Estimation of speed of sound using coherence factor and signal-to-noise ratio for improvement of performance of ultrasonic beamformer

Ultrasound beamforming is an indispensable process to obtain an ultrasound image. In the conventional ultrasonography, the speed of sound (SoS) in tissue is assumed to be constant to calculate the distance from the scattering point to each ultrasonic transducer element. However, the spatial distribution of the SoS in tissue is inhomogeneous. In this study, we developed a method to estimate the distribution of the SoS. In addition, the accuracy of the proposed method was investigated using a homogeneous phantom with a known SoS distribution. Furthermore, another experiment using a wire phantom was conducted to investigate whether the spatial resolution in a resultant ultrasound image was improved with the SoS distribution estimated by the proposed method. The best spatial resolution was achieved when the size of the transmit aperture was 6.4 mm (32 elements) when both the coherence factor and signal-to-noise ratio factor were evaluated with a 7.5 MHz linear array probe.