Informatics in Medicine Unlocked 18 (2020) 100285 Available online 28 December 2019 2352-9148/© 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Optothermal tissue response for laser-based investigation of thyroid cancer Michael O. Okebiorun, Sherif H. ElGohary * Department of Biomedical Engineering and Systems, Faculty of Engineering, Cairo University, 12613, Cairo, Egypt A R T I C L E INFO Keywords: 3D modelling Optothermal Finite element Thyroid cancer Monte Carlo ABSTRACT To characterize thyroid cancer imaging-based detection, we implemented a simulation of the optical and thermal response in an optical investigation of thyroid cancer. We employed the 3D Monte Carlo method and the bio-heat equation to determine the fluence and temperature distribution via the Molecular Optical Simulation Environ- ment (MOSE) with a Finite element (FE) simulator. The optothermal effect of a neck surface-based source is also compared to a trachea-based source. Results show fluence and temperature distribution in a realistic 3D neck model with both endogenous and hypothetical tissue-specific exogenous contrast agents. It also reveals that the trachea illumination has a factor of ten better absorption and temperature change than the neck-surface illu- mination, and tumor-specific exogenous contrast agents have a relatively higher absorption and temperature change in the tumors, which could be assistive to clinicians and researchers to improve and better understand the region’s response to laser-based diagnosis. 1. Introduction The thyroid gland is a crucial organ in the body as it is responsible for influencing body temperature, metabolism, and growth and develop- ment by the secretion of hormones such as thyroxine and thyroglobulin [1]. Autopsy studies have revealed the presence of thyroid nodules in 50% of the population, although 95% of these nodules are benign [2]. Assessment of these nodules are necessary as other studies have revealed the increase in the prevalence of thyroid cancers. Up until now, ultra- sound clinical scans have not been able to definitely classify these nodules into benign and malignant cases [3]. Therefore, fine needle aspiration (FNA) biopsy remains the safest and reliable thyroid cancer diagnostic technique [4]. Light-based diagnostic techniques have the potential of revealing more details in the diagnosis of thyroid cancer. This is due to photon properties such as: non-contact, non-invasive, potential for high- resolution and precise localization, wave tunability, polarization selec- tivity, and a variety of highly selective and specific light-tissue in- teractions [5]. These modalities usually employ lasers of wavelength between 500 and 1064 nm, and tissue response such as the absorption or thermal change can be measured and analyzed to generate images of the regions of interest. The optical absorption which defines the image contrast is determined by the presence of chromophores in the tissue. Haemoglobin, water, lipids, melanin, collagen, etc. are examples of these, with haemoglobin as the major in vivo chromophore due to its high absorption coefficient. In the detection of various cancers, exoge- nous contrast agents that improve optical properties have been pro- duced which upon intake can reveal more details. More specifically, contrast agents such as Indocyanine-green, Evans Blue, Gold nano- spheres, gold nanorods, gold nanoshells, etc. have been reported to help provide better spatial resolution and contrast in in vivo imaging [6–8]. Another idea is to identify tumor-specific biomarkers and compatible contrast agents which will help reveal more about the tumor in the re- gion of interest. The wavelength of the laser source will be set to the value that provides peak absorption of these contrast agents. Another study has revealed that two members of the metalloproteinase family (MMP), MMP-2 and MMP-9 are biomarkers for malignant thyroid le- sions [7]. This was visualized using an MMP-activatable photoacoustic probe with Alexa750 fluorescence as the exogenous contrast agent. Furthermore, the shape and position of the light source also determine the quality of the image produced in optical imaging. For example, the conventional method for prostate photoacoustic imaging is transrectal light illumination and pressure sensing, but Sherif et al. reported that transurethral light illumination and transrectal pressure sensing pro- duce better PA signals [9]. However, modelling of the fluence distribution in tissues have been quite challenging and various methods have been explored in this pro- cedure. The radiative transfer equation (RTE) has been regarded as the most accurate deterministic approach. This method however has a very high computational cost, although diffusion approximation has been * Corresponding author. E-mail address: sh.elgohary@eng1.cu.edu.eg (S.H. ElGohary). Contents lists available at ScienceDirect Informatics in Medicine Unlocked journal homepage: http://www.elsevier.com/locate/imu https://doi.org/10.1016/j.imu.2019.100285 Received 1 November 2019; Received in revised form 19 December 2019; Accepted 26 December 2019