RF Communication for Implantable Devices - WebInABox · • History of Implantable Devices and...
Transcript of RF Communication for Implantable Devices - WebInABox · • History of Implantable Devices and...
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RF Communication for Implantable Devices
Perry Li St. Jude Medical IESD
Sylmar, CA
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Overview
2
• Applications – CRM, Neuromodulation
• History of Implantable Devices and Telemetry
• Benefits and Uses of RF Telemetry
• Standards Requirements
• RF System Design for CRM Devices
• Challenges Unique To Implantable Devices
• Future Opportunities
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Electrical Signals in the Heart
3
Cardiac Tissue:
- Automaticity
- Excitability
- Conductivity
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Main Cardiac Conditions
4
• Bradycardia – slow heart rate – Pacemaker
• Tachycardia – ventricular fibrillation –
Implantable Cardioverter Defibrillator (ICD)
• Heart Failure – ventricular dissynchrony –
Cardiac Resynchronization Therapy (CRT)
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Tachycardia: Reentry
5
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Pacing Pulse and Defib Pulse
6
Time
Defibrillation Voltage
0
~850V
Vf_pos
Vi_neg
Vf_neg
tpos tneg
Pacing Voltage
Time
Vrtn
Vrtn 0
0.5V- 8V
Charge Balancing
Bi-Phasic Shock
Pacing Defibrillation
tpw
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Device, Leads, Programmer, Patient
7
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Neuromodulation Therapy
8
• Spinal Cord Stimulation (SCS) – Chronic pain
(eg: back pain)
• Deep Brain Stimulation (DBS) – Parkinson’s,
Tremors, OCD, possibly mood disorders
• Peripheral Nerve Stimulation
(PNS) – Chronic migraine
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SCS Therapy
9
• Implant in lower back with leads
along epidural layer of spine
• Electrodes along leads send
electrical pulses to the spine
• These pulses interfere with nerve
impulses that cause pain
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DBS Therapy
10
• Electrodes target specific areas
of the brain to stimulate
structures responsible for
chemical or motor deficiencies
• Directly modulates brain activity
in a controlled manner
• Unlike other surgical techniques,
the effects are reversible
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PNS Therapy
11
• Used to treat chronic
migraine patients who have
failed to respond to
pharmaceutical treatments
• Mild electrical pulses to
stimulate specific nerves, eg:
the occipital nerves which
are located behind the head
just above the neck area
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Device, Leads, Programmer, Patient
12
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History of Pacers/ICD/IPG
13
Pacemakers:
First implant 1958
Transvenous & demand pacing 1960’s
Dual chamber 1970’s
ICD:
First implant 1980
FDA Approval 1985
Abdominal implant pectoral implants
IPG:
First implant 1982
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Physical Design
14
Pacemaker ICD
Header
Titanium Case
Ports for leads
RF Antenna
Set Screws
Feedthru
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Huge Dynamic Ranges
15
-Battery currents: ~A (background)
~Amps (charging)
-Voltages: < mV (ECG/sensing)
> 850V (shocking)
- Device currents: Many 10’s of Amps
(shock delivery)
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Electrical Block Diagram
16
Sensing
HV
Protection
EMI
Filters
Sense
Multiplexing
Pace
Drivers
Pace
Multiplexing
ADC’s
MCU and
Programmable
Digital Functions
Clock
Generators
Memory
Telemetry
Rate Sensor
Patient Notifier
Battery-
and
Power-
Management
Battery
Header and
Case
Connections
Charge
Pumps
Magnet
Detect
Charger
Shock
Driver
Caps
Unique to ICD
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Evolution of Telemetry
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• Magnet / Trim-pots
– Device settings
– Battery voltage monitoring
• Inductive
– Short range magnetic field coupling
– 10’s of kbps
• RF
– Range of several meters
– 100’s of kbps
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Benefits of RF Telemetry
18
- At implant
- Remote monitoring
- At followups
- Therapy control
- Device control/configuration
- Real-time ECG streaming
- Firmware code downloads
Non-RF RF
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Home Monitoring
19
- Bed-side Monitor
- Scheduled Device
Interrogations
- Patient Initiated
Device Interrogation
- Landline or Cell Connection
- Interface to Online Patient
Care Network
Non-RF RF
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Administering Therapy
20
- Handheld programmer
- Turn on and off therapy
- Adjust level of therapy
- Wireless battery charging
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MICS Standard
21
• Medical Implant Communication Service (MICS)
• FCC (1999) and ETSI (2004) – adopted world-wide
• Licensed by Rule – no individual application
• 402-405 MHz (shared with weather balloons)
• Tissue penetration with low power
• 300kHz channels, < 25uW EIRP
• Communication Initiated Only By Base Unit
– Listen Before Talk / Clear-channel Assessment (LBT/CCA)
– Emergency Device Transmission
• Standard does not require interoperability
• Modulation: FSK, 2FSK, 4FSK
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ISM Band
22
• Industrial, Scientific, and Medical (ISM) radio bands
• 1985 – Unlicensed for commercial use
• 12 frequency bands from 6.7MHz to 246GHz
• Popular bands:
– 902-928 MHz
– 2.4-2.5GHz
• Interference from commercial
devices:
– 900MHz - GSM, Zigbee
– 2.4 - Bluetooth, Wifi, microwave
oven, etc
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Clear Channel Assessment
23
• Monitor Channel for > 10ms
• Power Below Determined Threshold
– Otherwise: Channel with lowest ambient power
– Second-quietest channel chosen as alternate
– Switch to pre-selected alternate in case of interference
– After 10ms monitoring of alternate channel
• Channel Can Remain In Use Unless Silent Period > 5sec
• Allowance For Switch To Pre-Selected Alternate Channel
• Emergency Transmission By Implant
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FDA Classification
24
• Class I – General Controls
– Not intended for supporting/sustaining life
– Bandages, gloves, hand-held instruments
• Class II – General/Special Controls
– Pre-market notification
– Powered wheelchairs, infusion pumps
• Class III – Pre-Market Approval
– Support or sustain life
– Pacemakers, ICD’s, replacement heart valves
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Equipment Authorization
25
• FCC: – Testing – showing compliance
with FCC standards
– Radiation Exposure – SAR
– Device Labeling
• FDA:
– Pre-Market Approval (PMA)
– Investigational Device Exemption (IDE)
– EMC, Robustness, Coexistence, QOS, Data Integrity
and Latency, Security, Risk Management
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Wakeup
26
• Duty-cycle communications
• 2.45 GHz ISM band
– 100mW EIRP in US,
10mW in some countries
– OOK modulation
– Duty-cycled “sniffing”
• MICS band
– “sniffing” using RSSI
• Inductive Wand
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RF IC
27
• Microsemi ZL70102 chip – 400MHz Tx and Rx, 2.45GHz Rx only for wakeup
– Max Tx Power = -1dBm, Rx sensitivity = -85dBm
– Transmit Current = 5mA, Sleep current = 10nA
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RF System Block Diagram
28
• Typical RF Block Diagram
– Match 1&2 on-chip capacitors for dynamic tuning
– SAW filter to allow only MICS band
– 2.4GHz notch filter to reject wakeup signal
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Challenges Unique to Implantable
Medical Devices
29
• Design for patient safety
• FDA, TÜV, and other international medical regulatory bodies
• FCC, ETSI, and other international wireless communications
regulatory bodies
• Medical reimbursement
• Long design/approval cycles
• Relatively low volume
• Long-lived designs and implants
• Deployed base of RF infrastructure
• Backward compatibility
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RF Technical Challenges
30
• Performance Requirements
• Size and Form-Factor
• Antenna Limitations
• Variable Implant Environment
• Power Limitations
• Interference
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• Dual band functionality: 400MHz and 2.4GHz – Higher tissue losses at 2.4GHz
– Free space path loss 8.7dB higher at 2.4GHz than 400MHz
• Minimum distance requirement
• Antenna radiation pattern – Main lobes should be focused
through front and back of
patient
– Good flip performance
Performance Requirements
31
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Size and Form-Factor
32
• Size
– Increasingly smaller header and can
size
• Pacemaker: 4 x 0.5 x 1.5 cm
• ICD: 3 x 1.3 x 1 cm
– Non-optimal header shape
– Seek high levels of integration
– More functions, channels, leads, etc.
– Hermetic feedthru connection
into can
• Hermetically Sealed Device
– Final calibrations without electrical
contacts
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Antenna Limitations
33
• Antenna Type
• Antenna Location – Internal - Header
– External
• Metal in header – Leads
– Connectors
– Anchors
• At 400MHz, wavelength = 75cm in air, 9cm in body
• Entire header coated in dielectric material
• Bio-degradable material
• Manufacturability
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Variable Implant Environment
34
• Implanted at variable
depths in human body
• Large antenna match and
body losses (40-45dB)
• Lead wrapped around
implanted device
• Impact of different tissue
layers. Dielectric
boundaries between layers.
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Variable Implant Environment
35
• Patient physiology
– Body type
– Age
– Gender
• Implant location
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Power Limitations
36
• Limited power level permitted outside the body in MICS
band
– 25uW or -16dBm per ITU-R SA.1346
– Downlink limitation
• FCC regulated SAR limit
– Partial body SAR Max 1g:
1.6 W/kg
– Full body SAR: 0.08 W/kg
– Uplink limitation
• Limited Tx output power requires better Rx sensitivity
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System Power
37
• Battery power is finite. Tx/Rx typically on short
periods of time. Wakeup sniffing every few
seconds.
• Average power – battery longevity
• Typical lifetime of CRM device > 7 years
• Background/listen current few 100’s of nA
• Peak power – battery ESR and chemistry
• Particularly limited in pacemakers
• Peak current limited to several mA
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Interference
38
• Interference from Implantable Device functions
– Pacing & Sensing
– Defibrillation shock
– Neuro stimulation
• Instruments in Operating
Room/Clinics
• Wireless Coexistence
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Future Opportunities
39
• Improved antennas – Electrical vs. Magnetic antennas
• Alternate frequencies – S. O’Driscoll, “Operating Frequencies for Wireless
Power Transmission to Implantable Medical Devices,”
IEEE International Microwave Symposium, 2011.
• Wireless power transfer
• Body Area Networks (BAN)
• Remote processing – Telemetry power vs. processing power
and capability
– Latency
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Thank you
40
Questions?