We have realized effective ultrasound (US) beamformings using steering of the plural beams and apodizations, i.e., lateral cosine modulations (LCMs) [1]. These LCMS can be used for B-mode imaging with a high lateral resolution and accurate measurement of tissue or blood displacement vector and/or strain tensor using our previously developed multidimensional autocorrelation and Doppler methods that yield the measurements of all displacement components simultaneously.
In order to obtain the better apodization function to be used for realizing a designed point spread function (PSF) than Fraunhofer approximation (FA), we developed a regularized linear optimization (LO) method through simulations. Moreover, to gain the insight about the ideal shape of the PSF, the accuracies of the 2D displacement vector measurements were compared for typical PSFs with distinct lateral envelop shapes. Because the power functions that had wide FWHMs and short lengths of the feet yielded accurate measurements, in conjunction with the reduction of electric consumption, we also developed the more effective nonlinear optimization (NLO) method, in which the feet of the main lobes in apodization function obtained by LO method were properly truncated. NLO also allows the decrease in the channels of US equipment. Through the experiments on human in vivo tissues (liver, breast, etc), in conjunction with virtual sources, the effectiveness of the improved LCM will be shown. We hope that our developed LCM will be used as a fundamental beamforming scheme in the next-generation US systems.
[1] C. Sumi et al, IEEE Trans UFFC, vol. 55, pp. 2607-2625, 2008.