2. Goal: Detect Medical Problems by non-
Invasively measuring Optical
Properties of Blood
Optical Blood Medical Example
Property Diagnostic Problem
(Symptom)
Fluorescence Zinc Protoporphyrin Iron Deficient
(ZPP) Concentration Anemia, Lead
Poisoning
Absorption Hemoglobin Anemia
Concentration
Scattering Hematocrit Low- Blood loss,
High - Dehydration
3. Beer-Lambert Law
Optical approaches leverage the Beer-Lambert
law which uses 3 variables to model light
entering (Ii) and exiting (Io) a sample.
Io = Ii 10 –2.303 ε(λ) c t /(64,500 g Hb/mole)
t – Sample thickness – cm
c – concentration of absorbent - g/liter (A typical
value of c for whole blood is 150 g Hb/liter.)
ε(λ) – extinction coefficient of absorbent, which
is a function of the light’s wavelength.
– Blood’s ε(λ) is very large for λ < 600 nm
– This is why a flashlight shone through the hand only
transmits red light.
4. Prior Work: Pulse Oximetry
A Pulse Oximeter non-
invasively determines Pulse
and Blood Oxygenation using
differential light absorption.
A Photodiode measures light
intensity of Red (660nm) &
Infrared (940 nm) LEDs shone
through Finger during
systole/diastole.
Blood Oxygenation is a
function of the “Ratio of
Ratios” of Light Intensities at
these points.
Webster, JG. Design of Pulse Oximeters
5. Prior Work: Masimo pt 1
Most non-invasive blood λ Hb02 ε(λ) Hb ε(λ)
nm cm-1/M cm-1/M
sensors extend the pulse
oximeter’s differential 610 1506 9443.6
absorption trick. Like the
620 942 6509.6
pulse oximeter, they
630 610 5148.8
target the finger using
660 319.6 3226.56
wavelengths above 600
nm, the so called ”Medical 700 290 1794.28
Spectral Window”, to 730 390 1102.2
collect enough light. 805 844 730.28
905 1209.2 769.8
Source: Masimo [US7377794]
7. Prior Work: Samsung pt 1
Samsung’s work [Yoon et. al. λ Hb02 ε(λ) Hb ε(λ)
2005] states“Three variables cm-1/M cm-1/M
of R569,805, R569,940, and
R569,975 were used for 569 44496 45072
calibration and prediction
models.” producing this
comment by one author: 660 319.6 3226.56
G Yoon <gyoon@snut.ac.kr> -
569nm is highly absorbing in 805 844 730.28
tissue and, at the same time,
569nm intensity is small 940 1214 693.44
compared with that at longer
wavelength. That is why you
may not get good signal. We 975 1144 389.288
used a custom-made LED array
that has several chips of 569nm
to increase intensity.
8. Prior Work: Samsung pt 2
569 nm lies
outside the
Medical
Spectral
Window
Medical
Spectral
Window
9. Our Research: Target Thumb Webbing
for Absorption instead of Finger
Our hypothesis: We can
extend the medical spectral
window by offsetting the
increase in extinction
coefficient at λ< 600 nm with a
decrease in sample thickness
[Sabrina Paseman 2008] did
this by targeting the thumb
webbing for fluorescence
measurements.
We do this for absorption.
This allows us to get better
absorption measurements by
increasing signal and so
decreasing noise based error.
It also allows us to detect
additional sources of error.
10. The Apparatus
We created an adjustable width clip
that fits either the subject’s index
finger or thumb webbing.
One end of the clip holds the same
5-LED package used by Samsung
and the other holds a fiber optic
cable which connects to a
spectrometer.
This allows us to double check the
LED’s wavelength, determine LED
intensity, see if there are any LED
artifacts, and observe any swamping
or fluorescing effects.
The LEDs and spectrometer were
controlled by an Arduino
microcontroller.
11. Experimental Approach 1
Clamp is adjusted to fit the subject’s index finger.
Subject removes finger so distance between
spectrometer and LED can be measured with a
micrometer.
Thumb webbing is placed over the entire LED
Spectrometer auto-adjusts the integration time to a
full scale reading and the data is collected.
Subject removes thumb webbing and places index
finger over LED. Data is collected with the same
integration time and plotted on the same axis for
comparison
12. Data: 569 nm Subject 1
Thumb webbing
Index Finger
54054.5 counts
Integration Time: 404.05 ms
Width: 0.7175 cm
4131.5 counts
13. Findings
Transmission increases 13 fold
Samsung’s LED chip has an artifact at around 875nm
when the 569nm LED is lit. If Samsung’s device uses
a photodiode to collect light, especially at low
intensities, much of the collected light would come
from the artifact rather than the 569nm absorption
This method limited the quality of the readings we
could take from subjects with darker skin
14. Experimental Approach 2
Hold LED underneath the thumb webbing
and the spectrometer on the other side.
Let the spectrometer auto-integrate and
capture the graph.
For data analysis, find the ratio between the
ratios of the peak counts at 569nm and the
integration time Counts thumb webbing
Integration timethumb webbing
Absorption Amplification =
Countsindex finger
Integration timeindex finger
22. Conclusions
Transmission increases across the board but
varies from subject to subject
Our suspicions about the artifact are
confirmed by our second set up
23. Further Research
See if there is a statistically significant
difference between the light absorption of
systolic and diastolic blood at 569, 660, 805,
940 and 975 nm.
Correlate more medical problems to
absorption differentials and fluorescent
phenomena.
– See if there is a statistically significant difference
between the fluorescence of systolic and diastolic
blood excited at 425 nm.
Collect
data for more subjects with varying
melanin contents
24. References
[Sabrina Paseman 2008] Paseman, Sabrina. The
Ferrometer: A Device to Detect Iron Deficient Anemia via
Non-Invasive Optical Measurement of Zinc
Protoporphyrin. Issue brief no. SO499. Los Angeles:
University of Southern California, 2008. PDF file.
[US7377794] "Multiple Wavelength Sensor Interconnect” –
p57 lists Masimo’s wavelengths
[Yoon et. Al. 2005] Yoon, Gilwon, Ph.D, et al. "Development
of a Compact Home Health Monitor for Telemedicine."
TELEMEDICINE AND e-HEALTH 11.6 (2005): 660-67.
PDF File.
“Tabulated Molar Extinction Coefficient for Hemoglobin in
Water”
http://omlc.ogi.edu/spectra/hemoglobin/summary.html
