Three-stage approach to ultrasound contrast detection

A new method for detecting ultrasound contrast agents using a three-stage pulsing sequence is proposed. The method is based on observations showing that 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 obtain a high resolution reference image without altering the agent. Higher power 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 several pulses to survey the target while destroying the agent. The new idea is to separate detection and destruction to circumvent a trade-off between sensitivity and resolution. Results from in vitro experiments with three different contrast agents are presented. The results are compared with harmonic power Doppler processed from the same data and show that an improvement in sensitivity is achievable by including the high power burst in the pulsing sequence. The results also show that the proposed filter reduces clutter artifacts from moving tissue.