Pulsed wave Doppler ultrasound is commonly used
in the assessment and diagnosis of cardiovascular diseases and
blood flow abnormalities. Doppler techniques have gained clinical
significance due to its safety, real-time performance and
affordability. Most modern medical ultrasound systems have one
or more Doppler modes. 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 a field
programmable gate array (FPGA) handles the front-end
processing and a PC performs the back-end processing. Two main
factors were considered during the design of the Doppler module.
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. Based on these criteria, the
processing was divided after the range gate integration where the
data rate drops significantly. In addition, a simple quadrature
demodulator was used based on a digital switching mixer and a
cascaded integrator comb (CIC) low pass filter. The design was
implemented and integrated into the targeted system. The Doppler
module was tested within the system environment 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 portable and handheld systems |
