A Digital Ultrasonic System for Small Animal Imaging

In this paper, a 50 MHz digital ultrasonic imaging system designed for small animals and its applications to mouse embryos and tumors are presented. Utilizing the programmability of a fully digital system, several advanced imaging techniques are developed and implemented. A synthetic aperture focusing technique is implemented to increase the penetration and extend the depth of focus of a mechanical scan system using a high frequency single crystal transducer. An adaptive weighting technique is introduced to further reduce the sidelobes and enhance image contrast. Experimental results demonstrate efficacy of the proposed two-step adaptive focusing technique. For flow imaging, several flow estimation algorithms are evaluated. Simulations and flow phantom experiments show that the butterfly search technique offers superior flow imaging performance particularly when the SNR is low and the pulse bandwidth is high. The system is tested by imaging mouse embryos and microcirculation of a mouse tumor in vivo. It is demonstrated that the system is capable of simultaneously acquiring B-mode, color Doppler mode and power Doppler mode small animal images. The system set-up, adaptive focusing technique, flow estimation algorithms and imaging results are shown.