Second harmonic imaging and harmonic Doppler measurements withAlbunex

摘要

Gaseous ultrasound contrast agents, such as Albunex, have beennshown to be valuable clinically for the better identification of certainnanatomic structures and for quantitating organ perfusion. However, thenapplication of a contrast agent sometimes also reduces the imagencontrast between the blood and the surrounding tissues. This papernpresents experimental results to show that this problem may benalleviated by using harmonic signals generated by nonlinearnbackscattering of these microbubbles. The results show that the secondnharmonic signal produced by Albunex is significant and that harmonicnimages in which backscattered echoes from solid tissues were filterednout, but not those from Albunex, can be obtained. In addition, ancontinuous wave Doppler arrangement has been implemented. It permitsnquantitative harmonic Doppler measurements at different frequencies,nconcentrations, and transmitted acoustic pressures. When Albunex wasncompared to polystyrene microsphere suspensions which possessnexclusively linear behavior, Doppler power at second and subharmonicnfrequencies could only be detected from these microbubbles. A comparisonnof results on Doppler powers measured at the first harmonic fromnpolystyrene spheres and Albunex indicates that at a transmittingnfrequency of 2.5 MHz, the Doppler power from Albunex is 12 dB strongernthan the polystyrene spheres, whereas at 5 MHz, the Doppler power fromnAlbunex is 3 dB weaker than that from the polystyrene spheres