Multiline Transmit Beamforming Combined With Adaptive Apodization

Increased frame rate is of high importance to cardiac diagnostic imaging as it enables examination of fast events during the cardiac cycle and improved quantitative analysis, such as speckle tracking. Multiline transmission (MLT) is one of the methods proposed for this purpose. In contrast to the single-line transmission (SLT), where one focused beam is sent in each direction, MLT beams are simultaneously transmitted and focused in several (2, 4, 6...) directions improving the frame rate accordingly. The simultaneous transmission is known to cause crosstalk artifacts due to the interference between the main lobes and the sidelobes of the transmitted and received beams. Usually, the artifacts are attenuated using a Tukey window apodization, but the lateral resolution is degraded. Several other methods, such as minimum variance beamforming and filtered delay multiply and sum beamforming were proposed to deal with these artifacts. The assumption examined in this paper is that a receive apodization can be chosen adaptively from a number of apodization windows in order to provide better artifact rejection and to increase the spatial resolution. The entire study was performed on an experimental MLT data set including wire and tissue mimicking phantoms, as well as in vivo cardiac data. The results demonstrate that application of a predefined apodization bank outperforms Tukey windowing alone, in terms of both resolution and receive crosstalk artifact rejections. Moreover, the achieved spatial resolution is superior to the nonapodized SLT, as measured from wire phantoms. The proposed method can also be combined with wider transmit beams, suitable for multiline acquisition.