Smartphone based Blood Oxygen Level Measurementusing Near-IR and RED Wave-guided Light

Nam Bui, Anh Nguyen, Phuc Nguyen, Hoang Truong, Ashwin Ashok, Thang Dinh, Robin Deterding, Tam Vu

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PhO2

Chronic Obstructive Pulmonary Disease (COPD)

24 Million Americans

have COPD

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Leading cause of death in the US, 2016

OFTENFOUND IN LATE STAGE

$34,000 treatment in ICU

Early detection of COPD is key to successful treatment

Heart rate

Blood pressure

Breathing rate

Wheezing sound

Oxygen saturation (SpO2)

Vital signs screening in COPD

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Oxygen Saturation needs to be measured frequently

Oxygen Saturation (SpO2)

𝑺𝒑𝟎𝟐 =𝑵𝒐. 𝒐𝒙𝒚𝒈𝒆𝒏𝒂𝒕𝒆𝒅 𝒉𝒆𝒎𝒐𝒈𝒍𝒐𝒃𝒊𝒏

𝑻𝒐𝒕𝒂𝒍 𝑵𝒐. 𝒉𝒆𝒎𝒐𝒈𝒍𝒐𝒃𝒊𝒏𝟏𝟎𝟎%

O2

O2

O2

O2

Oxygenated hemoglobin Deoxygenated hemoglobin

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Photon Detector

IR emitter Red emitter

AC

R IR

Non-invasive Measurement of Oxygen Saturation

Intensity

t

Intensity

t

ACIR

ACR

𝑺𝒑𝟎𝟐 = 𝒇𝑨𝑪𝑹𝑨𝑪𝑰𝑹

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Red and IR Wavelength Selection

At Red= 660 nm and IR = 960 nm, the difference of light absorption

by oxygenated hemoglobin and deoxygenated hemoglobin is largest.

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Absorbed by red

pigmentation

Harmful

Low penetration

Pros Cons

High accuracy Inconvenient

Costly

Smartphone-based blood oxygen measurement

Dedicated Hardware Solutions

A solution to capture the oxygen level and is

High accuracy.

Low-cost.

Easy to make by patients

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PhO2

Smartphone based Blood Oxygen Level Measurement

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IR emitter Red emitter

PULSE OXIMETER

Hardware Challenges

PHONE BASED PULSE OXIMETER

Light

Source

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Challenge. Phone’s camera IR filter

Sensor

IR filter

Existing Software-based Solutions

DigiDoc iHealthCare

RGB

Color

Image

Red Light

IR Light

DISADVANTAGES

Inaccurate: Green channel is mostly absorbed by red pigmentation.

Coarse-grained: one record per 10 seconds.

Solution.

Red and NIR for Oxygen Saturation Measurement

NIR

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NIR

is available in most of phone’s flashlight and is not filtered by the phone’s camera.has similar characteristics of hemoglobin absorption with the IR lights.

NIR

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PhO2 NIR Extraction Technique

Absorbed by redpigmentation

Green filter

Absorbed

NIR

Red and Green filter cuttoff

And 5 More Challenges…

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Smartphone’s camera picks up most of the lights

Finger movement and Contact pressure

Pressure

Micro movements

RGB Intensity

Conversion between RGB and light intensity

Flashlight heat can cause skin burn

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3D printed Optical Hardware Add-on

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Smartphone’s camera picks up most of the lights

RGB Intensity

Conversion between RGB and light intensity

Finger movement and contact pressure

Pressure

Micro movements

Flashlight can cause skin burn

3D printed Optical Hardware Add-on

Wavelength selection

𝝀𝑹= 678 nm

𝝀𝑵𝑰𝑹= 724 nm

𝑺𝒑𝟎𝟐 =𝜺𝑯𝒃 𝒓 − 𝜺𝑯𝒃 𝒓 𝑹

𝜺𝑯𝒃 𝒊𝒓 − 𝜺𝑯𝒃𝑶𝟐 𝒓 + 𝜺𝑯𝒃𝑶𝟐 𝒊𝒓 − 𝜺𝑯𝒃 𝒊𝒓 𝑹

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X:678

Y: 724

Z:1.002

𝜶

𝜶 = 𝒂𝒓𝒄𝒕𝒂𝒏(𝒂/𝒃)

a

b

Pressure Detection and Recommendation

No

rma

lized

In

ten

sit

y

PPG signal in a 7 seconds window

Sample

No

rma

lized

In

ten

sit

y

Sample

PPG signal in a 7 seconds window

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No

rma

lized

In

ten

sit

y

PPG signal in a 7 seconds window

Sample

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Heat Reduction with Distributed Lighting Source

𝐸𝑝 = ℎ𝑓

𝑬 =

2.55 mm 0.6 mmModifyBandpass filter

To maintain

the high light

intensity

𝑯

Detecting pressure

ROI detection and create thePPG signals

PPG

Identify the peaksand troughs

Calculate peak-to-peak ratio

95

%

Collecting raw data

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AlgorithmsPhO2

App overview

PPG display

Image frame

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In-lab experiments

• 3 males, 3 females

• 5 times performs the hyperventilation (a breath

holding technique to reduce oxygen).

• Totally 560 samples.

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PhO2 vs. Existing apps

Sp

O2 (

%)

Measurement Indices

DigiDoc

Sp

O2 (

%)

Measurement Indices

iHealthCareS

pO

2 (

%)

PhO2

Time (s)

Experimental results

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3.5%

In clinic experiment

In hospital experiment with patient.

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Fine-grained evaluation of the patient

Low Oxygen Level

Coughing

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Heat Reduction Evaluation

Hand multimeter

Thermalcouple Probe

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Output temperature of different add-on designs

0

10

20

30

40

50

60

Without Banpass Filter With Bandpass Filter

58.9

4538.5

36.840.3

37.6

Tem

peratu

re (

Cels

ius)

Large Tunnel Small Tunnel Multiple Small Tunnels

Conclusion

❑Accurately measuring oxygen level using low-cost opticalfilm filters.

❑Detect the appropriate contact pressure between fingerand phone’ camera.

❑3D-printed add-on to handle the problem of lightscattering and finger movement.

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Application for optical light based sensing

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Cholest-erol

Optical light

based sensing

Urea Lactate

Water

Alcohol Glucose

Smartphone based Blood Oxygen Level Measurementusing Near-IR and RED Wave-guided Light

Nam Bui, Anh Nguyen, Phuc Nguyen, Hoang Truong, Ashwin Ashok, Thang Dinh, Robin Deterding, Tam Vu

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PhO2