Although widely employed in medical diagnostic applications, most of the available commercial ultrasound (US) scanners do not always fit the needs of research users. Access to raw US data, portability, flexibility and advanced user control are essential features to explore alternative biomedical signal and imaging processing algorithms. In this paper, we present the initial results of a reconfigurable, cost-effective and modular 128-channel FPGA and PC-based US system, specifically designed for teaching and medical imaging research. The proposed system exploits the advantages of the MD2131 (Microchip Technology Inc.) beamformer source driver to generate arbitrary waveforms and the analog front-end AFE5805 (Texas Instruments Inc.) to obtain the maximum flexibility and wide data access to the various US data streams. Two applications involving plane wave excitation and delay-and-sum (DAS) beamforming are discussed. The results show that the open platform can help biomedical students and researchers to develop and evaluate different imaging strategies for medical US imaging and nondestructive testing (NDT) techniques, among other applications.