Pulse Oximetry for the Electronic Patch
Erik V. Thomsen
ATV: Har vi en innovativ sundhedssektor? 2. september 2010
Patient monitoring today
Vision: “Electronic Patch”
- wearable physiological monitoring
• Small patient monitoring
system
• Intelligent
• Wireless
• Easy to use
• Measure in natural
surroundings
• Improve life quality for
patients
Patch
Antenna
Electronics
Battery
LEDs
R. G. Haahr et al., Proc. IEEE EMBS conf., 2007
Photo detector
Transmission Pulse Oximetry
LED
Blood vessel
LED
Tdiastole
Tsystole
Detector
Detector
Signal
Infrared (940 nm)
Red (660 nm)
“Photoplethysmograms”
Time
Diastole
Systole
Reflective Pulse Oximetry
LED
Blood vessel
Detector
LED
Detector
Tdiastole
Tsystole
Signal
Infrared (940 nm)
Red (660 nm)
“Photoplethysmograms”
Time
Diastole
Systole
Photo detector design - LED’s
distance
High light level
Low info
Signal (au)
Attenuation
Information (au)
(au)
1.0
0.035
1.0
0.030
0.8
0.8
0.025
0.6
0.6
0.020
0.015
0.4
0.4
0.010
0.2
0.2
0.005
0.0
0.000
0.0
Low light level
High info
Light & Info
0.0
0.0
0.2
0.2
0.4
0.4
0.6
Distance (au)
0.8
1.0
Sensor design
•
•
•
•
Backside silicon photodiode
Large ring-shaped active area
Central hole for light sources
Free parameters: r and d.
r
d
Backside – active side
Front side – light entrance
Micro fabrication
Transmission through optical coating
•
Start: p-type floatzone Si wafer, NA = 1015 cm-3
Implantation by pre-deposition and diffusion
Passivation and optical filter: dry thermal SiO2
and PECVD SiN
Hole through wafer: Advanced silicon etching
(ASE).
90
Transmission (%)
•
•
•
100
80
70
60
R=
R=
R=
R=
50
40
500
600
700
800
Wavelength (nm)
Phosphor
Boron
SiO2
SiN
S. B. Duun, R. G. Haahr, K. Birkelund, and E. V. Thomsen, ”A Ring- Shaped
Photodiode Designed for Use in a Reflectance Pulse Oximetry Sensor in Wireless Health
Monitoring Applications”, IEEE Sensors Journal, 10, pp. 261-268, 2010.
Ti/Al/Pt
0 mm
15 mm
30 mm
40 mm
900
Sensor integration with patch
•
The front side of the PCB contains: MCU, RF, op-amps, and passive components
•
The chip is mounted at the backside of the PCB with conducting glue.
LEDs current control, I2C protocol
System on Chip (SoC)
Crystal, 32 MHz
Crystal, 32 kHz
Op.amp. (thermistor)
Si backside photodiode
Op.amps. (photodiode)
Commercial LEDs (660 nm and 940 nm)
64 kbit EEPROM, I2C protocol
R. G. Haahr et al., Proc. Body Sensor Network conf., 2008
S. B. Duun, R. G. Haahr, O. Hansen, K. Birkelund and E. V. Thomsen, ”High Quantum Efficiency Annular Backside
Silicon Photodiodes for Reflectance Pulse Oximetry in Wearable Wireless Body Sensors”, J. Micromech. Microeng. 20 07,
p. 5020, 2010.
Assembly
Clinical evaluation
4 Electronic Patches
SpO2 (commercial)
In/Ex-hale gasses
SaO2
ECG
Clinical evaluation
Masimo DST
T. Jensen, S. Duun, J. Larsen, R. G. Haahr, M. H. Toft, B. Belhage, and E. V. Thomsen, ”Independent component analysis
applied to pulse oximetry in the estimation of the arterial oxygen saturation (SpO2) - a comparative study”, Proc. Annual
International Conference of the IEEE Engineering in Medicine and Biology Society EMBC 2009, pp. 4039-4044, 2009
Mean Field ICA
Conclusions
• Demonstrated pulse oximetry in an
electronic patch
• Designed, micro fabricated and
characterized a ring-shaped photodiode
• Developed electronics and system
packaging
• Performed initial small scale clinical tests
• New patent idea developed, pending for
filing
Thank you for your attention!
Acknowledgements:
All partners in the Electronic Patch,
Post.doc
•
Karen Birkelund
Phd students
•
Sune Duun
•
Rasmus Haahr
Master students
•
Rasmus Haahr
•
Martin Filskov Laursen
•
Thomas Jensen
Other student projects
•
Emil Højlund Nielsen
•
Kim Degn Jensen
•
Lars Nørgaard
Bachelor students
•
Palle Raahauge
•
Peter Petersen
•
Henrik Dam
•
Anders Christensen
•
Mikkel Øberg
•
Michael Jørgensen
•
Steffen Rasmussen
•
Martin Uhd Grønbech
•
Peter Friis Østergaard
Funding
•
Danish Ministry of Science
•
Technology and Innovation
&
Collaborators
•
Jan Larsen (DTU Informatics)
•
Bo Belhage, Mette Toft, and
Nana Gulsted (Bispebjerg
hospital)