Source prebiasing for improved second harmonic bubble-response imaging

The use of the second harmonic bandwidth in order to improve the contrast e nhancement of vascular space provided by microbubble echo contrast is well established. A significant obstacle to improving on the contrast advantage of the second harmonic bandwidth arises from the linear response of tissue to the finite amplitude distortion produced second harmonic in the beam. A scheme in which the source wave contains a second harmonic component design ed to cancel out the second harmonic produced by finite amplitude distortio n in the focal region was computationally investigated, This prebiasing sch eme was found to offer significant reductions in the amplitude of the secon d harmonic in the focal region. These reductions were found in both the hom ogeneous tissue path case and in the inhomogeneous tissue path case. The re sulting clinical potential of source prebiasing is discussed. Also, it was observed that the inhomogeneous focusing of the finite amplitude distortion -produced second harmonic was significantly better than that of a same freq uency fundamental with an identical homogeneous path focal profile.