A Computational Study on the Role of Parameters for Identification of Thyroid Nodules by Infrared Images (and Comparison with Real Data)

Abstract

According to experts and medical literature, healthy thyroids and thyroids containing benign nodules tend to be less inflamed and less active than those with malignant nodules. It seems to be a consensus that malignant nodules have more blood veins and more blood circulation. This may be related to the maintenance of the nodule’s heat at a higher level compared with neighboring tissues. If the internal heat modifies the skin radiation, then it could be detected by infrared sensors. The goal of this work is the investigation of the factors that allow this detection, and the possible relation with any pattern referent to nodule malignancy. We aim to consider a wide range of factors, so a great number of numerical simulations of the heat transfer in the region under analysis, based on the Finite Element method, are performed to study the influence of each nodule and patient characteristics on the infrared sensor acquisition. To do so, the protocol for infrared thyroid examination used in our university’s hospital is simulated in the numerical study. This protocol presents two phases. In the first one, the body under observation is in steady state. In the second one, it is submitted to thermal stress (transient state). Both are simulated in order to verify if it is possible (by infrared sensors) to identify different behavior referent to malignant nodules. Moreover, when the simulation indicates possible important aspects, patients with and without similar characteristics are examined to confirm such influences. The results show that the tissues between skin and thyroid, as well as the nodule size, have an influence on superficial temperatures. Other thermal parameters of thyroid nodules show little influence on surface infrared emissions, for instance, those related to the vascularization of the nodule. All details of the physical parameters used in the simulations, characteristics of the real nodules and thermal examinations are publicly available, allowing these simulations to be compared with other types of heat transfer solutions and infrared examination protocols. Among the main contributions of this work, we highlight the simulation of the possible range of parameters, and definition of the simulation approach for mapping the used infrared protocol, promoting the investigation of a possible relation between the heat transfer process and the data obtained by infrared acquisitions.

Model-Optimizing Radiofrequency Parameters of 3D Finite Element Analysis for Ablation of Benign Thyroid Nodules

“…The simulated neck comprises skin, fat, muscle, thyroid, and an elliptic nodule within the thyroid lobe (Figure 1). The thickness of the different anatomical regions is in agreement with previous studies [31,34,35]. Specifically, we set a thickness of 1 mm for the skin, 6 mm for the fat region, 30 mm for the muscle, and 20 mm for the thyroid.…”

“…where k ref is the reference thermal conductivity of the tissue, r i = 0.0013 is a parameter that approximates the temperature dependence of k as in [36], T is the temperature, calculated during the simulation, and T ref = 37 • C is the body temperature. Table 2 lists the physical parameters considered for the RF electrode in agreement with the available literature [23,31]. Relative permittivity ε r (-) 1 1…”

“…Specifically, we set a thickness of 1 mm for the skin, 6 mm for the fat region, 30 mm for the muscle, and 20 mm for the thyroid. The dimensions of the thyroid nodule are within the ranges reported in the available literature [28,31] and are set in order to achieve a volume of the nodule equal to 20 mL, as in the study by Deandrea et al [7]. The simplified geometry is modelled by an extremely fine tetrahedral mesh with roughly 100 k elements.…”

“…where σ ref is the reference electrical conductivity of the tissue, p i = 1.5 percent and is the percentage of increase, in agreement with [36], T is the temperature, and T ref = 37 • C is the body temperature. [31,37] 0.21 [31,37] 0.49 [31,37] 0.52 [31,37] 0.89 [31] Density ρ (kg/m 3 ) 1109 [31,37] 911 [31,37] 1090 [31,37] 1050 [31,37] 1050 [31] Specific heat at constant pressure c p (J/kg•K) 3391 [31,37] 2348 [31,37] 3421 [31,37] 3609 [31,37] 3770 [ Metabolic heat Q m (W/m 3 ) 1829.85 [31] 464.61 [31] 1046 [31] 4200 [31] 42,000 [31] Frequency factor A (s Thermal conductivity varies as follows:…”

“…In addition, other studies considered the development of an FE model of the thyroid, but the simulations were focused on a different treatment method, e.g., focused ultrasound [29,30]. Other publications focused on the development of FE models of the neck region for the analysis of bioheat transfer in the human neck and subsequent comparison with images achieved with infrared thermography [25,31,32].…”