Plane-Wave Phase Coherence Imaging with Singular Value Decomposition

Recently, various adaptive imaging methods have been studied extensively for the improvement of ultrasound image quality. Some of those methods utilize the coherence among ultrasonic echo signals received by individual transducer elements in an ultrasonic probe. Such methods would be of value also for high frame-rate ultrasonic imaging because image quality is degraded due to unfocused transmit beams, such as plane and diverging transmit beams. In the present study, effects of sub-aperture delay-and-sum (DAS)beamforming and singular value decomposition (SVD)on the coherence-based imaging methods, i. e., coherence factor (CF)and phase coherence factor (PCF), were examined in high frame-rate plane-wave imaging. The performance of the proposed method was examined by phantom experiments in terms of the spatial resolution and image contrast. Sub-aperture beamforming improved the lateral spatial resolution and image contrast in PCF imaging but degraded that in CF imaging slightly. However, the visibilities of speckle echoes from diffuse scattering medium relative to echoes from strong scatterers were improved by sub-aperture beamforming in both imaging methods. SVD improved the spatial resolution significantly in both imaging methods, while it did not change image contrast so much. The performances of the coherence-based imaging methods could be controlled by combination of sub-aperture beamforming and SVD. Such characteristics of the proposed method would be beneficial for the improvement of image quality in high frame-rate plane-wave imaging.