The optical properties of biological tissue are important for photodynamic therapy and diagnostic techniques. Typically, optical properties are obtained using solutions of the radiative transport equation that express the optical properties in terms of readily measurable quantities. These solutions are either exact or approximate and correspond to the direct or indirect methods described by Wilson et al. Direct methods place stringent constraints on the sample to match the assumptions made for exact solution. For example, the direct method used by Flock et al.  required very thin samples in which multiple scattering could be ignored. Indirect methods relax the sample constraints but require approximations that are often invalid for tissue samples (e.g., nearly isotropic scattering or no internal reflection at the boundaries). The theory used in indirect methods usually falls into one of three categories: Beer's law, Kubelka-Munk, or the diffusion approximation.

Beer's law neglects scattering and is inappropriate for thick scattering materials. The Kubelka-Munk method and variants are still used, but are limited in their accuracy. Methods based on the diffusion approximation or a similar approximation (e.g., uniform radiances over the forward and backward hemispheres) tend to be more accurate than Kubleka-Munk. Techniques using the diffusion approximation include pulsed photothermal radiometry, time resolved spectroscopy, radial reflectance spectroscopy, weak localization, and an iterative technique that uses reflection and transmission measurements. These methods remain popular because they are easy to use, place relatively minor constraints on the type of sample, and are amenable to analytic manipulation. However, the diffusion approximation assumes that the internal radiance is nearly isotropic and consequently it is a poor approximation when scattering is comparable to absorption.

The IAD method consists of the following steps (1) Guess a set of optical properties; (2) Calculate the reflection and transmission using the adding-doubling method; (3) Compare the calculated values with the measured reflection and transmissions; and then (4) Repeat until a match is made. The set of optical properties that generates reflection and transmission values matching the measured values is taken as the optical properties of the sample. The results obtained using the IAD method are accurate for all optical properties and can be made arbitrarily precise at the cost of increased computation time. Furthermore, by avoiding an analytical solution, it is possible to incorporate the necessary corrections for measurements made with integrating spheres directly. Such corrections are usually quite awkward to implement analytically because the magnitude of the correction depends on the optical properties of the sample measured.


A. Dayton, "Light-Guided Lumpectomy: Visual and Frequency Domain Localization of Breast Lesions", Oregon Health & Science University, (2013).


J. A. Delgado Atencio, S. A. Prahl, S. Vázquez y Montiel, M. Cunill Rodríguez, F. Gutierrez Delgado, J. Castro Ramos, "Theoretical analysis and experimental validation of a two-fiber probe for biomedical spectroscopy applications," International Commission for Optics 22 General Congress, (2011, poster).

B. Morales Cruzado, S. A. Prahl, J. A. Delgado Atencio, S. Vázquez y Montiel, "Validation of GA-MCML algorithm against IAD program," International Commission for Optics 22 General Congress, (2011, poster).

S. A. Prahl, C. Y. Chen, V. Keränen, J. L. Ferracane, "Dynamic Optical Properties of Dental Composites," IADR/AADR/CADR 89th General Session, 90A, (2011, abstract only).

J. C. Ramella-Roman, A. Nayak, S. A. Prahl, "A Spectroscopic sensitive polarimeter for biomedical applications," J. of Biomedical Optics, 16, 047001 (2011).

M. Cunill Rodríguez, J. A. Delgado Atencio, S. Vázquez y Montiel, B. Morales Cruzado, S. A. Prahl, J. Castro Ramos, "Theoretical-Experimental Analysis of a Video Reflectometry Setup," International Commission for Optics 22 General Congress, (2011, poster).


A. Dayton, N. Choudhury, S. A. Prahl, "Light Guided Lumpectomy: Is Continuous Wave or Frequency Domain More Accurate," SPIE Proceedings on Biomedical Applications of Light Scattering IV, 7573, (2010).

A. Dayton, N. Choudhury, S. A. Prahl, "Measuring distance through turbid media: A simple frequency domain approach," SPIE Proceedings on Advanced Biomedical and Clinical Diagnostic Systems VIII, 7555, (2010).

Z. Eskandarian, S. Prahl, A. Douplik, "Theoretical and experimental estimation of anisotropy factor for mixed scatterers," Saratov Fall Meeting, Joint Workshop on Microscopic and Low-Coherence Methods in Biomedical and Non-Biomedical Applications III, (2010 abstract only).

V. T. Keränen, A. L. Dayton, S. A. Prahl, "Polyurethane phantoms with homogeneous and nearly homogeneous optical properties," SPIE Proceedings on Design and Performance Validation of Phantoms used in Conjunction with Optical Measurement of Tissue, 7567D, 1-4 (2010).


V. T. J. Keränen, A. J. Mäkynen, S. A. Prahl, M. T"ormänen, "A Scattering Measurement System to Determine the Optical Characteristics of Industrial Suspensions," Proceedings of the International Instrumentation and Measurement Technology Conference, 2009. I2MTC `09. IEEE, 570-573 (2009).


Y.-C. Chen, Z. Wang, M. Yan, S. A. Prahl, "Fluorescence Anisotropy Study of Molecularly Imprinted Polymers," Luminescence, 21, 7-14 (2006).


P. R. Bargo, S. A. Prahl, T. T. Goodell, R. A. Sleven, G. Koval, G. Blair, S. L. Jacques, "In vivo determination of optical properties of normal and tumor tissue with white light reflectance and an empirical light transport model during endoscopy," J. Biomedical Optics, 10, 034018-1-034018-15 (2005).


Y.-C. Chen, J. Brazier, M. Yan, S. A. Prahl, "Steady-State Fluorescence Anisotropy Studies Of Molecularly Imprinted Polymer Sensors," Proceedings of the Oregon Academy of Science, 40, 49 (2004 abstract only).


P. R. Bargo, S. A. Prahl, S. L. Jacques, "Optical Properties Effects upon the Collection Efficiency of Optical Fibers in Different Probe Configurations," IEEE J. Selected Topics Quantum Electron., 9, 314-321 (2003).

Y.-C. Chen, Z. Wang, M. Yan, S. A. Prahl, "Steady-State Fluorescence Anisotropy Studies of Molecularly Imprinted Polymer Sensors," Materials Research Society Proceedings of Organic, Soft, and Biological Materials --- Molecularly Imprinted Materials, 787, (2003).

T. P. Moffitt, S. A. Prahl, "A Dual Sized-Fiber Reflection Probe for Decreased Measurement Variability," Proceedings of the Oregon Academy of Science, 39, 40 (2003 abstract only).


T. P. Moffitt, S. A. Prahl, "Determining the Reduced Scattering of Skin in Vivo Using Sized-Fiber Reflectometry," SPIE Proceedings on Optical Biopsy IV, 4613, 254-263 (2002).

T. P. Moffitt, S. A. Prahl, "In Vivo Optical Properties of Skin Using Sized-Fiber Reflectometry," Proceedings of the Oregon Academy of Science, 38, 47 (2002 abstract only).

T. P. Moffitt, S. A. Prahl, "In Vivo Determination of Optical Properties of Skin in the UV Using Sized-Fiber Reflectometry," Laser Med. Surg., S14, 3 (2002 abstract only).


T. P. Moffitt, S. A. Prahl, "Sized-Fiber Reflectometry for Measuring Local Optical Properties," IEEE JSTQE, 7, 952-958 (2001).


M.-A. Descalle, S. L. Jacques, S. A. Prahl, T. L. Laing, W. R. Martin, "Measurements of Ligament and Cartilage Optical Properties at 351 nm, 365 nm, and in the Visible Range(440 to 800 nm)," SPIE Proceedings of Laser-Tissue Interaction, Tissue Optics, and Laser Welding III, 3195, 280-286 (1998).

H. Shangguan, S. A. Prahl, S. L. Jacques, L. W. Casperson, K. W. Gregory, "Pressure Effects on Soft Tissues Monitored by Changes in Tissue Optical Properties," SPIE Proceedings of Laser-Tissue Interaction IX, 3254, 366-371 (1998).


D. D. Royston, R. S. Poston, S. A. Prahl, "Optical Properties of Scattering and Absorbing Materials Used in the Development of Optical Phantoms at 1064 nm," J. Biomedical Optics, 1, 110-116 (1996).


S. A. Prahl, "The Adding-Doubling Method," Optical-Thermal Response of Laser Irradiated Tissue, chapter 5, 101-129 (1995).


J. W. Pickering, S. A. Prahl, N. van Wieringen, J. F. Beek, H. J. C. M. Sterenborg, M. J. C. van Gemert, "Double-Integrating-Sphere System for Measuring the Optical Properties of Tissue," Appl. Opt., 32, 399-410 (1993).

S. A. Prahl, M. J. C. van Gemert, A. J. Welch, "Determining the Optical Properties of Turbid Media by Using the Adding-Doubling Method," Appl. Opt., 32, 559-568 (1993).


J. W. Pickering, C. J. M. Moes, H. J. C. M. Sterenborg, S. A. Prahl, M. J. C. van Gemert, "Two Integrating Sphere with an Intervening Scattering Sample," J. Opt. Soc. Am. A, 9, 621-631 (1992).

S. A. Prahl, I. A. Vitkin, U. Bruggemann, B. C. Wilson, R. R. Anderson, "Determination of Optical Properties of Turbid Media Using Pulsed Photothermal Radiometry," Phys. Med. Biol., 37, 1203-1217 (1992).


S. A. Prahl, N. van Wieringen, M. J. C. van Gemert, A. J. Welch, "Iterated Adding-Doubling to Determine Optical Properties," Proceedings of the Optical Society of America, (1991 abstract only).


W. F. Cheong, S. A. Prahl, A. J. Welch, "A Review of the Optical Properties of Biological Tissues," IEEE J. Quantum Electron., 26, 2166-2185 (1990).

N. van Wieringen, S. A. Prahl, H. J. C. M. Sterenborg, M. J. C. van Gemert, "The Limitations of the Determination of the Optical Properties of Tissue Using a Double Integrating Sphere Set-Up with Collimated Incident Light," Lasers Med. Sci., 5, (1990 abstract only).


S. A. Prahl, A. J. Welch, M. P. Sartori, P. D. Henry, R. Roberts, G. L. Valderrama, K. Y. Jong, M. J. Berry, "Optical Properties of Normal Human Aorta from 200 to 2200 Nanometers," Lasers Surg. Med., 8, 142 (1988 abstract only).

S. A. Prahl, W. F. Cheong, G. Yoon, A. J. Welch, "Optical Properties of Human Aorta During Low Power Argon Laser Irradiation," SPIE Proceedings of Laser Interaction with Tissue, 908, 29-33 (1988).


W. F. Cheong, S. A. Prahl, A. J. Welch, M. J. C. van Gemert, C. R. Denham, "Optical Properties of Bladder Tissue and Optimal Dosage Predictions for Photoradiation Therapy," Lasers Surg. Med., 6, 190-191 (1986 abstract only).