TSS Group Translational System & Signal Processing Group Artifact Characterization and Removal for In-Vivo Neural Recording* M. K. Islam, A. Rastegarnia, A. T. Nguyen and Z. Yang Abstract Background: In vivo neural recordings are often corrupted by different artifacts, especially in a less-constrained recording environment. Due to limited understanding of the artifacts appeared in the in vivo neural data, it is more challenging to identify artifacts from neural signal components compared with other applications. The objective of this work is to analyze artifact characteristics and to develop an algorithm for automatic artifact detection and removal without distorting the signals of interest. Proposed method: The proposed algorithm for artifact detection and removal is based on the stationary wavelet transform (SWT) with selected frequency bands of neural signals. The selection of frequency bands is based on the spectrum characteristics of in vivo neural data. Further, to make the proposed algorithm robust under different recording conditions, a modified universal-threshold value is proposed. Results: Extensive simulations have been performed to evaluate the performance of the proposed algorithm in terms of both amount of artifact removal and amount of distortion to neural signals. The quantitative results reveal that the algorithm is quite robust for different artifact types and artifact-to-signal ratio. Comparison with existing methods: Both real and synthesized data have been used for testing the pro-posed algorithm in comparison with other artifact removal algorithms (e.g. ICA, wICA, wCCA, EMD-ICA, and EMD-CCA) found in the literature. Comparative testing results suggest that the proposed algorithm performs better than the available algorithms. Conclusion: Our work is expected to be useful for future research on in vivo neural signal processing and eventually to develop a real-time neural interface for advanced neuroscience and behavioral experiments. Test on Synthesized Data Proposed Algorithm Test on Real Data-1: Monkey Artifact SNR (dB) Amount of Artifact Reduction, λ (Ideal value = 100) Proposed wICA wCCA ICA EMD-ICA EMD- CCA 5 58 30 45.5 46.45 -1.82 9 10 85 8 40 33.1 -3.8 3.4 15 90 -1 37 38.2 22.25 1.3 20 60 5 29 25.1 26 16 25 18.5 -3.5 8.85 17.25 -5.5 4.2 Artifact SNR (dB) Signal SNR Improvement, ΔSNR Proposed wICA wCCA ICA EMD- ICA EMD- CCA 5 7.5 4 0.5 6.67 0.02 0.6 10 16 6.2 5 8 0.05 2.93 15 20 5 9.8 12.3 12.4 3.05 20 18 5.5 15.2 13.9 9.5 4.58 25 17.6 5.4 13.1 13.3 3.5 5.1 Artifact SNR (dB) Improve in Spectral Distortion Proposed wICA wCCA ICA EMD-ICA EMD- CCA 5 49.5 - 13.03 -4.17 -1.21 -5.35 -3.5 10 184 - 23 -7 -2.2 -10.5 -9 15 4.88e3 -25 -3.95 -2.52 -1.0 -70 20 5.34e4 -36.4 -1.92 -1.4 -9.6 -37.5 25 5.65e5 -40 16.15 5.69 -164.5 -60.48 Comparison with Other Methods SNDR Comparison Performance Metrics vs Artifact SNR SWT Coefficients’ Sub-bands 0 1 2 3 -4 -2 0 2 Type 1 0 2 4 6 8 10 -5 0 5 Type 0 Artifact Characterization 0 0.5 1 -2 -1 0 1 m p l i t u d e , m V Type 2 0 0.05 0.1 0.15 0.2 -10 -5 0 5 Ti S Type 3 Artifact Reduction Signal Distortion 10 -3 10 -2 10 -1 10 0 10 1 -60 -40 -20 0 20 40 60 Freq, kHz S N D R , d B SNDR Before SNDR After 4 6 8 10 12 14 16 18 20 10 -2 10 0 10 2 10 4 10 6 Artifact SNR in dB S p e c t r a l D i s t o r t i o n Artifactual Reconstructed 5 10 15 20 0 20 40 60 80 100 Artifact SNR in dB % a r t i f a c t r e d u c t i o n , l a m d a 4 6 8 10 12 14 16 18 20 0 0.05 0.1 0.15 0.2 Artifact SNR in dB R M S E Artifactual Reconstructed 5 10 15 20 0 5 10 15 20 25 30 Artifact SNR in dB d e l S N R i n d B Test on Real Data-2: Rat 0 1 2 3 4 5 6 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 Time, Sec A m p l i t u d e , m V Artifactual Reconstructed 2.6 2.8 3 3.2 3.4 3.6 3.8 4 -0.1 0 0.1 A m p l i t u d e , m V LFP Real Reconstructed 3.506 3.508 3.51 3.512 3.514 3.516 3.518 3.52 3.522 3.524 3.526 -8 -6 -4 -2 0 2 4 Time, Sec N o r m a l i z e A m p l i t u d e Spike Data Real Reconstructed 0 1 2 3 4 5 6 7 8 9 10 -6 -4 -2 0 2 0 1 2 3 4 5 6 7 8 -6 -4 -2 0 2 Amplitude, mV Time, Sec Type-2 Artifact Type-3 Artifact *Md Kafiul Islam, Amir Rastegarnia, Anh Tuan Nguyen, Zhi Yang: Artifact Characterization and Removal for In-Vivo Neural Recording. Journal of Neuroscience Methods 04/2014; 226(C):110-123. Artifact SNR (dB) Improve in Temporal Distortion, RMSE (Root Mean Square Error) Proposed wICA wCCA ICA EMD- ICA EMD- CCA 5 0.02 0.06 2.1e-3 0.023 1.6e-4 3.6e-3 10 0.044 0.082 -0.05 0.037 0.002 7e-3 15 0.102 0.10 0.07 0.085 0.08 0.016 20 0.17 0.098 0.145 0.164 0.137 0.06 25 0.32 0.114 0.28 0.243 0.031 0.12