Expanding the medical spectral window v3

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

mailto:[email protected]

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


13640.500 counts

Data: 569 nm Subject 1 Webbing

Thumb Webbing


32847.801 counts


Index Finger


61598.500 counts


Thumb Webbing

Integration Time: 208.91 ms60849.000 counts


Index Finger



Thumb Webbing


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

Expanding the medical spectral window v3

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