Motor unit innervation zones of external anal sphincter from multichannel surface EMG using 2D correlation

Ullah, Khalil and Afsharipour, Babak and Cescon, Corrado and Merletti, Roberto (2014) Motor unit innervation zones of external anal sphincter from multichannel surface EMG using 2D correlation. In: Proceedings of the XX Congress of the International Society of Electrophysiology and Kinesiology, 14-18 July 2014, Rome, Italy.

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AIM: A method, to detect automatically the location of innervation zones (IZ) from 16-channel surface EMG (sEMG) recordings from the external anal sphincter (EAS) muscle, is presented in order to guide episiotomy during child delivery and to avoid damaging the IZs during surgical interventions. The new algorithm (2DCorr) is applied to individual motor unit action potential (MUAP) templates and is based on bidimensional cross correlation between the interpolated image of each MUAP template and its two mirrored images. METHODS: The Multichannel single differential sEMG signals, recorded from EAS using an anal probe comprising an array of 16 equally spaced electrodes placed along the circumference of the probe as depicted in figure 2d, are decomposed using the Correlation Kernel Compensation (CKC) method in order to get the MUAP templates. Each MUAP template, represented as topographic image I where x, y are dimensions in time and space and the gray level is the signal amplitude, is first correlated with its flipped upside down and inverted version I’ and the maximum of the correlation matrix MCCM is identified. The image I is then correlated with its flipped upside down then flipped left right and inverted version I’’ and the maximum of this correlation matrix MCCR is identified. It was found that in case of bidirectional MUAP propagation MCCM ≥ 2MCCR/(N-1) and the IZ corresponds to the location of MCCM, while the opposite holds in case of unidirectional propagation and the location of the IZ is then under the channel showing the earliest signal. N is the number of channels where the MUAP propagation exists. RESULTS: The 2DCorr method is compared with two other existing methods (Radon transform, RT and template match, TM), using 1000 simulated MUAPs generated by means of a cylindrical model of the EAS, and 2000 MUAPs detected on the EAS of 150 pregnant females. The 2DCorr showed the lowest inter quartile range (IQR) error in identifying the innervation zone of both simulated and experimental MUAPs. For simulated MUAP the IQR error for 2DCorr, RT and TM methods was 0.23, 0.42 and 2.32 inter electrode distance (IED) respectively while for experimental MUAPs it was IQR = 0.32, 0.49 and 1.19 IED respectively. CONCLUSION: A novel method for automatic IZ location was developed and tested on simulated and on experimental MUAPs detected from the EAS with a lowest error w. r. t. the two previous methods.

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