The specific language skills and high development time of conventional FPGA core designs, prevents ultrasound researchers from rapidly prototyping and performing algorithmic adjustments. In this article, we present an OpenCL-based high-level synthesis approach that aims to efficiently design an FPGA beamformer for synthetic aperture imaging. The computing modules are encoded in OpenCL kernels, and after design space exploration are then emulated in RTL descriptions through the Altera OpenCL compiler. The throughput performance of the computing cores throughout the various stages of the design space exploration are documented, and they show that it is possible to achieve video performance (25 fps), while still displaying high levels of energy efficiency. We conclude that using high-level synthesis to rapidly adjusting imaging reconstruction algorithms pertinently addresses the issues previously described.