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Improving Non-Invasive Blood Analysis by Expanding the Medical
Spectral Window
Katherine Paseman
Goal: Detect Medical Problems by non-Invasively observing Physical Properties of Blood
Physical Property of Blood
Medical Diagnostic (Symptom)
Example Problem
Fluorescence Zinc Protoporphyrin (ZPP) Concentration
Iron Deficient Anemia, Lead Poisoning
Absorption Hemoglobin Concentration
Anemia
Scattering Hematocrit Low- Blood loss,High - Dehydration
Prior Non-Invasive Blood Analysis Work: Pulse Oximetry
Used to non-invasively determine Pulse and Blood Oxygenation.
Oxygenation determined using Time dependent behavior
Red (660nm), Infrared (940 nm) -> Finger -> Photodiode
Webster, JG. Design of Pulse Oxcimeters
Beer-Lambert Law
Io = Ii 10 –2.303 ε(λ) c t /(64,500 g Hb/mole)
t – cm c – g/liter (A typical value of c for whole
blood is 150 g Hb/liter.)
Prior Work: Masimo pt 1
Most non-invasive blood sensors (e,g, Masimo) extend the pulse oximeter’s differential absorption trick. Like the pulse oximeter, they target the finger using wavelengths above 600 nm, the so called ”Medical Spectral Window”, to collect enough light.
λnm
Hb02 Absorptioncm-1/M
Hb Absorptioncm-1/M
610 1506 9443.6
620 942 6509.6
630 610 5148.8
660 319.6 3226.56
700 290 1794.28
730 390 1102.2
805 844 730.28
905 1209.2 769.8
Prior Work: Masimo pt 2
Prior Work: Samsung pt 1
Samsung’s attempt to use lower wavelengths produced this comment by one of the study’s auhors:
G Yoon <[email protected]> - 569nm is highly absorbing in tissue and, at the same time, 569nm intensity is small compared with that at longer wavelength. That is why you may not get good signal. We used a custom-made LED array that has several chips of 569nm to increase intensity.
λ Hb02 Absorptioncm-1/M
Hb Absorptioncm-1/M
569 44496 45072
660 319.6 3226.56
805 844 730.28
940 1214 693.44
975 1144 389.288
Prior Work: Samsung pt 2
Our Research: Target Thumb Webbing for Absorption instead of Finger
Our idea is to extend the medical spectral window by targeting the thumb webbing for absorption.
[Sabrina Paseman 2008] did this for fluorescence.
Our hypothesis is that we can get better measurements than Samsung with a wider spectrum of wavelengths.
We do this by offsetting the increase in extinction coefficient with a decrease in sample thickness.
Interrogating thumb webbing gives us a wider window in which to view medical problems
Implications
Increasing the size of the window would allow us to: Detect Sources of error in Samsung’s work 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.
See if there is a statistically significant difference between the fluorescence of systolic and diastolic blood excited at 425 nm.
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.
Samsung’s work specifies “Three variables of R569,805, R569,940, and R569,975 were used for calibration and prediction models. It means that four wavelengths were used in hematocrit monitoring.” It is for this reason we look specifically at 569nm
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, integration time is adjusted and 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
Data: 569 nm Subject 1
Thumb webbing
Index Finger
Integration Time: 404.05 ms
54054.5 counts
4131.5 counts
Width: 0.7175 cm
Findings
Transmission increases 13 fold Samsung’s LED chip has an artifact at around 875nm
when the 569nm LED is lit. If their 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
Hold led underneath the thumb webbing and the spectrometer on the other side.
Re-integrate the spectrometer and record the integration time. Capture the graph.
For data analysis, find the ratio between the ratios of the peak counts at 569nm and the integration time
Experimental Approach 2
Countsthumb webbing
Integration timethumb webbing
Countsindex finger
Integration timeindex finger
Absorption Ratio =
Data: 569 nm Subject 1 Finger
Index Finger
Integration Time: 3097.90 ms
13640.500 counts
Data: 569 nm Subject 1 Webbing
Thumb Webbing
Integration Time: 99.70 ms
32847.801 counts
Data: 569 nm Subject 2 Finger
Index Finger
Integration Time: 1736.15 ms
61598.500 counts
Data: 569 nm Subject 2 Webbing
Thumb Webbing
Integration Time: 208.91 ms60849.000 counts
Data: 569 nm Subject 3 Finger
Index Finger
Integration Time: 3808.11 ms60534.000 counts
Data: 569 nm Subject 3 Webbing
Thumb Webbing
Integration Time: 114.73 ms55602.750 counts
Data: 569 nm
Subject Countstw Integrationtw
(ms)Countsif Integrationif
(ms)Ratio
1 32847.801 99.70 13640.500 3097.90 74.825
2 60849.000 208.91 61598.500 1736.15 8.209
3 55602.750 114.73 60534.000 3808.11 30.488
Conclusions
Transmission increases across the board but varies from subject to subject
Our suspicions about the artifact are affirmed by our second set up
Further Research
Collect data for more subjects with varying melanin contents
Observe wavelengths other than 569 nm Investigate the potential for finding pulse
readings through thumb webbing