In this study, we computationally evaluated the performance of dual-/tri-apodization focusing on the high-frequency ultrasound imaging since it suffers from high side-lobe level and noise components. However, the performance was mainly demonstrated by impulse response plotting without applying to ultrasound imaging Among them, the non-linear apodization method especially multi-apodization technique can be easily implemented and the processing time is short compared to other methods. To solve this problem, some researchers have proposed several methods such as constrained least squares (CLS), non-linear apodization, and dual-apodization with cross-correlation (DAX) methods However, the main-lobe width is increased resulting in reduced lateral resolution. The window functions realized by changing the amplitude of the signals can effectively suppress the side-lobe level. In order to reduce the side-lobe level, linear apodization methods by using various window functions were developed.
Although the conventional DAS beamforming can increase the energy of the ultrasound beam at the focal point, the side-lobe level also increases resulting in degraded contrast to noise ratio (CNR) A conventional delay and sum (DAS) beamforming enhances the signals from the selected location and reduces the signals from undesired direction by compensating arrival time of received signals. In the diagnostic ultrasound imaging by using an array transducer, a beamforming technique is commonly used for electrical transmit/receive focusing, beam steering, and dynamic focusing.
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