Difference of optimal dose of contrast agent between gray-scale and power Doppler imaging in assessing graded coronary stenosis by myocardial contrast echocardiography.

RATIONALE AND OBJECTIVES: In myocardial contrast echocardiography (MCE), power Doppler imaging is more sensitive to contrast agent (microbubble) than gray-scale B-mode imaging; however, no data exist regarding the optimal contrast dose in power Doppler imaging. This study examined the optimal dose of contrast agent for power Doppler in assessing coronary stenosis. METHODS: Three grades of coronary stenosis were produced in 6 open-chest dogs. MCE was performed with gray-scale and power Doppler during continuous infusion of 0.2 mL/min FS-069. Thereafter, MCE was repeated with power Doppler during continuous infusion of 0.1 mL/min FS-069. RESULTS: Although the videointensity in the stenosed bed with power Doppler (214 +/- 14) was greater than gray scale (35 +/- 17) during 0.2 mL/min FS-069 infusion (P < 0.0001), power Doppler failed to identify milder coronary stenoses because videointensity in stenosed bed was quickly saturated with contrast agent. The videointensity in the stenosed bed with power Doppler (127 +/- 49) during 0.1 mL/min FS-069 infusion was greater than gray scale (35 +/- 17) during 0.2 mL/min FS-069 infusion (P < 0.0001), and all levels of stenosis were identified with power Doppler, even though the dose of contrast agent was half of that of gray scale imaging. The correlation between videointensity and myocardial blood flow was better in the case of power Doppler at 0.1 mL/min FS-069 infusion (r = 0.77, P < 0.0001) than in the case of gray scale imaging at 0.2 mL/min FS-069 infusion (r = 0.66, P < 0.01). CONCLUSIONS: These data support the need for a lower dose of contrast agent for power Doppler than for gray scale to detect milder coronary stenosis and avoid saturation of imaging fields.