1. Improving Non-Invasive
Blood Analysis by
Expanding the Medical
Spectral Window
Katherine Paseman
2. Background: Detect Medical Problems by
non-Invasively Measuring Optical Properties
of Blood
Medical
Optical Blood Example
Diagnostic
Property Problem
(Symptom)
Fluorescence Zinc Protoporphyrin Iron Deficient
(ZPP) Concentration Anemia, Lead
Poisoning
Scattering Hematocrit Low- Blood loss,
High - Dehydration
Absorption/ Hgb Concentration Anemia
Transmittance SpO2 Blood Loss
3. Background: Beer-Lambert Law
Optical approaches leverage the Beer-Lambert law which models the
intensity of light entering (Ii) and exiting (Io) a sample using 3
variables,
Io = Ii × 10 –2.303 ε(λ) c t /(64,500 g Hb/mole)
t – Sample thickness – cm
c – Concentration of absorbent - g/liter
Note: 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.
Note: Blood’s ε(λ) is very large for λ < 600 nm (red) so it absorbs a lot of light
below this wavelength. This is why a flashlight (white light) shone through your
finger only transmits red light.
4. Example: Pulse Oximetry
• A Pulse Oximeter non-invasively
determines pulse and blood
oxygenation with photodiodes using
differential light absorption
• Blood Oxygenation is a
function of the “Ratio of Ratios”
of Light Intensities at these
points.
• A Photodiode measures light
intensity of Red (660nm) &
Infrared (940 nm) LEDs shone
through a finger during
systole/diastole.
Webster, JG. Design of Pulse Oximeters
5. Problem we address: Samsung
Hgb/Hct Monitor has >8%
error
Samsung’s work states “Three variables
of R569,805, R569,940, and
R569,975 were used for calibration Hb02 ε(λ) Hb ε(λ)
λ
and prediction models.” producing cm-1/M cm-1/M
this comment by one author: 569 44496 45072
660 319.6 3226.56
G Yoon <gyoon@snut.ac.kr> - “569nm
is highly absorbing in tissue and, at 805 844 730.28
the same time, 569nm intensity is 940 1214 693.44
small compared with that at longer
975 1144 389.288
wavelength. That is why you may not
get good signal. We used a custom- Samsung reported >8% error for
made LED array that has several chips Hemoglobin [Jeong et. Al. 2002] and
of 569nm to increase intensity.” Hematocrit [Yoon et. al. 2005].
6. Problem we address: Samsung
Hgb/Hct Monitor has >8%
error
Note:
569 nm lies
outside the
Medical
Spectral
Window
Medical
Spectral
Window
600 to 1000 nm
7. Our Hypothesis: Targeting Thumb
Webbing vs. Index Finger Mitigates
Measurement Error
The Beer-Lambert Law
explains that decreasing
sample thickness should
result in an increase in
transmittance.
This allows us to get better
absorption measurements
• Increases the signal
which decreases noise
based error.
• Allows us to detect
additional sources of
error.
8. The Apparatus
We created an adjustable clip
that fits either the 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 an Avantes AvaSpec-2048
spectrometer.
The both are controlled by an
Arduino microcontroller.
This allows us to double check
the LED’s wavelength, determine
LED intensity, see if there are
any LED artifacts (emissions at
wavelengths besides the primary
wavelength), and observe any
swamping or fluorescing effects.
9. Experiment 1: Approach
A clamp is adjusted to fit the subject’s index finger.
The subject removes their finger so that the spectrometer/LED
distance can be measured with a micrometer.
The thumb webbing is placed over the entire LED.
The spectrometer auto-adjusts the integration time to a full scale
reading and the data is collected.
The subject removes their thumb webbing and places their index
finger over the LED. The data is collected with the same integration
time and plotted on the same axis for comparison.
10. Experiment 1: Data
569 nm Subject 1
Thumb webbing
Index Finger
54054.5 counts
Integration Time: 404.05 ms
Width: 0.7175 cm
4131.5 counts
11. Experiment 1: Findings
General: Transmission increased 13 fold.
Artifacts: 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 peak.
Race: This method limited the quality of the readings we could take
from subjects with darker skin.
Age: Young people have smaller thumb webbing than older people.
12. Experiment 2: Approach
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.
( Countsthumb webbing
Integration timethumb webbing )
Absorption Amplification =
( )
Countsindex finger
Integration timeindex finger
19. Experiment 2: Data
Summary 569 nm
Subject Scopetw Integrationtw Scopeif Integrationif Ampli-
(ADC Counts) (ms) (ADC Counts) (ms) fication
1 32847.801 99.70 13640.500 3097.90 74.825
2 60849.000 208.91 33273.000 1736.15 15.198
3 55602.750 114.73 60534.000 3808.11 30.488
Subject1: 58 years old - light skinned
Subject2: 52 years old - dark skinned
Subject3: 16 years old - light skinned
20. Experiment 2: Findings
The signal is less noisy going through the thumb
webbing versus the finger
Amplification through thumb webbing is significantly
better, but the exact ratio varies from subject to
subject.
A spike at ~610 nm for all the finger readings could
either be an artifact or simply the edge of the medical
spectral window
“Artifact Amplification” was apparent in this
experiment as well
21. Key Finding:
“Artifact Amplification”
Why does the artifact size increase?
Blood is a low pass filter, attenuating small λ (high frequencies)
more than large λ.
LED Artifacts (usually) appear “above” (at a larger λ) the primary
emission λ.
If the LED’s primary λ is below 600 nm and the artifact is above, the
artifact will appear differentially amplified.
This amplification is a key consideration when designing with LEDs
that have this characteristic.
22. Conclusions
1. Our hypothesis is confirmed: transmission through thumb
webbing is better.1
2. “Artifact Amplification” was confirmed by both
experiments and will be a key design consideration going
forward.2
3. Low readings from people with darker skin in the first
experiment and smaller thumb webbing for younger
subjects indicate that probe design will be a key issue going
forward.
1,2
Both phenomena would partially explain
Samsung’s error numbers.
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
and ages
25. 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.
[Jeong et. Al. 2002] Jeong, Kye Jin, Su-Jin Kim, and
Kun Kook Park. "Noninvasive Total Hemoglobin
Measurement." Journal of Biomedical Optics 7.1
(2002): 45-50. PDF file.
“Tabulated Molar Extinction Coefficient for Hemoglobin in
Water” http://omlc.ogi.edu/spectra/hemoglobin/summary.html
