Dynamic coherence factor based on the standard deviation for coherent plane-wave compounding.

The ultrafast imaging technique based on plane wave transmission has been a commonly investigated imaging mode in medical ultrasound imaging. Coherent plane-wave compounding (CPWC) was proposed to improve the quality of plane-wave imaging (PWI), which obtained a high-quality image by summing the low-quality images formed by transmitting plane waves at different steering angles. Coherence factor (CF) weighting algorithms can effectively improve image contrast with low computational complexity. However, this usually introduces black artifacts and degraded speckle quality. In this paper, we propose a dynamic coherence factor (DCF) that is based on the angular difference of CPWC to adaptively determine the number of plane waves and utilizes several plane waves with small angular difference to evaluate coherence. To improve resolution and contrast-to-noise ratio (CNR), adjusted DCF (ADCF) introduces a parameter related to the standard deviation to adjust DCF. Furthermore, a square neighborhood ADCF (SN-ADCF) using a 2-dimensional average filter is designed to obtain higher contrast and speckle quality. The simulated, experimental and in-vivo datasets are used to evaluate the proposed methods. Results show that, in comparison with CF, DCF can achieve improved contrast ratio (CR), CNR and speckle signal-to-noise ratio (sSNR). ADCF achieves a maximal lateral full width at half maximum (FWHM) improvement by 40% and better speckle quality than CF. SN-ADCF causes about 20% improvements upon CF in CNR and sSNR, while maintaining a similar resolution performance. SN-ADCF also provides higher lateral resolution than the generalized coherence factor (GCF) and scaled coherence factor (scCF), meanwhile obtaining a comparable contrast and speckle quality. Therefore, SN-ADCF has a satisfying comprehensive performance, which can achieve a reasonable balance among resolution, contrast and speckle quality.