(A) study on the phase aberration correction by using analytic signal and generation of sinc wave in one dimensional array in ultrasound imaging system

Abstract

The ultrasound imaging system is one of the most widely used diagnostic tools in medicine due to its advantages such as safety, low cost, providing real-time imaging. However, the resolution of imaging is still not quite satisfactory, and more improvements are needed. The resolution of this system is generally dominated by the focusing capability and the ultrasonic properties in tissue. In part I of this dissertation, we propose a phase aberration correction method in transmit and receive focusing in linear array system. Difference of sound velocity in human tissue has on error in the geometrical focusing delay and this effect is called phase aberration. We estimate the time delay difference of two signals induced by aberration with calculating the complex cross correlation. We use bandwidth sampling technique called analytic signal, where we can use the phase information of rf frequency. Analytic signal is generated by analog pseudo Hilbert transformer, which is composed of two all pass filters with each output``s phase difference is about 90 degrees. We estimate the PDN``s performance and analysis of the estimation error in PDN. The aberrating medium generally exists in the near field of transducer, so we find the local phase difference of two adjacent pair elements in center of transmit aperture in each scanline separately. For summing the local phase error, we obtain the whole phase aberration profile in nearfield medium. From this profile, the transmit and receive focusing delays in each elements are controlled for improving resolution of image. Proposed aberration correction scheme is suitable for linear array transducer. This algorithm is very simple in hardware realization and, permits real time operation by using pseudo Hilbert transformer and high speed digital devices. We proved the method by experiment in cyst phantom. Part II is about diffraction limitted beam generation scheme in linear array transducer. We propose the method of generation of diff...