Use of polarized light imaging
and sensing in the clinical setting
Jessica C. Ramella-Roman, PhD
II Escuela de Optica Biomedica, Puebla, 2011
Short Bio
• Laura in Electrical Engineering, University of
Pavia, Italy (93)
• MS and PhD in Electrical Engineering from
Oregon Health & Science University (04)
– Advisor Steve Jacques
– Thesis on use of polarized light in
biophotonics
• Post doc at Johns Hopkins, APL (04,05)
– Polarized light interaction with rough surfaces
II Escuela de Optica Biomedica, Puebla, 2011
Short Bio cnt.
• Associate Professor in Biomedical Engineering
(05-present) at CUA
• Adjunct A. Prof. Johns Hopkins School of
Medicine (06-present)
• Guest Researcher NIST (04- present)
• Research – faculty.cua.edu/ramella
– Tissue oximetry, retina, skin using reflectance
spectroscopy and MI
– Small vessel Flowmetry and structural analysis
– Polarized light imaging and sensing for the detection
of skin cancer, vascular abnormalities
II Escuela de Optica Biomedica, Puebla, 2011
Course outline
• Lecture 1- Introduction and fundamentals of
polarimetry
• Lecture 2- Experimental Stokes and Mueller
matrix polarimetry
• Lecture 3 – Modeling – Monte Carlo 1
• Lecture 4 – Modeling – Monte Carlo 2
• Lecture 5 – Clinical applications of polarized
light sensing
II Escuela de Optica Biomedica, Puebla, 2011
Polarized light in bio-photonics
• Filtering mechanism
• Skin cancer imaging
• Imaging of
superficial features
• Vasculature
• others
*JBO 2002
II Escuela de Optica Biomedica, Puebla, 2011
64
y
Filtering mechanism
x
~2-4% parallel, sub surface
100% parallel
incidence
~4% parallel surface glare
40% unpolarized
Epidermis
papillary
dermis
reticular dermis
53% absorbed
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64
Filtering mechanism-surface glare
y
~2-4% parallel, sub surface
100% parallel
incidence
~4% parallel surface glare
40% unpolarized
Epidermis
papillary
dermis
reticular dermis
53% absorbed
II Escuela de Optica Biomedica, Puebla, 2011
64
x
Filtering mechanism-single scattering
~2-4% parallel, sub surface
100% parallel
incidence
64
Co
polarized
~4% parallel surface glare
y
40% unpolarized
Epidermis
papillary
dermis
reticular dermis
53% absorbed
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64
x
Filtering mechanism-multiple
scattering
64
y
~2-4% parallel, sub surface
100% parallel
incidence
x
~4% parallel surface glare
40% unpolarized
Cross
polarized
Epidermis
papillary
dermis
reticular dermis
53% absorbed
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64
Polarized light imaging of skin cancer
H&V
H
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64
par
-
per
par
+ per
Polarized image =
Par = Superficial + Deep
Per = Deep
Enhance superficial structures such as
skin cancer margins
II Escuela de Optica Biomedica, Puebla, 2011
Polarized imaging:
Basal-Cell Carcinoma
Unpolarized
Polarized
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64
compound nevus
normal
1-cm ruler
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pol
normal
freckle
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pol
tattoo
II Escuela de Optica Biomedica, Puebla, 2011
Imaging of superficial features
• Polarization signature
of roughness
• Cosmetic industry and
rendering community
• Skin cancer
i
Air
Skin top
surface
II Escuela de Optica Biomedica, Puebla, 2011
s
 

Fresnel Reflec
Vasculature enhancement
~2-4% parallel
sub surface
100% parallel
incidence
~4% parallel surface glare
40% unpolarized
capillary
transillumination
17
II Escuela de Optica Biomedica, Puebla, 2011
53% absorbed
Other techniques that use polarization
• Mueller matrix imaging - colon cancer
– De Martino et al. Opt. Exp. 2011
• Polarized light scattering spectroscopy –
eliminate multiple scattering with co/cross
polarized layout
– V. Backman et al. Nature 2001
• PS OCT – birefringence / structural components
– De Boer, Opt. Exp. 2005
• Particle sizing
• (….)
II Escuela de Optica Biomedica, Puebla, 2011
Polarization fundamentals
II Escuela de Optica Biomedica, Puebla, 2011
Polarization basics
• Polarization is a property that arises out of the
transverse (and vector) nature of the
electromagnetic (EM) radiation
• It describes the shape and the orientation of
the locus of the electric field vector (Ε)
extremity as a function of time, at a given
point of the space*.
*Ghosh
et al. JBO 2011
II Escuela de Optica Biomedica, Puebla, 2011
Electric Field vector (EM)
 


E y z , t   E oy cos  t  kz   y 
E x z , t  E ox cos  t  kz   x
x, y

=phases
=light frequency
k
= 2p/l
Eox,Eoy, =magnitude of electric field
l
=wavelength of light in free space
Y
E
Eoy
Eox
Z
II Escuela de Optica Biomedica, Puebla, 2011
X
Polarization Ellipse
y
h
2E0y
x
2E0y
 
2
Ex z ,t
2
E0 x
 
2

E y z ,t
2
E0 y

   
2Ex z ,t E y z ,t
cos   sin 
E0 x E0 y
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2
Jones vector formalism
E 
Ex

Ey
E ox e
E oy e
i
x
i
y
Advantages:
- Measurement of coherence and time dependent phenomena
- Speckle based techniques
Disadvantage
-Cannot handle depolarization
x, y = phases
Eox,Eoy, = magnitude of electric field
II Escuela de Optica Biomedica, Puebla, 2011
Jones matrix
• Polarized transfer of light – interaction with a
medium
E  JE
E 
x
E y

J11
J12 E x
J 21
J 22 E y
• J is a 2x2 complex matrix
II Escuela de Optica Biomedica, Puebla, 2011
Stokes vector formalism
•
•
•
•
Intensity based representation
Characterize the polarization state of light
E0x, E0y, Cartesian electric field component
=x-y phase difference
*
*

E
E

E
E
 I   x x
y y
  
*
*
E
E

E
E
x x
y y
Q 

S 
 
U   E x E *y  E y E *x
  
*
*
V  i E x E y  E y E x


 
2
2

E

E
 
0x
0y

  E 2  E 2

0x
0y
 

 2 E 0 x E 0 y cos  
 2 E E sin  

  0 x 0 y

II Escuela de Optica Biomedica, Puebla, 2011
Stokes vector formalism
• Four measurable quantities (intensities)
• Characterize the polarization state of light
• G.G. Stokes (1852)
 I   I  I 
H
V

  
Q   I H  I V 

S 


U  I  I
45
 45

  
V   I R  I L 
Advantages:
- Handles depolarization
- Easy experimental application
Disadvantage
- Cannot handle coherence
II Escuela de Optica Biomedica, Puebla, 2011
Stokes vector formalism
• Four measurable quantities (intensities)
• Characterize the polarization state of light
• G.G. Stokes (1852)
• Restriction on the Stokes parameters
I 
2
Q U
2
V
2
II Escuela de Optica Biomedica, Puebla, 2011
Poincaré sphere
• A geometrical
representation of
Stokes vectors
• Sphere with unit radius
• Linearly polarized states
are on the equator
• Circularly polarized
states are at the poles
• Partially polarized states
are inside the sphere
II Escuela de Optica Biomedica, Puebla, 2011
Linearly polarized light
 1 
J 

 0 



S



1 

1 
0 

0 
II Escuela de Optica Biomedica, Puebla, 2011
= E0x
= E0y
Linearly polarized light
 0 
J 

 1 
 1

1

S
 0

 0
= E0x
= E0y






II Escuela de Optica Biomedica, Puebla, 2011
Linearly polarized light
 1  1
J 

 1  2



S



1 

0 
1 

0 
II Escuela de Optica Biomedica, Puebla, 2011
Linearly polarized light
 1  1
J 

 1  2
 1

0

S
 1

 0






II Escuela de Optica Biomedica, Puebla, 2011
= -E0x
Circularly polarized light
 1  1
J 

 i  2



S



1 

0 
0 

1 
II Escuela de Optica Biomedica, Puebla, 2011
Circularly polarized light
 1  1
J 

 i  2
 1

0

S
 0

 1






II Escuela de Optica Biomedica, Puebla, 2011
Unpolarized light


S 



1 

0 
0 

0 
• Unpolarized light
cannot be described
through a Jones vector
• Stokes vector and
Mueller matrix
formalism is mostly
used in biophotonics
II Escuela de Optica Biomedica, Puebla, 2011
Mueller matrix
i, input
o, output
S o   M S i 
 I  m
11
o
  
m
Q
o
   21

U  m
31
o
  
V o  m 41
m12
m 13
m 22
m 23
m 32
m 32
m 42
m 43
II Escuela de Optica Biomedica, Puebla, 2011
m14  I i 
 
m 24 Q i 
m 34 U i 
 
m 44 V i 
Mueller matrix cnt.
i, input
o, output
S o   M i M i 1       M 2 M 1 S i 
Multiple Mueller Matrices Mi
II Escuela de Optica Biomedica, Puebla, 2011
Scattering matrix
• Mie theory
• Spheres, spheroids,
cylinders
 I  s
o
11
  
Q o  s12
U   0
o
  
V o   0
s12
0
s11
0
0
s 33
0
s 43
0  I i 
 
0 Q i 
s 43 U i 
 
s 33 V i 
If
not Stokes
vector
must
be rotated
Scattering
must
be in
reference
plane
onto that plane
D=0.01µm
II Escuela de Optica Biomedica, Puebla, 2011
Mueller Matrix
from microspheres solutions
m11
50
50
50
50
100
100
100
100
150
150
150
150
200
200
200
200
50 100 150 200
50 100 150 200
50 100 150 200
50 100 150 200
50
50
50
50
100
100
100
100
150
150
150
150
200
200
200
200
50 100 150 200
50 100 150 200
50 100 150 200
50 100 150 200
50
50
50
50
100
100
100
100
150
150
150
150
200
200
200
200
50 100 150 200
50 100 150 200
50 100 150 200
50 100 150 200
50
50
50
50
100
100
100
100
150
150
150
150
200
200
200
200
50 100 150 200
50 100 150 200
50 100 150 200
m44
50 100 150 200
*Cameron et al. JBO 2001
II Escuela de Optica Biomedica, Puebla, 2011
D= 2µm
Stokes polarimetry, metrics of
interest
II Escuela de Optica Biomedica, Puebla, 2011

Net degree of polarization
2
DOP 
Q U
2
V
I
0  DOP  1
II Escuela de Optica Biomedica, Puebla, 2011
2

Unpolarized portion of the beam
2
1
Q U
2
V
2
I
0  UNP  1
II Escuela de Optica Biomedica, Puebla, 2011
Degree of linear polarization
2
DOLP 
Q U
2
I
0  DOLP  1
II Escuela de Optica Biomedica, Puebla, 2011
Degree of circular polarization
DOCP 
V
I
0  DOCP  1

II Escuela de Optica Biomedica, Puebla, 2011
Principal angle of polarization
S 
h  0.5a tan  2 
 S 1 
Polarization Ellipse y
h
2E0y
 
2
Ex z ,t
2
E0 x
 
2

E y z ,t
2
E0 y

   
2Ex z ,t E y z ,t
2E0y
cos   sin 
2
E0 x E0 y
II Escuela de Optica Biomedica, Puebla, 2011
x
Tomorrow
• Experimental application of polarimetry
• Introduction to a typical Stokes vector
polarimeter
• Introduction to a typical Mueller Matrix
polarimeter
II Escuela de Optica Biomedica, Puebla, 2011
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Polarization fundamental