Presentation on theme: "In-situ AEP amplification and wireless recording of Auditory Evoked Potentials and Otoacoustic Emissions Yuri Sokolov, PhD Vivosonic Inc., Toronto, ON."— Presentation transcript:
1 In-situ AEP amplification and wireless recording of Auditory Evoked Potentials and Otoacoustic EmissionsYuri Sokolov, PhDVivosonic Inc., Toronto, ONEarly Hearing Detection and Intervention Conference Atlanta, March 3, 2005
2 Audiology clinicians experience significant frustrations with ABR and ASSR Auditory Brainstem Response (ABR) and Auditory Steady State Response (ASSR) are quite difficult to administer for many clinicians, particularly in post-screening assessment environments:Noise is FRUSTRATION # 1 reported by 84 % of U.S. clinicsNoise leads to unclear results and long test times – up to min, typical min per testLong test time results in low patient throughputRequirement of ≤ 5 kOhm impedance is challenging to achieve, often by abrading the skin until bleedingAbrading the skin increases the risk of infection (Ferree et al., Scalp electrode impedance, infection risk, and EEG data quality. Clin. Neurophysiol., 112, p )The above results in higher risks and operating costsSource: Tannenbaum, S: US infant post-screening market survey (The Hearing Review, Jan 2005).
3 The same signal can or cannot be detected depending on noise and SNR ABR and ASSR have very low amplitudes relatively to noise, but largely coincide with noise frequencyAEP signal recording, analysis, and detection is simply “about” three things:Signal,Noise, andSignal-to-Noise Ratio (SNR)The three major sources of noise in AEP are:PhysiologicalElectric field, RF, and power-lineMagnetic fieldSSNRNThe same signal can or cannot be detected depending on noise and SNR
4 ABR has diagnostic, screening, and threshold-finding applications Auditory Brainstem Response (ABR) is a transient response, provides valuable information on hearing thresholds and useful for differential diagnostics:ObjectiveNon-invasiveKnown generators (on the opposite from ASSR)Well researched over several recent decadesResponses are looked for in the time domain in the form of characteristic wavesRecommended by many established NHS protocolsAmplitude: μV (millionth of V)Frequency range: 50-3,000 HzSource: Multiple publications by J. Hall III, M. Hyde, C. Berlin, L. Hood, and others.
5 Click-ABR is used mostly for screening and differential diagnostics Diagnostic applicationResponse is generated by Acoustic Nerve and BrainstemHas characteristic wave structure70-80 dB nHL click typicalLooking for Waves I, III, V, and I-III, III-V, I-V intervalsDiagnostics of Acoustic Neuroma and Auditory NeuropathyStacked ABR® may detect smaller Acoustic NeuromaScreening application30-50 dB nHL 100 μs click stimulusLooking for Wave VTypically automated detection (e.g. AABR®)VIIIImsI-IIIIII-VI-VVmsAABR® is a registered trademark of Natus Medical Inc.Stacked ABR® is a trademark of Bio-logic Systems Corp.
6 Tone-burst ABR is used mostly for finding thresholds Established and recommended protocolTone bursts instead of click stimuli: typically 500 (difficult to record), 1000, 2000, 4000 HzFrequency-specificLevels vary to find the thresholdLooking for Wave V thresholdTechnically similar to screening click-ABR, but not automatedDetect thresholds up to 80 dB HLVms
7 ASSR is a promising tool for finding hearing thresholds Auditory Steady State Response (ASSR) has been proven to provide valuable information on hearing thresholds, particularly in infantsObjectiveNon-invasiveFrequency-specific, as tone-burst-ABRNot site-specific (generators are unknown)Typically faster than tone-burst ABRAccurate, particularly at higher HL, above 40 dB HLEffective at severe and profound hearing loss, up to 110 dB HL, while tone-burst ABR is limited to 80 dB HLSource: Multiple publications by T. Picton, S. John, D. Stapells, and others.
8 ASSR is a frequency-specific Evoked Potential Auditory Steady State Response (ASSR) is a tone-like response present as long as stimulus is presented.Elicited by amplitude (AM) or Frequency (FM) or combined AM+FM modulation of carrier frequencies.Audiometric carrier frequencies: 500, 1000, 2000, 4000 HzModulation40 Hz – sensitive to sleepHz – insensitive to sleepResponses are looked for in the frequency domain – at modulation frequencies, not carrier frequenciesThresholds – for carrier frequenciesMultiple-frequency ASSR responsesAmplitudes: nV (billionth of V)Frequencies – AM and/or FMHzSource: Multiple publications by T. Picton, S. John, D. Stapells, and others.
9 Noises are introduced by multiple sources in most clinical environments PhysiologicalEEG – increases in sleepECG – does not decrease in sleepEOG, EMG – decrease in sleepElectric and magneticPower line noise: 50 or 60 Hz and their harmonicsElectric field noiseMagnetic field noiseRadio-frequency (RF) interferences
10 Multiple sources introduce physiological noises in AEP recording Noise on the scalpFrequency range, HzAmplitudeEEG awake3-405 -10 μVEEG sleep3-162 – 400 μVElectrooculogram (EOG)0.5-10μVElectrocardiogram (ECG)0.5-5080 μV – 2 mVElectromyogram (EMG)30-50010 μV - 2 mVSource: Cutmore, James (1999). Identifying and reducing noise in physiological recordings. Int. J. Physiol., V. 32, No. 2, pp
11 ECG noises may be stronger in infants than in adults The heart is positioned more centrally – aligned with the sagittal plainThe heart is much larger relatively to the bodyThe heart is closer to the headThe heart-beat rate is twice higher than in adultsTemporary post-natal heart conditions may increase ECG noise frequency - up to 100 Hz
12 Filtering after the first stage of amplification introduces distortion in conventional AEP amplifiersNoiseEPAmp 1BPFAmp 2SaturationDistorted signalDistorted signalHigh gain in the 1st stage results in saturation by the unfiltered, often EEG noise, i.e. reaching the maximum voltage of the 1st stage’s dynamic range. Saturation distorts the signal: The 1st stage output contains periods of the maximum voltage, and these periods become interruptions in EP signal after band-pass filtering (BPF).Low gain reduces EP amplitude and signal-to-noise ratio (SNR) at the amplifier output.Both saturation and low gain complicate signal detection.
13 Differential AEP amplifier Electric field noises are introduced through wires and cables acting like antennasIntroduced by:Electronic equipmentElectric wiringImproper groundingTypical strength of electric fields in North American clinics:, average 5.5 V/m, range V/m (5 Hz – 2 kHz band)*Noise amplitude: up to 10 mV (1 mV = a thousandth of V)Can be reduced by:Shielding of input-circuit wiresShielding of wires and circuitsProper groundingUnshielded lead wiresElectric fieldsDifferential AEP amplifier* Source: - Web site of Environmental Health Science, NIH, U.S. Government.
14 Looped lead wires and cables Differential AEP amplifier Magnetic field noises are introduced through wires and cables acting like antennasIntroduced by:TransformersElectric motors and wiringLooped wires and cablesTypical strength of magnetic fields in North American clinics: average 1.7 mG, range mG (milliGauss) (5 Hz – 2 kHz band)*Noise amplitude: up to 10 mVCan be reduced by:Reducing wire/cable lengthPositioning, NOT movingReducing loop areaTwisting wiresVery thick shielding (steel)Looped lead wires and cablesMagnetic fieldsLoop areaDifferential AEP amplifier* Source: - Web site of Environmental Health Science, NIH, U.S. Government.
15 “Garbage” IN “Garbage” OUT Long lead wires and cables introduce large electro-magnetic field noises in a conventional amplifierEPAmpEMIA/DDSPGround leadOther leads“Garbage” IN “Garbage” OUTAmp – amplifierA/D – analog-to-digital conversionDSP – digital signal processing
16 RF noise may strongly interfere with EP recording Radio-frequency (RF) noise comes from various sources:Cell phones, pagers, Blackberry, wireless intercomFM-systems, FM-radioWireless computer networks used in many hospitalsPDAs (Personal Digital Assistants), PalmtopsMedical equipment (ICUs, operating rooms, general offices)Office equipment: copiers, fax-machines, computersIntroduce mostly electrical noiseInterferes at EP (low) frequencies despite RF frequencies are much higher – in MHz and GHz ranges – because of amplifier non-linearityThere is no common-mode rejection (CMR) at frequencies ≥ 20 kHzAmplitude: up to 10 mV (thousandth of V)Source: Kitchin et al. (2003). Input filter prevents instrumentation-amp RF-rectification errors. EDN, Nov 13, p
17 Power Line noise comes from Power line noise is not only 60 Hz and comes from both electric field and AC power linesPower Line noise comes fromElectric field – picked up by electrode wires & cablesAC power outlets when plugged into the wall – introduced through electronic circuits, power suppliesThrough USB computer ports (5 V) – introduced through electronic circuitsInterferes with EP at a number of frequencies – mostly 50 / 60 Hz & harmonics:60 Hz, 120 Hz, 180 Hz, 240 Hz … due to amplifier non-linearityAmplitude: up to 10 mV and higherAC outletAMPPCUSBPower-line noise in AEP amplifiersHz
18 Low A/D resolution can significantly affect AEP recording due to insufficient dynamic range Integrity™TypicalLow
19 Noises in AEP recording Putting all things together: ABR and especially ASSR are very small signals as compared to noises in AEP recordingSignalFrequency, HzAmplitude, nV (dB)AEP SignalsASSR10 – (0)ABR50 - 3,000, (10-20)MLR, (15-25)LLR, (16-60)P3001 - 155, , (15-65)Noises in AEP recordingElectrooculogram (EOG)0.5-1010, , (60-85)EEG awake3-405, , (55-60)EEG sleep3-162, , (65-90)Electrocardiogram (ECG)(up to 100)80, ,000, (70-110)Electromyogram (EMG)30-50010, ,000, (70-110)Electric, magnetic, RF50/60 Hz, MHz, GHzUp to 10,000,000 (up to 120)
20 Clinical ABR/ASSR testing is challenging in practice Long testing timeBest reported:19 minutes (Luts, Wooters, unpublished), 21 minute (Perez-Abalo et al., 2001)Typical minutes (John et al., 2003), up to 90 – 120 min (Tannenbaum, 2004)Sensitivity to electromagnetic interferencesElectromagnetically shielded booth requiredSensitivity to electrode impedanceRequires rubbing the skinNeed for sedation in many casesDifficult to administer in electro-magnetically shielded booth
21 In-situ AEP amplification and filtering is a novel method of noise reduction in Auditory Evoked PotentialsAmplifier is mounted in-situ – directly on the ground electrode pad, with no leadLead length to non-inverting (+) and inverting (-) electrodes minimized to the distance between electrodesFiltering prior to amplificationGains optimized for ASSR and ABRImpedance mismatch monitored in real timeRisk of wrong electrode connection minimized
22 In-situ amplification largely eliminates electro-magnetic field-induced noises A/DDSPEMIEPIn-situ pre-amplifier, the Amplitrode™, is mounted directly on the ground electrode eliminating ground lead. The other leads are very short and shielded.This significantly reduces electric and magnetic field-induced and allows for a clearer EP signal at the amplifier output.
23 Filtering prior to amplification allows optimizing gain and reducing physiological and RF noises Higher gain:150,000 for ASSR15,000 for ABRExceptionally low intrinsic noise:< 350 nV in 10-10,000 Hz<10 nV in 0.05 Hz bands in HzEP signals at the Amplitrode™ output have large amplitude, contain little noise, have high SNR, and therefore, can be easier converted from analog to digital form, recorded, and detected.NoiseEP
24 In-situ amplification and wireless communications make AEP testing efficient Reduced physiological noiseLargely reduced electromagnetic noiseNo big “boxes”Less attention to electrode impedanceEasy mounting on electrode padsNo need to achieve ≤5 kOhm impedanceNo hassles with long lead wires and cablesLess risk of electrode lead misconnection
25 Amplitrode™ monitors electrode mismatch in real time Electrode impedance mismatch (EIMM) is more relevant than electrode impedance*.Amplitrode™ measures EIMM in real time during testing, not only prior to it.Operator is notified of EIMM immediately.Reduces set up time.Measuring EIMM and very high input impedance of the Amplitrode™ eliminates the need for skin abrasion – no need to achieve impedance below 5 kOhm.Ferree et al. (2001). Scalp electrode impedance, infection risk, and EEG data quality. Clin. Neurophysiol., 112, p
26 Amplitrode™ eliminates the risk of improper mounting Amplifier is mounted on the ground electrode pad.The other two leads have different length.Electrode button release makes easy mounting and dismounting amplifier and clips on electrode pads.It is much easier to use even for less experienced practitioners.
27 In-situ AEP recording speeds up testing ABR800 clicks100 clicks400 clicks1600 clicksSubject: Normal hearing female, 24 yrs, R earPlace: Vivosonic office, EMI ≥ 0.5 mGaussPhone: ER-3A (correction for 0.9 ms)Stimulus: Click, 30 dB nHL, 21.1/sec, ipsi3200 clicks
28 ABR in a shielded room (<1 V/m, 0.1 mG) In “ideal” electro-magnetically shielded room, the benefit of in-situ amplification and filtering is less pronouncedABR in a shielded room (<1 V/m, 0.1 mG)Subject: T.V., 44, normal hearingStimulus:1000 clicks21.1 clicks per secondArtifact Rejection disabledER-3A Insert HeadphonesRecording:Montage Fz/A110.66 ms windowBand-pass filter: Hz for Bio-Logic Navigator ProHz for AmplitrodeSource: I. Kurtz, T. Venema, 2004 (unpublished).
29 ABR in moderate electric (12 V/m) and magnetic ( 5.5 mG) fields Outside a shielded room, the benefit of in-situ amplification and filtering is very significantABR in moderate electric (12 V/m) and magnetic ( 5.5 mG) fieldsCorrelation coefficient = 0.81Correlation coefficient = 0.43Subject: T.V., 44, normal hearingStimulus:1000 clicks21.1 clicks per secondArtifact Rejection disabledER-3A Insert HeadphonesRecording:Montage Fz/A110.66 ms windowBand-pass filter: Hz for Bio-Logic Navigator ProHz for AmplitrodeSource: I. Kurtz, 2004 (unpublished).
30 Wireless recording of OAE and AEP provides mobility and additional noise reduction Wireless communication with PCNo cable to the PCNo noise coming back into the EP and OAE amplifiers from AC power supplyNo cable-related hasslesMobilityTesting can be controlled form anywhere within the reach of Bluetooth®The patient or a baby’s mother can move around – without the need to disconnect electrodes, connectors, or transducersAdult and senior patients can take a relieving break.In the Operating Room, testing can be done from a distance, without cables getting in the way.Battery operationNo AC-power-related noise in the amplifier circuits
31 Bluetooth® is a wireless communications protocol Digital signal in GHz rangeNoise-like, broadband (no fixed carrier frequency – unlike FM-radio)Low energy – below 0.1 mGLimited area – 30 feet (10m)Encoded – secure for medical informationFDA-approved for various medical applicationsBluetooth®
32 Integrity™ is the world’s first and only wireless OAE, ABR, and ASSR system Amplitrode™VivoLink™ER-3AVivoLink™ interface moduleGenerates DPOAE, TEOAE, ABR, and ASSR stimuliConditions stimuli forER-3A Insert PhonesB-71 Bone ConductorConverts EP signals from the Amplitrode™ into digital form, 16 bitProcesses signals and communicates to the computer software through Bluetooth®Integrity™ computer program controls the OAE, ABR, and ASSR, functionsProtocol setting – modularTest control – modularData management - integratedB-71Integrity™Wireless Bluetooth communication
33 Thank you for your interest! Questions?Thank you for your interest!