of low intensity Doppler signals, particularly in color Doppler technique. Agents like Echovist with reproducible bubble size and concentration are superior to hand agitated solutions. Physical limitations of flow detection may be compensated by increased echogenicity. This offers considerable improvement in diagnostic accuracy of color Doppler. (ECHOCARDIOGRAPHY, Volume 8, September 1991)