Second harmonic imaging and harmonic Doppler measurements with Albunex

The application of ultrasound contrast agents, such as Albunex, sometimes reduces the image contrast between blood and the surrounding tissues. This paper proposes experimental procedures that could alleviate this problem considerably by using harmonic signals generated by nonlinear backscattering of the microbubbles. In addition, its application on Doppler can minimize the clutter problem resulted from the motion of surrounding tissues and thus enables the detection of slow blood flow, in both power Doppler and color Doppler imaging modes. Results show that: (1) second harmonic signal produced by Albunex is significant and harmonic images that filter out backscattered echoes from solid tissues, but not those from Albunex, can be obtained; (2) when these microbubbles are compared to polystyrene microsphere suspensions which possess exclusively linear behavior, Doppler power at second and subharmonic frequencies could only be detected from Albunex