Abstract
Ultrasound (US) Doppler systems are routinely used for the diagnosis of cardiovascular diseases. Depending on the application, either single tone bursts or more complex waveforms are periodically transmitted throughout a piezoelectric transducer towards the region of interest. Extraction of Doppler information from echoes backscattered from moving blood cells typically involves coherent demodulation and matched filtering of the received signal, followed by a suitable processing module. In this paper, we present an embedded Doppler US system which has been designed as open research platform, programmable according to a variety of strategies in both transmission and reception. By suitably sharing the processing tasks between a state-of-the-art FGPA and a DSP, the system can be used in several medical US applications. As reference examples, the detection of microemboli in cerebral circulation and the measurement of wall _distension_ in carotid arteries are finally presented.
Highlights
The well-known Doppler effect consists in the frequency shift of a wave, originated from the relative movement between the source and the receiver
This tendency is further encouraged by high-speed programmable devices such as digital signal processors (DSPs) and field programmable gate arrays (FPGAs), which have the calculation power requested to perform all needed processing in real time
In the multichannel multigate (MCMG) system, the basic tasks necessary to control the transmission of US bursts by a piezoelectric transducer and to extract the desired Doppler information from the received echoes are shared between two state-of-the-art programmable devices: an FPGA from the Stratix family (Altera, San Jose, Calif) [6] and a DSP from the TMS320C67 family (Texas Instruments, Austin, Tex) [7]
Summary
The well-known Doppler effect consists in the frequency shift of a wave, originated from the relative movement between the source and the receiver. The detected Doppler shift is generally in a range of a few kHz. In order to reliably measure the frequency shifts caused by the movement of erythrocytes, both the transmit (TX) and receive (RX) sections of an US system must be suitably configured. The availability of high-speed, high-resolution (12–14 bit) Analog-to-Digital (AD) converters allows directly sampling the radio-frequency (RF) echo signal, according to the same approach followed in the so-called Software Defined Radio. This tendency is further encouraged by high-speed programmable devices such as digital signal processors (DSPs) and field programmable gate arrays (FPGAs), which have the calculation power requested to perform all needed processing in real time.
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