Analysis of thyroid thermographic images for detection of thyroid tumor: An experimental-numerical study

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

Radiofrequency (RF) ablation represents an efficient strategy to reduce the volume of thyroid nodules. In this study, a finite element model was developed with the aim of optimizing RF parameters, e.g., input power and treatment duration, in order to achieve the target volume reduction rate (VRR) for a thyroid nodule. RF ablation is modelled as a coupled electro-thermal problem wherein the electric field is applied to induce tissue heating. The electric problem is solved with the Laplace equation, the temperature distribution is estimated with the Pennes bioheat equation, and the thermal damage is evaluated using the Arrhenius equation. The optimization model is applied to RF electrode with different active tip lengths in the interval from 5 mm to 40 mm at the 5 mm step. For each case, we also explored the influence of tumour blood perfusion rate on RF ablation outcomes. The model highlights that longer active tips are more efficient as they require lesser power and shorter treatment time to reach the target VRR. Moreover, this condition is characterized by a reduced transversal ablation zone. In addition, a higher blood perfusion increases the heat dispersion, requiring a different combination of RF power and time treatment to achieve the target VRR. The model may contribute to an improvement in patient-specific RF ablation treatment.

Finite element analysis to predict temperature distribution in the human neck with abnormal thyroid: A proof of concept

BACKGROUND AND OBJECTIVE

Hyperthyroidism, hypothyroidism, goiter and cancer are some of the dysfunctions that can occur concerning the thyroid, an important body homeostasis regulatory gland located in the cervical region. These disorders are mostly caused by changes in metabolism and can impair quality of life. This study presents a non-invasive approach that can detect changes in thyroid metabolism through the finite element analysis and medical images. The objective of this work was to develop a numerical model to represent the temperature distribution in the human neck with and without the presence of thyroid nodules. The patient-specific computational model for the case with thyroid nodules was calibrated with infrared thermography.

METHODS

A three-dimensional geometrical model of the neck was constructed based on the segmentation of magnetic resonance (MR) images. The Finite Element Method (FEM) was used to simulate heat diffusion and convection in the cervical region. The infrared thermography image was used to calibrate the heat transfer constants to obtain the surface temperature of the human neck model containing the enlarged thyroid with nodules. Subsequently, another case for the entire neck with an abnormally large thyroid without the nodules was simulated using the calibrated physical constants.

RESULTS

Results of the simulations with and without the presence of thyroid nodules were compared, showing the influence of the generation of heat from the nodules, allowing observation of the thermal differences on the cervical surface and at the thyroid itself. The model with nodules presented higher skin temperature distribution in the anterior triangle region when compared to the case without nodules. An average of 0.36^∘C of absolute error and 1% of relative error was obtained for the calibration between the simulated model and the infrared image.

CONCLUSIONS

This research consists of an innovative approach by comparing the results obtained via FEM simulation and the corresponding infrared image of the same neck region under study. Since there are great variability and uncertainties in the determination of the thermal constants, we applied a procedure for calibrating them based on a patient-specific case, which involves a multinodular goiter accompanied by hyperthyroidism. This proof-of-concept study allows the creation of comparative scenarios between the FEM simulations and the corresponding infrared image. Thus, it is expected that, in the future, this approach could be used to include the effect of drugs in the treatment strategies of thyroid diseases and disorders.

On the possibility of using temperature to aid in thyroid nodule investigation

Thyroid nodules are common, and their investigation is very important to exclude the possibility of cancer. The increase in blood vessels of malignant tumours may be related to local temperature augmentation detectable on the skin surface. The objective of this paper is to evaluate the feasibility of Infrared Thermography for cancer identification. For this purpose, two studies were performed. One used numerical modelling to simulate regional metabolic temperature propagation to evaluate whether a nodule is perceptible on the skin surface. A second study considered thyroid nodule identification by using convolutional neural networks (CNNs). First, variations in nodular size and fat thickness were investigated, showing that the fat layer has an important role in regional heat transfer. In the second study, the training process achieved accuracy of 96% for in-sample and 95% for validation. In the testing phase, 92% accuracy, 100% precision and 80% recall were achieved. Thus, the presented studies suggest the feasibility of using Infrared Thermography with the CNN Artificial Intelligence technique as additional information in the investigation of thyroid nodules for patients without a very thick subcutaneous fat layer.

Microstructure-based non-Fourier heat transfer modeling of HIFU treatment for thyroid cancer

BACKGROUND AND OBJECTIVES

High intensity focused ultrasound is an emerging non-invasive technique for the thermal ablation of cancer. Modeling of high intensity focused ultrasound as a method to induce hyperthermia, by considering non-equilibrium convective heat transfer has been under-represented in the previous studies. Therefore, in the present study, we aimed to study the effect of blood vessels during high intensity focused ultrasound ablation of thyroid cancer. In addition, high intensity focused ultrasound modeling was greatly improved by considering non-Fourier heat transfer.

METHODS

The modified dual-phase-lag model was used for the modeling of heat transfer in thyroid cancer during the ultrasound irradiation. The model parameters were linked with the tissue's microstructure parameters. Meanwhile, an interfacial convective heat transfer was considered between the blood vessels and the extravascular matrix. The extent of the vascular region was determined using the field emission scanning electron microscopy images. The non-linear Westervelt equation was solved for the sound wave to determine the heat source for the induced hyperthermia treatment.

RESULTS

Referring to the acoustic results, sharp-wave ripples were observed due to the inclusion of notable amplitudes of excited harmonics. The thermal results showed a maximum temperature rise of 25.08°C and 51.47°C at the powers of 5 W and 10 W using the modified dual-phase-lag model, while the Pennes model predicted a temperature rise of 28.77°C and 55.5°C at the same powers. It was also concluded that a constant blood temperature, overestimates the dissipated energy and the temperature reduction during the cooling period, as a 15% deviation in the tumor temperature was observed from the non-equilibrium state at 10.65 s exposure and 10 W power. Eventually, the calculation of the ablated volumes indicated that the volumes were up to 4.5 times larger by the Pennes model compared to the modified dual-phase-lag model.

CONCLUSIONS

It can be concluded from the results that there should be a serious concern on the high intensity focused ultrasound modeling based on the parameters of blood vessels. Based on the thermal maps, the cancerous tissue should be exposed to a higher energy level of ultrasound waves in order to cause the desired damage against the estimated energy level predicted by the Pennes model.

Infrared Thermographic Evaluation of Temperature Modifications Induced during Implant Site Preparation with Steel vs. Zirconia Implant Drill

Background: The heat produced during implant site osteotomy can potentially interfere with and influence the osseointegration process of a dental implant. The objective of this in vitro investigation was to measure the temperature changes during simulated osteotomies in bovine rib bone. The measurements were made at the apical area of the osteotomies with steel implant drills compared to zirconia implant drills. Methods: Steel cylindrical drills (2 mm) and zirconia cylindrical drills (2 mm) were evaluated in vitro using bovine rib bone for a total of five groups based on the number of osteotomies performed with each drill: 10, 20, 40, 90, or 120 osteotomies. Bone and apical drill temperatures were measured by means of infrared thermography. The drilling time for each osteotomy was measured for each preparation. Results: Statistically significant differences were found in the temperature measurements in the bone and apical portion of the drills between the study groups (p < 0.05). A statistically significant difference was observed for drilling time preparation between steel cylindrical drill (2 mm) and zirconia cylindrical drills (2 mm) (p < 0.01). Conclusions: The drill material has an impact on the temperature changes that occur at its apical portion during bone preparation for implant placement.