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Journal ArticleDOI

Contrast mechanisms in polarization-sensitive Mueller-matrix optical coherence tomography and application in burn imaging

01 Sep 2003-Applied Optics (Optical Society of America)-Vol. 42, Iss: 25, pp 5191-5197
TL;DR: The experimental results obtained from rat skin samples show that Mueller OCT provides complementary structural and functional information on biological samples and reveal that polarization contrast is more sensitive to thermal degeneration of biological tissue than amplitude-based contrast, suggesting significant potential for application in the noninvasive assessment of burn depth.
Abstract: We investigate the various contrast mechanisms provided by polarization-sensitive (PS) Mueller-matrix optical coherence tomography (OCT). Our PS multichannel Mueller-matrix OCT is the first, to our knowledge, to offer simultaneously comprehensive polarization-contrast mechanisms, including the amplitude of birefringence, the orientation of birefringence, and the diattenuation in addition to the polarization-independent intensity contrast, all of which can be extracted from the measured Jones or the equivalent Mueller matrix. Theoretical analysis shows that when diattenuation is negligible, the round-trip Jones matrix represents a linear retarder, which is the foundation of conventional PS-OCT, and can be calculated with a single incident polarization state, although the one-way Jones matrix generally represents an elliptical retarder; otherwise, two incident polarization states are needed. The experimental results obtained from rat skin samples, which conform well with the histology, show that Mueller OCT provides complementary structural and functional information on biological samples and reveal that polarization contrast is more sensitive to thermal degeneration of biological tissue than amplitude-based contrast. Thus, Mueller OCT has significant potential for application in the noninvasive assessment of burn depth.

Summary (2 min read)

1. Introduction

  • Since it was first reported approximately a decade ago as a high-resolution noninvasive medical imaging modality, optical coherence tomography OCT has received tremendous attention.
  • Several branches of OCT have been developed based on various contrast mechanisms, such as polarization1–6 and Doppler shift,7,8 in addition to the amplitude-based contrast in conventional OCT.
  • The analyses indicate that when diattenuation is negligible, one incident polarization state is adequate for the acquisition of the Jones matrix.

2. Polarization-Based Contrast

  • Therefore, diattenuation provides anisotropic amplitude-based contrast, as it incurs no phase retardation.
  • The phase retardation of a light field, induced by the local birefringence between the two orthogonal eigenpolarizations, can be expressed as d k n Ls dLs , where k is the wave vector corresponding to the central wavelength of the incident light in vacuum;.
  • Because highly birefringent collagen is a predominant structural component in most biological tissues, this intrinsic contrast mechanism is prevalent in the biomedical applications of Mueller OCT.
  • The authors will use subscripts 1 and 2 to describe the one-way and round-trip parameters, respectively.
  • The orientation of the fast axis can thus be calculated as 2 arc tan E2vE2h . (4).

3. Calculation of the Round-Trip Jones Matrix

  • The round-trip Jones matrix J2 can be expressed with the one-way Jones matrix J1 , according to the Jones reversibility theorem, as J2 J1TJ1 , (5) where the superscript T represents the transpose operation.
  • A retarder is called elliptical when its eigenpolarizations are elliptical polarization states.
  • Except in some special samples, the orientations of the birefringent fibers in biological samples, take skin, for example, are not collinear, and as a result, J1 generally represents a homogeneous elliptical retarder if diattenuation is negligible in the sample.
  • Therefore, at least two incident polarization states, either applied at the same time or applied sequentially, are required.
  • The transpose symmetry in the roundtrip Jones matrix is critical for eliminating the arbitrary phase difference between the two measured Jones vectors corresponding to the two incident polarization states to yield the correct Jones matrix.

4. Experiment

  • The authors have built a novel multichannel Mueller OCT,5,6 which can acquire the Jones matrix of a sample with a single scan for each one-dimensional depth image A line image .
  • Therefore, a Mueller matrix reveals the real morphologic structure as well as the polarization-based features of a sample.
  • In contrast, the retardation image Fig. 1 c reveals the distribution of birefringent components deeper into the dermis.
  • The calculated intensity image, the retardation image, the diattenuation image and the histological image are shown in Figs.
  • The burn region cannot be identified in the intensity image; but it can be clearly seen with marked contrast in the retardation and diattenuation images as verified by the polarization histological image.

5. Discussion

  • The differences between conventional OCT and Mueller OCT in their sensitivities to different optical properties of a sample result from their different contrast mechanisms.
  • Otherwise, 2 m and 2 m are also functions of both 1 i and d1 i in the optical path, making the retardation image complex to interpret rigorously unless the local polarization properties can be calculated, which is possible only with Mueller OCT.
  • By use of this strategy layer by layer, the one-way Jones matrix of each segment can thus be extracted, and the images of the local polarization parameters can be calculated, which should be free of fringes because the retardation of each segment should be much less than .
  • Layers 1 and 3 are highly birefringent, indicating the keratin in the epidermis and the dermal papilla, respectively.
  • Besides birefringence, scattering can also alter the polarization state of light and cause phase retardation.

6. Conclusion

  • In summary, a unique feature of Mueller OCT is its capability of separating various contrast mechanisms, in which the amplitude-based contrast is sensitive to the boundaries formed primarily by regions of different indexes of refraction, whereas the phasebased polarization contrast and the orientation-based contrast originate from the components of biological tissues with optical polarization effect.
  • Experimen- tal results show that phase-based polarization contrast is more sensitive to thermal degeneration of biological tissues than amplitude-based contrast.
  • The combination of amplitude-based contrast with phase-based polarization contrast and the orientation-based contrast provides more comprehensive information about biological tissues.
  • Phase-based polarization contrast is a promising imaging mechanism for assessing burn depth in vivo.

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Contrast mechanisms in polarization-sensitive
Mueller-matrix optical coherence tomography and
application in burn imaging
Shuliang Jiao, Wurong Yu, George Stoica, and Lihong V. Wang
We investigate the various contrast mechanisms provided by polarization-sensitive PS Mueller-matrix
optical coherence tomography OCT. Our PS multichannel Mueller-matrix OCT is the first, to our
knowledge, to offer simultaneously comprehensive polarization-contrast mechanisms, including the am-
plitude of birefringence, the orientation of birefringence, and the diattenuation in addition to the
polarization-independent intensity contrast, all of which can be extracted from the measured Jones or the
equivalent Mueller matrix. Theoretical analysis shows that when diattenuation is negligible, the round-
trip Jones matrix represents a linear retarder, which is the foundation of conventional PS-OCT, and can
be calculated with a single incident polarization state, although the one-way Jones matrix generally
represents an elliptical retarder; otherwise, two incident polarization states are needed. The experi-
mental results obtained from rat skin samples, which conform well with the histology, show that Mueller
OCT provides complementary structural and functional information on biological samples and reveal that
polarization contrast is more sensitive to thermal degeneration of biological tissue than amplitude-based
contrast. Thus, Mueller OCT has significant potential for application in the noninvasive assessment of
burn depth. © 2003 Optical Society of America
OCIS codes: 120.2130; 170.4500; 260.5430; 170.1870.
1. Introduction
Since it was first reported approximately a decade
ago as a high-resolution noninvasive medical imaging
modality, optical coherence tomography OCT has
received tremendous attention. Several branches of
OCT have been developed based on various contrast
mechanisms, such as polarization
1–6
and Doppler
shift,
7,8
in addition to the amplitude-based contrast in
conventional OCT. OCT has found applications in
imaging of the retina, cornea, gastrointestinal tract,
artery, tooth, bladder, blood flow, and brain cortex.
9
Another potential application of OCT is the evalua-
tion of burns in biological tissue.
10
The contrast of
an OCT image is provided by the optical properties of
a sample that modify the parameters of the light
field, including the amplitude and the polarization
state. The parameters characterizing the structur-
ally isotropic or averaged optical properties
11
of a
sample include the absorption coefficient 共␮
a
, scat-
tering coefficient 共␮
s
, scattering anisotropy g, and
refractive index n; and the parameters characteriz-
ing the polarization properties of a sample include
birefringence amplitude n, orientation, and elliptic-
ity and diattenuation amplitude D, orientation, and
ellipticity, which provide polarization-based contrast
in polarization-sensitive OCT PS-OCT.
Because of the interference-based heterodyne de-
tection scheme used in OCT, a scattering sample acts
as a nondepolarizing medium.
4
The polarization
properties of a nondepolarizing sample can be com-
pletely characterized by either a Mueller matrix or a
Jones matrix, and the two matrices are equivalent.
12
Therefore, to provide comprehensive information
about polarization of a sample, the most general PS-
OCT should measure the Jones or the Mueller ma-
trix. Upon acquisition of the Jones or the Mueller
matrix, any polarization parameters can be ex-
tracted. We define Mueller-matrix OCT as PS-OCT
that can measure the Mueller or the Jones matrix of
a sample. Therefore, Mueller-matrix OCT is the
most general form of PS-OCT.
The authors are with Texas A&M University, 3120 TAMU, Col-
lege Station, Texas 77843-3120. S. Jiao, W. Yu, and L. V. Wang
LWang@tamu.edu are with the Optical Imaging Laboratory, De-
partment of Biomedical Engineering. G. Stoica is with the De-
partment of Pathobiology.
Received 18 January 2003; revised manuscript received 28 May
2003.
0003-693503255191-07$15.000
© 2003 Optical Society of America
1 September 2003 Vol. 42, No. 25 APPLIED OPTICS 5191

In this paper, we investigate the various contrast
mechanisms provided by Mueller-matrix OCT. The
properties of the round-trip Jones matrix are ana-
lyzed for conditions with and without diattenuation
in a sample. The analyses indicate that when diat-
tenuation is negligible, one incident polarization
state is adequate for the acquisition of the Jones ma-
trix. When diattenuation cannot be neglected, two
incident polarization states are necessary, and the
transpose symmetric property of the round-trip Jones
matrix rst discovered by our group
5
offers a critical
condition for the calculation of the Jones matrix cor-
rectly. Experimental results with biological sam-
ples are presented.
2. Polarization-Based Contrast
Diattenuation is a description of the dependence of
transmittance on the incident polarization states and
is dened as
D P
q
2
P
r
2
P
q
2
P
r
2
, (1)
where P
q
and P
r
represent the amplitude transmit-
tances for the two orthogonal eigenpolarizations of a
polarization element. Therefore, diattenuation pro-
vides anisotropic amplitude-based contrast, as it in-
curs no phase retardation. Birefringence is a
description of the anisotropic dependence of the
phase velocity of light in a sample on the incident
polarization states. The phase retardation of a light
eld, induced by the local birefringence between the
two orthogonal eigenpolarizations, can be expressed
as
d k
nL
s
⬘兲dL
s
,
where k
is the wave vector corresponding to the cen-
tral wavelength of the incident light in vacuum; L
s
is
the physical path length that the light travels in the
birefringent medium; nL
s
⬘兲 is the local birefrin-
gence; and dL
s
is the local physical path length.
The phase retardation provides a unique phase-based
polarization-contrast mechanism reecting the am-
plitude of birefringence, which exists in various bio-
logical components such as collagen, keratin, myelin,
and elastic bers. Because highly birefringent col-
lagen is a predominant structural component in most
biological tissues, this intrinsic contrast mechanism
is prevalent in the biomedical applications of Mueller
OCT. In addition, many degenerative processes of
biological tissues alter birefringence and should,
thus, be detectable by Mueller-matrix OCT.
In a PS-OCT system, the detected variation of the
polarization state of the scattered light in reference to
the incident light is affected by the round-trip polar-
ization effect of a sample, which can be characterized
with a round-trip Jones matrix J
2
. We will use sub-
scripts 1 and 2 to describe the one-way and round-trip
parameters, respectively. After acquisition of the
round-trip Jones matrix, the round-trip retardation
共␾
2
and diattenuation D
2
for each pixel of the OCT
image can be calculated with the following formulas,
13
2
2cos
1
1
2
trJ
2
det J
2
兾兩det J
2
trJ
2
*
trJ
2
*J
2
2det J
2
12
, (2)
D
2
1
4det J
2
2
trJ
2
*J
2
兲兴
2
12
, (3)
respectively, where *, tr, and det represent the Her-
mitian transpose conjugate, trace, and determinant
of the matrix, respectively. The fast eigenvector of
J
2
at each pixel of the OCT image,
E
2
E
2h
E
2v
,
can be calculated through standard algorithms. The
orientation of the fast axis can thus be calculated as
2
arc tan
E
2v
E
2h
. (4)
3. Calculation of the Round-Trip Jones Matrix
The round-trip Jones matrix J
2
can be expressed with
the one-way Jones matrix J
1
, according to the Jones
reversibility theorem, as
J
2
J
1
T
J
1
, (5)
where the superscript T represents the transpose op-
eration. A polarization element is called homoge-
neous when the two eigenvectors of its Jones matrix
are orthogonal. A retarder is called elliptical when
its eigenpolarizations are elliptical polarization
states. A linear retarder is a special case in which
the eigenpolarizations are linear, and a Faraday ro-
tator is another special case in which the eigenpolar-
izations are circular. We can prove that when two or
more linear retarders are cascaded, the overall re-
tarder is generally elliptical unless the axes of the
retarders are aligned. Except in some special sam-
ples, the orientations of the birefringent bers in bi-
ological samples, take skin, for example, are not
collinear, and as a result, J
1
generally represents a
homogeneous elliptical retarder if diattenuation is
negligible in the sample.
When diattenuation is negligible in a sample, J
1
can be expressed as
J
1
共␾
1
,
1
,
1
cos共␾
1
2 i sin共␾
1
2cos 2
1
i sin共␾
1
2sin 2
1
exp共⫺i
1
i sin共␾
1
2sin 2
1
expi
1
cos共␾
1
2 i sin共␾
1
2cos 2
1
J
1
1,1 J
1
1,2
J
1
1,2* J
1
1,1*
. (6)
5192 APPLIED OPTICS Vol. 42, No. 25 1 September 2003

The fast and slow eigenvectors are
cos
1
sin
1
expi
1
and
sin
1
exp共⫺i
1
cos
1
,
respectively, where
1
is an auxiliary angle and
1
represents the phase difference between the two com-
ponents of the fast eigenvector.
1
is the phase dif-
ference between the two eigenvalues the
retardation. The azimuth 共␣
1
of the major axis of
its fast eigenpolarization can be expressed as
tan2
1
兲⫽tan2
1
cos
1
.If
1
0, J
1
is transpose
symmetric, representing a linear retarder, and
1
represents the orientation of the fast axis.
From Eq. 5, we have J
2
J
2
T
, i.e., J
2
is transpose
symmetric. As a result, J
2
represents a linear re-
tarder, and we can thus conclude that the round-trip
transformation effect of an elliptical retarder is
equivalent to the one-way transformation of a linear
retarder. This conclusion is the foundation of con-
ventional PS-OCT, in which a sample is treated as a
linear retarder. Since only two parameters are
needed to characterize a linear retarder, the number
of parameters needed to characterize the round-trip
polarization properties of a sample is reduced to two.
This conclusion allows the acquisition of this type of
round-trip Jones matrix with only one incident polar-
ization state. For an incident polarization state
E
i
E
ih
E
iv
,
the output polarization state
E
o
E
oh
E
ov
detected by PS-OCT can be expressed as
E
oh
E
ov
J
2
E
ih
E
iv
. (7)
Because of the orthonormal transformation property
of J
2
, the inherent property of a retarder, we also
have
E
ov
*
E
oh
*
J
2
E
iv
*
E
ih
*
. (8)
The round-trip Jones matrix can thus be calculated
as
J
2
E
oh
E
ov
*
E
ov
E
oh
*
册冋
E
ih
E
iv
*
E
iv
E
ih
*
1
. (9)
When diattenuation cannot be neglected in a sam-
ple, one incident polarization state is not sufcient to
acquire its round-trip Jones matrix because ve real
parameters 关␾
2
,
2
, amplitude transmittances P
q2
and P
r2
, and the orientation of diattenuation 共␪
d2
兲兴
are needed to characterize such a system. There-
fore, at least two incident polarization states, either
applied at the same time or applied sequentially, are
required. The transpose symmetry in the round-
trip Jones matrix is critical for eliminating the arbi-
trary phase difference between the two measured
Jones vectors corresponding to the two incident po-
larization states to yield the correct Jones matrix.
This arbitrary phase difference can be caused either
by the nonidentity of the power spectra when two
light sources are used or by the imperfection of the
longitudinal scanning mechanism when the two in-
cident polarization states are applied sequentially.
Because it ignores the diattenuation effect com-
pletely, conventional PS-OCT is not valid for biolog-
ical samples possessing diattenuation and cannot
provide diattenuation contrast.
4. Experiment
We have built a novel multichannel Mueller OCT,
5,6
which can acquire the Jones matrix of a sample with
a single scan for each one-dimensional depth image
A line image. The Jones matrix can be further
transformed into an equivalent Mueller matrix.
The Mueller matrix is preferred because its rst el-
ement, M
00
, represents the intensity transformation
property of a sample and is free of both the effects of
the sample polarization and the polarization state of
the incident light. Therefore, a Mueller matrix re-
veals the real morphologic structure as well as the
polarization-based features of a sample.
The tail of a rat was imaged in situ with Mueller
OCT after the skin was shaved and scrubbed with
glycerin. The OCT and polarization-histologic im-
ages are shown in Figs. 1a1f . There are no sig-
nicant differences between the M
00
image Fig. 1b兲兴
and the conventional OCT image for this particular
sample Fig. 1a兲兴, both of which are amplitude based.
The effect of polarization on a conventional OCT im-
age depends on several parameters, for example, the
incident polarization state, the value and orientation
of the birefringence, and the accumulated phase re-
tardation. When fringes are present in the conven-
tional OCT image, the difference between these two
images is dramatic.
5
The intensity and retardation
images reveal different characteristics of the sample.
The intensity images clearly reveal the boundaries of
the structures in the epidermis and only the shallow
dermal region. In contrast, the retardation image
Fig. 1c兲兴 reveals the distribution of birefringent
components deeper into the dermis. The absolute
value of the retardation difference between each
pixel and its previous pixel in the same A line is
calculated to obtain a differential retardation image
Fig. 1d兲兴. The birefringent regions correspond-
ing to the supercial keratin layer and collagen-rich
dermal papillae and nonbirefringent regions cor-
responding to fat and the living epidermis are
shown more clearly in the differential retardation
image than in the raw retardation image. The im-
1 September 2003 Vol. 42, No. 25 APPLIED OPTICS 5193

age of the orientation of the fast axis Fig. 1e兲兴
revealed structures that we believe to be related to
the distribution of the orientation of the birefrin-
gent bers collagen and keratin. In the gure,
we can see that the orientation of the fast axis
varies from region to region as also observed in the
polarization histology. Although the amplitude-
and phase-based polarization signals should have
comparable signal-to-noise ratios because they are
computed from the same measurements, the
contrast-to-noise ratio can be different depending
on the availability of the two contrasts in the sam-
ple; therefore, the two contrast mechanisms can
provide information into different depths.
To evaluate the sensitivity of the phase-based po-
larization contrast in burn-depth determination, we
imaged an ex vivo skin samplefrom a rat belly
containing a burn lesion. The burn lesion was made
by touching the skin with a heated approximately
100 °C electric iron for less than 1 s. The calculated
intensity image, the retardation image, the diattenu-
ation image and the histological image are shown in
Figs. 2a2d. The burn region cannot be identied
in the intensity image; but it can be clearly seen with
marked contrast in the retardation and diattenuation
images as veried by the polarization histological im-
age.
Figure 3 shows the depth proles of retardation of
the burn and normal regions, respectively. Each
curve is an average of 10 proles in the central area
of the burn region and in the normal region to the
right side of the burn region. The loss of birefrin-
gence in the burn region compared with the normal
tissue can be seen clearly. This gure further dem-
onstrates that phase-based polarization contrast pro-
vides a sensitive mechanism for evaluating thermal
degeneration of biological tissue. Because birefrin-
gence and diattenuation are related to the function of
Fig. 1. a Conventional OCT image in logarithmic scale, b intensity image M
00
, in logarithmic scale, c retardation image, d
differential retardation image, e image of the orientation of the fast axis, f polarization histologic image of an in situ rat tail. The height
of each image is 750 m. The gray scales are for the orientation 共␪
2
and the retardation 共␾
2
images. The conventional OCT image was
obtained with vertical linear polarization states for both the incident and the reference beams. F, fat; K, keratin; DP, dermal papilla.
Fig. 2. a Intensity image M
00
, in logarithmic scale, b retardation image, c diattenuation image, d polarization histologic image of
a piece of ex vivo rat skin with a burn lesion. The height of each image is 750 m. The gray scales are for the retardation 共␾
2
and the
diattenuation D
2
images. B, burn region.
5194 APPLIED OPTICS Vol. 42, No. 25 1 September 2003

several kinds of biological component such as colla-
gen, Mueller OCT is a type of functional imaging.
5. Discussion
The differences between conventional OCT and
Mueller OCT in their sensitivities to different optical
properties of a sample result from their different con-
trast mechanisms. Conventional OCT is an
amplitude-based detection system, which detects the
local relative variations of path-length-resolved re-
ectance from tissues. By modifying an existing
theoretical model of OCT
14
to include the effect of
polarization, we can express the signal in conven-
tional OCT as
I
˜
d
L
r
2I
s
I
r
12
⫺⬁
RL
s
兲兴
12
cos关␤共L
s
兲兴exp
关⫺4共⌬LL
c
2
cosk
LdL
s
, (10)
where L
s
and L
r
are the round-trip optical path
lengths of the sample and reference arms, respec-
tively; L L
s
L
r
is the round-trip optical path-
length difference; L
c
is the coherence length of the
light source; I
r
is the intensity of the reference beam;
I
s
is the reected intensity of the sample arm; RL
s
兲⫽
dI
s
L
s
dL
s
I
s
is the path-length-resolved reec-
tance of the sample; and ␤共L
s
is an equivalent angle
between the polarization states of the reference and
the backscattered sample beams, dened as
cos关␤共L
s
兲兴 E
s
L
s
E
r
E
s
L
s
E
r
,
where E
s
L
s
and E
r
are the electric vectors of the
sample and the reference beams, respectively, and
the angle brackets denote a time average. The in-
tegrand is nonzero mainly in the interval L L
c
.
The integration produces a signicant value only
when RL
s
varies sharply across a dimension of L
c
;
otherwise, the integral tends to be zero because of the
cosine term in the integrand. A sharp variation of
RL
s
is caused by interfaces between regions of dif-
ferent optical properties. Conventional OCT is, in
principle, very sensitive to discontinuity of the refrac-
tive index 共⌬n as a result of specular reection. As
studied by Pan et al.,
14,15
conventional OCT is also
sensitive to variations of the anisotropy 共⌬g and the
scattering coefcient 共⌬␮
s
, but it is insensitive to
variation of the absorption coefcient 共⌬␮
a
. We can
see in Eq. 10 that the polarization effect of a sample
contributes to the recorded conventional OCT signal
as an amplitude modulation and is superimposed on
the backreection effect; consequently, conventional
OCT has difculty in separating the polarization ef-
fect from the real morphologic effect of the sample.
To account for the meanings of the measured re-
tardation image, we can divide each depth scan into
a number of homogenous segments, each of which has
a length less than the axial resolution; each segment
can be characterized by a Jones matrix J
1
i兲共i 1, 2,
..., which is a function of the equivalent local bire-
fringence 关␦ni兲兴, orientation of the fast axis 关␪
1
i兲兴,
amplitude transmittances P
q1
i and P
r1
i兲兴, and ori-
entation of the diattenuation 关␪
d1
i兲兴. For single
backscattering and even multiple small-angle scat-
tering, the equivalent round-trip Jones matrix of con-
tiguous m segments of the sample from the surface to
the mth segment can be expressed as
J
2
m
i1
m
J
1
T
i
im
1
J
1
i .
The equivalent round-trip parameters for the m seg-
ments, such as the retardation
2
m
, orientation of the
fast axis
2
m
, and diattenuation, can be calculated
from J
2
m
. When
1
1兲⫽␪
d1
1兲⫽␪
1
2兲⫽␪
d1
2兲⫽
...⫽␪
1
m兲⫽␪
d1
m,if
2
m
,
2
m
in the retar-
dation image increases with depth, whereas
2
m
keeps constant; if
2
m
covers a range greater than ,
it causes fringes in both the retardation and the ori-
entation images because a retarder J共␾
2
m
⫹␲,
2
m
is equivalent to a retarder J共␲
2
m
,
2
m
⫾␲2,
共␾
2
m
,
2
m
⑀关0,␲兴兲, a phenomenon observed in the
retardation and orientation images of samples like
porcine tendon.
5
In this case, the differential retar-
dation image reects a map of the local birefringence.
Otherwise,
2
m
and
2
m
are also functions of both
1
i and
d1
i in the optical path, making the retar-
dation image complex to interpret rigorously unless
the local polarization properties can be calculated,
which is possible only with Mueller OCT.
The Jones matrix of the rst pixel of each A line
represents the round-trip Jones matrix of the rst
segment, i.e., J
2
1
J
1
T
1J
1
1.IfJ
1
1 can be cal-
culated from J
2
1 by developing some effective algo-
rithms, the rst segment can be peeled off to yield the
round-trip Jones matrix of the second segment, J
1
T
2J
1
2兲⫽关J
1
T
1兲兴
1
J
2
2
J
1
1
1. By use of this
strategy layer by layer, the one-way Jones matrix of
each segment can thus be extracted, and the images
of the local polarization parameters can be calcu-
lated, which should be free of fringes because the
retardation of each segment should be much less than
. This algorithm is important in ber-based PS-
OCT system for eliminating the polarization dis-
Fig. 3. Average of 10 depth proles of the retardation around the
center of the burn area and the normal region to the right of the
burn area.
1 September 2003 Vol. 42, No. 25 APPLIED OPTICS 5195

Citations
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Journal Article
TL;DR: A novel optical system for bidirectional color Doppler imaging of flow in biological tissues with micrometer-scale resolution is described and its use for in vivo imaging of blood flow in an animal model is demonstrated.
Abstract: We describe a novel optical system for bidirectional color Doppler imaging of flow in biological tissues with micrometer-scale resolution and demonstrate its use for in vivo imaging of blood flow in an animal model. Our technique, color Doppler optical coherence tomography (CDOCT), performs spatially localized optical Doppler velocimetry by use of scanning low-coherence interferometry. CDOCT is an extension of optical coherence tomography (OCT), employing coherent signal-acquisition electronics and joint time-frequency analysis algorithms to perform flow imaging simultaneous with conventional OCT imaging. Cross-sectional maps of blood flow velocity with <50-μm spatial resolution and <0.6-mm/s velocity precision were obtained through intact skin in living hamster subdermal tissue. This technology has several potential medical applications.

601 citations

Journal Article
TL;DR: In this article, a polarization-sensitive optical coherence-domain reflectometer capable of characterizing the phase retardation between orthogonal linear polarization modes at each reflection point in a birefringent sample is presented.
Abstract: We present a polarization-sensitive optical coherence-domain reflectometer capable of characterizing the phase retardation between orthogonal linear polarization modes at each reflection point in a birefringent sample. The device is insensitive to the rotation of the sample in the plane perpendicular to ranging. Phase measurement accuracy is ±0.86°, but the reflectometer can distinguish local variations in birefringence as small as 0.05° with a distance resolution of 10.8 μm and a dynamic range of 90 dB. Birefringence-sensitive ranging in a wave plate, an electro-optic modulator, and a calf coronary artery is demonstrated.

601 citations

Patent
13 Dec 2007
TL;DR: In this paper, a method for increasing the sensitivity in the detection of optical coherence tomography and low coherence interferometry (LCI) signals by detecting a parallel set of spectral bands, each band being a unique combination of optical frequencies, is presented.
Abstract: Apparatus and method for increasing the sensitivity in the detection of optical coherence tomography and low coherence interferometry (“LCI”) signals by detecting a parallel set of spectral bands, each band being a unique combination of optical frequencies. The LCI broad bandwidth source is split into N spectral bands. The N spectral bands are individually detected and processed to provide an increase in the signal-to-noise ratio by a factor of N. Each spectral band is detected by a separate photo detector and amplified. For each spectral band the signal is band pass filtered around the signal band by analog electronics and digitized, or, alternatively, the signal may be digitized and band pass filtered in software. As a consequence, the shot noise contribution to the signal is reduced by a factor equal to the number of spectral bands. The signal remains the same. The reduction of the shot noise increases the dynamic range and sensitivity of the system.

446 citations

Patent
08 Sep 2004
TL;DR: In this article, the first and/or second electro-magnetic radiations have a spectrum whose mean frequency changes substantially continuously over time at a tuning speed that is greater than 100 Tera Hertz per millisecond.
Abstract: An apparatus and method are provided. In particular, at least one first electro-magnetic radiation may be provided to a sample and at least one second electro-magnetic radiation can be provided to a non-reflective reference. A frequency of the first and/or second radiations varies over time. An interference is detected between at least one third radiation associated with the first radiation and at least one fourth radiation associated with the second radiation. Alternatively, the first electro-magnetic radiation and/or second electro-magnetic radiation have a spectrum which changes over time. The spectrum may contain multiple frequencies at a particular time. In addition, it is possible to detect the interference signal between the third radiation and the fourth radiation in a first polarization state. Further, it may be preferable to detect a further interference signal between the third and fourth radiations in a second polarization state which is different from the first polarization state. The first and/or second electro-magnetic radiations may have a spectrum whose mean frequency changes substantially continuously over time at a tuning speed that is greater than 100 Tera Hertz per millisecond.

394 citations

Patent
29 Sep 2005
TL;DR: In this paper, a system and method for imaging of a sample, e.g., biological sample, are provided, where at least one source electro-magnetic radiation forwarded to the sample and a reference may be generated.
Abstract: A system and method for imaging of a sample, e.g., biological sample, are provided. In particular, at least one source electro-magnetic radiation forwarded to the sample and a reference may be generated. A plurality of detectors may be used, at least one of the detectors capable of detecting a signal associated with a combination of at least one first electro-magnetic radiation received from the sample and at least one second electro-magnetic radiation received from the reference. At least one particular detector may have a particular electrical integration time, and can receive at least a portion of the signal for a time duration which has a first portion with a first power level greater than a predetermined threshold and a second portion immediately preceding or following the first portion. The second portion may have a second power level that is less than the predetermined threshold, and extends for a time period which may be, e.g., approximately more than 10% of the particular electrical integration time.

393 citations

References
More filters
Journal ArticleDOI
TL;DR: Using a low-coherence Michelson interferometer, the authors measured two-dimensional images of optical birefringence in bovine tendon as a function of depth, which allowed rapid noncontact investigation of tissue structural properties.
Abstract: Using a low-coherence Michelson interferometer, we measure two-dimensional images of optical birefringence in bovine tendon as a function of depth. Polarization-sensitive detection of the signal formed by interference of backscattered light from the sample and a mirror in the reference arm give the optical phase delay between light that is propagating along the fast and slow axes of the birefringent tendon. Images showing the change in birefringence in response to laser irradiation are presented. The technique permits rapid noncontact investigation of tissue structural properties through two-dimensional imaging of birefringence.

963 citations

Journal ArticleDOI
TL;DR: In this article, a color Doppler optical coherence tomography (CDOCT) was proposed for in vivo image of blood flow in a hamster subdermal tissue.
Abstract: We describe a novel optical system for bidirectional color Doppler imaging of flow in biological tissues with micrometer-scale resolution and demonstrate its use for in vivo imaging of blood flow in an animal model. Our technique, color Doppler optical coherence tomography (CDOCT), performs spatially localized optical Doppler velocimetry by use of scanning low-coherence interferometry. CDOCT is an extension of optical coherence tomography (OCT), employing coherent signal-acquisition electronics and joint time-frequency analysis algorithms to perform flow imaging simultaneous with conventional OCT imaging. Cross-sectional maps of blood flow velocity with <50-µm spatial resolution and <0.6-mm/s velocity precision were obtained through intact skin in living hamster subdermal tissue. This technology has several potential medical applications.

643 citations

Journal ArticleDOI
TL;DR: In this article, a polarization-sensitive optical coherence-domain reflectometer capable of characterizing the phase retardation between orthogonal linear polarization modes at each reflection point in a birefringent sample is presented.
Abstract: We present a polarization-sensitive optical coherence-domain reflectometer capable of characterizing the phase retardation between orthogonal linear polarization modes at each reflection point in a birefringent sample. The device is insensitive to the rotation of the sample in the plane perpendicular to ranging. Phase measurement accuracy is ±0.86°, but the reflectometer can distinguish local variations in birefringence as small as 0.05° with a distance resolution of 10.8 μm and a dynamic range of 90 dB. Birefringence-sensitive ranging in a wave plate, an electro-optic modulator, and a calf coronary artery is demonstrated.

621 citations

Journal Article
TL;DR: A novel optical system for bidirectional color Doppler imaging of flow in biological tissues with micrometer-scale resolution is described and its use for in vivo imaging of blood flow in an animal model is demonstrated.
Abstract: We describe a novel optical system for bidirectional color Doppler imaging of flow in biological tissues with micrometer-scale resolution and demonstrate its use for in vivo imaging of blood flow in an animal model. Our technique, color Doppler optical coherence tomography (CDOCT), performs spatially localized optical Doppler velocimetry by use of scanning low-coherence interferometry. CDOCT is an extension of optical coherence tomography (OCT), employing coherent signal-acquisition electronics and joint time-frequency analysis algorithms to perform flow imaging simultaneous with conventional OCT imaging. Cross-sectional maps of blood flow velocity with <50-μm spatial resolution and <0.6-mm/s velocity precision were obtained through intact skin in living hamster subdermal tissue. This technology has several potential medical applications.

601 citations

Journal Article
TL;DR: In this article, a polarization-sensitive optical coherence-domain reflectometer capable of characterizing the phase retardation between orthogonal linear polarization modes at each reflection point in a birefringent sample is presented.
Abstract: We present a polarization-sensitive optical coherence-domain reflectometer capable of characterizing the phase retardation between orthogonal linear polarization modes at each reflection point in a birefringent sample. The device is insensitive to the rotation of the sample in the plane perpendicular to ranging. Phase measurement accuracy is ±0.86°, but the reflectometer can distinguish local variations in birefringence as small as 0.05° with a distance resolution of 10.8 μm and a dynamic range of 90 dB. Birefringence-sensitive ranging in a wave plate, an electro-optic modulator, and a calf coronary artery is demonstrated.

601 citations