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    Home > Active Ingredient News > Study of Nervous System > IEEE trans: Measuring electrical stimulation-induced muscle responses with an optically pumped magnetometer

    IEEE trans: Measuring electrical stimulation-induced muscle responses with an optically pumped magnetometer

    • Last Update: 2021-06-16
    • Source: Internet
    • Author: User
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    In electrophysiological diagnosis, muscle signals, also called compound muscle action potentials (CMAP), are usually recorded on the body surface with surface electrodes
    .
    These EMG signals are triggered by electrical stimulation of different efferent nerve fibers

    .
    The recorded waveforms are analyzed by derived measurements such as nerve conduction velocity, signal amplitude, and distal movement latency, and the results are manually compared with age-appropriate normative data

    .
    Compared with the current recording technology using surface electrodes, magnetic sensing has potential advantages.
    For example, it does not require electrodes to contact the skin, thereby avoiding skin preparation, possible infections or allergic reactions, and body tissues do not affect physiological signals

    .
    These devices operate based on the zero-field resonance of spin-polarized rubidium atoms

    .
    The resulting resonance depends on the strength of the applied magnetic field; therefore, these devices can measure small magnetic fields in the low pT range

    .
    The significant advantage of this system is that it does not require any expensive liquid helium cooling and bulky equipment

    .
     

    This article successfully carried out average and non-average magnetic measurements on the muscles innervated by peripheral nerves (abductor pollicis brevis)
    .
    Perform proximal electrical stimulation in a magnetically shielded room (MSR)

    .
    The results of the magnetic measurement are reported in detail, and the neuroelectrogram data is used as a reference for verification

    .
    Finally, the applicability of OPMs in clinical applications is discussed

    .

    This article successfully carried out average and non-average magnetic measurements on the muscles innervated by peripheral nerves (abductor pollicis brevis)
    .
    Perform proximal electrical stimulation in a magnetically shielded room (MSR)

    .
    The results of the magnetic measurement are reported in detail, and the neuroelectrogram data is used as a reference for verification

    .
    Finally, the applicability of OPMs in clinical applications is discussed

    .

    A typical representative biomagnetic field generated by a neuroelectric dipole source (neuron or muscle tissue)

     The stimulation electrode is located at the location of the median nerve of the subject
    .
    The distance between the electrode and the nerve is minimized by ultrasound stimulation, and the stimulation intensity required to stimulate the entire nerve is reduced

    .
    Next, the subject will be examined by electroencephalography (ENG)

    .
    Generally speaking, motor nerve segments are examined by applying stimulation currents at the proximal and distal ends of the segment and recording the compound muscle action potential (CMAP) of the innervated muscles

    .
    By default, the amplitude, latency, and nerve conduction velocity (NCV) are automatically calculated based on the two recorded CMAPs

    .
    These values ​​are used to determine neuropathology

    .
    Monitor the skin temperature to keep the temperature between 32 and 34°C.
    During the measurement, avoid any physiological effects on electrophysiological variables, including conduction velocity, remote latency (DML) and waveform

    .
    The compound muscle action potential of the abductor pollicis brevis (APB) in the abdominal tendon was recorded with electrodes

    .
      

    Use OPM (4×QZFM zero field magnetometer) to measure magnetic induction in a passive magnetic shielded room to reduce external distortion
    .
    Use MSR (Vacuumschmelze GmbH&Co.
    KG, Hanau, Germany) to effectively suppress interference from the environment.
    MSR is used to suppress electromagnetic AC fields with frequencies higher than 100Hz

    .
    The magnetic shield of the chamber reduces the signal whose frequency starts above 1 Hz by approximately 60 dB, thereby significantly reducing the environmental magnetic noise

    .
    Therefore, MSR is generally suitable for successful measurement of biomagnetic signals because the residual ambient magnetic field is less than 50nT

    .
    A shielded room that meets this high-tech standard is a prerequisite for the successful operation of OPM

    .
    The recorded OPM signals were averaged over 30 single stimuli

    .

    Magnetogram measurement

    OPM measurement shows that the average OPM amplitude response at 300Hz is about -8dB, and the linear attenuation steepness from 100 to 450Hz is about -0.
    027dB/Hz

    .
    In addition, for motor nerve conduction studies, only one test for each stimulation site (one stimulation to the subject) can be used to achieve a complete description of typical conventional variables

    .
    Distal stimulation is critical to the true conduction velocity of nerve fibers, because a single proximal stimulus cannot be calculated

    .
    For nerve conduction velocity, excluding muscle depolarization time and neuromuscular junction transmission, two stimulation sites must be used: a distal end and a proximal end

    .
    Due to the occurrence of strong stimulation artifacts covering physiological signals, remote stimulation near the magnetometer cannot be achieved

    .
    In addition, these sensitive sensors are completely saturated by the stimulation current

    .
    Therefore, the optical pumping magnetometer currently has no significant diagnostic advantage compared with traditional electrical methods

    .

    For the accurate diagnosis of neuromuscular diseases, without any electrical stimulation application, it is very valuable to use single fiber EMG to identify the firing rate and signal shape behavior of contracted muscle fibers
    .
    Therefore, in most cases, the use of needle electrodes is inevitable

    .
    The typical duration of recorded single-fiber muscle signals-also called single motor unit potential (SMUP) 

    .
    But OPM cannot detect it

    .
    Only the larger physiological signals are magnetically recorded and analyzed

    .
    Magnetoencephalogram and magnetocardiogram (MCG) are more suitable for clinical applications than electromyography
    .

    Magnetoencephalogram and magnetocardiogram (MCG) are more suitable for clinical applications than electromyography
    .

    E.
    Elzenheimer, H.
    Laufs, W.
    Schulte-Mattler and G.
    Schmidt, "
    Magnetic Measurement of Electrically Evoked Muscle Responses With Optically Pumped Magnetometers ," in 
    IEEE Transactions on Neural Systems and Rehabilitation Engineering

    E.
    Elzenheimer, H.
    Laufs, W.
    Schulte-Mattler and G.
    Schmidt, "
    Magnetic Measurement of Electrically Evoked Muscle Responses With Optically Pumped Magnetometers ," in 
    Magnetic Measurement of Electrically Evoked Muscle Responses With Optically Pumped Magnetometers IEEE Transactions on Neural Systems and Rehabilitation Engineering

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