Optimization of frequency dependent receive apodization

To improve the directivity of a receive beamformer, the scalar apodization weigths are replaced by filters. For a frequency dependent apodization without changing the delay scheme of the dynamic receive beamformer, symmetric FIR filters are used. Different image quality measures are investigated and discussed that allow to quantify the dynamic range (contrast) and detail resolution of an ultrasound system by evaluation of the 2D point spread function. For an automated optimization of the apodiza- tion filter transfer functions, the chosen image quality measures are continuous and sufficiently smooth so that a local search algo- rithm can find a global optimum. It is shown that apodization filters with a small number of taps are sufficient if an additional filter is added after the summation point. Compared to a conventional apodization, this approach offers a significant improvement in image quality and can be achieved with moderate hardware effort well suited for FPGA- based beamformer frontends.

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