Techniques for perfusion imaging with microbubble contrast agents

The acoustic properties of ultrasound contrast agents vary widely with agent composition and insonation conditions. For contrast imaging, methods are required to match RF and Doppler processing to each combination of transmission parameters and agent and tissue properties. We propose a method that uses the measured or modeled echoes from agent and tissue to specify directly the characteristics of RF and Doppler filters for contrast imaging. The proposed method is sufficiently general to cover most common imaging techniques including harmonic greyscale, Doppler, and pulse inversion imaging. Using this method, sample filters were designed to detect myocardial perfusion with the contrast agent Optison/sup TM/ (Mallinckrodt Medical, St. Louis, MO) under selected imaging conditions. Simplified power Doppler filtering, using a weighted sum of the Doppler samples, matched the performance of more complicated matrix filters. By coordinating the selection of RF and Doppler filters rather than designing these filters sequentially, agent-to-tissue contrast was increased by up to 3.9 dB. Under some conditions, fundamental RF filtering outperformed harmonic filtering for intermittent Doppler imaging.