(A) study on a diagnostic ultrasound imaging technique employing the modified bandwidth focusing method

Abstract

The ultrasound focusing used in a conventional diagnostic B-scanner is achieved through the coherent addition of the appropriately delayed pulse echo signals backscattered from an imaging volume of interest. This thesis presents a new method of focusing called modified bandwidth focusing where digital time domain operations supersede the analog delay lines and the sampling rate requirement on analog-to-digital converter is greatly relaxed as compared with that required for the synthetic focusing. The modified bandwidth focusing method reduces speckle noise fluctuations at the cost of lateral resolution, providing a smoother B-mode image. Computer simulations and water tank experiments using the ultrasonic experimental setup are carried out to demonstrate the validity of the proposed modified bandwidth focusing method.