Intraoperative Somatosensory Evoked Potential Monitoring Based On Time-frequency Analysis

Spine surgery is one of the most utility to treat many spine and spinal cord diseases.But it has the risk of damaging spinal cord and neurological functional disorder or permanent crippledom and paraplegia.Intraoperative spinal cord monitoring can detect spinal cord function during surgery,so as to adopt methods immediately in abnormal situation,prevent unreversible neurological function damage.However,false positive and false negative cases have always been a serious problem which doctors and monitoring staffs concerned.Therefore,the research of improve intraoperative spinal cord monitoring is very important.Our study aims at extracting time-frequency characteristic from somatosensory evoked potential(SEP) during surgical treatment of cervical surgery and scoliosis, and confirm the distributing range of normal SEP in time-frequency domain(TFD), studying the reliability of spinal cord monitoring by somatosensory evoked potential (SEP) which has been processed by time-frequency analysis.A total of 62 patients with cervical diseases by surgery were enrolled during January 1997 to January 2006. Cortical evoked potentials of 62(100%) cases were effective,female 20,male 42, aged 12～82 years(mean age 58.3 ) A total of 183 patients with scoliosis by surgery were enrolled during September 1998 to January 2006.Cortical evoked potentials of 168(92%) cases were effective,female 129,male 39,aged 7～40 years(mean age 16.8) subcortical evoked potential of 183(100%) cases were effective,female 144, male 39,aged 7～40 years(mean age 16.69).Short time fourier transform(STFT) were applied to analyze the intraoperative somatosensory evoked potential,three monitoring parameters in time-frequency domain were extracted and compared with time domain parameters.The peak power showed less variability than amplitude.Peak time of median nerve(MN) SEP(C3',C4') centered at(19.8±3.2) ms,from 10 to 29 ms,peak frequency centered at(125.2±13.0) Hz,from 90 to 164Hz;Peak time of posterior tibial nerve(PTN) SEP(Cz') centered at(41.2±4.1) ms,from 29 to 55 ms,peak frequency centered at(53.6±6.2) Hz,from 37 to 79Hz;Peak time ofPTN SEP(Cv) centered at(30.1±2.9)ms,from 21 to 39 ms,peak frequency centered at(81.8±4.9) Hz,from 67 to 111Hz.It is demonstrated that normal cortical and subcortical SEP has a stable distribution range in TFD of STFT,peak power showed less variability than amplitude, the peak in TFD is stable and easy to identify,which provides the basis in setting automatic judgment criteria for clinical monitoring.