2ND-HARMONIC IMAGING AND HARMONIC DOPPLER MEASUREMENTS WITH ALBUNEX(R)

Gaseous ultrasound contrast agents, such as Albunex(R), have been show n to be valuable clinically for the better identification of certain a natomic structures and for quantitating organ perfusion, However, the application of a contrast agent sometimes also reduces the image contr ast between the blood and the surrounding tissues, This paper presents experimental results to show that this problem may be alleviated by u sing harmonic signals generated by nonlinear backscattering of these m icrobubbles. The results show that the second harmonic signal produced by Albunex(R) is significant and that harmonic images in which backsc attered echoes from solid tissues were filtered out, but not those fro m Albunex(R), can be obtained, In addition, a continuous wave Doppler arrangement has been implemented, It permits quantitative harmonic Dop pler measurements at different frequencies, concentrations, and transm itted acoustic pressures, When Albunex(R) was compared to polystyrene microsphere suspensions which possess exclusively linear behavior, Dop pler power at second and subharmonic frequencies could only be detecte d from these microbubbles, A comparison of results on Doppler powers m easured at the first harmonic from polystyrene spheres and Albunex(R) indicates that at a transmitting frequency of 2.5 MHz, the Doppler pow er from Albunex(R) is 12 dB stronger than the polystyrene spheres, whe reas at 5 MHz, the Doppler power from Albunex(R) is 3 dB weaker than t hat from the polystyrene spheres.