Medical ultrasound imaging using the fully adaptive beamformer

Medical ultrasound beamforming is conventionally done using a classical delay-and-sum operation. This simplest beamforming suffers from drawbacks. Indeed, in phased array imaging, the beamformed radiofrequency signal is often polluted with off-axis energies. We investigate the use of an adaptive beamforming approach widely used in array processing, the fully adaptive beamformer, to reduce the bright off-axis energies contribution. We show that the fully adaptive beamformer cannot be applied to medical ultrasound as it was initially derived since the medical ultrasonic medium produces coherent or highly correlated signals and the algorithm fails to work within this context. Spatial smoothing preprocessing is introduced which allows the fully adaptive beamformer to operate. A complementary preprocessing that uses the received data obtained using consecutive transmission lines further improve the performances. Very promising results for the application of adaptive array processing techniques in medical ultrasound are obtained.