Three-stage approach to ultrasound contrast detection

A new method for detecting ultrasound contrast agents using a three-stage p ulsing sequence is proposed. The method is based on observations showing th at the scattering properties of contrast agents are modified by ultrasonic insonation at high power, but remain unchanged at low power. The objective of the first stage of the pulsing sequence is to use low power pulses to ob tain a high resolution reference image without altering the agent. Higher p ower pulses in the second stage modify the contrast agent. The third stage detects the changes imposed to the contrast agent using low power pulses. A temporal filter is proposed to discriminate contrast response from clutter signal. The method is similar to power Doppler methods in that it uses sev eral pulses to survey the target while destroying the agent. The new idea i s to separate detection and destruction to circumvent a trade-off between s ensitivity and resolution. Results from in vitro experiments with three dif ferent contrast agents are presented. The results are compared with harmoni c power Doppler processed from the same data and show that an improvement i n sensitivity is achievable by including the high power burst in the pulsin g sequence. The results also show that the proposed filter reduces clutter artifacts from moving tissue.