Implementation of a Pulsed-Wave Spectral Doppler Module on a Programmable Ultrasound System

Pulsed wave Doppler ultrasound is commonly used in the diagnosis of cardiovascular and blood flow abnormalities. Doppler techniques have gained clinical significance due to its safety, real-time performance and affordability. This work presents the development of a pulsed wave spectral Doppler module, which was integrated into a reconfigurable ultrasound system. The targeted system adopts a hardware-software partitioning scheme where an FPGA handles the front-end and a PC performs the back-end. Two factors were considered during the design. First, the data transfer rate between hardware and software should be minimum. Second, the design should use as few of the FPGA resources as possible. Accordingly, the processing was divided after the range gate integration where the data rate drops significantly. In addition, a quadrature demodulator was used based on a switching mixer and a cascaded integrator comb filter. The design was implemented and integrated into the targeted system. The system was tested using a string phantom and on human volunteers. The results showed that this simple design could achieve performance comparable to designs that are more sophisticated. However, it is limited by the number of available frequencies. Hence, it is suitable for systems with limited resources such as handheld systems.