Analysis of speckle in ultrasound-stimulated acoustic emission imaging

Abstract

In this work, a new theoretical perspective is presented to study the phenomenon of speckle in vibro-acoustography (VA). The vibro-acoustography is an imaging method based on Ultrasound-Stimulated Acoustic Emission (USAE). This imaging method is based  on  the  acoustic  field  emitted  from  scatterers inside an object due to a highly  focused  oscillating  radiation force. A hydrophone is used to measure the acoustic waves.  The acoustic filed measured by the hydrophone is dependent on the resolution and the cell volume of the ultrasound beam. The resolution cell also defines the point-spread function (PSF) of the system. The acoustic field emanating from the scatteres can interfere constructively or destructively. Thus, the number and distribution of the scatterers influence image formation and texture. Constructive and destructive interference were simulated based on the field scattered by point-scatterers that are randomly distributed over specific spatial locations. To study the statistical distribution of the image, we calculated the first-order statistical distribution of the gray levels of the image. A set of USAE images obtained from tridimensional scattering medium were simulated for scatterer densities ranging from 1 and 80 scatterer/mm³. Statistical properties of the images produced from the magnitude and phase of the acoustic emission field were analyzed. Statistically, the data were fitted using gaussian and lognormal curves. It was observed that depending on the scatterer densities, texture, and statistical distribution of the image are changed. Therefore, this research aimed to study the image formation in vibro-acoustography systems when coherent radiation is multiply scattered by a random medium.