M-sequence excitation of ultrasonic backscatter signals for cancellous bone evaluation

Abstract

In the evaluation of cancellous bone using ultrasonic backscatter, the amplitude of the backscatter signal is usually quite weak and the signal-to-noise ratio (SNR) is relatively low. This study used the m-sequence as the excitation to enhance the intensity and the anti-noise performance of the backscatter signal. The minimum peak sidelobe (MPS) filter was used to decode the received backscatter signal. The finite-difference time-domain (FDTD) simulation results show that the amplitude of the backscatter signal gets an enhancement of approximately 3.6 times with m-sequence than the monopulse excitation, and the decoded signal is approximately 93.9% identical to the ideal response of monopulse excitation. When the SNR decreased, the correlation coefficient between the monopulse signal and the ideal response decreased significantly, while the correlation of the m-sequence response changed little and remained steady, proving that the m-sequence signal gets a very good anti-noise performance. In vitro experiments were performed with bovine cancellous bones. In vitro results showed that the amplitude of the backscatter signal get an enhancement of approximately 3.8 times with m-sequence than the monopulse excitation, and the decoded signal was 94.6% identical to the ideal response of monopulse excitation. This study suggested that the ultrasonic backscatter of m-sequence excitation could be used for cancellous bone evaluation.