A comparative study using both coded excitation and conventional pulses in the evaluation of signal to noise ratio sensitivity and axial resolution in ultrasonic A-mode scan

Resumo

In this paper, we have made a comparative study of backscattering of ultrasound conventional and chirp codified pulses. We simulated the interaction of these two different pulses with a computational phantom constructed with variable amplitude and phase scatterers following a Gamma distribution. We have used the echo signal-to-noise ratio (eSNR) metric of the backscattered signals from both coded excitation pulse (CEP) and conventional pulse (CP) for various scenarios, as well as the evaluation of the axial resolution (AR) of the system, using both pulses. The computational phantoms were created with regular and variable scatterers spacing with amplitude and phase variation for three transducers: 2.25, 5.0 and 7.5 MHz center frequencies. The duration of the excitation CEP was 18 μs with chirp frequency bandwidth varying from a multiplying factor of 3.7, 2.0 and 1.2 times the transducer bandwidth, respectively. The pulse compression was performed using matched (MF) and mismatched (MMF) filters. The results for different transducers and phantoms are in accordance to the literature, and they have given an improvement of the SNR for coded pulse above 20 dB (in average) over conventional pulse excitation. In addition, the axial resolution for both codified and conventional pulses are in the same range. For a 2.25 MHz transducer, ARs were 1.33, 1.18 and 1.38 λ for CP, CEP/MF and CEP/MMF filters. Similarly, ARs for 5 MHz for all above three conditions were 1.34, 1.14 and 1.29 λ, and for the 7.5 MHz transducer 1.31, 1.23 and 1.38 λ. Our results have confirmed the increase in gain and very close agreement of the AR. Further research and development should be carried out to use the potentialities of CEP techniques in medical ultrasound imaging equipment.