Cochlear Implant Update
Presented on Thursday, 12 May 2011
Susan Johnston, Clinical Scientist
An Overview of Radio Aids and Cochlear Implants
Why use FM?
Deaf children find it difficult to listen in class due to
- background noise;
Even with the latest audiological technology, these problems cannot be solved by a hearing aid or cochlear implant alone.
Background noise affects the understanding of speech
- the speech signal drops by 6dB with every doubling in distance. It becomes contaminated with reverberation and background noise;
- delivery of an '‘uncontaminated'’ speech signal is particularly important for young children;
- there needs to be a good signal-to-noise ratio.
For adults to make sense of a speaker in noise they need to have the speaker's voice (signal) 6dB louder than the background noise (noise). This is a signal-to-noise (SNR) ratio of +6dB. However, a child needs +16dB SNR ratio and a deaf child needs a +20–30dB SNR ratio.
An FM system decreases the distance between speaker and listener delivering the sound direct to the ear and can deliver improvements in SNR of at least +15dB.
Soundfield systems can improve SNR by around +10dB but are dependent on room acoustics.
An FM system works like this:
- The person speaking wears or holds a transmitter microphone, or the transmitter is placed in the middle of the group (picking up speech from all around).
- Using radio waves, the FM system sends speech signals to the listener, who wears a FM receiver usually behind the ear.
There are many different types of FM system but each consists of a transmitter worn by the teacher and a receiver worn by the pupil.
The receiver may be connected to the hearing aid or cochlear implant by direct audio input (DAI) shoes or FM adaptors.
Interference with cochlear implants
FM systems and cochlear implants operate on radio frequencies and there can be some overlap of frequency harmonics. UK FM systems operate in the 173-175 MHz band and speech processors between 2.5MHz and 49MHz depending on the individual system.
Certain FM channels are not recommended for some implants.
An FM radio aid transmits much less power than a cochlear implant system therefore it is more susceptible to interference.
Radio frequency energy generated by the speech processor can be present on the FM interface cable which is also the aerial of the receiver. This increases potential interference and can result in poor range and poor sound quality.
Generations of wireless FM technology
2000 The first miniaturized universal FM receiver. This device could be connected to almost all brands of hearing aid or cochlear implant, opening up wireless FM technology to almost all hearing-impaired children.
2003 Phonak launches the first miniature multifrequency universal radio receiver,
2006 MLxS was succeeded by the MicroMLxS.
2006 Phonak's new Freedom MicroLink – an integrated FM receiver for the Nucleus Freedom processor.
2007 Phonak's new Dynamic FM platform and inspiro transmitter as well as the first Dynamic FM receiver MLXi are launched.
2011 ML14i – design-integrated Dynamic FM receiver for Cochlear's CP810
Quality Standards for the use of personal FM systems
Promoting easier listening for deaf children
14 July 2008
The document is aimed at those who commission services and at practitioners including paediatric audiologists, educational audiologists, teachers of deaf children and parents interested in the use of personal FM systems.
QS1 recommends "Every child with a hearing loss should be considered as a potential candidate for provision with a personal FM system as part of their amplification package, in line with a written policy on candidacy."
For children with cochlear implants there are some important general considerations.
QS4 recommends "Initial fitting and setting up of an FM system with a cochlear implant speech processor must be carried out by an appropriately trained CI centre professional. This should take place at the implant centre."
Readiness for FM for cochlear implant users
- The child should have a stable 'map'.
- The child must be able to report on sound quality.
- Situations for appropriate use must be established.
- Compatibility of FM system and CI considered.
Any required mapping changes to the child’s speech processor need to be made before the FM fitting at the implant centre, for example a specific programme may be needed with a correct mixing ratio of 1:1 and auto sensitivity should be enabled on the FM programme for Nucleus devices.
There are differences between the different manufacturers' speech processors and the way they are set up to work with personal FM systems. For this reason it is not possible to produce a generic procedure.
It is always important to consult the cochlear implant centre when first fitting a personal FM system to a CI user.
Detailed information about the setting up of different FM systems with the range of cochlear implants used in the UK is available in SOECIC (2007) www.soecic.com.
Monitoring and checking considerations
It is vital for both the fitting of a hearing aid and a cochlear implant with an FM system that correct procedures and policies are followed and that the whole system is evaluated regularly.
The equipment must be kept in good working order to maximise the benefits for users. There should be daily checks of the equipment, both the hearing instrument and all components of the FM system.
There are two main issues to be addressed:
- Assuring settings in CI speech processors are correct.
- Correct order of switch on (for some equipment).
- Checking for signal coming through.
Ensuring the FM receiver is set optimally to give FM advantage
Electroacoustic procedures are available for checking Nucleus speech processors and personal FM systems. These are used at the clinic together with speech tests matching performance with and without the FM system to set optimal gain.
The FM QS Good Practice Guide gives suggestions for monitoring and checking FM systems. For example with cochlear implants:
- Are the batteries working in the speech processor?
- Has the correct adaptor been used and is the equipment connected properly?
- Can you listen to the FM using listening earphones?
- Are you using the correct program for FM?
- Is the transmitter microphone working?
- Are the transmitter and receiver on the same frequency?
- Is the transmitter microphone muted?
- Are you using an appropriate frequency channel for the type of speech processor?
There are specific frequencies best avoided when setting up a personal FM system with some cochlear implant speech processors. Currently, these are:
– 172.500MHz and 175.000MHz with the Nucleus CI 22 series of implants (before 1997).
– 173.350MHz and 174.000MHz with the Nucleus CI 24 series (since 1997).
The complete channel coding comparison chart between narrow band personal FM system manufacturers ©Ewing Foundation, Paul Harris et al 2008 can be used for reference.
Recommended channels for the Freedom MicroLink are H06, H07, H16, H17, H18, H19, H20, H47, H48, H57, H59, H77, H78, H79, H85, H86, H87, H88, H89, H90.
Unlike traditional FM systems with fixed gain settings, Dynamic FM automatically varies the gain of the FM receiver with changes in the ambient noise level. It has shown significant benefit in speech recognition scores in noise for cochlear implant users.
Jace Wolfe et al (2009) Evaluation of Speech Recognition in Noise with Cochlear Implants and Dynamic FM. J Am Acad Audiol 20:409–421
Functions on Esprit 3G
Program 1- standard map with monitor earphones disabled (use with MicroLink)
Program 2- Autosensitivity with monitor earphones enabled (allows earphones to be used)
T loop system
W whisper setting
Troubleshooting Esprit 3G
- No output – Switch off/on then change batteries.
- No signal with signal check then change coil cable.
- Ensure TWM switch in correct position.
- Use listening earphones - crackling or no sound- use lapel microphone and contact clinic.
Esprit 3G and Personal FM
- Use the 3G adaptor to connect the FM receiver
- Switch processor off then on again.
- To listen in to the MicroLink: Plug in monitor earphones, reduce processor sensitivity to zero and listen to the signal from microlink alone (Use P2).
- Adaptor should be set to FM+M.
- Ensure the receiver and transmitter are on the same frequencies.
Esprit 3G and Accessories
Accessories can be plugged in using the adaptor plug and accessory adaptor cable.
Use monitor earphones to listen to the microphone with the access plug.
Functions on Freedom
- Microphone cover
- Select button
- +/- button
Hold select button for 2 sec to switch the processor on/off.
Quick press select button to change the program.
Press select and – button to lock and unlock the processor buttons.
+/- button change sensitivity/volume
Press + and – buttons together to select an accessory. ( T MT or EA)
Press all three buttons to reset to default settings.
Freedom error codes
- H1 – Flat battery > Change batteries
- H2 – Low battery > Change batteries
- H3 – Coil error > Check coil position/change coil
- H4 – Audio error > Lapel mic/contact clinic
- H5 - Program error > Change program/clinic
Connecting accessories to the Freedom
Accessories can be plugged in at the base of the Freedom using the accessory adaptor cable. Take care with the shaped socket.
Turn the processor off then on again. Press + and – together until EA appears on the display.
Monitor earphones can be used to listen in to the sound signal from the accessory or built in telecoil.
An integrated FM receiver.
- Use H06 or above with the Freedom due to possible interference with coil transmission frequency.
- 1:1 mixing ratio programmed into the Freedom.
- Freedom MicroLink gain can be programmed at the clinic.
Connecting an FM system
- Remove battery rack and replace with MicroLink Freedom.
- Ensure fully inserted into socket.
- Switch on processor.
- Press + and – together until EA appears on the display
- If listening in with earphones plug in prior to switch on. To listen to the FM signal turn sensitivity of the processor down to zero.
- Monitor earphones will deactivate after 90 seconds.
Freedom and MLX
- An MLXs or MLXi can be used with the bodyworn configuration.
- Requires a special babyworn cable.
- MLX plugs directly into the port on the cable.
- Switch the processor off then on again.
- Press + and – buttons together until EA appears on the display.
Behind the ear
Functions on CP810
Lower button ON/Off
Socket for transmit cable
CP810 Remote control
- Can be used to show status of processor
- Help with troubleshooting
- Adjust volume and sensitivity – not recommended in children
- Change programs
Functions on CP810
To switch ON press and hold lower button for count of two.
LED will flash once for p1, twice for p2 then flash amber if not on head.
LED will flash green to incoming sound. This allows you to check that the microphone(& FM) is picking up sound and transmitting to the implant.
Connecting 3 pin Euro Radio Aids
Compatible with Phonak MLxS, MicroMLxS, MLxi and Oticon R2.
- Connect the FM using the euro FM adaptor.
- Listen in to FM using the port on the listening earphones.
- Turn processor sensitivity down to zero using remote control.
Order for connecting 3 pin Euro Radio Aids
- Insert the Euro FM receiver into the three pin socket on the Euro Accessory Adaptor.
- Turn on the Euro FM receiver by pushing the latch to the on position.
- Turn ON the processor.
- Connect the Euro Accessory Adaptor to the processor accessory socket.
Integrated ML14i receiver
Listen in to FM using the port on the listening earphones.
Turn processor sensitivity down to zero using remote control.
Functions on Opus 2
Has child safety locks
Test device light flashes in response to sound (this can be used to test FM system)If processor has power and test device is not responding retry and change cable.
Connecting FM system to Opus2
- Switch off the processor and replace the battery cover with accessory cover.
- Plug in 3pin FM receiver. Select FM+M on switch.
- Mixing ratio is automatically 50/50 when radio aid is plugged in.
Opus2 FM Systems
Opus2 remote control
Implant Hi res 90k
Speech processors Harmony/Auria
Functions on Harmony
- Standard hook
- Accessory hook
Each uses a different mixing ratio. Suitable programs for each type of earhook must be set up in the clinic.
Connecting Harmony and FM
- Remove earhook on Harmony by twisting and pulling off
- Push on the iconnect earhook
- Plug the MLX into the socket on the iconnect.
- Ensure no.10 battery is inserted into the back of the iconnect earhook
- Use the one dot position on the MLX
Harmony and FM Systems
- Use indicator light on Harmony to monitor function or purchase a Harmony listening check.
- Contact clinic to check which program to use with the FM.
Harmony and accessories
Use direct connect cable and hook to connect other equipment.
Telephone: 01563 827323
Care and maintenance: resources
If you need help or think we can do some thing better please let us know.
Pictures courtesy of Cochlear, Medel and Advanced Bionics and phonak respectively.