Improvements on USCT SAFT imaging by divergence compensation

The use of Synthetic Aperture Focusing Technique (SAFT) for reflectivity ultrasound tomography has limitations due to the low signal-to-noise ratio. To overcome this fact in reflectivity ultrasound tomography, some studies have been showing improvements, propounding to take advantage of ultrasound transmission phenomena. Nevertheless, they do not take into account the characteristic divergence of ultrasound propagation. To contribute to a solution, we propose an improvement called weighted-SAFT, and test it with simulated media. In this study, the following were used: k-Wave toolbox for data generation on heterogeneous medium (sound speed, density, and attenuation); numerical phantoms with different combination, size, geometry, and location of the simulated objects; Fast Marching Method for phase aberration correction and time of flight, based on Refraction tomography, to calculated the SAFT weighting. The data set was generated using 192 simulated single-element transducers (1 MHz) uniformly distributed along the perimeter of a circular area. The SAFT reconstructions were made using the raw received signal and, separately, the envelope of the signal. SAFT-reconstructions using the signal envelope shows a diffuse appearance, and the edges of the objects in these regions can not be delimited. It is observed how the weighting SAFT leads to a more balanced distribution of intensity values throughout the image, partially compensating the ultrasound divergence effect and improving the image contrast.