Lookup-table-based experimental inverse model for real-time skin tissue diagnostics

Abstract

A lookup table (LUT)-based inverse model was designed and used to analyze the property of in vivo skin tissues. The investigated wavelength range was from 400 nm to 1300 nm. The LUT was created based on experimental measurements of 35 tissue-simulating phantoms. This LUT was then used to fit measured values of 3 types of pig skin in an inverse model. The results show that this LUT-based inverse model can be used to adequately analyze the optical property of pigment and dark pigment skin tissues. However, this LUT-based inverse model is not suitable to analyze the optical properties of non-pigment skin, because the maximum value of the diffuse reflectance spectrum in LUT is less than the measured diffuse reflectance spectrum of non-pigment skin. In addition, the fitting method for the LUT and the optimization routine need further improvement.

Popular Abstract

Nowadays, optics properties of a tissue become an important tool for both diagnostics and therapeutics applications. When light is emitted into a tissue, optical properties of that tissue can affect the penetration depth of light and the amount of light escaping from the tissue. This process includes both absorption and scattering of light, which are two main characteristics of optics properties. The absorption of light is due to different chromophores that absorbing light in tissue. The intensity of light will attenuate when passing through it. The scattering of light is due to some cells and fibers that scattering light and change the direction of light propagation [1]. It depends on the structure of tissue as well [2]. Specially, skin is a layered tissue. It can be divided into three layers: the epidermis, dermis and subcutaneous tissue layers [1]. In epidermis layer, melanin is the main absorber. It has thickness around 100 μm. Hemoglobin is the dominant absorption component for dermis layer, which has thickness around 1.5 mm. The subcutaneous tissue layer has thickness around few millimeters, consisting of a large number of fat cells. The penetration depth of visible light can reach the subcutaneous layer to some extent. In general, different tissues contain different chromophores, scattering components and structures. Furthermore, optical properties of healthy and diseased tissues are different as well. Therefore, it is important to measure the spectrum that reflecting optical properties of tissue, which can be further used to distinguish tumor tissue and therapeutics applications.
The spectra reflecting optical properties of tissue is diffuse reflectance spectrum, which detects the light escaping from tissue. To analyze optical properties in this spectrum, one method is to use the diffusion approximation of the transport equation, the other one is using lookup table [3, 4, 5]. The theoretical equation can analyze diffuse reflectance in limit situation. The lookup table contains diffuse reflectance, absorption and scattering properties which are already known. It can be obtained either by experimental measurement, or by Monte Carlo simulation [6]. Monte Carlo simulation has become a prevailed method. It can model complex structure of tissue. However, the long computing time is a disadvantage. Experiment measurement can capture complete behavior of phantoms and environment without approximation. Meanwhile, the accuracy of measurement depends on the investigator. In this project, lookup table based on experimental measurement is used to analyze the diffuse reflectance spectra ranged from 400 nm to 1300 nm. It is created by 35 phantom measurements, and further fitted to a polynomial expression by using standard routines in Matlab. Finally, modeled diffuse reflectance spectra are compared with the in vivo measurements of three types of pig skin, which are non-pigment, pigment and dark pigment skins.

Reference
[1] Maeda, T., Arakawa, N., Takahashi, M., & Aizu, Y. (2010), Monte Carlo simulation of spectral reflectance using a multilayered skin tissue model, Optical review, 17(3), 223-229.
[2] Forrester KR, Shymkiw R, Yeung G, Irwin P, Tulip J, Bray RC, Spatially resolved diffuse reflectance for the determination of tissue optical properties and metabolic state, InBiOS 2000 The International Symposium on Biomedical Optics 2000 Jun 13 (pp. 333-344), International Society for Optics and Photonics.
[3] Rajaram N, Nguyen TH, Tunnell JW, Lookup table-based inverse model for determining optical properties of turbid media, Journal of biomedical optics, 2008 Sep 1;13(5):050501-1.
[4] Farrell TJ, Patterson MS, Wilson B, A diffusion theory model of spatially resolved, steady-state diffuse reflectance for the noninvasive determination of tissue optical properties in vivo, Medical physics, 1992 Jul 1;19(4):879-88.
[5] Nichols BS, Rajaram N, Tunnell JW, Performance of a lookup table-based approach for measuring tissue optical properties with diffuse optical spectroscopy, Journal of biomedical optics, 2012 May 1;17(5):0570011-8.
[6] Palmer GM, Ramanujam N, Monte Carlo-based inverse model for calculating tissue optical properties, Part I: Theory and validation on synthetic phantoms, Applied optics, 2006 Feb 10;45(5):1062-71.

• author: Li, Xueying
• supervisor: Nina Reistad
• organization: Department of Physics; Atomic Physics
• course: FYSM30 20162
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: Lookup-table, Phantom, Absorption coefficient, Reduce scattering coefficient, Diffuse reflectance spectrum, Collimated transmission spectroscopy, in vivo, Skin tissue, Forward model, Inverse mode
• language: English
• id: 8923741
• date added to LUP: 2022-01-28 09:33:43
• date last changed: 2022-01-28 09:33:43