Casson, AJ

Rodriguez-Villegas, E

Wireless ambulatory EEG (AEEG) monitoring over long periods of time is currently infeasible due to battery limitations and the EEG analysis time required. A detailed comparison of methods for reducing the amount of AEEG data is presented. It is concluded that a discontinuous recording scheme can alleviate both of the above problems. Discontinuous monitoring introduces data interpretation and practical issues which are discussed. With suitable low power algorithm implementations and realistic system expectations such systems are deemed to be feasible. © 2007 IEEE

Casson, Alexander J.

Rodriguez-Villegas, Esther

The University of Manchester - Institutional Repository

Data reduction techniques to facilitate wireless and long term AEEG epilepsy monitoring

Casson, A

Spiral - Imperial College Digital Repository

Alexander Casson and Esther Rodriguez-Villegas.Circuits and Systems research group, Department of Electrical and Electronic Engineering, Imperial College London.PROPOSED SYSTEMDATA REDUCTION MECHANISMSThe ambulatory electroencephalogram (AEEG) is a key tool in epilepsy diagnosis. It allows monitoring of the patient's brain activity, which can be used to indicate the presence of epilepsy, in the daily life environment.However, wireless systems and truly long term monitors, of the scale of months, are currently infeasible due to battery limitations. Online, real-time, and low power data reduction is required to make these systems possible.Discontinuous monitoring, only transmitting interesting sections of data, is proposed as the most suitable data reduction method. When interpreting the data produced care must be taken as the system will have some false detections. The system simply generates an altered data set for analysis. This must be interpreted to identify epileptic features and reject non-features in the same way as continuous signals currently are. THE PROBLEMCurrent Ambulatory EEG units have several limitations:1. Electrodes must remain attached for the duration of the testing and wearing them must be socially acceptable.2. Systems can weigh up to 1kg limiting their portability.3. The compliance of wires from the electrodes to the recording unit can limit patient movement.4. Long term recordings generate large amounts of data for storage, approximately 1GB every 24 hours.5. This data is time consuming for a neurologist to analyse, taking of the order of two hours per 24 hour recording [1]. Wireless systems could alleviate the portability issues but are infeasible due to the amount of power needed and the restriction in battery size for a small, portable device. Online data reduction is required. This data reduction can also reduce the amount of data for analysis allowing longer recordings to be made.Reduced quality methods go against the overwhelming trend over time for EEG systems to have better sampling rates and improved spatial resolution.Compression methods offer significant data reduction, but lack low power implementations and do not improve the interpretation time.Only discontinuous monitoring reduces the data to be both transmitted and analysed. If AEEG monitoring is to be truly long term, of the scale of months, it will not be possible to analyse all of the data and so a data selection scheme is necessary. Such schemes should be suitable for low power hardware implementation.!"#$%&$'()*+,-$./0)(*+)12$34)42)1(,$(5$64170846$+,3$691:46&;$%$<=1,$>408(9?@61(=-$A(=&$"B-$,(&$C-$99&$130-140, 1999.!C#$'&$/,)(,1(=$+,3$D&$E(,4==+-$.FF'$3+)+$2(*984661(,$)42?,1G046-;$H1(*4312+=$F,I1,4481,I-$JFFF$Transactions on, vol. 44, no. 2, pp. 105-114, 1997.[3] J. Cardenas-Barrera, J. Lorenzo-Ginori, and E. Rodriguez-K+=31A1+-$./$L+A4=4)-packets based +=I(81)?*$5(8$FF'$61I,+=$2(*984661(,-;$M4312+=$J,5(8*+)126$+,3$)?4$J,)48,4)$1,$M43121,4-$A(=&$CN-$no. 1, pp. 15-27, 2004.!O#$P&$H&$Q1=6(,$+,3$R&$F*486(,-$.P91:4$34)42)1(,S$+$84A14L$+,3$2(*9+816(,$(5$+=I(81)?*6-;$<=1,$Neurophysiol, vol. 113, no. 12, pp. 1873-1881, 2002.!T#$>&$<(,1,U-$./0)(*+)43$34)42)1(,$(5$491=49)12$4A4,)6$1,$)?4$1,)4812)+=$FF'$061,I$)?4$L+A4=4)$)8+,65(8*-;$H+2?4=(8V6$)?4616-$W,1A4861)41)$M++6)812?)-$CXXT&!B#$P&$D+)4=-$.J,)4==1I4,)$=(L$9(L48$218201)$5(8$4=42)8(4,249?+=(I8+9?@-;$M+6)48V6$)?4616-$J*9481+=$College London, 2006.[7] Stellate. (2007) Stellate Systems home page. [Online]. Available http://www.stellate.com.DATA REDUCTION TECHNIQUES TO FACILITATE WIRELESS AND LONG TERM AEEG EPILEPSY MONITORINGLossey compressionLossless compressionReduced qualityReduced qualityFull recording (baseline)MethodDiscontinuous: GotmanDiscontinuous: Example CWT method cDiscontinuous: Example CWT method cResults taken from [3]Results taken from [2]4 channels, 8 bit, 120Hz sampling 32 channels, 8 bit, 120Hz sampling32 channels, 16 bit, 200Hz samplingNotesResults taken from [1] and [4]140ms recording after an automated detection5s recording after an automated detection8 data sets154 data setsN/AN/AN/AApproximate amount of EEG tested200 hours41 hours (400 events)41 hours (400 events)YesNoYes bYes bNoLossey?YesYesYesNoNoNoNoNoReduces analysis time?YesYesYes100100100100100Sensitivity a / %Unknown797981-8939-6296700Data reduction / %90-959450a Sensitivity is the number of events correctly identified over the total number of events.b Lossey as intrinsically contains less information than the baseline.c Developed from [5] and [6] and analysed with new data as part of this work.A current AEEG system (taken from [7]).Our proposed system with no presence other than on the head.DATA INTERPRETATIONMETHODA discontinuous monitor only generates an altered data set for analysis. It reduces the amount of raw data that is presented to the neurologist but does not replace them or their role in diagnosis.The fact that a data section has been recorded should not be taken as proof that activity is present, only that it is likely to be and so should be checked by a human expert.REQUIRED ALGORITHM PERFORMANCEStandard algorithms detect features: wanted features must be identified with few false detections. However, when only selecting data sections, all possible events should be identified even at the cost of more false detections. These wrong recordings are rejected by the interpreting neurologist. Toleration of false detections makes algorithms significantly simpler and aids low power design.Optimal algorithms and implementations will be the subject of future work.A discontinuous monitor only records AEEG traces in periods before and after an automated detection.This significantly reduces the data for both transmission and analysis. 1234

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Data reduction techniques to facilitate wireless and long term AEEG epilepsy monitoring

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