Sistema para processamento de sinais de ultrassom utilizando excitação chirp com filtros casado e descasado

Abstract

Ultrasonic excitation techniques based on the application of chirp-coded pulse (ECC) have been studied to improve the signal-to-noise ratio (SNR) of signals and images, especially in deeper regions of the biological media. The main advantages of these techniques are to temporally lengthen the transmission pulse to increase the acoustic power using linear frequency modulation and, subsequently, at reception, apply compression filters to recover the signals. In this work, a system was proposed for simulation and experimental evaluation of Sinusoidal Conventional Excitation (ECS) and Chirp-Coded Excitation (ECC) signals in the formation of ultrasonic signals from one-dimensional computational and experimental ultrasound phantoms. The system consists of a computer, in which a Graphical User Interface (GUI) was implemented on the MATLAB platform, and a reconfigurable hardware architecture using the DE2-115 FPGA kit, and a proprietary board with the MD2134 arbitrary waveform generator, developed by the Ultrasound Group of the Federal University of Technology – Paraná (UTFPR). The main advantages of the system are flexibility and ease of use for generating complex pulses, allowing the configuration of the parameters of central frequency, frequency range for chirp signals, windowing function and pulse duration, among others. In the reception stage, the digitized data of the ultrasound echoes with a sampling rate of 80 MSPS are acquired via the USB interface for post-processing. The ECS backscattered signals with a frequency of 1.6 MHz, Hanning window and duration of 3 cycles were compared with the echo signals generated by ECC pulses, configured with a frequency range of 1.6 MHz ± 400 kHz, Tukey window of 25% with duration of 5 µs, 10 µs and 20 µs, with the application of the matched filter (FC) and mismatched filter (FDC) to evaluate the signal compression. These experiments were performed by simulation in MATLAB and with the real echo signals acquired with an acrylic experimental phantom with two groups of wires. The results indicate that the system is suitable for carrying out simulated and experimental studies using conventional and coded pulses to evaluate pulse compression.