Objective Assessment Of Hearing Loss In Neonates
Dr. B. Padmapriya1, P. ElakiyaJothi2
1Associate Professor, Department of Biomedical Engineering, PSG College of Technology, Coimbatore, India 2Student, Department of Biomedical Engineering, SSN College of Engineering,
Chennai, India
Abstract
Deafness, which refers to varying degrees of hearing loss, is one of the most common sensory disorders. Deafness has become a global public health problem and significantly a baby's development can be affected by hearing loss. Better chance of developing language, speech and communication skills, when finding these in early stages. Audiometry is a test that evaluates the hearing ability of a person with the application of sound stimulus at different frequencies and intensities. Implementing the hearing screening technique, infants with hearing loss can be identified within the first few months of their birth. The hearing loss can be detected by recording and processing the Auditory Brainstem Response (ABR) in response to the given stimulus which is sent inside the ear. ABR signal consist of conduction pathway of hearing, if absence of any wave in this signal infers/ locates where the conduction is truncated. In this Work, ABR signals are acquired through Electroencephalogram (EEG) hardware where DAQ acts as a driver that drives the acquired signal from EEG hardware to LabView, and then using Audiometer trigger signals are generated. The acquired EEG signal is then processed and analysed using LabView which could aid for the detection of hearing loss.
KeyWords—Audiometry, Auditory Brainstem Response, Electroencephalogram, Audiometer, LabView.
INTRODUCTION
Congenital hearing loss refers to the loss of hearing from the time of birth. It can be genetic (hereditary) or result from other factors: before birth (prenatal), during the time of birth (perinatal) or after birth (postnatal period). Types of hearing loss might be conductive, sensorineural or mixed: depending on how the disorders affect the hearing pathways.
Developments and improvements in the ABR are seen in the first few months of life in premature infants. Myelinisation and hyperbilirubinemia gives the significance of repeating ABR and behavioral threshold assessments over a time period to monitor for any changes. It is important to differentiate between improvements in hearing thresholds together with normalization of the ABR, versus an improvement in hearing thresholds with persisting abnormality of the ABR. An improvement in auditory thresholds does not necessarily translate to an improvement in functional auditory performance if the ABR is still abnormal.[1] It has been generally accepted that children diagnosed with hearing loss should be suggested with appropriate hearing aids when behavioral thresholds show a significant hearing loss.
Unfortunately infants will not be able to perform Visual Reinforcement Audiometry (VRA)[3]
until approximately 8 months developmental age. Hence application of another technique is
needed for early diagnose of this defect. Recording an EEG evoked potential signal using surface mount electrodes and digitization of data is done. Analysis of the signal gives the assessment of the brain signals and interprets events related to the auditory organ of the infant.
In newborns and childhood the given onset of Auditory Neuropathy Spectrum Disorder (ANSD)[2][9][10] can occur with hearing loss screened using Otoacoustic Emission (OAEs)[4]
can pass their screen, clinicians need to be alert to the possibility of undiagnosed in the infant population. Concerns are raised if children demonstrate significantly poorer speech discrimination than expected given their pure tone audiogram, and/or inconsistent auditory behaviour that is not explained by intermittent middle-ear pathology.[11] If OAEs are detected in the presence of a significant pure tone loss, are absent for degrees of loss where they are expected to be present.
A. Electroencephalography
The electrical activity of the brain is measured using Electroencephalogram and the graphical representation of it is known as Electroencephalography. The electrical activity is produced when neurons are fired. It is a unique and valuable measure of electrical function of the brain.
It is a graphical display of differences in voltage between two sites of brain function recorded over time. There are four types: Delta, Thet a, Alpha and Beta.
B. Auditory Brainstem Response
ABR audiometry is a neurologic test of auditory brainstem function in response to auditory (click) stimuli. First described by Jewett and Williston in 1971, ABR audiometry is the most common application of auditory evoked responses.[12]
C. Auditory Pathway
In the brain stem cochlear nuclei is present where the first relay of the primary auditory pathway, which receive Type I spiral ganglion axons (auditory nerve); an important decoding of the basic signal occurs at this level: duration, intensity and frequency. In the superior olivary complex of brain stem the second major relay occurs: the majority of the auditory fibres synapse there having already crossed the midline. Apart this relay, the message is carried through the third neuron to the level of the superior colliculus (mesencephalus). An essential role in sound localization is performed by these two relays.
Before the cortex the last relay occurs in the medial geniculate body (thalamus) where an important integration occurs that is sthe preparation of a motor response (eg vocal response).[5] The final neuron of the primary auditory pathway links the thalamus to the auditory cortex, where the message, already largely decoded during its passage through the previous neurons in the pathway, is recognized, memorized and perhaps integrated into a voluntary response.
D. ABR Waveforms
Fig.1 Waveforms of ABR
The waveforms generally are EEG waveforms that are obtained as a response from the patient during testing due to the auditory pathway explained above.
Table 1. Origin of each wave
Wave Origin Latency
I Cochlear Nerve 1.60ms
II Doral and Ventral Nucleus 2.96ms
III Superior Olivary Complex 4.16ms
IV Nucleus of Lateral Lemniscus 4.96ms
V Inferior Colliculus 5.96ms
VI Medical Geniculate body -
VII Auditory Radiation -
Fig.1 shows the different waves of ABR and their corresponding time period is given in the Table 1.
METHODOLOGY
A. Data Collection - ABR Recording
The recording of ABR signal was made using the Olimex equipment and National Instruments. The recording signal can be displayed on the computer screen.[6] The block diagram of the proposed methodology is given in Fig.2.
Subject and Environment Description:
The environment of the recording must be in a quiet condition. The recordings were done in a sound-proof room and well air- conditioned, to create a comfortable environment for the subject and for the recording session. The subjects were asked to close their eyes during recording session because a blink of an eye is cause the main artifact or interference during recording of an EEG signal.
Fig.2 Block Diagram
Five subjects in the age range of 10-15 were selected to undergo the recording. Among them one of the subjects has hearing problems. Subjects were explained about the propose and need of recording.[7][8]
Electrodes:
The electrodes used here are surface electrodes. The recording can be done in two ways namely, ipsilateral and contralateral.
Fig.3 Electrode positions on the scalp.
The placements of electrodes are shown in the Fig.3 and the configuration is given in the Table 2.
Table 2. Electrode Configuration
Channel (+) Reference (-) Ground
Vertex Right Mastoid Forehead
When a stimulus is given and the signal response is also recorded from the same ear is called as Ipsilateral type of recording. But in Contralateral method recording of the signal is done from the other side of the ear where the stimulus is applied.
B. Hardware
The hardware components used in this work are EEG-Analog ASM from OLIMEX and DAQ. This is used to acquire the EEG signal. This Hardware contains two EEG channels in which one is used to acquire the EEG signal and the other one is made as virtual ground. The
DAQ from National Instruments is used for interfacing the EEG amplifier and the LabVIEW in a way it acts as a sensor that converts the analog EEG signal acquired and gives it as a digital signal to LabVIEW.
The designed hardware features are Configurable for both active and passive electrode, configurable for both disposable and permanent electrodes, AEP system voltage out 2000μV,200μV,50μV,GND, isolator to avoid leakage current and system noise and option to select the frequency (1-64 Hz) for Auditory evoked potential system.
C. LabView
This system is light weight two-channel EEG calibrator with auditory evoked potential measurement system. This portable auditory evoked potential device is easy to use and operate. The system amplifies the EEG signal for auditory stimuli generation with various dB and frequency and sends the data to your computer through DAQ[13] (recommended NI-DAQ, Road Runner and Analog Discovery of Diligent). The training software is used for analysis of data with save option.
D. Operating Sequence
Sequence of steps to be followed to acquire the output as follows
• Connect disposable electrode or permanent electrode jag in appropriate port.
• Connect the CH 1 output to the analog pin of DAQ.
• Connect Headphone or Loudspeaker with respect to ACA (Aided Cortical Assessment) or CTE (Cortical Tone Evaluation) method for stimuli selection.
• Select the file path in which stimuli’s stored with different dB and different frequency.
• Run the program and select the samples to read of the Auditory Evoked potential signal.
• Auditory Evoked potential signal will be displayed on waveform graph.
• Select the cut-off frequency for the low-pass filter (recommended 40 Hz).
• Press on Apply LP filter button and analyze the power spectrum.
• Select the cut-off frequency for the baseline filter (recommended 0.16-0.50 Hz)
• Press on Apply Baseline filter button and analyze the power spectrum.
• The raw and the filtered data can be saved as excel file and can be used for further signal processing in MATLAB or LABVIEW.
The improvement in the signal to noise ratio depends on the following factors.
• Cable placement and position.
• Isolation to the acquisition system. It avoids the leakage current to the patient as well as noise coupling through the mains.
E. EEG Waveform Testing Software
The Auditory Evoked potential waveform testing software is designed in LABVIEW software. It mainly consists of three windows. They are,
1. Evoked Potential 2. Statistical Analysis
AEP EEG-FEATURE EXTRACTION
One is waveform window and the other one is power spectrum of signal in dB. To eliminate the power line interface low-pass filter can be applied by selecting the cut-off frequency 40Hz is selected as the default cut-off frequency for the low-pass filter. The order of the low- pass filter is selected as 10.The user can change the order of the filters only by using the Back-End window. The base-line filter is a high-pass filter to avoid the base-line wandering of the signal. The recommended frequency range for the filter is in between 0.16Hz to 0.5Hz.The high-pass filter is selected as Butterworth filter of order 2.
1. Evoked Potential Screen:
• Run the Auditory Evoked Potential Testing Software.
• And also connect the headphone or loudspeaker with the PC or laptop.
• Each waveform graph has ON and OFF buttons to hold and play the waveforms.
• Before that connect the electrode on the scalp. The electrode placements are, o Active Electrode – Cortex position of head
o Ground Electrode – Forehead
o Reference Electrode – Mastoid position near ear
• Turn ON the waveform graphs. If you want to hold the waveform, you should turn OFF the waveform and then you can export it to Excel by Right Click-Export-export to excel.
2. Statistical Analysis Screen:
• In this screen it displays Ongoing EEG, Histogram, EPOCH detection and Parameter waveform.
• And also it displays Cycle Average, Positive peak, Negative peak, Peak to Peak and mean of auditory evoked potential.
• Stabilize the patient for Auditory evoked potential.
• Then Apply 80dB, 250 Hz stimuli through headphone or loudspeaker.
• The Auditory Epoch will occur and it can be seen in Epoch detection waveform.
3. EEG Feature Extraction Screen:
• This screen is to display the EEG feature extraction with delta, alpha, beta and theta.
4. EEG Wave Components:
• This screen is to display the EEG wave components with delta, alpha, beta and theta.
RESULTSANDDISCUSSION
The experimental procedure was done for various subjects like Subject I, Subject II, Subject III based on certain criteria like age (13, 14, and 15) and hearing ability (Normal hearing, Partial Hearing loss and Complete hearing loss) respectively, during sleep condition.
Fig.4 window shows the different module in which the Epoch is detected clearly that determines the ability of hearing.
Fig.4 Statistical Analysis Window of Subject I
As the experiment is conducted during sleep condition, the Delta wave is dominant of all other waves so that it is easy to identify and this is to be analysed for result.
Fig.5 EEG Wave Components Window of Subject I
Fig.5 gives the matching waveform for ABR signal in Delta waveform so that it is extracted and compared with the original signal which shows the presence of Wave V as shown in the Fig.6 which gives a result that the subject is capable of hearing ability with conformation.
Fig.6 Normal ABR signal Vs Extracted ABR signal of Subject I
The below window shown in Fig.7 explains the Statistical Analysis Module of Subject II, that the Epoch is detected partially, indicates the partial hearing ability of the subject.
Fig.7 Statistical Analysis Window of Subject II
Subject III is also tested with same parameters and checked for the result.
Fig.8 Statistical Analysis Window of Subject III
Fig.8 gives the Statistical Analysis Window showing that Epoch is not detected that it indicates the complete loss of hearing ability.
Fig.9 EEG Wave Component Window of Subject III
Fig.9 shows the ABR signal that belongs to Subject III where the Delta waveform is extracted.
Fig.10 Original ABR Waveform Vs Extracted Waveform of Subject III
The extracted delta waveform is compared with the original signal where Wave V is absent as shown in the Fig.10 that concludes to a result that the corresponding subject is not capable of hearing with conformation.
CONCLUSION
A software based application for detecting hearing ability of neonates which can be implemented on any PC equipped with LabView environment with an audio card and headphones are presented in this paper.
The acquired EEG signal (Evoked potential, Statistical analysis and feature extraction) is processed and analysed using LabView, the changes in amplitude of Epoch detection signal varies with respect to peak that indicates the degree of hearing loss as shown in Fig.6 and Fig.10.
The acquired data and diagnostic information can be stored easily on the PC and displayed at any time. Thus, early detection of hearing loss will help in implementation of proper hearing aid and development of other sensory response of newborn.
Future work may be extended as
• EEG acquisition hardware using wireless technique.
• Sending the acquired signal using Bluetooth technique.
• Controlling the equipment using android application.
• EEG hardware will be miniaturized in size and cost efficient (with minimal cost).
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