real-time multichannel computerized electrogastrograph

1228 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 44, NO. 12, DECEMBER 1997

Real-Time Multichannel ComputerizedElectrogastrograph

Mingying Zhou,* Hui Zhang, Robert Shaw, and Frank S. Barnes,Life Fellow, IEEE

Abstract—The purpose of this study was to develop a real-time multichannel computerized electrogastrograph (EGG) tomeasure and analyze electrical signals from the human abdom-inal surface. A soft-contact matrix composed of 25 cutaneouselectrodes is embedded evenly in a latex mat. The mat can befirmly attached to the abdominal surface by drawing a vac-uum between the matrix and the stomach. Twenty-five high-amplification filter/amplifiers provide a high signal-to-noise ratioand flat amplitude response for a signal between 0.02 and 0.12Hz (1.2–7.2 cpm). The computer program provides waveformand frequency analysis for any chosen channel and mappinganalyses for all 25 channels. A two-dimensional propagationexploration program was also developed. Using four differentmapping analysis program subroutines, the optimal points foranalyzing the EGG signals can be reliably found and variabilityof these locations can be observed easily. Results show differencesin the EGG mappings of normal and abnormal subjects.

Index Terms—Amplifier, electrode, electrogastrogram, electro-gastrograph, filter, mapping, signal analysis, stomach.

I. INTRODUCTION

T HE first electrogastrogram (EGG) was made by Alvarezin 1921 [1]. The recorded signal resembled a sine wave

with a frequency of three cycles per min (cpm) [1]. Sincethen, and especially since 1985, the EGG has been extensivelyinvestigated. The EGG provides information on the frequencyand the degree of contraction as well as distension of thestomach [2]–[10]. The clinical usefulness of the EGG is nowone of the main research areas. For instance, there have beenreports of observations of gastric motility disorders [11]–[16],gastric ulcer and gastroparesis with the EGG [17], [18].

In order to explore the clinical validation of the EGG, thefollowing needed improvements have been suggested [19]:

• improved signal quality;• multiple electrodes;• validated, computer-assisted mapping analysis;• more study relating EGG results to gastric conditions.

Manuscript received February 10, 1995; revised March 31, 1997.Asteriskindicates corresponding author.

*M. Zhou is with the Medical Testing Technology Institute, 3601 LarkwoodCourt, Boulder, CO 80304 USA.

H. Zhang is with Columbia University, New York, NY 10027 USA. He isalso with the Medical Testing Technology Institute, Boulder, CO 80304 USA.

R. Shaw is with Breece Hill Technologies, Inc., and the Medical TestingTechnology Institute, Boulder, CO 80304 USA.

F. S. Barnes is with the Department of Electrical and Computer Engineering,University of Colorado, Boulder, CO 80309 USA.

Publisher Item Identifier S 0018-9294(97)07598-8.

II. COMPOSITION OF THEREAL-TIME MULTICHANNEL

COMPUTERIZED ELECTROGASTROGRAPH

A. Configuration of the Electrogastrograph

The electrodes are the sensors for acquiring the signals fromthe subject and sending them to the recording and analyzingapparatus. In principle any nonpolarizable electrode is appro-priate. However, the mechanical properties, size, and shape ofelectrodes must also to be considered. Ideally, electrodes formultichannel recordings should be of minimal size with short,highly flexible leads.

Disposable electrodes from various electrocardiogram(EKG) suppliers were tried in this study. However, noneof these electrodes was found suitable for mapping analysisbecause their large size resulted in placement difficulties. Itwas also extremely difficult to place many single electrodesand obtain both consistent contact impedance and consistentrelative spacing. Additionally, the polystyrene foam of theelectrodes did not have the flexibility required for the soft,moving abdominal area.

In order to obtain the desired quality of the EGG signal, asoft-contact, multichannel, cutaneous, vacuum electrode ma-trix, embedded evenly in a latex mat, was developed. Thematrix is a 5 5 array of 25 Ni on stainless-steel electrodesthat are spaced 3.1 cm apart, center-to-center. The direct skincontact area of each electrode is 50 mm. The dc impedanceof the electrodes ranged from 60–100 k. The mat can befirmly attached to the abdominal surface by extracting the airfrom a cavity formed by the electrodes, latex membrane, andthe abdomen, through vacuum air flow tubes. With the subjectlying in a supine position, the mat was placed on the abdominalarea and connected to the filter/amplifier through disconnectplugs. The leads from the electrodes to the plugs are extraflexible, 26-gauge, seven-strand, shielded wire. Fig. 1 showstop and underside views of the multichannel electrode matrix.

From the stomach, two distinct types of electrical activitieshave been observed and reported by researchers using internalelectrodes. One is called electrical control activity (ECA)which occurs at a rate of about 3 cpm in man. The otheris called electrical response activity (ERA), which can occuronly once following each control activity. The periodic com-ponents of the EGG’s lie in the frequency band from 1 cpm(bradygastria) to 9 cpm (tachygastria). The gastric potentialson the abdomen are in the range of 50–500V.

The electrogastrograph, therefore, must be equipped withsuitable filters and amplifiers to selectively amplify the signalin a useful frequency band, and eliminate interfering signals

0018–9294/97$10.00 1997 IEEE

ZHOU et al.: REAL-TIME MULTICHANNEL COMPUTERIZED ELECTROGASTROGRAPH 1229

(a) (b)

Fig. 1. Views of the newly designed complete soft-contact multichannel cutaneous vacuum electrode matrix. (a) Top (connection) side and (b) un-der (electrode) side.

from breathing, generated static potentials, and the heart. Itwas these requirements which led us to the development of anEGG active filter/amplifier system.

The filter/amplifier consists of several stages of amplifierswith highpass and lowpass filters. The high input impedance(10 M ) and very low output impedance make the responseof such a filter/amplifier essentially independent of source andload impedance. The first stage has a large amplification gainand a high signal-to-noise ratio. The circuit was designed witha total gain of 5500 and a maximum 10-V peak-to-peakamplifier input noise. A time constant of 30 s was chosen.High and low cutoff frequencies are at 0.02 and 0.12 Hz(1.2–7.2 cpm) with rolloff rates at 18 dB/octave.

The electrode matrix and the active filter/amplifiers providedan improved real-time, multichannel, computerized electro-gastrograph. The very low level EGG signals travel onlythe short distance (1 m) from the subject to the inputplugs of the filter/amplifiers. The signal from each channelis amplified and filtered via individual filter/amplifiers withthe desired frequency bandwidth. The desired EGG signalsare then digitized with an A/D converter and stored in thecomputer (IBM, model 486, DX-33 MHz). The EGG signalsfrom the 25 electrodes can also be directly viewed in real-time. Illustrated in Fig. 2 are 2-min segments of 25-channelEGG signals recorded from a normal subject [Fig. 2(a)] andan abnormal subject [Fig. 2(c)], each in their preprandial state.

B. Processing, Analysis of the EGG Signal,and Software Design

A 32-channel, 12-b, (A/D) converter (model PC-1232) isconnected to the computer. Data are digitized through theconverter with a sampling frequency of 4.27 Hz. The samplingfrequency of 4.27 Hz was chosen so that one screen display of

512 data points would be a 2-min segment. Signal processingcan be done either on-line or off-line, depending on theapplication. In order to ensure the precision of the calculation,a calibration program adjusts the zero offset of each channel.

The software for signal processing and analysis consistsof three routines: waveform analysis for a chosen channel,frequency analysis for a chosen channel, and mapping analysison all 25 channels. The analyses of the EGG data by theseroutines were done for time period segments of 2 min. In ourhuman subject measurements, data were taken for 20–30-minperiods. The analyses were done for enough 2-min segments tocover the total time, and then were combined. The waveformanalysis consists of calculating the positive and negative peakamplitudes from the baseline, the positive andnegative peak derivatives of every cycle,the cycles per min, and the absolute area integral of thetotal EGG signals. Also basic statistical calculations such asmean value, standard deviation, and coefficients of variationon waveform analysis results are calculated. The frequencyanalysis of the EGG signal is derived from the power spectrumanalysis utilizing the periodogram method. The mappings areformed by two-dimensional (2-D) polynomial interpolationwith Neville’s algorithm [20]. For the four different mappingsdiscussed below, the related values of EGG’s from 25 chan-nels (5 5 array) are interpolated with an 8080 arbitrarilyselected array and are displayed on the computer monitor in15 distinct colors.

The mapping analysis capability includes four subroutines:iso-power spectrogram (IPSG), iso-average amplitudegram(IAAG), iso-percentage power spectrogram (IPPSG), and iso-areagram (IAG). The IPSG subroutine produces a 2-D color-coded map of power over the plane of the electrodes. TheIPSG subroutine proceeds in the following manner: the power


(a) (c)

(b) (d)

Fig. 2. Two-minute segments of EGG signals recorded from subjects in preprandial state and their IPSG’s. (a) 25-channel EGG signals from a normalsubject, (b) IPSG from same normal subject, (c) 25-channel EGG signals from an abnormal subject, and (d) IPSG from same abnormal subject. The numbersshown on the top of the columns with the 15 color ranges are the global maximum values of the power spectrum in the two regions. The numbers shown oneach submapping are its corresponding frequencies and the maximum power for each of the six frequency bands. The submappings with their maximumpower <15% of the global maximum power of their region remain blank.

spectrum analysis is done for each of the 25 channels and 25sets of data are generated. Each set of data is first dividedinto two frequency “regions” ( 2 cpm and 2–7 cpm); and themaximum value of power (“global” maximum value) and thefrequency at which it occurs is recorded. (This is done becausethe components at 2 cpm region are sometimes not related tothe EGG signals, and the global maximum value in this regionmay be very different from the global maximum value in the

2–7 cpm region [8].) The two global maximum values for eachregion are used for normalizing the power in their region. Eachglobal maximum value is then divided into 15 equally spacedincrements and each increment level is assigned a color thatwill be used to display the various signal levels relative to theglobal maximum value.

Next, the region from 2–7 cpm is divided into five “fre-quency bands”: 2–3 cpm, 3–4 cpm, 4–5 cpm, 5–6 cpm,


and 6–7 cpm. There is a total of six frequency bands—thefive just mentioned plus the separately normalized band of

2 cpm. In each of these six frequency bands, the maximumpower and its corresponding frequency over all of the 25channels are found. This frequency is called the “centralfrequency” for that band. Each of the remaining 24 channels isnow examined at the central frequencies to find the maximumpower for each channel for each of the six frequency bands.This produces 25 maximum power values at each of sixfrequency bands. The Neville’s algorithm is used to producean array of 80 80 (6400) values of power (in each of thesix frequency bands). Finally, these values are normalized andassigned a corresponding color. The final result is six coloredmaps (one for each frequency band) of the power over theplane of the electrodes. These can be seen in Fig. 2.

The average amplitude is calculated directly from the powerspectrum and the IAAG maps the calculated results. Similarto the IPSG, the average amplitude of the EGG’s differentfrequency components can be easily seen on the colored mapsof IAAG.

The amplitude of the recorded signal of the EGG is de-pendent not only on the source of the signal, but also onthe distance and the electrical transmission characteristics ofthe tissue between the source and the recording site. Therelative frequency compositions of the of the EGG’s whichare recorded from the 25 channels are somewhat different. Toobtain the dominant frequency of the EGG at each recordingsite, the IPPSG subroutine (which maps the percentage of thesignal in a given frequency band) was developed. As in theIPSG, the regions of 2 cpm and 2–7 cpm are processedseparately. For the former region the denominator part of theIPSG ranges from 0.5–7.25 cpm and for the latter region from2–7.25 cpm.

The IAG subroutine was designed for mapping the absoluteamplitude integral of the EGG waveforms with respect toany arbitrary reference of time. The IAG (one colored mapof amplitude integral on the plane of electrodes) is used toobserve the variations in absolute amplitude alone.

In most of the recorded EGG waveforms in our study, theupstroke phases, the down stroke phases, and their turningpoints have been obtained. The propagation exploration (PE)subroutine was designed to display the motion of the extremeamplitudes across the matrix for the purpose of showing thepropagation direction (see Fig. 3). In order to make this visible,25 circles, representing the electrode matrix, are displayed onthe monitor. The phase determines the color of the circle.Red denotes the upstroke phase. Blue denotes the downstroke phase. The color is reversed at the turning point. Thepropagation direction can be detected by analyzing the EGGwaveforms simultaneously from the 25 channels and observingthe location of the circles’ color changes.

III. EXPLORATION OF THE HUMAN STOMACH

USING THE ELECTROGASTROGRAPH

Twelve volunteers (five male and seven female, 20–52 yearsof age) with no history of gastrointestinal disease formedthe control group, nine subjects (three male, six female;

ages 37–74 years) with various gastrointestinal disorders (oneof them often complains gastric discomfort; two had totalgastrectomies; three have been diagnosed with gastritis; theother three have been diagnosed with gastric ulcer) participatedin the study [21]. The study was approved by the HumanResearch Committee and Dean of the Graduate School atthe University of Colorado, Boulder. All subjects were askednot to ingest heavy meals, medication or alcohol the daybefore the experiment and to keep an overnight (8–12 h)fast. Test sessions were scheduled between 7:30 a.m. and11:00 a.m. the next morning. EGG recordings sessions lastedabout 30 min.

The subjects were in a supine position while the EGGsignals were being recorded. For the unipolar recording thecentral terminal (the right arm, left arm, and right foot wereconnected together) was used as a common reference point.In bipolar recording, the point 2,2 on electrode matrix (55array) was connected as a common reference point. The matwas firmly attached to the abdominal surface using constantvacuum air flow. The average total impedance of electrode-conductive gel-body-ground measured during this study wasabout 70 k , which is smaller than the 300 k found inthe EKG electrodes that we tried. Subjects willingly acceptedwearing the electrode array. The only issue raised was atemporary itching (about 1 min) from some subjects whenthe array was removed.

Several unipolar and bipolar methods have been used inEGG recordings. To date, most researchers prefer using bipolarrecording for their experimental conditions [22]–[26]. Theyhave found a considerably higher percentage of interpretableEGG’s with a detectable ECA pattern than has been seen withunipolar recording. However, it is obvious that the locationof the electrode sensing the potential variations cannot bedetermined using the bipolar recording approach. The sourceof the potential variation is of no importance when only therepetition frequency of the signal is to be determined, but itis very important when the wave shape of the signal is to beanalyzed.

However, using the electrode matrix, the comparison ofunipolar recording with respect to a central terminal and localbipolar recording shows no significant differences for thedetection of the ECA. Usually, the waveform recorded fromthe unipolar method is more sinusoidal and has less noisewith respect to both pattern and amplitude [9]. In addition,we observed that with a bipolar recording the signals near thereference point (within 4 cm), are smaller than the ones fromdistal sites (4–14-cm distant).

Differing EGG amplitudes and waveforms can be obtainedfrom different sites with unipolar recording. The largest signalrelated to the EGG may be identified on any of the mappingsof the IAG, IAAG, and IPSG. Furthermore, the largest signalon the IPPSG map of frequency indicates the most distinctEGG waveform.

We have observed that most normal subjects (nine oftwelve), had similar IAAG, IPSG, and IPPSG patterns withonly minor variations in the IAG pattern, while most abnormalsubjects (six of nine) had differing patterns with the IAGhaving the greatest differences. The reason for the differences


Fig. 3. Illustration of a sample of propagation exploration. The direction of the propagation was detected from upper right to lower left starting with thepictures in sequence from 1–8. The time of the propagation over the plan of the electrodes from the starting to the end was 2.1 s.

between the IAG and the IAAG, IPSG, and IPPSG was dueto the differing distribution of the amplitudes of the frequencycomponents between the regions of2 cpm and 2–7 cpm.Furthermore, for most of the abnormal subjects the amplitudesin the 2–7-cpm region differed in the space defined by the 25electrodes. There was no difference in the patterns betweenIAAG and IPSG. The former shows us directly the averageamplitude and the latter the power spectrum.

Examples of the power spectrum and mapping analysesof the EGG signals recorded from a normal subject andan abnormal subject with gastritis are shown in Figs. 4 and5, respectively. There are three differences to be noted: thesignals at the region of 2 cpm are much larger in the abnor-mal subject than those in the normal subject; the frequencycomposition is more complicated in the abnormal subjectthan in the normal subject; the distribution of the dominantfrequency is more nearly constant in the normal subject.

By analyzing the multichannel unipolar recorded EGGsignals systematically and observing the EGG waveforms, wefound an abnormal subject whose maximum amplitude pointchanged position by as much as 8 cm during the test period.We also found that for most of the subjects, both normal andabnormal, the maximum amplitude points changed position by3.2 1.5 cm ( ). These displacements may be the resultof variation in stomach position. Similarly, we have observedthat the point with the highest power from different frequencycomponents does not always stay at the same region of thestomach. This is shown rather clearly on the IPPSG [Fig. 5(b)].

The propagation of the electrogastric activity can be directlyobserved using the described instrument. The propagationdirection of the signals is not very stable. In most cases, thepropagation direction looked like it was along the longitudinalaxis of the stomach, from upper right to lower left of thematrix (see Fig. 3). The time for propagation from the first to


(a)

(b)

Fig. 4. The results of (a) the power spectrum and (b) the mapping analyses of the EGG signals that were recorded from a normal subject (same as in Fig. 2)in preprandial state. The numbers shown on the tops of each submapping are its corresponding frequencies and the maximum values.

the last of 25 channels is only 1.5 0.58 s. ( ) withunipolar recording and 2.8 1.2 s. ( ) with bipolarrecording. Note that these unipolar and bipolar measurementswere not made at the same time, because we had only oneinstrument.

Short, repeated “explosions” of high amplitude of the EGGwaves occurred with greater frequency in abnormal subjects(four of nine), than in normal subjects (two of 12). Most ofthe time, this kind of event was observed only from severaladjacent channels, not all 25 channels.

IV. DISCUSSION

EGG’s have been investigated a great deal since the firstmeasurement was made by Alvarez in 1921 [1]. Physiologicaland pathological significance of the EGG have since beenshown. However, eliminating the contact artifact between

the electrode and skin, and finding the best placement ofthe recording electrodes are problems which have remainedunsolved, especially when alterations of the stomach positionhave been taken into account. In order to further reveal thesignificance of the EGG, multichannel recording and mappingof the results are attractive.

The frequency components of the EGG signal cover therange from 0.15–12 cpm, and the bandwidth of the amplifiershould be designed wider than the frequency of the EGG’s.Historically, however, most articles regarding the frequencyof EGG’s have concentrated on the range of 2–6 cpm inspite of abnormal stomachs with bradygastria or tachygastriawhich may contain a broader range of frequencies [2], [3],[10], [27]–[30]. Noise in wider bandwidth amplifiers tends tomake it difficult to observe the EGG signal in real-time. Inorder to ensure real-time observation of the EGG signal and


(a)

(b)

Fig. 5. The results of (a) the power spectrum and (b) the mapping analyses of the EGG signals that were recorded from an abnormal subject (same as inFig. 2) with gastritis in preprandial state. The numbers shown on the top of each submapping are its corresponding frequencies and the maximum values.

a reliable comparison among the frequency components, wehave designed the amplifiers with equal gains and frequencybandwidths of 1.2–7.2 cpm.

With the application of the mapping analysis, we have foundthat the maximum amplitude point may change position. Thesedisplacements may be the result of variation of the stomachposition. It is suggested that, in previous studies, the amplitudevariation of the EGG at only a few points may result partiallyfrom differences of the recording site or slight displacement ofthe stomach. In order to exclude the factor of the displacementof the stomach during a recording period, it will be interestingto explore whether or not using the location of the largestsignal from mapping analyses would be appropriate for ana-lyzing the frequency and amplitude components of the EGG’s.

The disparities of the frequency and amplitude components ofthe EGG waveforms and their gradients have been reflectedin mapping analysis. Investigating the relations between theposition of the stomach and its electrical mapping, and thepatterns of the variation of the gradient may enhance thepotential significance of the recorded EGG’s for physiologicaland pathological research.

The region with the highest power from different frequencycomponents does not always stay at the same location of thestomach. Further investigations are needed in order to explorethese phenomena and to reveal the origins of the variations ofthe frequency components of the overall signal. Systematicallyanalyzing the results of the four subroutines of the mappinganalyses will provide an opportunity for further understanding


the distribution characteristics of the EGG’s at the recordingmatrix plane.

We have selected the frequency with the maximum power,amplitude, or percentage as the dominant and central fre-quency. Then the mapping of the selected variables hasbeen formed by choosing maximum power, amplitude, orpercentage for the 25 channels of the EGG. Perhaps theselection of the maximum values of the root mean squareamplitude for mapping will prove to be more appropriate forextracting information from the EGG. A variety of approachesneeds to be explored.

We have chosen the direction of the motion of the extremeamplitudes in time and space to explore the propagationdirection. Two-dimensional plotting of the location of theextreme amplitudes provides more information about variationof propagation direction. Exploring the propagation propertiesof different frequency components on two dimensions mayalso be helpful in revealing their origins and clarifying thesignificance of the EGG’s.

Sometimes a burst of a giant waveform, or “explosion”(between 500 V and 1 mV), has been observed. The causeand significance of giant waveform bursts remains unclear tous. These giant waveforms occur on only several adjacentchannels. We have treated these bursts as artifacts. Giantwaveform bursts will affect the mapping-analysis results andtherefore were not used in the mapping.

The elimination of artifacts resulting from breathing and theremaining high frequency components of the EGG signals hasalready been explored by several investigators in great detail[26], [31]–[38]. We suggest that a study be done in the futureto determine the physiological and pathological significanceof the mapping of the EGG’s.

In conclusion, the combination of the latex-embedded elec-trodes with vacuum controlled contacts and the filter/amplifierhas solved some of the problems which have limited theclinical use of the EGG [39]. Of particular importance areconsistent electrode placement and low, consistent contactimpedance. This plus the use of multiple electrodes and thecomputer subroutines, enable one to map changes in the EGGas well as the location of areas with relatively large electricalactivity. The use of the multichannel recording and mappinganalyses has provided more information on the variation ofthe EGG’s than have previous approaches.

ACKNOWLEDGMENT

The authors would like to give special thanks to B. Phillips,M.D., R. Levine, M.D., J. Day, M.D., and S. Oliver, M.D.,for their enthusiastic support of this research and for recom-mending individuals to participate in this study. They wouldalso like to thank Prof. R. E. West, Prof. J. F. Fuller and hiswife, J. Fuller, for their great help in the preparation of thismanuscript. They would also like to express appreciation forthe comments they received from the reviewers.

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Mingying Zhou received the B.S.E.E. degree fromShanghai College of Building Material Sciences(merged into Tongji University in 1996), Shanghai,China, in 1981 and the M.S. and Ph.D. degreesin electrical and computer engineering from theUniversity of Colorado at Boulder in 1988 and 1993,respectively.

She also was trained in both Western and tradi-tional Chinese medicine in Shanghai, China duringthe early 1970’s and practiced both there until 1984.She is the Director of the Medical Testing Tech-

nology Institute, Boulder, CO. She also has a private practice in traditionalChinese medicine in Boulder, CO. Her research interests include the advancedelectrogastrographs and their applications.

Hui Zhang received the B.Sc. degree in biologyfrom East China Normal University, Shanghai,China, in 1981 and the M.Sc. degree in electricalphysiology from Shanghai College of TraditionalChinese Medicine in 1985.

Between 1991 and 1993, he was a Post-DoctoralFellow at Harvard Medical School, Cambridge,MA. From 1994 to 1995, he worked as ResearchAssociate in Medical Testing Technology Institute,Boulder, CO. Since the end of 1995, he has workedin Columbia University Presbyterian Medical

Center, New York. His research interests are computerized electrogastrographand electrocardiography. He is also engaged in signal processing and mappingtechniques, with application on physiology research interests.

Robert Shaw has worked as an electrical engineerin the computer disk and tape drive research and de-velopment industry for the last 21 years. He workedwith M. Zhou in electrogastrograph research from1991 and later with the Medical Testing TechnologyInstitute, Boulder, CO until 1995. He is currentlywith Breece Hill Technologies Inc., Boulder, CO,working on computer tape library research anddevelopment.

Mr. Shaw holds two patents on phase-lock-loopdesigns and has a patent pending on a pump motorcontrol circuit.

Frank S. Barnes (S’54–M’58–F’70–LF’96) re-ceived the B.S.E.E. degree from Princeton Univer-sity, Princeton, NJ, in 1954 and the Ph.D. degreein electrical engineering in 1958 from StanfordUniversity, Palo Alto, CA.

He joined the University of Colorado in 1959,where he is currently a Professor of Electricaland Computer Engineering. His research interestsinclude the applications of electron devices,microwaves, and low frequency electrical andmagnetic fields and ultrasound to biologicalsystems.

Dr. Barnes is a Fellow of the American Association of the Advancementfor Science and the International Engineering Consortium. He has served asDistinguished Lecturer for the IEEE Electron Device Society from 1994 to1997. He is a member of the Board of Directors of the BioelectromagneticsSociety (BMS) and has also served as Vice President for Publications forIEEE.

real-time multichannel computerized electrogastrograph

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