WO2002053012A2

WO2002053012A2 - A CLINICAL ELECTRODIAGNOSTIC DIGITAL INSTRUMENT FOR ELECTROMYOGRAPHY (emg) AND/OR NERVE CONDUCTION MEASUREMENT

Info

Publication number: WO2002053012A2
Application number: PCT/IN2001/000046
Authority: WO
Inventors: Roland Suresh Devasahayam
Original assignee: Indian Institute Of Technology
Priority date: 2001-01-04
Filing date: 2001-03-22
Publication date: 2002-07-11
Also published as: AU2001255055A1; WO2002053012A3; WO2002053012A8; AU2001255055A8

Abstract

A clinical electrodiagnostic digital instrument for electromyography (EMG) and/or nerve conduction measurement. At least one signal pickup channel (1D) comprising a pair of pickup electrodes (4d, 5d) are adapted to be removably fixed at a location for instance (C) on palm (10) under testing. The pick up electrodes are connected to a biopotential amplifier (7d), a frequency filter (8d) and an isolator (9d). Optionally a stimulator channel (11) comprising a pair of stimulation electrodes (12a, 12b) are adapted to be removably fixed at a location, for instance D on hand (6) close to the location under testing and connected to an electronic stimulator (13). The isolator and electronic stimulator are connected to a stereo input jack (2) which is connectable to stereo multimedia card of a PC (3). Ref Fig. 3. Also a method of calibrating the instrument jointly with the multimedia card.

Description

TITLE OF INVEJNΓTION

A clinical electrodiagnostic digital instrument for electromyography (EMG) and/or nerve conduction measurement.

This invention also relates to a method of calibrating the above clinical electrodiagnostic digital instrument jointly with the multimedia card of a personal computer.

PRIOR ART

Diagnosis of certain neuromuscular diseases and evaluation of recovery from these diseases are done using a class of instruments called clinical electrodiagnostic instruments or clinical electrophysiological instruments. The testings done by these instruments are broadly classified into two groups namely electromyography (EMG) and evoked responses from nerves. EMG is the technique of measuring electrical signals from muscles and is used in clinical diagnosis of muscle and motor nerve diseases. Nerve conduction measurement involves artificial stimulation of a nerve by applying a signal to the nerve and recording the resulting evoked electrical signals or responses from the same nerve, another connected nerve or from connected muscles for studies of the nervous system.

Clinical electrodiagnostic instruments may be analog type which makes use of cathode ray oscilloscopes (CRO) for signal processing and display. Electrodiagnostic analog instruments are inherently incapable of numerical calculations. A typical clinical electrodiagnostic digital instrument for EMG and/or nerve conduction measurement comprises at least one signal pickup channel and optionally a stimulator channel connected to a dedicated microprocessor or personal computer (PC) through a dedicated data acquisition system. The signal pickup channel comprises a pair of pickup electrodes connected to a biopotential amplifier, a frequency filter and an isolator. The stimulator channel comprises a pair of stimulation electrodes connected to an electronic stimulator. The dedicated data acquisition system includes components such as analog to digital converter, memory, timer and digital filter. It is complicated in construction and difficult to maintain and is also expensive due to the data acquisition system being complicated in construction and expensive. A dedicated microprocessor or PC also adds to the cost of the instrument. Because it can function only in combination with the dedicated microprocessor or PC it is not versatile in use and its scope of use and computational power are limited to its configuration with the microprocessor or PC. A dedicated data acquisition system is custom made and its use is limited to the designed instrument and it has limited proven performance. Hie performance characteristics of the dedicated data acquisition system may vary from manufacturer to manufacturer. Clinical electrodiagnostic digital instruments for EMG require components such as digital to analog converters, audio output amplifiers, audio speakers and high capacity storage (hard disks) for audio play back or review. Such components are very expensive. Resolution and accuracy of reading of a given electrodiagnostic digital instrument is limited to the number of bits used therein due to the dedicated nature of the instrument. DISCLOSURE OF INVENTION

An object of the invention is to provide a clinical electrodiagnostic digital instrument for electromyography and/or for nerve conduction measurement, which is simple in construction and easy to maintain and is also economical.

Another object of the invention is to provide a clinical electrodiagnostic digital instrument for electromyography and/or nerve conduction measurement, which is versatile and may be configured with any computer or computer network thereby providing computational power available for essentially limitless calculations.

Another object of the invention is to provide a clinical electrodiagnostic digital instrument for electromyography and/or nerve conduction measurement, which facilitates electromyography and or nerve conduction measurement at different locations of a human body simultaneously.

Another object of the invention is to provide a clinical elecfxodiagnostic digital instrument for electromyography and/or nerve conduction measurement, which is capable of giving desired level of resolutions and accuracy of readings.

Another object of the invention is to provide a clinical diagnostic digital instrument for electromyography and/or nerve conduction measurement which has inherent aucho output capability during recording as well as playback. Another object of the invention is to provide a method of cahbrating the above clinical electrodiagnostic digital instrument jointly with the multimedia card of a personal computer.

According to the invention there is provided a clinical electrodiagnostic digital instrument for electromyography (EMG) and/or nerve conduction measurement comprising at least one signal pickup channel and optionally atleast one stimulator channel connected to an audio input jack which is connectable to multimedia card of a personal computer (PC), the signal pick up channel comprising a pair of pickup electrodes adapted to be removably fixed at a location of a human body under testing and connected to a biopotential amplifier, a frequency filter and an isolator and the stimulator channel comprising a pair of stimulation electrodes adapted to be removably fixed on the human body close to the location under testing and comiected to an electronic stimulator, the isolator and electronic stimulator being connected to ih input jack.

According to an embodiment of the invention the instrument comprises one signal pick channel connected to one channel of a multimedia card through one channel of an audio input jack.

According to another embodiment of the invention the instrument comprises two signal pickup channels comiected to tir two channels of a stereoaudiomultimedia card through the two channels of stereoau io input jack.

According to another embodiment of the invention the instrument comprises one signal pickup channel and one stimulator channel connected to the two channels of a stereoaudio multimedia card through the two channels of a stereoaudio input jack.

The high frequency filters of the multimedia cards are designed to remove frequencies below 20 Hz. Electromyography and evoked nerve signals are generally within frequencies of 20Hz-10KHz. Therefore, audio input circuitry of multimedia cards is suitable for processing electromyography and evoked nerve signals. Multimedia cards are, however, designed to accept signals from a variety of sources from microphones to electronic musical instruments. These signals are not standardised in terms of voltage but only in terms of relative magnitude or power ie decibels (dB). Variations in analog amphfications in the audio input circuitry of multimedia cards are inevitable across manufacturers of multimedia cards. Therefore, calibration (tuning or standardisation) of the multimedia card with the signal pickup channel for voltage gain is required to be carried to get accurate readings by the instrument.

The multimedia cards are available as stereocards or quadrophonic cards.

According to the invention there is also provided a method of caHbrating a clinical electrodiagnostic digital instrument for electromyography (EMG) and/or nerve conduction measurement as described above jointly with a multimedia card of a personal computer (PC) comprising :

(a) applying a precision amplitude input signal from an analog signal generator to the input of the biopotential amplifier in each pickup channel;

(b) electronically setting by software control the analog gains of the audiomixer with volume control in the input amplifier of each audio channel in the multimedia card to the minimum gain value and deteπniniiig the magnitude of the minimum gain value in digital data form;

(c) electronically setting by software control the analog gains of the audiomixer with volume control in the input amplifier of each audio channel in the multimedia card to the maximum gain value and determining the magnitude of the maximum gain value in digital data form;

(d) adjusting the gain of each biopotential amphfier in each pickup channel such that the combined gain of the biopotential amphfier and minimum analog gain of the multimedia card results in a digital value of 2 -1 where N is the number of bits of resolution of each audio channel of the multimedia card when the input signal to each pickup channel equals the largest possible signal amplitude;

(e) recording the digital value of the signal magnitude for each audiochannel of the multimedia card at various intermediate analogue gain settings for each audiochannel of the multimedia card and making a lookup table of intermediate gain settings.

The following is a detailed description of the invention with reference to the accompanying drawings, in which : 1

Fig 1 is block diagram of a clinical electrodiagnostic digital instrument for EMG according to an embodiment of the invention;

Fig 2 is block diagram of a clinical electrodiagnostic digital strument for EMG according to another embodiment of the invention;

Fig 3 is block diagram of a clinical electrodiagnostic digital instrument for EMG and or nerve conduction measurement according to an embodiment of the invention; and

Fig 4 represents two evoked responses recorded with a typical instrument of Fig 3.

Referring to Fig 1 of the accompanying drawings, the instrument comprises a signal pickup channel 1 A connected to one channel of a stereo audio input jack 2 which in turn is connected to one channel of a stereo multimedia card (not shown) of a personal computer (PC) 3. The signal pick up channel comprises pair of pick up electrodes 4a and 5a adapted to be removably fixed at a location A of hand 6 under testing. The pick up electrodes are connected to a biopotential amphfier 7a, a frequency filter 8a and an isolator 9a which in turn is connected to the one channel of the audio input jack. The instrument is either battery powered or powered by a well isolated power supply. During operation of the instrument, the pick up electrodes sense the electrical signals from the muscles at the location under testing which are generally in the range of about 10 μv to 50 mV. The electrical signals are amplified by the biopotential amphfier and frequency filtered by the filters to remove frequencies outside the desirable range which is within 20 Hz to 10 KHz. The frequency filtered signals are input to the one channel of the multimedia card of the PC through the audio input jack. The multimedia card may comprise, besides the audio channels, audio mixer with voltage gain adjustment or volume control, analog to digital converter, digital to analog converter, audio amplifiers speakers and high capacity storage. The multimedia card controls the voltage gain of the input signal and converts the signal into digital data suitable for use by the PC which stores, displays and performs calculations on the digital data. The multimedia card may also receive the digital data and convert the digital data into analog form and output to the speakers during measurement as well as playback. The other audio channels of the input jack and multimedia card are not made use of in the embodiment of Fig 1.

Referring to Fig 2 of the accompanying drawings, the instrument comprises two signal pick up channels IB and 1C connected to two channels of a stereo audio input jack 2 which in turn are connected to two channels of a stereo multimedia card (not shown) of a PC 3. The pick up electrodes 4b and 5b of channel IB are adapted to be removably fixed at a location A of hand 6 and connected to biopotential amphfier 7b, frequency filter 8b and isolator 9b. Similarly the pickup electrodes 4c and 5c of channel 1C are adapted to be removably fixed at a location B of hand 6 and connected to biopotential amphfier 7c, frequency filter 8c and isolator 9c. The isolators 9b and 9c of the two channels are connected to the two channels of the stereo audio jack which in turn are connected to the two channels of the stereo multimedia card. The multichannel instrument of Fig 2 facilitates EMG at two different locations A and B simultaneously. Referring to Fig 3 of the accompanying drawings, the instrument comprises a signal pickup channel ID connected to one channel of a stereoaudio input jack 2 which in turn is connected to one channel of a stereo multimedia card (not shown) of a PC3. The pickup electrodes 4d and 5d of channel ID are adapted to be removably fixed at a location C in the palm 10 of hand 6 and connected to biopotential amplifier 7d, frequency filter 8d and isolator 9d. The isolator 9d is connected to the one channel of the stereoaudio input jack. The instrument also comprises a stimulator channel 11 comprising a pair of stimulation electrodes 12a and

12b adapted to be removably fixed at a location D of the hand close to the palm. The stimulation electrodes are connected to an electronic stimulator 13 which in turn is connected to the other channel of the stereo audio input jack. The two channels of the audio input jack are also connected to the two channels of the stereo multimedia card. An electrical stimulus is applied to the stimulation electrodes at time T_<> from the electronic stimulator. This stimulus initiates biological activity at the location D where the stimulation electrodes 12a and 12b are fixed and the effects of this initiated biological activity travel in ύin hand and reaches the location C in the palm where it is picked up by the pickup electrodes. The time at which the response at the location C in the palm is observed is noted at i. At the time the stimulus is applied (T₀), a synchronization signal is also sent from the stimulator to the multimedia card. The mteivening region between the two sets of electrodes determines the time taken between the apphcation of the stimulus and the observed response. i - T₀ gives the latency of the evoked response which is processed by the multimedia card and PC as described earlier. The amplitude of this sj ichronization signal is not important. It is a binary signal and only its time of occurrence is important. Hence there is no need to calibrate the amplitude of the synchronization signal from the stimulator. Using a typical instrument of Fig 3 two evoked responses were recorded as shown in Fig 4 of the accompanying drawings. Each plot in Fig 4 begins at the time of stimulation. The recording sites ie locations were the same, but the stimulation sites were different. The latency is shown by an arrow. In case the instrument of Fig 3 is to record only EMG, then the PC is programmed to ignore signal from the electronic stimulator.

According to the invention the dedicated data acquisition system and dedicated microprocessor and PC have been eliminated. Instead a simple and inexpensive audio input jack is used and it may be plugged into a multimedia card of any PC or network of PCs provided with multimedia card(s). Thus the invention may be configured with any PC or network of PCs provided with multimedia card(s). Due to elimination of the dedicated data acquisition system and dedicated microprocessor and PC, the instrument of the invention is simple in construction and easy to maintain and is economical. It may be configured with any PC or network of PCs to provide versatility of operation and computational power for essentially limitless number of calculations.

Multimedia cards are mass produced, widely tested and used and robust and of proven performance and reliability. Therefore, the instrument of the invention is also very reliable and of high performance. The instrument of the invention may comprise multichannels to facilitate electromyography and nerve conduction measurement at different locations of a human body simultaneously. It has audio output capability during recording as well as review or playback because multimedia cards are inbuilt with audiochannels, audiomixer with voltage gain adjustment or volume control, analog to digital converter,digital to analog converter, audio amplifiers, audio speakers and high capacity storage. Because it may be configured with any PC or network of PCs it is capable of giving any desired level of resolution and accuracy of readings depending upon the number of bits in the multimedia cards in the PC or network of PCs. Currently multimedia cards containing upto 16 bits, 20 bits or 24 bits are available to give correspondingly high resolution and accuracy of readings.

The above embodiments of the instrument are to be construed to be by way of examples. Several variations of the invention are possible without deviating from the scope thereof. The input jack and multimedia card each may comprise only one audio channel. The instrument may comprise more than two pick up channels. The instrument also may comprise two or more stimulator channels and corresponding number of pickup channels. In both the above cases the audio input jack and the multimedia card have to have corresponding number of channels. The frequency filters are optional as the instrument will work without them. But frequency filters are desirable for accurate measurements. The instrument will work without the isolators also but they are required from safety considerations. Such variations of the instrument are to be construed and understood to be within the scope of the invention.

At the time of installation of the instrument, analog gain calibration jointly with the multimedia card of the PC is carried out as follows:

Step 1 : A precision amplitude signal from an analog signal generator is applied to the input of the biopotential amphfier in each pickup channel. This signal may be for instance a sinusoid of fixed frequency between 200 Hz and 4000Hz and fixed magnitude say 1 mV.

Step 2 : The analog gains of the audio mixer with volume control in the input amphfier of each audio channel in the multimedia card is electronically set by software to the minimuin gain value, designated Gi. The input sinusoidal data are read and the magrntude of the rainimu gain data in digital value is determined and designated as A_\.

Step 3 : The analog gains of the audio mixer with volume control in the input amplifier of each audio channel in the multimedia card is electronically set by software to the maximum gain value, designated G₂.

The input sinusoidal data are read and the magnitude of the maximum gain data in digital value is deteπnined and designated as ..

Ensure that the sinusoidal data as read in digital form is not saturated. If it is saturated, then reduce the magnitude of the sinusoid in the analog signal generator and repeat steps 2 and 3.

Step 4 : The peak-to-peak amplitude of the input signal from the signal generator to each pick up channel is electronically set by software control to be Mi R. where Mi is the largest biopotential signal that will be observed during normal use of the instrument and R is analog gain range of the audio mixer with volume control of the multimedia card ie A₂/Aι .

The voltage gain (volume control) of each audio channel in the multimedia card is electronically set by software control to its maximum value. With the input signal switched on continuously the digital values in the PC are read and the gain control in each biopotential amphfier is adjusted so that the digital value of the peak-to-peak amplitude is maximum, ie, 2^N-1 where N = number of bits of resolution of each audio channel of the multimedia card. This means that when the signal amplitude is Mj and the audio input gain setting is minimum Gi the digital reading will be 2^N-1 which is the maximum input range or the minimum overall gain of the instrument.

Step 5 : At various intermediate gain values of each audio channel of the multimedia card the digital value of the signal magnitude for each gain setting is read. Using these readings a look-up table of intermediate gain settings for the instrument is obtained. Therefore, all the gain settings of the instrument are completely calibrated and do not assume linearity or accuracy among different manufacturers of multimedia cards.

The joint eahbration of both the pickup channel and multimedia card is necessary only once during the matehing of the pickup channel with any manufacturer's multimedia card for a PC; ie only during installation of the instrument.

If the smallest range of biopotential signals that will be observed during normal use of the instrument is M₂ (this value varies depending on the user, but is typically 200μV or less), the desired gain range Q = Mι M₂ is compared with the value of R. If Q is greater than R which is usually the case then the remaining amplification is obtained by "soft magnification". This means that in order to obtain a full scale range of Mz the data is displayed with the digital value 2^N/(Q R) occupying the full scale.

Thus maximum input range or minimim overall gain of the instrument is obtained by multimedia audio analog gain set to Gi and full scale display containing 2^N-ldigital levels of information (digital resolution is N bits), and minimum input range or maximum overall gain of the instrument is obtained by multimedia audio analog gain set to G₂ and full scale display containing 2^N/(Q R)digital levels of information (digital resolution is log₂[2^N/(Q R)] bits) and intermediate input ranges are obtained using a combination of the analog gain in the audio input and "soft

The analog gain cahbration may be illustrated by the following typical examples :

(a) The instrument is to be provided with a maximum input full scale reading of 50mV and a minimum input full scale reading of 195μV. The available multimedia audio card has 16 bit digital resolution, and a software controlled analog gain range of 16.

N= 16, R = 16, Q=50mV/195μV=256

2* = 65536

In this case the input full scale reading from 50mV to

3.125mV may be obtained by adjusting the software controlled analog audio gain of the multimedia card. The digital resolution for these input full scale reading is 16 bits. For input full scale reading from 3.125mV to

195μV, the software controlled analog audio gain is kept at its maximum and "soft magnification" is used. The digital resolution progressively reduces until at the input full scale reading of 195μV the digital resolution is 12 bits.

(b) For the same requirements as in the illustration at (a) above if a 20 bits multimedia audio card is used : N = 20, R = 16, Q = 50mV/195μV=256

2^W = 1048576

In this case the input full scale reading from 50mV to 3.125 may be obtained by adjusting the software controlled analog audio gain of the multimedia card. The digital resolution for these input full scale reading is 20 bits. For input full scale reading from 3.125mV to 195μV, the software controlled analog audio gain is kept at its maximum and "soft magnification" is used. The digital resolution progressively reduces until at the input full scale reading of 195μV the digital resolution is 16 bits.

Claims

1) A clinical electrodiagnostic digital instrument for electromyography (EMG) and or nerve conduction measurement comprising at least one

5 signal pickup channel and optionally atleast one stimulator channel connected to an audio input jack which is connectable to multimedia card of a personal computer (PC), the signal pick up channel comprising a pair of pickup electrodes adapted to be removably fixed at a location of a human body under testing and connected to a biopotential amplifier, a w frequency filter and an isolator and the stimulator channel comprising a pair of stimulation electrodes adapted to be removably fixed on the human body close to the location under testing and connected to an electronic stimulator, the isolator and electronic stimulator being connected to the input jack.

15

2) A clinical electrodiagnostic digital instrument as claimed in claim 1, which comprises one signal pick channel connected to one channel of a multimedia card through one channel of an audio input jack.

20 3) A clinical electrodiagnostic digital instrument as claimed in claim 1, which comprises two signal pickup channels connected to the two channels of a stereoaudio multimedia card through the two channels of a stereoaudio input jack.

25 4) A clinical electrodiagnostic digital instrument as claimed in claim 1, which comprises one signal pickup channel and one stimulator channel connected to the two channels of a stereoaudio multimedia card through the two channels of a stereoaudio input jack. 5) A clinical electrodiagnostic digital instrument for electromyography (EMG) and/or nerve conduction measurement substantially as herein described particularly with reference to Fig 1 or Fig 2 or Fig 3 of the accompanying drawings.

6) A method of calibrating a clinical electrodiagnostic digital instrument for electromyography (EMG) and/or nerve conduction measurement as claimed in claim 1 jointly with a multimedia card of a personal computer (PC) comprising :

(a) applying a precision amplitude input signal from an analog signal generator to the input of the biopotential amphfier in each pickup channel;

(b) electronically setting by software control the analog gains of the audiomixer with volume control m the input amplifier of each audio channel in the multimedia card to the nώnmum gain value and deterrmning the magnitude of the minimuni gain value in digital data form;

(c) electronically setting by software control the analog gains of the audiomixer with volume control in the input amphfier of each audio channel in the multimedia card to the maximum gain value and detemώiing the magnitude of the maximum gain value in digital data form;

(d) adjusting the gain control of each biopotential amphfier in each pickup channel such that the combined gain of the biopotential amplifier and minimum analog gain of the multimedia card results in a digital value of 2^-1 where N is the number of bits of resolution of each audio channel of the multimedia card, when the input signal to each pickup channel equals the largest possible signal amphtude;

7) A method as claimed in claim 6, wherein the precision amphtude input signal is sinusoid of fixed frequency between 200 Hz and 4000 Hz and fixed magnitude between lOOμV and 10 V

8) A method of calibrating a clinical electrodiagnostic digital instrument for electromyography (EMG) and/or nerve conduction measurement as claimed in claim 1 jointly with a multimedia card of a Personal Computer (PC) substantially as herein described.