## Investigation of depth selectivity of polarization gating for tissue characterization

Optics Express, Vol. 13, Issue 2, pp. 601-611 (2005)

http://dx.doi.org/10.1364/OPEX.13.000601

Acrobat PDF (192 KB)

### Abstract

Polarization gating has been widely used to selectively probe the structure of superficial biological tissue. However, the penetration depth selectivity of polarization gating has not been well understood. Using polarized light Monte Carlo simulations, we investigated how the optical properties of a scattering medium and light collection geometry affect the penetration depth of polarization gating. We show that, for a wide range of optical properties, polarization gating enables attaining a very shallow penetration depth, which is on the order of the mean free path length. Furthermore, we discuss the mechanisms responsible for this surprisingly short depth of penetration of polarization gating. We show that polarization-gated signal is generated primarily by photons emerging from the surface of the medium within a few mean free path lengths from the point of incidence.

© 2005 Optical Society of America

## 1. Introduction

1. K. Sokolov, R. Drezek, K. Gossage, and R. Richards-Kortum, “Reflectance spectroscopy with polarized light: is it sensitive to cellular and nuclear morphology,” Opt. Express **5**, 302–317 (1999), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-5-13-302. [CrossRef] [PubMed]

12. S. G. Demos and R. R. Alfano, “Optical polarization imaging,” Appl. Opt. **36**, 150–155 (1997). [CrossRef] [PubMed]

1. K. Sokolov, R. Drezek, K. Gossage, and R. Richards-Kortum, “Reflectance spectroscopy with polarized light: is it sensitive to cellular and nuclear morphology,” Opt. Express **5**, 302–317 (1999), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-5-13-302. [CrossRef] [PubMed]

6. Y. Kim, Y. Liu, R. K. Wali, H. K. Roy, M. J. Goldberg, A. K. Kromine, K. Chen, and V. Backman, “Simultaneous measurement of angular and spectral properties of light scattering for characterization of tissue microarchitecture and its alteration in early precancer,” IEEE J. Sel. Top. Quantum Electron. **9**, 243–257 (2003). [CrossRef]

8. J. R. Mourant, T. M. Johnson, S. Carpenter, A. Guerra, T. Aida, and J. P. Freyer, “Polarized angular dependent spectroscopy of epithelial cells and epithelial cell nuclei to determine the size scale of scattering structures,” J. Biomed. Opt. **7**, 378–387 (2002). [CrossRef] [PubMed]

9. V. Backman, R. Gurjar, K. Badizadegan, L. Itzkan, R. R. Dasari, L. T. Perelman, and M. S. Feld, “Polarized light scattering spectroscopy for quantitative measurement of epithelial cellular structures in situ,” IEEE J. Sel. Top. Quantum Electron. **5**, 1019–1026 (1999). [CrossRef]

13. V. Backman, M. B. Wallace, L. T. Perelman, J. T. Arendt, R. Gurjar, M. G. Muller, Q. Zhang, G. Zonios, E. Kline, T. McGillican, S. Shapshay, T. Valdez, K. Badizadegan, J. M. Crawford, M. Fitzmaurice, S. Kabani, H. S. Levin, M. Seiler, R. R. Dasari, I. Itzkan, J. Van Dam, and M. S. Feld, “Detection of preinvasive cancer cells,” Nature **406**, 35–36 (2000). [CrossRef] [PubMed]

14. H. K. Roy, Y. Liu, R. K. Wali, Y. Kim, M. J. Goldberg, A. K. Kromine, and V. Backman, “Four-dimensional elastic light scattering fingerprints as preneoplastic markers in the rat model of colon carcinogenesis,” Gastroenterology **126**, 1071–1081 (2004). [CrossRef] [PubMed]

15. A. Wax, C. H. Yang, M. G. Muller, R. Nines, C. W. Boone, V. E. Steele, G. D. Stoner, R. R. Dasari, and M. S. Feld, “In situ detection of neoplastic transformation and chemopreventive effects in rat esophagus epithelium using angle-resolved low-coherence interferometry,” Cancer Res. **63**, 3556–3559 (2003). [PubMed]

*in vivo*implementation.

*a priori*surprisingly short penetration depth has not been established [6

6. Y. Kim, Y. Liu, R. K. Wali, H. K. Roy, M. J. Goldberg, A. K. Kromine, K. Chen, and V. Backman, “Simultaneous measurement of angular and spectral properties of light scattering for characterization of tissue microarchitecture and its alteration in early precancer,” IEEE J. Sel. Top. Quantum Electron. **9**, 243–257 (2003). [CrossRef]

9. V. Backman, R. Gurjar, K. Badizadegan, L. Itzkan, R. R. Dasari, L. T. Perelman, and M. S. Feld, “Polarized light scattering spectroscopy for quantitative measurement of epithelial cellular structures in situ,” IEEE J. Sel. Top. Quantum Electron. **5**, 1019–1026 (1999). [CrossRef]

## 2. Methods

### 2.1 Polarized light Monte Carlo simulations

16. L.-H. Wang, S. L. Jacques, and L.-Q. Zheng, “MCML - Monte Carlo modeling of photon transport in multi-layered tissues,” Comput. Methods Programs Biomed. **47**, 131–146 (1995). [CrossRef] [PubMed]

17. S. Bartel and A. H. Hielscher, “Monte Carlo simulation of the diffuse backscattering Mueller matrix for highly scattering media,” Appl. Opt. **39**, 1580–1588 (2000). [CrossRef]

22. G. Yao and L. V. Wang, “Propagation of polarized light in turbid media: simulated animation sequences,” Opt. Express **7**, 198–203 (2000), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-7-5-198. [CrossRef] [PubMed]

*θ*and azimuthal angle

*ϕ*was determined using Mie theory. The sampling of

*θ*and

*ϕ*was performed using an efficient algorithm developed by Jaillon et al [18

18. F. Jaillion and H. Saint-James, “Description and time reduction of a Monte Carlo code to simulate propagation of polarized light through scattering media,” Appl. Opt. **42**, 3290–3296 (2003). [CrossRef]

17. S. Bartel and A. H. Hielscher, “Monte Carlo simulation of the diffuse backscattering Mueller matrix for highly scattering media,” Appl. Opt. **39**, 1580–1588 (2000). [CrossRef]

18. F. Jaillion and H. Saint-James, “Description and time reduction of a Monte Carlo code to simulate propagation of polarized light through scattering media,” Appl. Opt. **42**, 3290–3296 (2003). [CrossRef]

^{7}photons in our simulations. As discussed below, the numerical experiments were designed to ensure that (1) the light collection geometry modeled in the simulations emulated realistic experimental conditions and (2) the output of the numerical simulations is analogous to those typically recorded in experiments.

### 2.2 Monte Carlo simulations of polarization gating

*p*(

*r*,

*ϕ*) to denote the probability of photons emerging from a scattering medium at radial distance

*r*from the source (i.e. the point of incidence) per unit area, where

*ϕ*is the azimuthal angle.

*P*(

*r*,

*ϕ*)≡

*rp*(

*r*,

*ϕ*) is the probability of photons emerging from a scattering medium at radial distance

*r*per unit length.

1. K. Sokolov, R. Drezek, K. Gossage, and R. Richards-Kortum, “Reflectance spectroscopy with polarized light: is it sensitive to cellular and nuclear morphology,” Opt. Express **5**, 302–317 (1999), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-5-13-302. [CrossRef] [PubMed]

3. A. Myakov, L. Nieman, L. Wicky, U. Utzinger, R. Richards-Kortum, and K. Sokolov, “Fiber optic probe for polarized reflectance spectroscopy in vivo: Design and performance,” J. Biomed. Opt. **7**, 388–397 (2002). [CrossRef] [PubMed]

5. S. L. Jacques, J. R. Roman, and K. Lee, “Imaging superficial tissues with polarized light,” Lasers Surg. Med. **26**, 119–129 (2000). [CrossRef] [PubMed]

6. Y. Kim, Y. Liu, R. K. Wali, H. K. Roy, M. J. Goldberg, A. K. Kromine, K. Chen, and V. Backman, “Simultaneous measurement of angular and spectral properties of light scattering for characterization of tissue microarchitecture and its alteration in early precancer,” IEEE J. Sel. Top. Quantum Electron. **9**, 243–257 (2003). [CrossRef]

9. V. Backman, R. Gurjar, K. Badizadegan, L. Itzkan, R. R. Dasari, L. T. Perelman, and M. S. Feld, “Polarized light scattering spectroscopy for quantitative measurement of epithelial cellular structures in situ,” IEEE J. Sel. Top. Quantum Electron. **5**, 1019–1026 (1999). [CrossRef]

11. J. M. Schmitt, A. H. Gandjbakhche, and R. F. Bonner, “Use of polarized-light to discriminate short-path photons in a multiply scattering medium,” Appl. Opt. **31**, 6535–6546 (1992). [CrossRef] [PubMed]

*I*

_{‖}) and orthogonal (cross-polarized signal

*I*

_{⊥}) to that of the incident light, respectively. The co-polarized signal is generated by both low-order scattering (primarily from scatterers located close to the surface) and multiple scattering (primarily from scatterers located deeper into the medium). On the other hand, the cross-polarized signal is predominantly generated by the multiply scattered photons from the deeper layers of the medium. Because multiple scattering depolarizes scattered light [5

5. S. L. Jacques, J. R. Roman, and K. Lee, “Imaging superficial tissues with polarized light,” Lasers Surg. Med. **26**, 119–129 (2000). [CrossRef] [PubMed]

**5**, 1019–1026 (1999). [CrossRef]

11. J. M. Schmitt, A. H. Gandjbakhche, and R. F. Bonner, “Use of polarized-light to discriminate short-path photons in a multiply scattering medium,” Appl. Opt. **31**, 6535–6546 (1992). [CrossRef] [PubMed]

12. S. G. Demos and R. R. Alfano, “Optical polarization imaging,” Appl. Opt. **36**, 150–155 (1997). [CrossRef] [PubMed]

*I*

_{⊥}from

*I*

_{‖}. The resulting signal

*ΔI*=

*I*

_{‖}-

*I*

_{⊥}is referred to as the differential polarization signal and predominately determined by the single and low-order scattering in the superficial layer of the scattering medium.

**9**, 243–257 (2003). [CrossRef]

**5**, 1019–1026 (1999). [CrossRef]

*D*of the sample and, thus, its optical thickness

*τ*, which is defined as

*τ*=(

*µ*

_{s}+

*µ*

_{a})

*D*where

*µ*

_{s}and

*µ*

_{a}are the scattering and absorption coefficients, respectively. For each

*D*and

*τ*, the co- and cross-polarized signals were recorded for various radii of collection

*R*, i.e.

*I*

_{‖}(

*τ*,

*R*)=

*P*

_{‖}(

*r*,

*ϕ*)

*drdϕ*and

*I*

_{⊥}(

*τ*,

*R*)=

*P*

_{⊥}(

*r*,

*ϕ*)

*drdϕ*.

*τ*increases, the differential polarization signal (

*ΔI*(

*τ*,

*R*=3

*mm*)=

*I*

_{‖}(

*τ*,

*R*)-

*I*

_{⊥}(

*τ*,

*R*)) first increases and then reaches a plateau at

*τ*

_{c}~3. Here, the differential polarization signal is normalized by the maximum intensity for large

*τ*. This curve is referred to as the

*saturation curve*. Varying

*τ*provides a simple yet efficient method for quantifying the contribution of different depths to the differential polarization signal. Indeed,

*ΔI*(

*τ*)=

*C*(

*τ*′)

*dτ*′, where

*C*(

*τ*) is the contribution of depth

*τ*to the polarization-gated signal. The fact that the saturation curve

*ΔI*(

*τ*) levels off after

*τ*

_{c}~3 indicates that the differential polarization signal is determined by scattering events occurring at

*τ*<

*τ*

_{c}and the contribution from the deeper scatterers to the differential polarization signal is negligible. For comparison, as shown in Fig. 1(b), for the same range of

*τ*, the unpolarized light intensity

*I*

_{‖}+

*I*

_{⊥}continues increasing without reaching a plateau, in agreement with previous experimental observations that unpolarized light has considerably greater penetration depth relative to that of the polarization-gated signal.

*ΔI*(

*τ*) with

*τ*. The saturation curve can be used as a convenient tool to analyze polarization gating. First, it provides a simple method to quantify the penetration depth. Here we define the penetration depth T of differential polarization signal as the optical depth

*τ*such that the saturation curve reaches 90% of its saturation value, i.e.

*ΔI*is primarily generated by photons scattered within

*τ*< T. Furthermore, we point out that

*I*

_{‖}and

*I*

_{⊥}obtained from the Monte Carlo simulations are the same quantities that are measured in polarization gating experiments. Therefore, the analysis based on our numerical simulations can be directly linked to the experimental data.

## 3. The effect of optical properties of the medium and light collection geometry on the depth selectivity of polarization gating

*µ*

_{s}, absorption coefficient

*µ*

_{a}, and anisotropy factor

*g*. In all simulations, all optical parameters were chosen to be within the physiological range [23

23. B. C. Wilson and S. L. Jacques, “Optical reflectance and transmittance of tissues - principles and applications,” IEEE J. Quantum Electron. **26**, 2186–2199 (1990). [CrossRef]

*R*, in our numerical studies presented in this section.

### 3.1 Effect of scattering coefficient

*µ*

_{s}on the depth of penetration of polarization gating, we varied

*µ*

_{s}while keeping other optical parameters constant:

*g*=0.809 and

*µ*

_{a}=0.1 cm

^{-1}. As discussed in Methods, we defined the depth of penetration of polarization-gated signal T as the optical depth

*τ*(

*τ*=(

*µ*

_{s}+

*µ*

_{a})

*D*, where

*D*is the physical penetration depth) such that the saturation curve reaches 90% of its saturation value. (Such normalization of T by the mean free path

*l*

_{s}=1/(

*µ*

_{s}+

*µ*

_{a}) is convenient, because, as discussed below, the physical penetration depth

*D*is proportional to the optical depth, which scales with

*l*

_{s}.) Figure 2(a) shows the dependence of the penetration depth T on

*µ*

_{s}for different light collection radii

*R*. The dimensionless parameter

*R*/

*l*

_{s}’ is used as the measure of the light collection geometry, where

*l*

_{s}’ is the transport mean free path length defined as

*l*

_{s}′=1(

*µ*

_{s}(1-

*g*)). (The rationale for such normalization is primarily due to practical considerations: In an experiment,

*R*is on the same order of magnitude as

*l*

_{s}’, which, in turn, is relatively easy to determine experimentally. Furthermore, for a given tissue type the range of

*l*

_{s}’ is usually known. Given that

*l*

_{s}’ characterizes the spatial extend of light propagation in tissue, experimentalists routinely compare the radius of light collection with

*l*

_{s}’.) As shown in Fig. 2(a), for a given

*R*/

*l*

_{s}’, the penetration depth is independent of

*µ*

_{s}, and falls within 1.5–2.7 range, as expected. This short penetration depth agrees well with the values previously reported from the experiments in biological tissue [1

**5**, 302–317 (1999), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-5-13-302. [CrossRef] [PubMed]

**5**, 1019–1026 (1999). [CrossRef]

*µ*

_{s}.) However, as further illustrated in Fig. 2(b), T does depend on

*R*/

*l*

_{s}’. Specifically, the penetration depth increases with

*R*/

*l*

_{s}’. This trend levels off for

*R*>

*l*

_{s}’. For

*R*≫

*l*

_{s}’, T is independent of either

*µ*

_{s}or

*R*and approaches a limiting value of 2.7. The rationale for this behavior is discussed in section 4.

### 3.2 Effect of absorption

*µ*

_{a}within the physiological range from 0.01 to 10 cm

^{-1}while keeping the other optical parameters constant at

*µ*

_{s}=200 cm

^{-1}and

*g*=0.809. Figure 3 shows the dependence of the penetration depth of differential polarization signal on

*µ*

_{a}for different

*R*/

*l*

_{s}’. For

*R*<

*l*

_{s}’, T is essentially independent of

*µ*

_{a}. Indeed, for

*R*/

*l*

_{s}’=0.5, T~1.2 and changes only by 2% over a wide range of

*µ*

_{a}=0.01-10 cm

^{-1}. On the other hand, for

*R*>

*l*

_{s}’, T is somewhat dependent on

*µ*

_{a}. For instance, for

*R*/

*l*

_{s}’=10, T decreases by 10% when

*µ*

_{a}increases from 0.01 to 10 cm

^{-1}. However, in the range of

*µ*

_{a}< 1 cm

^{-1}, T is independent of

*µ*

_{a}. For example, T decreases only by less than 1% when

*µ*

_{a}changes from 0.01 to 1 cm

^{-1}. Furthermore, as illustrated in Fig. 3(b), the penetration depth increases with

*R*/

*l*

_{s}’. This trend levels off for

*R*≫

*l*

_{s}’ when T reaches its limiting value, which, in turn, depends on

*µ*

_{a}as discussed above.

### 3.3 Effect of anisotropy factor

23. B. C. Wilson and S. L. Jacques, “Optical reflectance and transmittance of tissues - principles and applications,” IEEE J. Quantum Electron. **26**, 2186–2199 (1990). [CrossRef]

*g*on the penetration depth T for different

*R*in the presence of weak absorption (

*µ*

_{a}=0.1 cm

^{-1},

*µ*

_{s}=200 cm

^{-1}). In the case when

*R*/

*l*

_{s}’<1, T is essentially independent of

*g*. Indeed, within a wide range of

*g*=0.65-0.95, the penetration depth does not exceed 2. However, in case of a large area of light collection, e.g.

*R*/

*l*

_{s}’>2, a different picture emerges: although for

*g*<0.9 the depth of penetration is not sensitive to

*g*, it rapidly increases with

*g*for

*g*>0.9.

*µ*

_{a}=0.1 cm

^{-1}) and strong absorption (

*µ*

_{a}=10 cm

^{-1}) for

*R*/

*l*

_{s}’=10. Contrary to the case of weak absorption, where T is increased dramatically with

*g*for

*g*>0.9 and

*R*/

*l*

_{s}’>2, in the case of strong absorption, T~1-3 and is much less sensitive to

*g*for

*g*=0.65-0.95.

### 3.4 Summary

*l*

_{s}, i.e. T<2 (Fig. 2(a)). Specifically, this conclusion holds if one of the following criteria is satisfied:

*R*<

*l*

_{s}’,

*µ*

_{a}is not much smaller than

*µ*

_{s}, and

*g*<0.9. These conditions are satisfied in many tissue optics applications. However, outside this domain, T may exceed the value of two: it increases with R,

*g*, and 1/

*µ*

_{a}. In particular, T has only a weak dependence on either

*R*or

*µ*

_{a}. Indeed, for

*g*<0.9, T does not exceed the value of 3 for arbitrary

*R*and

*µ*

_{a}. It is only in the case of highly forward-directed scattering (

*g*>0.9), which applies only to certain tissue types including some types of epithelia, when the physical penetration depth is not limited by

*l*

_{s}any longer and substantially increased. In this case, if a short penetration depth is desirable, T can be reduced by choosing

*R*<

*l*

_{s}’, as discussed above.

## 4. Discussion

*a priori*surprisingly short depth of penetration of polarization-gated signal.

### 4.1 Relationship between the radial intensity distribution and the depth of penetration of polarization gating

5. S. L. Jacques, J. R. Roman, and K. Lee, “Imaging superficial tissues with polarized light,” Lasers Surg. Med. **26**, 119–129 (2000). [CrossRef] [PubMed]

11. J. M. Schmitt, A. H. Gandjbakhche, and R. F. Bonner, “Use of polarized-light to discriminate short-path photons in a multiply scattering medium,” Appl. Opt. **31**, 6535–6546 (1992). [CrossRef] [PubMed]

12. S. G. Demos and R. R. Alfano, “Optical polarization imaging,” Appl. Opt. **36**, 150–155 (1997). [CrossRef] [PubMed]

24. D. Bicout, C. Brosseau, A. S. Martinez, and J. M. Schmitt, “Depolarization of multiply scattered waves by spherical diffusers - Influence of the size parameter,” Phys. Rev. E **49**, 1767–1770 (1994). [CrossRef]

*P*

_{‖}(

*r*) and

*P*

_{⊥}(

*r*) of photons emerging from the surface. Figure 5(a) shows a typical example of the spatial intensity distributions for co-polarized, cross-polarized and differential polarized signals,

*P*

_{‖}(

*r*),

*P*

_{⊥}(

*r*) and Δ

*P*(

*r*)=

*P*

_{‖}(

*r*) -

*P*

_{⊥}(

*r*), respectively, at

*g*=0.809,

*µ*

_{s}=200 cm

^{-1}and

*µ*

_{a}=0.1 cm

^{-1}. As evident from Fig. 5(a), for

*r*<

*l*

_{s}’, which correspond to relatively short photon path lengths, the intensity of the co-polarized signal is much higher than that of the cross-polarized signals. This result indicates that the polarization of photons emerging at short radial distance

*r*from the point of incidence is mostly preserved, i.e.

*P*

_{‖}(

*r*)≫

*P*

_{⊥}(

*r*). However, when

*r*>

*l*

_{s}’,

*P*

_{‖}(

*r*)~

*P*

_{⊥}(

*r*) and Δ

*P*(

*r*)→0 (i.e. Δ

*P*(

*r*>

*l*

_{s}’)≪Δ

*P*(

*r*<

*l*

_{s}’)), indicating that these photons have approximately equal probability of emerging from the tissue surface either in co-polarized or cross-polarized state. Thus, because

*ΔI*(

*r*)=

*ΔP*(

*r*′)

*dr*′, we conclude that the short depth of penetration of polarization gating is due to the fact that the differential polarization signal primarily selects photons emerging from the surface of the medium within only a few mean free path lengths from the point of incidence (Fig. 5(a)). In turn, such reduction of the effective collection area ensures that the photons contributing to the polarization-gated signal can emerge only from relatively short depths. Indeed, the relationship between the radial intensity distribution and the corresponding penetration depth is well known and further illustrated in Fig. 5(b). This color intensity map shows the logarithm of the probability density distribution of photons as a function of optical depth at each radial distance r. This figure clearly demonstrates that the photons emerging at a few mean free path lengths do not penetrate the medium deeper than a few

*l*

_{s}.

### 4.2 The effect of optical properties on the radial intensity distribution of polarization-gated signal

*W*also result in a shorter penetration depth. The effect of

*µ*

_{a},

*µ*

_{s},

*g*, and

*R*on the depth of penetration of polarization gating can be understood based on how these parameters affect the width of Δ

*P*(

*r*). In particular, the width of Δ

*P*(

*r*) is independent of

*µ*

_{s}, and, therefore, scattering coefficient does not affect the optical penetration depth. On the other hand, higher absorption attenuates long photon paths and, thus, reduces the width of Δ

*P*(

*r*) as well as T. Moreover, in a highly forward scattering regime (

*g*>0.9), polarization is preserved for longer light paths [25

25. V. Sankaran, M. J. Everett, D. J. Maitland, and J. T. Walsh, “Comparison of polarized-light propagation in biological tissue and phantoms,” Opt. Lett. **24**, 1044–1046 (1999). [CrossRef]

*P*(

*r*) and T. Finally, the effect of light collection radius

*R*on T can be viewed as due to the dependence

*W*on

*R*. For

*R*>

*l*

_{s}’,

*W*is essentially independent of R and, thus,

*T*does not change with

*R*. On the other hand, for

*R*<

*l*

_{s}’,

*W*is approximately proportional to

*R*, and the depth of penetration can be controlled by choosing an appropriate

*R*.

## 5. Conclusion

*R*<

*l*

_{s}’,

*µ*

_{a}is not much smaller than

*µ*

_{s}, and

*g*<0.9. These conditions are satisfied in many tissue optics applications. However, outside this domain the penetration depth of polarization gating increases with

*R*,

*g*, and 1/

*µ*

_{a}. We found that the penetration depth has a relatively weak dependence on either

*R*or

*µ*

_{a}. Although the effect of

*g*is more pronounced, it is only in the case of highly forward-directed scattering (

*g*>0.9), which applies only to a few specialized tissue types, when the penetration depth is not limited by

*l*

_{s}any longer and substantially increased. In this case, if a short penetration depth is desired, it can be reduced by limiting the area of light collection to

*R*<

*l*

_{s}’.

*in vivo*. The size of such probes is restricted to a few hundreds of microns or a few millimeters. In this particular scenario, the penetration depth of differential polarization signal is not expected to depend strongly on the specifics of the optical properties of tissue and is on the order of one mean free path, which is in good agreement with the previously reported values [1

**5**, 302–317 (1999), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-5-13-302. [CrossRef] [PubMed]

**9**, 243–257 (2003). [CrossRef]

**5**, 1019–1026 (1999). [CrossRef]

## Acknowledgments

## References and Links

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5. | S. L. Jacques, J. R. Roman, and K. Lee, “Imaging superficial tissues with polarized light,” Lasers Surg. Med. |

6. | Y. Kim, Y. Liu, R. K. Wali, H. K. Roy, M. J. Goldberg, A. K. Kromine, K. Chen, and V. Backman, “Simultaneous measurement of angular and spectral properties of light scattering for characterization of tissue microarchitecture and its alteration in early precancer,” IEEE J. Sel. Top. Quantum Electron. |

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9. | V. Backman, R. Gurjar, K. Badizadegan, L. Itzkan, R. R. Dasari, L. T. Perelman, and M. S. Feld, “Polarized light scattering spectroscopy for quantitative measurement of epithelial cellular structures in situ,” IEEE J. Sel. Top. Quantum Electron. |

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11. | J. M. Schmitt, A. H. Gandjbakhche, and R. F. Bonner, “Use of polarized-light to discriminate short-path photons in a multiply scattering medium,” Appl. Opt. |

12. | S. G. Demos and R. R. Alfano, “Optical polarization imaging,” Appl. Opt. |

13. | V. Backman, M. B. Wallace, L. T. Perelman, J. T. Arendt, R. Gurjar, M. G. Muller, Q. Zhang, G. Zonios, E. Kline, T. McGillican, S. Shapshay, T. Valdez, K. Badizadegan, J. M. Crawford, M. Fitzmaurice, S. Kabani, H. S. Levin, M. Seiler, R. R. Dasari, I. Itzkan, J. Van Dam, and M. S. Feld, “Detection of preinvasive cancer cells,” Nature |

14. | H. K. Roy, Y. Liu, R. K. Wali, Y. Kim, M. J. Goldberg, A. K. Kromine, and V. Backman, “Four-dimensional elastic light scattering fingerprints as preneoplastic markers in the rat model of colon carcinogenesis,” Gastroenterology |

15. | A. Wax, C. H. Yang, M. G. Muller, R. Nines, C. W. Boone, V. E. Steele, G. D. Stoner, R. R. Dasari, and M. S. Feld, “In situ detection of neoplastic transformation and chemopreventive effects in rat esophagus epithelium using angle-resolved low-coherence interferometry,” Cancer Res. |

16. | L.-H. Wang, S. L. Jacques, and L.-Q. Zheng, “MCML - Monte Carlo modeling of photon transport in multi-layered tissues,” Comput. Methods Programs Biomed. |

17. | S. Bartel and A. H. Hielscher, “Monte Carlo simulation of the diffuse backscattering Mueller matrix for highly scattering media,” Appl. Opt. |

18. | F. Jaillion and H. Saint-James, “Description and time reduction of a Monte Carlo code to simulate propagation of polarized light through scattering media,” Appl. Opt. |

19. | M. J. Rakovic, G. W. Kattawar, M. Mehrubeoglu, B. D. Cameron, L. V. Wang, S. Rastegar, and G. L. Cote, “Light backscattering polarization patterns from turbid media: theory and experiment,” Appl. Opt. |

20. | X. Wang and L. Wang, “Propagation of polarized light in birefringent turbid media: A Monte Carlo study,” J. Biomed. Opt. |

21. | X. Wang, G. Yao, and L.-H. Wang, “Monte Carlo model and single-scattering approximation of polarized light propagation in turbid media containing glucose,” Appl. Opt. |

22. | G. Yao and L. V. Wang, “Propagation of polarized light in turbid media: simulated animation sequences,” Opt. Express |

23. | B. C. Wilson and S. L. Jacques, “Optical reflectance and transmittance of tissues - principles and applications,” IEEE J. Quantum Electron. |

24. | D. Bicout, C. Brosseau, A. S. Martinez, and J. M. Schmitt, “Depolarization of multiply scattered waves by spherical diffusers - Influence of the size parameter,” Phys. Rev. E |

25. | V. Sankaran, M. J. Everett, D. J. Maitland, and J. T. Walsh, “Comparison of polarized-light propagation in biological tissue and phantoms,” Opt. Lett. |

**OCIS Codes**

(170.0170) Medical optics and biotechnology : Medical optics and biotechnology

(260.5430) Physical optics : Polarization

(290.1350) Scattering : Backscattering

**ToC Category:**

Research Papers

**History**

Original Manuscript: November 23, 2004

Revised Manuscript: January 14, 2005

Published: January 24, 2005

**Citation**

Yang Liu, Young Kim, Xu Li, and Vadim Backman, "Investigation of depth selectivity of polarization gating for tissue characterization," Opt. Express **13**, 601-611 (2005)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-2-601

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### References

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