Non invasive tissue oximetry using
reflection mode Near Infrared
Spectroscopy system
Periyasamy1
Research Scholar
Dr.Ashutosh Mishra1 and Dr.Sneh Anand1
1Centre
for
Biomedical Engg
Indian Institute of Technology Delhi
Motivation

Oxygen –basis for human survival

Level of oxygen that a particular
organ receives is very importance
as it determines proper functioning
of the body parts (organs)

For example: DM patients suffer
from some form of lower extremity
problem(neuropathy,
vascular
complication) are due to oxygen
level changes(reduced blood flow)
and decreased perfusion.
Importance of tissue oxygen level in any organ
Deficiency of oxygen in tissue
Tissue oxygenation - relative conc. of
oxyhemoglobin & myoglobin, depends on the
balance between oxygen delivery, as reflected
by the product of blood flow and oxygen
content and consumption.

Tissue oxygenation and hemoglobin
concentration are sensitive indicators
of tissue status (Ferrari, et al., 1992 )

A sudden dip in the tissue
oxygenation can be a direct
indication
of
many
harmful
conditions like tissue degeneration,
microbial infection etc.

Non-invasive, real time, local
measurement of tissue O2 and HbT is
not commercially available
Currently available Diagnostics methods
Palpable pulse, Ankle brachial Index(ABI) by Doppler
Blood flow or perfusion by Laser Doppler Imaging(LDI)
Oxygen consumption and partial pressure by Transcutaneous
oximetry.
Altered blood flow status and arterial oxygen saturation by Photo
Plethysmography(PPG) and pulse oximetry
Objectives

To design and develop an reflection mode NIRS
system

To non-invasively monitor the oxygenation level
in the tissue

To calculate oxy and deoxy hemoglobin
concentration using Modified Beer Lambert law
Why we chosen NIR light ?
Electromagnetic spectrum
 Penetrate the biological tissue deeper
 Property : Oxygenated hemoglobin and deoxygenated
hemoglobin both absorb light differently in this
region.
 At 780 nm, deoxygenated blood has a higher
absorption, whereas at 830 nm, oxygenated blood has
a higher absorption.
Near infrared spectroscopy
Applications :
 Non-ionizing & non invasive optical technique
 UV/VIS spectral region (<650), light can
penetrate only superficial tissue volume [Jobsis et
al 1977]
 Investigates the differential absorption spectra of
chromophores (oxy and deoxy hemoglobin) and
functional information in tissue [Fantini et al
1999]

Non-invasive assessment of brain function in
newborn [Wolf M et al 2007]

In-vivo muscle metabolism measurement
[Yuanqing Lin et al 2002]

Monitor foetal hypoxaemia and in newborn
infants to detect birth apnoea and hypoxia.

Useful for blood analyte monitoring and non
invasive imaging of tissue [E. Ciurczak & J.
Drennen 2002].

Monitor healing of burns

Used for assessment and identification of
breast cancer
 Measure both arterial and venous saturation
because it is based on NIR wavelength(700nm1100nm)
 Healthy and diseased soft tissues can be
potentially differentiated, due to their different
absorption or scattering coefficients
Comparison between NIRS and Pulse oximetry
Different wavelengths are used in both these techniques
NIRS is far more penetrating effect than Pulse oximeter because sources of light is in NIR wavelength
NIRS characterize more chromophores than Pulse oximeter

NIRS - assessment of all the vascular compartments
(Arterial, Venous and capillary).

Measure hemo dynamics, metabolic and fast neuronal
responses to brain activation


Measure relative changes in pulsatile components of
the cerebral blood flow and cerebral blood volume
based on the shape of the heartbeat pulse waveform.
Used in patients with low perfusion states and
peripheral vascular. It gives exact oxygen level in the
blood.

Pulse oximeter - only
compartment by time
measurements
the arterial
gating the

Reliable and commonly used to monitor
systemic oxygen supply only.

Pulse oximeter utilizes the arterial
oscillations to extract arterial oxygen
saturation SaO2 and does not exploit all of
the information from the heartbeat
oscillations
Design of NIR sensor Probe
NIRS probe design consideration
Selection of Light source and Detector

Wavelength

Bandwidth

Power

Stability

sensitivity

Portability, ease-of-use, etc.
NIR light interaction with tissue to monitor oxygenation
Two modes of operation
NIR light interaction
Three main process:
Monte Carlo Simulation of Light
Transport in tissue

Absorption

Scattering

Reflection.
 It is a stochastic and random process
It based on the transport equation and the random walk of photons
in absorbing and scattering medium
 It provides a physical simulation of photon migration through the
tissue
Limitation
• Computation time is more
• Require lot of memory
Lambert Laws
Lambert Beers law
I = I0 10 -ε [c] L
or
log ( I0/I) = ε [c] L
where
I0  light in
I  light out
ε  extinction coefficient
L  the optical path length
[c] solute concentration
Modified Beer Lambert law
OD = - log10 (I/ I0) = ε.C.L + G
Where
G  factor that accounts for the measurement geometry
L=dxB
Where
L  optical path length value in the scattering medium.
d  Source-Detector separation
B  differential path length factor (DPF)
11
Feasibility study done so far…
Methodology and Preliminary Results
Modulating frequency waveform to drive
the laser diode
Probe design configuration
Block diagram of NIRS system - simple prototype
Preliminary Results
DATA COLLECTION : Data of two subjects(mean age 25) has been recorded with
following procedure
Procedure :

Step 1: The subject is first asked to relax for at least five minutes
by meditation.
 Step2: Then patient’s body part (forefinger) is cleaned to avoid
any unnecessary disturbance by dirt etc in the light reflection
process.
 Step 3: Now we place the forefinger on the NIRS probe as shown
in fig “with out occlusion” and switch on the power supply to
observe the change in light intensity in the Oscilloscope (CRO).
 Step 4:Then note down the peak voltage (in mV) value from the
CRO.
 Step 5: Once the occlusion is done for 5-10 seconds by using BP
cuff, then proceed the step 3 and 4 respectively
Placement Fore finger over NIRS probe
Result Calculation
14
Peak value (mV) “With” and “Without occlusion”
Laser diode Subject 1 Subject 1 Subject 2 Subject 2
wavelength without
with
without
with
Occlusion Occlusion Occlusion Occlusion
780nm
18mV
42mV
20mV
40mV
830nm
23mV
38mV
21mV
41mV
Calculation of Change in optical density
Optical path length L =0.6 cm
No of
Subjects
Subject1
Subject2
ΔOD780nm ΔOD830nm
-0.367
-0.301
-0.218
-0.290
ε Extinction coefficient taken from literature
Method of Calculation
Δ [OHb] = [(εDHb830X ΔOD780) - (ε DHb 780 X ΔOD830)] / [L ( εOHb780 X εDHb830 - εOHb830 X εDHb780)]
Δ [DHb] = [(εOHb780X ΔOD830) - (ε OHb 830X ΔOD780)] / [L ( εOHb780 X εDHb830 – εOHb830 X εDHb780)]
Δ [THb] = Δ [OHb] + Δ [DHb]
Δ [THb] =83.6+10.5=94.1µM/L
Tissue oxygenation Index TOI = (Δ [OHb] / Δ [THb]) x100
TOI = 88.8%
Δ [OHb] = 83.6 µM/L
Δ [DHb] =10.5 µM/L
Observation and Summary-Preliminary result
References






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[1] J.Mobley and T.Vo-Dinh, Optical properties of tissue, Biomedical photonics handbook, CRC Press
2005, pp. 2-1-2-74
[2] M. Cutler, Transillumination of the breast, Surg. Gynecol. Obstet. Vol. 48, 1929, 721-727.
[3] Liss, J.M., White, L., Mattys, S., Spitzer, S., Lansford, K., Lotto,A.J., and Caviness, J.Classifying
Dysarthrias by Speech Rhythm Metrics. Auditory Cognitive, Neuroscience Society (ACNS) Conference
2009
[4] Alper Bozkurt, Arye Rosen, Hare Rosen and Banu Onaral A portable near infrared spectroscopy
system for bedside monitoring of newborn brain, BioMedical Engineering OnLine 2005, 4:29
[5] A.Pifferi, P.Taroni, G.Valentini and S.Andersson-Engels, Real-time method for fitting time-resolved
reflectance and transmittance measurements with a Monte Carlo model, Appl.Opt 1998, 37, 27742780.
[6] Jöbsis F.F, Noninvasive infrared monitoring of cerebral and myocardial oxygen sufficiency and
circulatory parameters, Science 1977,198: pp. 1264–1267
[7] E. Ciurczak and J. Drennen, Near-Infrared Spectroscopy in Pharmaceutical and Medical
Applications, Marcel-Dekker, Inc. New York, 2002.
[8] Wolf M, et al. Progress of near infrared spectroscopy and imaging instrumentation for brain and
muscle clinical applications. J. Biomed. Opt. 2007; 12, 062104. Review
THANK YOU
Centre for
Biomedical Engg
Indian Institute of Technology Delhi