1. In-situ AEP amplification and wireless recording of Auditory Evoked Potentials and Otoacoustic Emissions
Yuri Sokolov, PhD
Vivosonic Inc., Toronto, ON
Early 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. clinics
Noise leads to unclear results and long test times – up to min, typical min per test
Long test time results in low patient throughput
Requirement of ≤ 5 kOhm impedance is challenging to achieve, often by abrading the skin until bleeding
Abrading 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 costs
Source: 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 frequency
AEP signal recording, analysis, and detection is simply “about” three things:
Signal,
Noise, and
Signal-to-Noise Ratio (SNR)
The three major sources of noise in AEP are:
Physiological
Electric field, RF, and power-line
Magnetic field S
SNR N
The 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:
Objective
Non-invasive
Known generators (on the opposite from ASSR)
Well researched over several recent decades
Responses are looked for in the time domain in the form of characteristic waves
Recommended by many established NHS protocols
Amplitude: μV (millionth of V)
Frequency range: 50-3,000 Hz
Source: 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 application
Response is generated by Acoustic Nerve and Brainstem
Has characteristic wave structure
70-80 dB nHL click typical
Looking for Waves I, III, V, and I-III, III-V, I-V intervals
Diagnostics of Acoustic Neuroma and Auditory Neuropathy
Stacked ABR® may detect smaller Acoustic Neuroma
Screening application
30-50 dB nHL 100 μs click stimulus
Looking for Wave V
Typically automated detection (e.g. AABR®) V
III I ms
I-III
III-V
I-V V ms
AABR® 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 protocol
Tone bursts instead of click stimuli: typically 500 (difficult to record), 1000, 2000, 4000 Hz
Frequency-specific
Levels vary to find the threshold
Looking for Wave V threshold
Technically similar to screening click-ABR, but not automated
Detect thresholds up to 80 dB HL V ms

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 infants
Objective
Non-invasive
Frequency-specific, as tone-burst-ABR
Not site-specific (generators are unknown)
Typically faster than tone-burst ABR
Accurate, particularly at higher HL, above 40 dB HL
Effective at severe and profound hearing loss, up to 110 dB HL, while tone-burst ABR is limited to 80 dB HL
Source: 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 Hz
Modulation
40 Hz – sensitive to sleep
Hz – insensitive to sleep
Responses are looked for in the frequency domain – at modulation frequencies, not carrier frequencies
Thresholds – for carrier frequencies
Multiple-frequency ASSR responses
Amplitudes: nV (billionth of V)
Frequencies – AM and/or FM Hz
Source: Multiple publications by T. Picton, S. John, D. Stapells, and others.

9. Noises are introduced by multiple sources in most clinical environments
Physiological
EEG – increases in sleep
ECG – does not decrease in sleep
EOG, EMG – decrease in sleep
Electric and magnetic
Power line noise: 50 or 60 Hz and their harmonics
Electric field noise
Magnetic field noise
Radio-frequency (RF) interferences

10. Multiple sources introduce physiological noises in AEP recording
Noise on the scalp
Frequency range, Hz
Amplitude
EEG awake
3-40
5 -10 μV
EEG sleep
3-16
2 – 400 μV
Electrooculogram (EOG)
0.5-10 μV
Electrocardiogram (ECG)
0.5-50
80 μV – 2 mV
Electromyogram (EMG)
30-500
10 μV - 2 mV
Source: 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 plain
The heart is much larger relatively to the body
The heart is closer to the head
The heart-beat rate is twice higher than in adults
Temporary 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 amplifiers
Noise EP
Amp 1
BPF
Amp 2
Saturation
Distorted signal
Distorted signal
High 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 antennas
Introduced by:
Electronic equipment
Electric wiring
Improper grounding
Typical 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 wires
Shielding of wires and circuits
Proper grounding
Unshielded lead wires
Electric fields
Differential 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 antennas
Introduced by:
Transformers
Electric motors and wiring
Looped wires and cables
Typical 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 mV
Can be reduced by:
Reducing wire/cable length
Positioning, NOT moving
Reducing loop area
Twisting wires
Very thick shielding (steel)
Looped lead wires and cables
Magnetic fields
Loop area
Differential 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 amplifier EP
Amp
EMI
A/D
DSP
Ground lead
Other leads
“Garbage” IN “Garbage” OUT
Amp – amplifier
A/D – analog-to-digital conversion
DSP – 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 intercom
FM-systems, FM-radio
Wireless computer networks used in many hospitals
PDAs (Personal Digital Assistants), Palmtops
Medical equipment (ICUs, operating rooms, general offices)
Office equipment: copiers, fax-machines, computers
Introduce mostly electrical noise
Interferes at EP (low) frequencies despite RF frequencies are much higher – in MHz and GHz ranges – because of amplifier non-linearity
There is no common-mode rejection (CMR) at frequencies ≥ 20 kHz
Amplitude: 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 lines
Power Line noise comes from
Electric field – picked up by electrode wires & cables
AC power outlets when plugged into the wall – introduced through electronic circuits, power supplies
Through USB computer ports (5 V) – introduced through electronic circuits
Interferes with EP at a number of frequencies – mostly 50 / 60 Hz & harmonics:
60 Hz, 120 Hz, 180 Hz, 240 Hz … due to amplifier non-linearity
Amplitude: up to 10 mV and higher
AC outlet
AMP PC
USB
Power-line noise in AEP amplifiers Hz

18. Low A/D resolution can significantly affect AEP recording due to insufficient dynamic range
Integrity™
Typical
Low

19. Noises in AEP recording
Putting all things together: ABR and especially ASSR are very small signals as compared to noises in AEP recording
Signal
Frequency, Hz
Amplitude, nV (dB)
AEP Signals
ASSR
10 – (0)
ABR
50 - 3,000
, (10-20)
MLR
, (15-25)
LLR
, (16-60)
P300
1 - 15
5, , (15-65)
Noises in AEP recording
Electrooculogram (EOG)
0.5-10
10, , (60-85)
EEG awake
3-40
5, , (55-60)
EEG sleep
3-16
2, , (65-90)
Electrocardiogram (ECG)
(up to 100)
80, ,000, (70-110)
Electromyogram (EMG)
30-500
10, ,000, (70-110)
Electric, magnetic, RF
50/60 Hz, MHz, GHz
Up to 10,000,000 (up to 120)

20. Clinical ABR/ASSR testing is challenging in practice
Long testing time
Best 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 interferences
Electromagnetically shielded booth required
Sensitivity to electrode impedance
Requires rubbing the skin
Need for sedation in many cases
Difficult to administer in electro-magnetically shielded booth

21. In-situ AEP amplification and filtering is a novel method of noise reduction in Auditory Evoked Potentials
Amplifier is mounted in-situ – directly on the ground electrode pad, with no lead
Lead length to non-inverting (+) and inverting (-) electrodes minimized to the distance between electrodes
Filtering prior to amplification
Gains optimized for ASSR and ABR
Impedance mismatch monitored in real time
Risk of wrong electrode connection minimized

22. In-situ amplification largely eliminates electro-magnetic field-induced noises
A/D
DSP
EMI EP
In-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 ASSR
15,000 for ABR
Exceptionally low intrinsic noise:
< 350 nV in 10-10,000 Hz
<10 nV in 0.05 Hz bands in Hz
EP 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.
Noise EP

24. In-situ amplification and wireless communications make AEP testing efficient
Reduced physiological noise
Largely reduced electromagnetic noise
No big “boxes”
Less attention to electrode impedance
Easy mounting on electrode pads
No need to achieve ≤5 kOhm impedance
No hassles with long lead wires and cables
Less 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
ABR
800 clicks
100 clicks
400 clicks
1600 clicks
Subject: Normal hearing female, 24 yrs, R ear
Place: Vivosonic office, EMI ≥ 0.5 mGauss
Phone: ER-3A (correction for 0.9 ms)
Stimulus: Click, 30 dB nHL, 21.1/sec, ipsi
3200 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 pronounced
ABR in a shielded room (<1 V/m, 0.1 mG)
Subject: T.V., 44, normal hearing
Stimulus:
1000 clicks
21.1 clicks per second
Artifact Rejection disabled
ER-3A Insert Headphones
Recording:
Montage Fz/A1
10.66 ms window
Band-pass filter: Hz for Bio-Logic Navigator Pro
Hz for Amplitrode
Source: 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 significant
ABR in moderate electric (12 V/m) and magnetic ( 5.5 mG) fields
Correlation coefficient = 0.81
Correlation coefficient = 0.43
Subject: T.V., 44, normal hearing
Stimulus:
1000 clicks
21.1 clicks per second
Artifact Rejection disabled
ER-3A Insert Headphones
Recording:
Montage Fz/A1
10.66 ms window
Band-pass filter: Hz for Bio-Logic Navigator Pro
Hz for Amplitrode
Source: I. Kurtz, 2004 (unpublished).

30. Wireless recording of OAE and AEP provides mobility and additional noise reduction
Wireless communication with PC
No cable to the PC
No noise coming back into the EP and OAE amplifiers from AC power supply
No cable-related hassles
Mobility
Testing 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 transducers
Adult 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 operation
No AC-power-related noise in the amplifier circuits

31. Bluetooth® is a wireless communications protocol
Digital signal in GHz range
Noise-like, broadband (no fixed carrier frequency – unlike FM-radio)
Low energy – below 0.1 mG
Limited area – 30 feet (10m)
Encoded – secure for medical information
FDA-approved for various medical applications
Bluetooth®

32. Integrity™ is the world’s first and only wireless OAE, ABR, and ASSR system
Amplitrode™
Vivo
Link™
ER-3A
VivoLink™ interface module
Generates DPOAE, TEOAE, ABR, and ASSR stimuli
Conditions stimuli for
ER-3A Insert Phones
B-71 Bone Conductor
Converts EP signals from the Amplitrode™ into digital form, 16 bit
Processes signals and communicates to the computer software through Bluetooth®
Integrity™ computer program controls the OAE, ABR, and ASSR, functions
Protocol setting – modular
Test control – modular
Data management - integrated
B-71
Integrity™
Wireless Bluetooth communication

33. Thank you for your interest!
Questions?
Thank you for your interest!