Performance improvement of magneto-acousto-electrical tomography for biological tissues with sinusoid-Barker coded excitation

By combining magnetics, acoustics and electrics, the magneto-acoustic-electrical tomography（MAET） proves to possess the capability of differentiating electrical impedance variation and thus improving the spatial resolution. However,the signal-to-noise ratio（SNR） of the collected MAET signal is still unsatisfactory for biological tissues with low-level electrical conductivity. In this study, the formula of MAET measurement with sinusoid-Barker coded excitation is derived and simplified for a planar piston transducer. Numerical simulations are conducted for a four-layered gel phantom with the 13-bit sinusoid-Barker coded excitation, and the performances of wave packet recovery with side-lobe suppression are improved by using the mismatched compression filter, which is also demonstrated by experimentally measuring a three-layered gel phantom. It is demonstrated that comparing with the single-cycle sinusoidal excitation, the amplitude of the driving signal can be reduced greatly with an SNR enhancement of 10 dB using the 13-bit sinusoid-Barker coded excitation. The amplitude and polarity of the wave packet filtered from the collected MAET signal can be used to achieve the conductivity derivative at the tissue boundary. In this study, we apply the sinusoid-Barker coded modulation method and the mismatched suppression scheme to MAET measurement to ensure the safety for biological tissues with improved SNR and spatial resolution, and suggest the potential applications in biomedical imaging.

Optimization of ultrasonic elastography by coded excitation and transmit-side multi-frequency compounding

To improve the quality of ultrasonic elastography, by taking the advantage of code excitation and frequency compounding, a transmitting-side multi-frequency with coded excitation for elastography （TFCCE） was proposed. TFCCE adopts the chirp signal excitation scheme and strikes a balance in the selection of sub-signal bandwidth, the bandwidth overlap and the number of sub-strain image based on theoretical derivation, so as to further improve the quality of elastic image. Experiments have proved that, compared with the other optimizing methods, the elastographyic signal-to-noise ratio（Re-SN） and contrast-to-noise ratio（Re-CN） are improved significantly with different echo signal-to-noise ratios （ReSN） and attenuation coefficients. When ReSN is 50 dB, compared with short pulse, Rc-SN and Re-CN obtained by TFCCE increase by 53% and 143%, respectively. Moreover, in a deeper investigation （85-95 mm）, the image has lower strain noise and clear details. When the attenuation coefficient is in the range of 0-1 dB/（cm.MHz）, Re-SN and Re-CN obtained by TFCCE can be kept in moderate ranges of 5〈Re-SN〈6.8 and 11.4〈Re-CN〈15.2, respectively. In particular, for higher tissue attenuation, the basic image quality cannot be ensured with short pulse excitation, while mediocre quality strain figure can be obtained by TFCCE. Therefore, the TFCCE technology can effectively improve the elastography quality and can be applied to ultrasonic clinical trials.

Characterization and analysis of coded excitation ultrasound parameters for rock properties

Coded excitation technology （CET） can effectively enhance the penetration and resolution of ultrasonic testing. To analyze the influence of rock properties on pulse compression performance （PCP） of coded excitation signals （CES）, a numerical simulation, and an ultrasonic experiment on different rock samples are performed; and the detection ability of several CESs are also investigated and compared. The results of experiments showed that the loss of the signal-to-noise ratio （SNR） of Barker coded signal with tapered linear frequency modulated carrier （BTLFM） is always less than Barker coded signal with sine carrier （BS）, while the resolution loss of BTLFM is lower than tapered linear frequency modulated signal （TLFM）. In sum, the results not only verifiy the effectiveness of CET, but also provide a basis for the parameter settings of coded signals used in rock ultrasonic testing.

An Approach to Hide Secret Speech Information

This paper presented an approach to hide secret speech information in code excited linear prediction (CELP)-based speech coding scheme by adopting the analysis-by-synthesis (ABS)-based algorithm of speech information hiding and extracting for the purpose of secure speech communication. The secret speech is coded in 2.4 Kb/s mixed excitation linear prediction (MELP), which is embedded in CELP type public speech. The ABS algorithm adopts speech synthesizer in speech coder. Speech embedding and coding are synchronous, i.e. a fusion of speech information data of public and secret. The experiment of embedding 2.4 Kb/s MELP secret speech in G.728 scheme coded public speech transmitted via public switched telephone network (PSTN) shows that the proposed approach satisfies the requirements of information hiding, meets the secure communication speech quality constraints, and achieves high hiding capacity of average 3.2 Kb/s with an excellent speech quality and complicating speakers’ recognition.

A speech coding algorithm based on harmonic-stochastic excitation

A very low bit rate algorithm for encoding speech signals at 825 bps based on a mixed harmonic and stochastic modeling of the excitation signal is presented. The algorithm is more robust in the V/UV decision, reliable pitch estimation, and excitation signals synthesis. The bit allocation schedules in every case and the analysis-by-synthesis processes of the parameters are also described. The Diagnostic Rhyme Test (DRT) results show that the performance of the proposed algorithm is comparable to that of the MELP algorithm at 2.4 kbps, and the speech distinctness is 90.25%.

A Novel Frame Error Concealment Scheme Based on Gain Control for TCX Audio Codec

A novel frame error concealment scheme is proposed to improve the decoded audio quality of the receiver for transform coded excitation（TCX）audio codec.This scheme,which is a gain control approach based on the stability of linear predictive coding（LPC）filter,predicts the lost frames by utilizing the linear spectrum frequency and different continuous attenuation factor of different kinds of lost frames.Signal noise ratio（SNR）test and multiple stimuli with hidden reference and anchor（MUSHRA）test are conducted to evaluate the performance of this approach in adaptive multi-rate wideband plus（AMR-WB＋）audio codec.Compared with the original frame error concealment scheme,our scheme achieves better audio recovery quality in AMR-WB＋audio codec.

Detection of long bones based on Barker code excited ultrasonic guided waves

Single pulse excited ultrasonic guided wave surfers high attenuation during the propagation in long bones.This results in small amplitude and low signal-to-noise ratio（SNR）of measured signals.Thus,the Barker code excitation is introduced into long bone detection to improve the quality of received signals,due to its efficiency in increasing amplitude and SNR.Both simulation and in vitro experiment were performed,and the results were decoded by the weighted match filter（WMF） and the finite impulse response- least squares inverse filter（FIRLSIF）,respectively.The comparison between the results of Barker code excitation and sine pulse excitation was presented.For 13-bit Barker code excitation,WMF produced 13 times larger amplitude than sine pulse excitation,while FIR-LSIF achieved higher peak-sidelobe-level（PSL） of -63.59 dB and better performance in noise suppression.The results show that the Barker code excited guided waves have the potential to be applied to the long bone detection.