Digital Thermal Imaging Research Articles

Results of a Study for Spatiotemporal Cloudiness Emission Structures in the LWIR Range

The results of experimental studies for the spatiotemporal structures of cloudiness emission in the LWIR (long-wave infrared) range using thermal imaging equipment are presented. Video streams with a minimum frequency of 50 Hz lasting more than 40 minutes, representing a sequence of digital thermal images for the sky fixed area, were used as initial data. In the process of studying, the spatiotemporal structures of cloudiness emission, time intervals (correlation radii) were estimated, the cross-correlation coefficients between frames of video streams being decreased from 1 to 0.5 during them. It has been established that for weather situations characterized by the cumulus cloudiness amount presence of (1–3) points, (4–6) points, and (7–9) points, the correlation radii are (45–75) s, (3–4) min and (5–6) min, respectively. For other types of atmospheric background (with altocumulus, cumulonimbus cloudiness and clear sky), the correlation radius exceeded the video recording time, i.e. such weather situations have a low rate of complete renewal for the cloudiness form.

A machine learning system to identify progress level of dry rot disease in potato tuber based on digital thermal image processing

This study proposed a quick and reliable thermography-based method for detection of healthy potato tubers from those with dry rot disease and also determination of the level of disease development. The dry rot development inside potato tubers was classified based on the Wiersema Criteria, grade 0 to 3. The tubers were heated at 60 and 90 °C, and then thermal images were taken 10, 25, 40, and 70 s after heating. The surface temperature of the tubers was measured to select the best treatment for thermography, and the treatment with the highest thermal difference in each class was selected. The results of variance analysis of tuber surface temperature showed that tuber surface temperature was significantly different due to the severity of disease development inside the tuber. Total of 25 thermal images were prepared for each class, and then Otsu’s threshold method was employed to remove the background. Their histograms were extracted from the red, green, and blue surfaces, and, finally, six features were extracted from each histogram. Moreover, the co-occurrence matrix was extracted at four angles from the gray level images and five features were extracted from each co-occurrence matrix. Totally, each thermograph was described by 38 features. These features were used to implement the artificial neural networks and the support vector machine in order to classify and diagnose the severity of the disease. The results showed that the sensitivity of the models in the diagnosis of healthy tubers was 96 and 100%, respectively. The overall accuracy of the models in detecting the severity of tuber tissue destruction was 93 and 97%, respectively. The proposed methodology as an accurate, nondestructive, fast, and applicable system reduces the potato loss by rapid detection of the disease of the tubers.

Clinical utility of smartphone-based digital infrared thermal imaging in predicting vascular compromise in free flaps

Abstract Background: Flap monitoring plays an important role in avoiding morbidity in free flap. Clinical monitoring is considered the gold standard, but it is subjective. Digital thermal imaging captures and displays the infrared radiation emitted from an object. This is useful in assessing temperature difference between two surfaces, as well as variation of temperature. Smartphone thermal imaging can be used to assess the tissue perfusion, which requires little training. Materials and Methods: The aim was to assess the validity of Digital Thermal Imaging in early diagnosis of flap failure, compared to conventional clinical methods. Eleven patients of microvascular-free flap reconstruction for defects following malignancy and trauma were included in the study for January 25, 2019–March 25, 2021. Flaps were monitored using three different methods – clinical monitoring, biochemical monitoring, and digital thermal imaging done at the following interval: (1) intraoperative (end of surgery), (2) hourly – for the first 48 h, (3) every 4th hourly on postoperative days 3–5, and (4) every 6th hourly on postoperative days 5–10, and the results were tabulated. Results: Flap temperature was observed to be higher compared to the surrounding skin when there was an event of venous thrombosis. The surrounding skin temperature was to be measured on the side opposite to the side where the flap was raised to do vascular anastomosis. The increase in the temperature difference almost coincided with the clinical and biochemical indicator of failing flaps. Conclusion: Monitoring of the flap temperature and comparing it with the surrounding skin temperature can be incorporated along with the gold standard. It is a simple, objective, and noncontact method compared to clinical monitoring and biochemical methods. A large sample size, multicentric, randomized controlled study is required to validate the same.

The Thermal Image of Sun Orientation and Openings in Residential Buildings with Modern Tropical Design Concept in Medan City

This study aims to analyze thermal imagery of the sun's orientation and the formation of openings in residential houses with a modern tropical design concept in Medan. The method used is temperature measurement and building thermal identification using a digital thermal imaging tool, namely Flir CX-3, which is carried out during the day, as well as measuring the WWR (window-to-wall ratio) value of the building. The results of the thermal image analysis show that the North-South orientation gets lower temperatures compared to the East-West orientation, even though it has a larger WWR value of 12.9% and 20.9%. Based on the results of this analysis, it is suggested to consider the orientation of the sun in designing residential houses in the city of Medan. Houses with a North-South orientation are the best choice for maximum thermal comfort and natural lighting, supported by large openings as one of the characteristics of modern tropical architecture.

A Randomized, Blinded and Controlled Study Using Digital Thermal Imaging to Measure Temperature Change Associated with Acupuncture in Dogs with Back Pain

Digital thermal imaging provides an objective and measurable evaluation of the changes in radiant energy emitted by the body. This study sought to determine the effects of acupuncture immediately after back pain treatment in dogs through digital thermal imaging. Dogs ≥ 6 months exhibiting clinical symptoms of back pain with pain scale 1 or 2 (0-4 scale) were recruited for the study. Subjects (n=24) were randomly assigned to the Acupuncture Group (n=12) which received dry needle acupuncture at GV-14, BL-23 bilateral, Bai-hui and Shen-shu for 15 minutes or the Control Group (n=12) which was not treated but waited 15 minutes. Digital thermal images were obtained before and after the acupuncture treatment (Acupuncture Group) or the waiting period (Control Group) by a person blinded to the group assignments. Maximal temperature was recorded within the affected surface area and absolute change of temperature was compared between study groups. Group comparison of subject signalment data, baseline pain score, and baseline (pre-treatment) temperature (all p-values > 0.05) suggested group comparability for the study. The mean±SD temperature change in the Acupuncture Group was 1.60±0.51°F, and in the Control group was 0.44±0.26°F. The overall temperature change difference between the two subject groups was statistically significant (p = 2.96×10-6). The results from this study indicate that local acupuncture treatment at a site of pain can lead to temperature changes in the location which may have effects on pain reduction. Future studies to investigate the association of acupuncture created temperature change and pain mitigation are warranted.

Thermal imaging potential and limitations to predict healing of venous leg ulcers

Area analysis of thermal images can detect delayed healing in diabetes foot ulcers, but not venous leg ulcers (VLU) assessed in the home environment. This study proposes using textural analysis of thermal images to predict the healing trajectory of venous leg ulcers assessed in home settings. Participants with VLU were followed over twelve weeks. Digital images, thermal images and planimetry of wound tracings of the ulcers of 60 older participants was recorded in their homes by nurses. Participants were labelled as healed or unhealed based on status of the wound at the 12th week follow up. The weekly change in textural features was computed and the first two principal components were obtained. 60 participants (aged 80.53 ± 11.94 years) with 72 wounds (mean area 21.32 ± 51.28cm2) were included in the study. The first PCA of the change in textural features in week 2 with respect to week 0 were statistically significant for differentiating between healed and unhealed cases. Textural analysis of thermal images is an effective method to predict in week 2 which venous leg ulcers will not heal by week 12 among older people whose wounds are being managed in their homes.

İdiyopatik Granülomatöz Mastitli Hastalarda Dijital Kizilötesi Termal Görüntüleme (Diti) İle Sistemik Steroid Yanitinin Değerlendirilmesi

İdiyopatik Granülomatöz Mastitli Hastalarda Dijital Kizilötesi Termal Görüntüleme (Diti) İle Sistemik Steroid Yanitinin Değerlendirilmesi

Digital Thermal Image Processing to Identify Bone Propagation Characteristics

In this paper we present the results of experiments performed in segments of beef bone on the conditions associated with the propagation of sound. Thermal image processing is used. The proposed method consists of the separation of the image in its main channels and a complementary binary image is constructed according to the threshold weighted by each of these grayscale images. The experimental part was carried out in a set of images varying the exposure time of the sample. The results obtained allow us to see the feasibility of the proposed methodology, as well as its application to identify some type of condition such as osteoporosis.

Spectral emissivity and temperature of heated surfaces based on spectrometry and digital thermal imaging – Validation with thermocouple temperature measurements

The spectral emissivity of an object is required to measure its temperature remotely, based on thermal imaging from a high-speed digital camera. However, it is often difficult to obtain the spectral emissivity of objects under transient conditions, as is the case with burning fuels; hence, the accuracy of the temperature measurement is compromised. This manuscript describes a method of temperature measurement of objects with simultaneous use of a spectrometer and a high-speed camera. The method was demonstrated by viewing the bead of an R-type thermocouple heated by a premixed natural gas flame to temperatures in the range of 1450–1530 K, and by comparing such remote temperature measurements with those obtained based on the thermocouple’s voltage output. The spectral emissivity of the heated thermocouple was acquired from spectroscopic analysis of its output radiation, in the wavelength range of 500–1000 nm. It was shown that the thermocouple approached graybody behavior at the upper end of this band. It was also shown that spectral emissivity of R-type thermocouple is close to the emissivity of S-type thermocouple, reported in the literature in the wavelength range of 500–700 nm and, also, close to the emissivity of pure platinum. This suggests that the effect of rhodium on the platinum emissivity is negligible. The temperature of the R-type thermocouple was measured at four different flame conditions (by varying the fuel/air equivalence ratio) using the spectrometer and the high-speed camera, and it was compared with the thermocouple temperature measurements. The flame was either steady or unsteady; the latter condition was implemented to evaluate the transient response of the measurements. In both cases, the comparison showed that the results of the three different temperature measurement methods have very high consistency and were within 11 K in the explored temperature range. Hence, this method is suitable for temperature measurements of objects of varying temperature and emissivity, such as solid fuel particles during their combustion.

Wavelet-Based Thermal Image Analysis Methods

Image enhancement is primarily aimed at improving the image quality so that the resulting image is better for a particular application than the original image. Improving the image is the job of applying such improvements, such as a visually more attractive image, to the output image. Improvement of thermal images in quality control, color and gray photography, medical problems, research and development, risk management systems, academic, law enforcement and defense infrared digital thermal imaging. Specific changes to the gray image, histogram equalization (HE), rapid Fourier transformation, image fusion and denoise have been used. The process of making images more accessible is to develop pictures. These effects include highlighting the interesting details of the objects, removing noise from photographs, making images more attractive visually, increasing the edge and contrast between images.

Diagnosis of Photovoltaic (PV) Panel Defects Based on Testing and Evaluation of Thermal Image

Abstract Photovoltaic (PV) solar energy can only be economical if the PV module operates reliably for 25–30 years under field conditions. The PV module and it overall reliability can be radically affected by faults during the manufacturing process, in real field conditions, transportation, and installation. So, there is a need for diagnosing defects in PV modules to improve their reliability. Operating temperature plays the key role for improving the efficiency of PV panels. The temperature within the PV cell unevenly increases because of such defects in the cell. As such, it is very important to monitor the temperature and temperature distribution in PV panels in order to locate such defects. Infrared thermography (IRT) plays a major role in predictive and preventive maintenance of PV panels and can determine the severity of the problem. This article investigates the delamination, snail trails, and bubbled faults of PV panels using digital thermal image analysis and their feature extraction. Real time experiments were conducted, and the test results are presented in this article. Thermal images of panels are captured using a (FLIR) T420bx® thermal imager. The thermal images of panels are analyzed by segmenting the image using the k-means clustering algorithm. Histogram statistical features such as mean, standard deviation, variance, entropy, skew, and kurtosis are extracted from the segmented thermal image. Based on these features, the defects in PV panels are identified with reasonable accuracy.

Wildfire effects on permafrost and soil moisture in spruce forests of Interior Alaska

In the summer of 2015, hundreds of forest fires burned across the state of Alaska. Several uncontrolled wildfires near the town of Tanana on the Yukon River were responsible for the largest portion of the area burned statewide. In July 2017, field measurements were carried out in both unburned and burned forested areas nearly adjacent to one another, all within 15 miles of the village of Tanana. These surveys were used to first visually verify locations of different burn severity classes, (low, moderate, or high), estimated in 2016 from Landsat images (collected before and after the 2015 Tanana-area wildfires). Surface and soil profile measurements to 30-cm depth at these same locations were collected for evidence of moss layer and forest biomass burning. Soil temperature and moisture content were measured to 30-cm depth, and depth to permafrost was estimated by excavation wherever necessary. Digital thermal infra-red images of the soil profiles were taken at each site location, and root-zone organic layer samples were extracted for further chemical analysis. Results supported the hypothesis that the loss of surface organic layers is a major factor determining post-fire soil water and temperature changes and the depth of permafrost thawing. In the most severely burned forest sites, complete consumption of the living moss organic layer was strongly associated with both warming at the surface layer and increases in soil water content, relative to unburned forest sites. Soil temperatures at both 10-cm and 30-cm depths at burned forest sites were higher by 8–10 °C compared to unburned sites. Below 15 cm, temperatures of unburned sites dropped gradually to frozen levels by 30 cm, while soil temperatures at burned sites remained above 5 °C to 30-cm depth. The water content measured at 3 cm at burned sites was commonly in excess of 30% by volume, compared to unburned sites. The strong correlation between burn index values and depth to permafrost measured across all sites sampled in July 2017 showed that the new ice-free profile in severely burned forest areas was commonly 50-cm deeper than in unburned soils.

Enhancement techniques for abnormality detection using thermal image

Digital thermal imaging is considered as a non-invasive diagnostic tool and a real-time monitoring technique for indicating the physiological changes of the underlying tissue from the superficial thermal signature. A thermal camera can detect temperature variations in the body, as low as 0.1°C. The observed colour pattern depends on the prevailing temperature of the target in a controlled environment. This colour-based thermal pattern is further processed for identifying abnormalities. This process of identification is done by applying various methods such as histogram equalisation, Otsu thresholding and morphologic function. These steps are applied to thermal images of a foot acquired from volunteers and abnormalities were identified. The identification process was based on a threshold obtained from the histogram and it was found to be in the range of 76–80.

THE EFFECT OF IMAGE ENHANCEMENT METHODS DURING FEATURE DETECTION AND MATCHING OF THERMAL IMAGES

Abstract. A successful image matching is essential to provide an automatic photogrammetric process accurately. Feature detection, extraction and matching algorithms have performed on the high resolution images perfectly. However, images of cameras, which are equipped with low-resolution thermal sensors are problematic with the current algorithms. In this paper, some digital image processing techniques were applied to the low-resolution images taken with Optris PI 450 382 x 288 pixel optical resolution lightweight thermal camera to increase extraction and matching performance. Image enhancement methods that adjust low quality digital thermal images, were used to produce more suitable images for detection and extraction. Three main digital image process techniques: histogram equalization, high pass and low pass filters were considered to increase the signal-to-noise ratio, sharpen image, remove noise, respectively. Later on, the pre-processed images were evaluated using current image detection and feature extraction methods Maximally Stable Extremal Regions (MSER) and Speeded Up Robust Features (SURF) algorithms. Obtained results showed that some enhancement methods increased number of extracted features and decreased blunder errors during image matching. Consequently, the effects of different pre-process techniques were compared in the paper.

Thermal skin reference values in healthy late pregnancy

Digital thermal imaging has been employed in medicine for over 50 years. However, its use has been focused on vascular, musculoskeletal and neurological conditions, while other potential applications, such as obstetrics, have been much less explored.This paper presents a study conducted during 2011 at the Hospital of Braga on a group of healthy pregnant women in the last third of gestation. The analysis focused on characterizing typical pregnant women steady temperature profiles in specific defined regions of interest (ROI), and determining if the thermal symmetry values for late pregnant healthy women are in line with the values for non-pregnant healthy women.A temperature distribution pattern was found in the defined ROI. The obtained thermal symmetry value had a maximum of 0.3±0.2°C, and there was no evidence for the influence of age (p>0.05) in the observed group. The influence of the BMI requires further investigation since one ROI (P2 right) presented a p=0.059, close to the threshold of statistical evidence in the influence of BMI. The study group presented symmetry values in line with non-pregnant reference values, but the profiles in temperature distribution are different. Assumptions can therefore now be used with higher confidence when assessing abnormalities in specific pathologic states during pregnancy using the defined ROI. This work represents a first contribution towards establishing guidelines for future research in this specific field of study.

A pilot evaluation study of high resolution digital thermal imaging in the assessment of burn depth

Thermal imaging is a tool that can be used to determine burn depth. We have revisited the use of this technology in the assessment of burns and aim to establish if high resolution, real-time technology can be practically used in conjunction with clinical examination to determine burn depth. 11 patients with burns affecting upper and lower limbs and the anterior and posterior trunk were included in this study. Digital and thermal images were recorded at between 42h and 5days post burn. When compared to skin temperature, full thickness burns were significantly cooler (p<0.001), as were deep partial thickness burns (p<0.05). Superficial partial thickness burns were not significantly different in temperature than non-burnt skin (p>0.05). Typically, full thickness burns were 2.3°C cooler than non-burnt skin; deep partial thickness burns were 1.2°C cooler than non-burnt skin; whilst superficial burns were only 0.1°C cooler. Thermal imaging can correctly determine difference in burn depth. The thermal camera produces images of high resolution and is quick and easy to use.

A Prospective Study of Computerized Digital Infrared Image Analysis (NoTouch BreastScanTM) in Biopsy Proven Breast Cancers.

Abstract Introduction: Early detection of breast cancer is known to have a more favourable outcome. Currently clinical breast examination and imaging modalities, primarily mammography are used for screening purposes. In India, more than 85% of the population is below the age of 50 years, wherein the sensitivity of mammography is at best 64%. Additional drawbacks of the procedure are physical discomfort and ionizing radiation dose to the patient. So newer techniques have been investigated which detect cancer induced neovascularity with digital thermal imaging. The purpose of this clinical study was to determine the efficacy of a software assisted thermal image analysis tool to distinguish between benign and malignant lesions of the breast.Methods: A prospective study was conducted in women who presented to the breast clinic with clinically or mammographically suspicious breast lesions. They also underwent thermal imaging of the breast. All mammographically suspicious lumps were subjected to histopathological confirmation. The mammography and infrared (IR) reports were compared to the histopathology.Results: In 90 women, 180 breasts were independently analyzed by both digital IR software analysis and mammography. Eighty five out of these 180 had suspicious lesions on mammography or clinical examination which were subjected to pathological confirmation. Mammography being the present diagnostic gold standard, all normal mammograms in clinically normal breast were considered as non-malignant. The sensitivity and specificity of digital thermography in detecting malignant lesions was 88.24% and 70.52% respectively with NPV of 87.01% and PPV of 72.82%. While for mammography the sensitivity and specificity were 96.25% and 96.7% with NPV of 96.7% and PPV of 96.25%. In women below 50 years of age (62/90) the sensitivity and specificity of digital thermography was 89.83% and 64.61% with NPV of 87.5% and PPV of 69.74%. Further, in the same subset no statistically significant difference was detected in the sensitivity of digital thermography to that of mammography (p = 0.7263).Conclusion: Our initial experience shows that the detection rate by digital thermal imaging is comparable to mammography in clinically palpable breast tumors. We also note that there is no significant difference in sensitivity of thermal imaging in women on either side of 50 making it a potentially testable tool for screening in younger women. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5028.

SITHON: An Airborne Fire Detection System Compliant with Operational Tactical Requirements

In response to the urging need of fire managers for timely information on fire location and extent, the SITHON system was developed. SITHON is a fully digital thermal imaging system, integrating INS/GPS and a digital camera, designed to provide timely positioned and projected thermal images and video data streams rapidly integrated in the GIS operated by Crisis Control Centres. This article presents in detail the hardware and software components of SITHON, and demonstrates the first encouraging results of test flights over the Sithonia Peninsula in Northern Greece. It is envisaged that the SITHON system will be soon operated onboard various airborne platforms including fire brigade airplanes and helicopters as well as on UAV platforms owned and operated by the Greek Air Forces.

Spatial assessment of the physiological status of wheat crops as affected by water and nitrogen supply using infrared thermal imagery

This work addresses the need for meaningful spatial indices of the physiological condition of field crops for site-specific management and variable rate application in precision agriculture. Precision agriculture is designed to target crop inputs according to within-field requirements to increase profitability while protecting the environment. The objectives of this work were to (a) develop a canopy physiological stress index with spatial resolution commensurate with the needs of site-specific management, and (b) test the physiological meaning of this index by exploring its association with key processes and variables at leaf and crop levels. We report results from a single-year field experiment where different levels of irrigation, wheat crop density, and nitrogen supply were applied to increase the expression of within-season variability. We defined a canopy stress index (CSI) as the difference between canopy (Tc), and air temperature (Ta), normalised by vapour pressure deficit (VPD): CSI = (Tc – Ta)/VPD. A novel method to extract canopy temperatures (Tc) from complex digital thermal images was developed, thus allowing for the spatial characterisation of CSI. CSI is expected to be positive and high if the capacity of the canopy to dissipate heat is reduced as when stomata close. CSI accounted for 80% of the variation in growth rate and yield, compared with 46–49% explained by the normalised difference vegetation index (NDVI). Most of the variation in crop response variables was related to water supply. The physiological meaning of this index was reinforced by its significant association with gas exchange variables measured at the leaf-level. The potential for the use of digital thermal imaging in precision agriculture is discussed.

Thermology and facial telethermography: Part II. Current and future clinical applications in dentistry.

Selected clinical applications using thermal imaging as an aid in dentistry are reviewed. Facial skin temperature can easily be measured in a clinical setting, without direct skin contact, by monitoring the emitted infrared radiation. This is the basis of static area telethermography (SAT) and dynamic area telethermography (DAT). SAT has recently been shown to be of help to the dentist in (1) the diagnosis of chronic orofacial pain, (2) as a unique tool in assessment of TMJ disorders, (3) as an aid in assessment of inferior alveolar nerve deficit, and (4) as a promising research tool. DAT, recently made possible by advances in computing technology combined with advanced infrared sensor technology, extracts quantitative information about hemodynamic processes from hundreds to thousands of digital thermal images of the affected facial areas, measured and collected within less than 3 min. DAT has promise of offering a better insight into aberrations of the neuronal control of facial skin perfusion and aiding our understanding of the correlation between orofacial pain and facial thermal abnormalities. This promising new insight may help in the management of orofacial pain.