A computational study on the role of parameters for identification of thyroid nodules by infrared images (and its comparison with real data)
Authors: Montero José R. González , Damião Charbel , Moran Maira B. H. , Fontes Cristina A. P. , Filho Rubens Cruz , Balarini Giovanna , Conci Aura 
Published: January 2021

According to experts and medical literature, a healthy thyroid gland, or a thyroid containing benign nodules, tend to be less inflamed and less active than one with malignant nodules. It seems to be a consensus that malignant nodules have more blood veins and it may be related to the maintenance of high and constant temperatures. Investigation of these characteristics, detectable by infrared sensors, and answering if they constitute patterns of malignancy are the aims of this work. Experiments considering biological heat transfer analysis by Finite Element numerical simulations are used to show the influence of nodule and patient characteristics on the identification of malignancy of thyroid nodule by thermography. The used and approved protocol for infrared examination are analyzed and simulated during all its phase that is on transient and steady state behavior, in order to verify how and when their influence can be really recognized in patients. Simulation results and the analysis of infrared exams show that the tissues between the skin and the thyroid, as well as the nodule size, have influence in superficial temperatures. Other thermal parameters of thyroid nodules are also investigated and show little influence on surface temperatures. These characteristics must be considered in nodular infrared analysis and diagnosis by thermography. The infrared examinations of patients that meet the hypotheses related to the vascularization of the nodule confirm the numerical results. All details of the physical parameters used in the simulations, characteristics of the nodules, and their complete thermal examinations are public and available, turning possible that the presented simulation could be compared with other types of heat transfer solutions. This study is a concrete contribution to the answer of under what conditions thermography can be useful in the identification of thyroid nodules.

Author summary

Thyroid nodules are very common health problems. These nodules may have different characteristics, and some of them could influence the temperature of the region. Many works in the medical literature report that the healthy thyroid and even benign nodules tend to be less inflamed and active than malignant nodules and therefore should exhibit some variation in patterns of behavior related to the temperature variation between them. The focus of this work is to analyze some parameters of the nodules and details of the patients that can influence the identification and diagnosis of thyroid nodules by infrared images. To reach the objective, simulations of bioheat transfer in the neck (using a simple neck geometry and Finite Elements Analysis in COMSOL Multiphysics Software) and real infrared examinations (performed with a FLIR Infrared Camera model SC620 and a proposed protocol) were analyzed. Our results show the thermal insulation effect of the neck fat tissue, and that the effect of nodule sizes can be decremented by a thicker layer of fat. The analysis of the nodule parameters as blood perfusion rate and metabolic heat, which could be related with the nodule vascularization (an important condition related with malignancy), suggest that the thermal effects of thyroid nodules on the neck surface are not sufficient to differentiate benign from malign, and for this other features or methods must be considered.