Ph. Chang et al., 2ND-HARMONIC IMAGING AND HARMONIC DOPPLER MEASUREMENTS WITH ALBUNEX(R), IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 42(6), 1995, pp. 1020-1027
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.