Frequency smoothed robust Capon beamformer applied to medical ultrasound imaging

Recently, adaptive array beamforming has been applied to medical ultrasound imaging and achieved promising performance improvement. However, the current robust Capon beamformer with spatial smoothing (RCB-SS) is implemented in the time domain, which does not fully utilise the large bandwidth of ultrasound signals and spatial smoothing reduces the effective aperture. In this dissertation, we propose a robust Capon beamformer with frequency smoothing (RCB-FS) and compare its performance with RCB-SS. To further reduce the speckle noise and utilise the large bandwidth of the signal, we combine RCB-FS and frequency com- pounding (FC) and propose a robust Capon beamformer with frequency smoothing combined with frequency compounding (RCB-FS-FC). The proposed RCB-FS method shows a narrower mainlobe width, lower sidelobes, better reconstruction at higher depths and less speckle than RCB-SS. FC is an e ective method to improve the contrast resolution and suppress speckle noise by combining sub-band images, at the expense of resolution. Compared to standard FC, the proposed RCB-FS-FC method has a better contrast resolution and speckle reduction and a significant improvement in resolution. RCB-FS offers a promising approach to find the optimal weights for the transducers in forming the sub-band images needed for frequency compounding