Preliminary study on the separation of specular reflection and backscattering components using synthetic aperture beamforming

Purpose: In the early stages of atherosclerosis, the luminal surface of the arterial wall becomes rough due to injury and detachment of endothelial cells. This roughening can potentially be estimated with ultrasound since the electrical echo signal from the transducer is sensitive to both the angle of incidence to an extended surface as well as the roughness of the surface. Specifically, as the roughness of an interface increases, specular reflection is substituted by scattering. We propose a method that attempts separation of reflection and backscattering components in the received echo signals. Method: Assuming the predominant propagation directions of the reflected and scattered waves can be somewhat controlled by the emitted sound field, separation of those components was attempted using synthetic aperture imaging with a transmit beam, focused at a point more distant than the imaging depth. Specifically, two dedicated beamforming processes were used for generation of reflection-emphasized and backscattering-emphasized images. Result: Experimental verifications on a phantom using an ultrasound system with a limited number of active transmit–receive channels yielded a difference between these two images of 8 dB. The results further showed a similar (slightly improved) lateral spatial resolution size of 0.41 mm for the backscattering-emphasized image compared with conventional B-mode imaging (0.47 mm). Conclusion: A new technique for separation of the reflection and backscattering components using synthetic aperture beamforming with a transmit beam featuring a large focal distance was proposed. The technique demonstrated a partial separation of the reflection and backscattering components, which potentially may be used to estimate surface roughness.