Transcutaneous innervation zone imaging from high-density surface electromyography recordings.

OBJECTIVE: It is of great value to accurately localize innervation zones (IZs) to better diagnose and treat neuromuscular diseases, but it is challenging to do so noninvasively from surface electromyography (sEMG) recordings because of the blurring/distorting effect of the low conductive fat tissues. This study aimed to develop an innovative transcutaneous IZ imaging (TIZI) technique to precisely and efficiently localize the IZ distribution directly over the muscle surface in vivo from high-density sEMG recordings (HD-sEMG). APPROACH: The TIZI technique was implemented by incorporating HD-sEMG recording, signal decomposition, finite element analysis and inverse calculation. The performance of TIZI was evaluated on the flexor digitorum superficialis (FDS) muscle with simulated sEMG signal and experimental signal recorded from both healthy (n = 3) and stroke participants (n = 4). The accuracy of imaging was validated by both of the Pearson correlation coefficient (PCC) and localization error (LE) between the TIZI results and the 'true' IZ distribution. MAIN RESULTS: In the simulation study, results have shown PCCs of 99.85% ± 0.11%, 99.79% ± 0.08%, 99.63% ± 0.22% and 99.31% ± 0.54% at the depth of 10, 15, 20 and 25 mm and SNR of 25 dB. PCCs of 98.74% ± 1.78% and 97.82% ± 1.20% were respectively obtained for experimental signals acquired from the healthy and spastic FDS muscles. The TIZI provided smaller LEs of 1.4 ± 0.92 mm and 2.02 ± 1.3 mm, compared to LEs of 7.42 ± 2.29 mm and 7.8 ± 1.77 mm from skin observations in healthy and spastic FDS, respectively. SIGNIFICANCE: Results have demonstrated the high performance of the proposed TIZI technique by transcutaneous imaging of the IZ distribution of the skeletal muscles. The performance improvement can be attributed to the elimination of the blurring/distorting effect caused by the low conductive fat and high conductive skin tissues. TIZI may provide an advanced neurological tool for the clinical treatment of neuromuscular diseases, such as guiding botulinum neurotoxin injections in spasticity management.