Medical Engineering & Physics 26 (2004) 363–369 www.elsevier.com/locate/medengphy Optical characterization of mammalian tissues by laser reﬂectometry and Monte Carlo simulation D. Kumar, R. Srinivasan, Megha Singh  Biomedical Engineering Division, Indian Institute of Technology, Chennai 600 036, India Received 7 January 2003; received in revised form 3 December 2003; accepted 19 February 2004 Abstract The optical characterization of various goat organs/tissues, by measurement of the spatial variation of the diﬀuse reﬂectance from the surface by laser multi-probe reﬂectometer, is carried out. For determination of the optical parameters, these proﬁles are matched by iterative procedures with that obtained by Monte Carlo simulation by best-ﬁt procedure with chi value 0.99. The ﬁrst set of measurements is carried out with milk phantom. Thereafter, the absorption and scattering coeﬃcients and anisotropy para- meter of goat’s heart, lungs, kidney, liver, spleen, skeletal muscle, brain and adipose tissues are measured. These parameters vary over a wide range, which is in agreement with results reported by others. Based on these data, their laser scattering proﬁles along the depth in terms of depth of penetration (DP) and maximum scattered beam width (MSBW) are determined. These are maximum (0.030 and 0.038 m) for kidney and minimum (0.007 and 0.006 m) for spleen, respectively. The backscattered intensity measured 0.002, 0.004 and 0.006 m away from the beam entry point shows the maximum contribution from the respective depths, irrespective of the nature of the organs/tissues. # 2004 IPEM. Published by Elsevier Ltd. All rights reserved. Keywords: Biological tissues; Laser reﬂectometry; Monte Carlo simulation; Optical parameters; Surface and depth proﬁles 1. Introduction Laser radiation possesses unique characteristics and is extensively used in clinical sciences for diagnostic and therapeutic applications. These applications are dependent on the optical characteristics of target tissues and organs [1]. The light beam incident upon soft tissues (human breast) is backscattered, absorbed and transmitted, whereas, for thicker tissues (human forearm), a part of this is backscattered and the remaining portion is absorbed. These processes depend upon skin pigmentation, tissue composition, blood content and the structural nature of collagen ﬁbers, which determine the spatial distribution of photons within the irradiated tissues. The light absorption is mainly attributed to tissue pigments such as melanin, bilirubin, hemoglobin, etc. Similarly, the discontinuities in refractive index at microscopic level lead to scatter- ing from the tissues. The absorption and scattering of photons from bio- logical tissues are characterized by the absorption coef- ﬁcient and scattering coeﬃcient representing the attenuation of incident radiant intensity due to absorp- tion and scattering per incremental unit photon path length in a tissue. The variation of anisotropy para- meter shows the directional dependence of the scatter- ing process, given as 1, 0 and 1 for backward, isotropic and forward scattering, respectively [2]. Thus, by description of these processes in terms of their optical parameters, biological tissues could be char- acterized. The most common technique for direct measurement of these parameters is the double inte- gration sphere [3], but due to its speciﬁc requirement of tissue samples, this could not be applied to intact organs. For this purpose, indirect techniques are found to be more appropriate. These are based on the experi- mental measurement of spatial variation of reﬂectance proﬁle on the tissue surface, followed by its matching  Corresponding author. Tel.: +91-4422578176. E-mail addresses: msingh@iitm.ac.in, msingh_iitm@yahoo.com (M. Singh). 1350-4533/$ - see front matter # 2004 IPEM. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.medengphy.2004.02.012