Behavioral Study of Ultrasound Wave Propagation in Biological Tissues

The biological tissue has a complex structure which shows an unpredictable behavior for ultrasonic waves. The acoustical properties of various tissues are different and phenomenon like scattering diffraction, attenuation and nonlinearity. The nonlinearity leads to the distortion of the transmitted beam while spreading energy in higher harmonics, and images are acquired preferably by receiving those of second harmonic, known as tissue harmonic imaging (THI). The harmonic image often demonstrates improved contrast resolution due to higher harmonic frequencies and therefore detects smaller objects. High frequencies are, however, attenuated more in biological tissues as the beam propagates, leading to reduced depth of penetration inside the objects under scan. A new imaging technique named "super-harmonic imaging" (SHI) has been proposed recently. It takes advantage of the higher harmonics (third to fifth) arises from nonlinear propagation. It provides further enhancement in resolution with acceptable penetration depth and signal-to-noise ratio (SNR). The dedicated phased array transducer and propagation model that enables the full exploitation of SHI are the topics of ongoing research.