A Novel Latency Estimation Algorithm of Motor Evoked Potential Signals

Abstract

Evaluation of motor evoked potential (MEP) signals elicited by transcranial magnetic stimulation (TMS) over the motor cortex provide a measure of cortico-motor excitability at the time of stimulation. In the research and clinical medical practice, the MEP latency is a relevant neurophysiological parameter to determine conduction time for neural impulses from the cortex to peripheral muscles. State changes at different levels of signal propagation through the neural tissue can significantly influence MEP latency, based on which different medical diagnoses can be issued. This study aims to present the Squared Hard Threshold Estimator (SHTE), which is a novel and improved algorithm for MEP latency estimation. Analyses presented in the paper were based on the SHTE algorithm, which was efficiently applied to a large number of MEP signals recorded from hand muscles. The SHTE algorithm was compared with other prominent methods such as the absolute hard threshold estimation (AHTE) algorithm, the statistical measures (SM) algorithm, and manual assessment. Results obtained in terms of robustness test and statistical analysis show that the proposed SHTE algorithm is reliable in estimating MEP latency, especially for the MEP signals having peak-to-peak (PTP) amplitudes lower than one hundred microvolts. Compared with the AHTE and SM algorithms, the SHTE shows a lower percentage deviation index in MEP latency estimation of the MEP signals with the PTP amplitudes lower than one hundred microvolts. Hence, the proposed SHTE algorithm represents an improved armamentarium in automatic MEP latency estimation.

Assessment of Motor Evoked Potentials in Multiple Sclerosis

“…According to the current research state, all algorithms show an accurate estimation of the latency for the peak-to-peak amplitudes greater than 100 µV. However, for the peak-to-peak amplitudes between 50 and 100 µV, the SHTE algorithm shows a slightly better accurate latency estimation than AHTE and SM, which is validated by performing a robustness test and calculating the percentage of the deviation index (PDI) [ 68 ]. We believe that there is room for improvement in latency estimation for the MEPs with peak-to-peak amplitudes of less than 100 µV; this is generally for research and clinical purposes, in order to evaluate corticospinal tract integrity.…”

“…The automated latency estimation algorithms could be divided into the following categories: algorithms based on the absolute hard threshold estimator (AHTE), which are based on using hard threshold and so-called magic number [ 69 ], and algorithms that are based on statistical measures (SM), which use a standard deviation metric to find a magic number to determine the onset of the MEP [ 70 , 71 , 72 ]. Further, there is an algorithm based on the squared hard thresholded estimator (SHTE), where the coefficients of the MEP are squared and then thresholded to obtain a magic number and, thus, obtain the onset of the MEP [ 68 ]. Finally, there is an algorithm based on approximating the first derivative to find the time point of the initial deflection to determine the onset of the MEP [ 73 ].…”

“…Legend: the red dashed line denotes the mean response of all MEPs, and the blue dash-dotted line represents the median response of all MEPs. MEP latency and amplitude estimation was performed by a custom-made Matlab script (R2021a) using an automatic algorithm, developed by Šoda et al (2020) [ 68 ].…”

“…Reference values were taken and adapted according to * Rossini et al from 2015 [ 17 ]. MEP latency and amplitude estimation was performed by a custom-made Matlab script (R2021a) using an automatic algorithm, developed by Šoda et al in 2020 [ 68 ], which can automatically detect peak-to-peak MEP amplitudes lower than 50 µV.…”

The Patho-Neurophysiological Basis and Treatment of Focal Laryngeal Dystonia: A Narrative Review and Two Case Reports Applying TMS over the Laryngeal Motor Cortex

“…The corticospinal excitability measures (RMT, amplitude, and latency of motor evoked potentials for upper extremity muscles) and corticobulbar excitability measure (motor evoked potential latency from cricothyroid muscle) performed with single pulse transcranial magnetic stimulation (TMS) over the primary motor cortex (Nexstim NBS System 4 of the manufacturer Nexstim Plc., Helsinki, Finland) [ 4 , 94 , 95 ]. The MRI of the subject’s head was performed with Siemens Magnetom Area having Tim (76 × 18) of strength 1.5 T. MRI images were used for the 3D reconstruction of individual brain anatomy.…”