Architecture The document discusses active implantable medical devices (AIMDs) and provides an example of a cochlear implant. It begins with an overview of AIMDs, noting they are medical devices inserted by surgery to maintain physiological functions using energy. The auditory system is used as an example to illustrate sensory processing. The cochlear implant works by replacing the function of the inner ear using a microphone, processor and electrode array. The document outlines considerations for AIMD design like restoring sensory function, leveraging microelectronics, and solving coupled constraints.

1. Theory of operation
Architecture
Design
Active Implantable Medical Device Design :
The cochlear implant example
Nicolas Veau1
1 Neurelec, MXM group
SAME conference, October 6th , 2010
SAME2010 Active Implantable Medical Devices

2. Theory of operation
Architecture
Design
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

3. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

4. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
What is an Active Implantable Medical Device ?
Denition and examples
Medical Device: Maintain human physiological functions.
Implantable: Inserted into the human body by surgery.
Active: Uses energy to power its sensors and actuators.
Brain stimulators Heart stimulators
SAME2010 Active Implantable Medical Devices

5. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
Economical environment
1 The AIMD is mainly used for :
Sensory and functional prosthesis for invalidating disabilities.
Automated drug delivery for chronicle diseases therapies.
Health monitoring and prevention.
Health care outsourcing.
2 The AIMD aims to :
Improve the quality of life by reducing disabilities, anxiety.
Extend the life time by monitoring vital signs.
Decrease the societal cost by improving the patient autonomy.
3 The AIMD market growth is driven by :
The rehabilitation of disability considered as a public priority.
The population aging.
The over weighted people growth.
The emergence of new geographic markets.
SAME2010 Active Implantable Medical Devices

6. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
Economical environment
1 The AIMD is mainly used for :
Sensory and functional prosthesis for invalidating disabilities.
Automated drug delivery for chronicle diseases therapies.
Health monitoring and prevention.
Health care outsourcing.
2 The AIMD aims to :
Improve the quality of life by reducing disabilities, anxiety.
Extend the life time by monitoring vital signs.
Decrease the societal cost by improving the patient autonomy.
3 The AIMD market growth is driven by :
The rehabilitation of disability considered as a public priority.
The population aging.
The over weighted people growth.
The emergence of new geographic markets.
SAME2010 Active Implantable Medical Devices

7. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
Economical environment
1 The AIMD is mainly used for :
Sensory and functional prosthesis for invalidating disabilities.
Automated drug delivery for chronicle diseases therapies.
Health monitoring and prevention.
Health care outsourcing.
2 The AIMD aims to :
Improve the quality of life by reducing disabilities, anxiety.
Extend the life time by monitoring vital signs.
Decrease the societal cost by improving the patient autonomy.
3 The AIMD market growth is driven by :
The rehabilitation of disability considered as a public priority.
The population aging.
The over weighted people growth.
The emergence of new geographic markets.
SAME2010 Active Implantable Medical Devices

8. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

9. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
The auditory system
How does the ear work ?
External Ear: Antenna amplier conduction line
Middle Ear: Impedance matching Automatic Gain Control
Inner Ear: Analog-to-Digital Converter
SAME2010 Active Implantable Medical Devices

10. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
The auditory system
How does the internal ear work ?
Basilar membrane: Transform pressure variation in membrane
displacement. Behave as an analog delay line.
Corti Organ: Sense the displacement pattern on the basilar
membrane.
[2]
SAME2010 Active Implantable Medical Devices

11. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
The auditory system
How does the inner ear work ?
Inner Hair Cell: Amplitude time-space sampler. Low frequency
detector.
Outer Hair Cell: Frequency and phase time-space sampler. Up to
16kHz detector.
[2] [3]
SAME2010 Active Implantable Medical Devices

12. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
The auditory system
Auditory pathway from the inner ear to the brain
Auditory pathways: Autocorrelators feedback loops
Cortex: Correlators and associative memory
[2]
SAME2010 Active Implantable Medical Devices

13. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

14. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
Cochlear Implant
How does the cochlear implant work ?
External ear middle ear = Microphone DSP
Inner hair cell Outer hair cells = Electrode array
[1]
SAME2010 Active Implantable Medical Devices

15. Theory of operation Overview
Architecture The auditory system
Design The cochlear implant system
Cochlear Implant
Clinical needs and their impacts on the electronics requirements
1 Reliability
1 System reliability
2 Data transfer reliability
2 Clinical performance
1 Good signal processing for voice, music, noise environment
2 Better stimulation with higher temporal and spatial resolution
3 User friendly interface
4 Data fusion
3 Low invasiveness
1 Miniaturization
2 Maintenance surgery
3 Active time
SAME2010 Active Implantable Medical Devices

16. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

17. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
AIMD architecture
Physical view
Subsystems : Constraints :
Stimulation Connections
Sensors Encapsulation
Energy transfer/storage Manufacturing
Communications Agreements
SAME2010 Active Implantable Medical Devices

18. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
AIMD architecture
Functional view
SAME2010 Active Implantable Medical Devices

19. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
AIMD architecture
Data path view
SAME2010 Active Implantable Medical Devices

20. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

21. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Electrode array
Characteristics
Clinical targets :
Preserve neurons
Activate neurons on demand
Monitor neuron activity
Electrode array characteristics :
Mechanical control : toxicity, insertion trauma, infection
Precise current control : in amplitude, time, in space
Tissue impedance measurements
Electrode arrays
[4]
SAME2010 Active Implantable Medical Devices

22. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Electrode array
3D current control
Virtual electrodes : Allow current steering and focusing for higher
neuron selectivity.
Complex waveforms : Allow better neuron preservation and
ecient stimulations.
Virtual electrodes concept
[4]
SAME2010 Active Implantable Medical Devices

23. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Implantable sensors
The interface with the outside world
RAIC
Acoustic sensor Bio-signal sensor
t pic N1 : en
et
pic P1 : 70
entre 400
fRAIC compri
1 kHz et 1
Amplitude de
entre 20 µV et
courant de st
Low noise, low power Neural response
Automatic gain control. Neural synchrony
Helium-leak test compliant Stimulation loop back
Low prole, small volume Time variability oset
SAME2010 Active Implantable Medical Devices

24. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Radio communication
Trans-cutaneous communication interface
Usages: Remote control, tting, multimedia accessories
Description du canal de propagation:
Figures: Below 3mW in 64kbps DL. Below 1µ W in standby.
1Mbps max.
Dilemma: Antenna)
FA ( Inverted Energy/Data transfer, Magnetic/Electromagnetic
Peau Cartilage Graisse Equivalent
Epaisseur 1 mm 4 mm 34 mm 39 mm
on: Permittivité 38.01 38.77 5.28 9.55
relative r
Link budget Antenna réalisé 8.55 13.98
Modèle
Conductivité 44.25 52.63
sous HFSS
Facteur de 0.0226 0.0190 0.1170 0.07151
perte
Caractéristiques des 3 tissues du model équivalent à 2.45 GHz
http://niremf.ifac.cnr.it/tissprop/htmlclie
Antenne IFA dessinée sous HFSS
Loss between external ear and F=2.45GHz, BW=80MHz,
implant : - 25dB @ 2.45GHz Z =50Ω L 30.35 mm
in
l 0.5 mm
SAME2010 Active ImplantableHMedical Devices
2 mm

25. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

26. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Battery
Safety : Backup system, safe chemistry, hot swap,
EN45502-2-3.
Protection : Titanium casing with feed-through, over and
under charge, emergency stop.
Energy transfer : Capacity vs., charging time, charging time
after 10 years.
Inductive charging : EN45502-2-3, expected eciency above
70%
Energy distribution : 0.9 V.
SAME2010 Active Implantable Medical Devices

27. Theory of operation The AIMD system
Architecture The AIMD interfaces
Design The AIMD components
Processing units
1 Intensive processing routines : Physiological noise ltering,
artifact reduction, sensor data fusion, stimulations building,
signal features extractions ...
2 Processing units : ASIC, ASP, FPGA, DSP, DMA, MCU
3 Software architecture : Usually no RTOS, no vendors libraries
for safety reasons, specic development and test guidelines.
Generic datapath
SAME2010 Active Implantable Medical Devices

28. Theory of operation Modeling tools
Architecture Simulation tool
Design
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

29. Theory of operation Modeling tools
Architecture Simulation tool
Design
Analytical models
Multi-physics models
1 Captures tight physics interactions : acoustic, viscosity and
thermal combined eects.
2 Ecient for variable sensitivity analysis and optimization under
constraints.
3 Supported by simpler and easier to understand lumped
elements representations.
Subcutaneous microphone
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!#$%'()'* +,!'-.-/01230 (
SAME2010 Active Implantable Medical Devices

30. Theory of operation Modeling tools
Architecture Simulation tool
Design
Analytical models
Statistical and biological models
1 The model computes the neurons population recruited by
electrical stimulation according to their ring rate.
2 This model is used to identify the virtual electrodes that
maximize spatial selectivity and directivity of a stimulation
Current focusing and steering
Current Focusing − Contour Plot of Number of Neurons Fired Current Focusing − Number of Neurons Fired Current Steering − Contour Plot of Number of Neurons Fired Current Steering − Number of Neurons Fired
2.5 90 100 2.5 90 100
σ=0 α=0
2 80 90 σ = 0.5 2 80 90 α = 0.25
σ = 0.75 α = 0.5
1.5 80 1.5 80
70 σ=1 70 α = 0.75
electrode α=1
1 70 1 70
60 60 electrode
Neurons Fired
Neurons Fired
0.5 60 0.5 60
Location (x)
Location (x)
50 50
0 50 0 50
40 40
−0.5 40 −0.5 40
30 30
−1 30 −1 30
−1.5 20 20 −1.5 20 20
−2 10 10 −2 10 10
−2.5 0 0 −2.5 0 0
0 0.2 0.4 0.6 0.8 1 −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 0 0.2 0.4 0.6 0.8 1 −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5
σ values Location along Neural Clusters(x) α values Location along Neural Clusters(x)
SAME2010 Active Implantable Medical Devices

31. Theory of operation Modeling tools
Architecture Simulation tool
Design
Numerical models
Physics models
1 Useful for complex geometry and numerous interfaces
2 Reduce the number of prototypes and cost
3 Computations intensive, slow optimization convergence
4 Expensive tools, dicult to set them up, lack of
interoperability with others tools.
Antenna Magnetic systems Piezoelectric systems
SAME2010 Active Implantable Medical Devices

32. Theory of operation Modeling tools
Architecture Simulation tool
Design
Numerical models
Statistical and biological models
A simplistic 3D model of the cochlea
Accompanying electrode array
Generated potentials and currents through the cochlea when
the electrodes were stimulated.
Neural response to electrical stimulation was observed.
BEM and HodgkinHuxley model method
[6]
SAME2010 Active Implantable Medical Devices

33. Theory of operation Modeling tools
Architecture Simulation tool
Design
Outline
1 How can an AIMD restore lost human sensory functions ?
Overview
Sensory processing : The auditory system example
Sensory prosthesis : The cochlear implant example
2 How can microelectronics benet to AIMD's performances ?
The AIMD system
The AIMD interfaces
The AIMD components
3 How to solve strongly coupled constraints in an AIMD design ?
Modeling tools
Simulation tool
SAME2010 Active Implantable Medical Devices

34. Theory of operation Modeling tools
Architecture Simulation tool
Design
Cochlear implant simulator
SAME2010 Active Implantable Medical Devices

35. Bibliography I
[1] Digisonic SP system
http://neurelec.com/
NEURELEC, Vallauris
[2] Pujol R. al.
Extracts from the website Promenade autour de la cochlée
http://www.cochlee.org
INSERM U. 254, Montpellier
[3] Kiang N., Rho J., Northrop C., Liberman M. Ryugo D.
Hair-cell innervation by spiral ganglion cells in adult cats
Science, 1982, 217, 175-177
[4] Cu electrodes.
http://neurelec.com
NEUROMEDICS, Vallauris
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36. Bibliography II
[5] O Connor K.N. Puria S.
Middle-ear circuit model parameters based on a population of
human ears
The Journal of the Acoustical Society of America, 2008, 123,
197
[6] Gramfort A., Papadopoulo T., Olivi E., Clerc M.
OpenMEEG: opensource software for quasistatic
bioelectromagnetics
HAL-INRIA. May 2010.
SAME2010 Active Implantable Medical Devices