Analysis of the value of infrared thermal imaging technology in the diagnosis of emergency pulmonary infections

Materials

Two hundred patients who were seen in the emergency department of our hospital from October 2020 to December 2021 were selected for this study, of which 108 patients were accompanied by pulmonary infections and 92 patients were not accompanied by pulmonary infections. Both groups of patients were tested by infrared thermography. The study complied with medical ethics standards and was approved by the Medical Ethics Committee of the First Affiliated Hospital of Guangzhou Medical University, and informed consent was obtained and signed by the patients and their families.

Inclusion and exclusion criteria

Inclusion criteria: Patients in the infection group: Met clinical diagnostic criteria for lung infection¹² AND had confirmatory findings on chest X-ray (reference standard). Clinical manifestations included chest pain, cough, sputum production, etc. Routine blood examination showed elevated leukocyte count. Auscultation revealed obvious rales in the lungs; patients’ compliance was good and they could cooperate with the study throughout the whole process; all the patients were aware of the contents of the study and signed an informed consent form.

Exclusion criteria: Patients with incomplete clinical data; patients with lung inflammation and infection caused by malignant tumours and other diseases; patients with cardio-cerebral-cerebrovascular diseases; patients with vital organ disorders and serious immune system diseases; patients with other mental disorders and communication difficulties.

Detection methods

Using X-ray examination as the gold standard, an X-ray film camera (Siemens, BLX-5) was used to conduct chest X-ray scanning for all patients. Before the test, patients were required to maintain a standing position, and line films were taken in lateral and orthogonal positions, with the voltage parameter set at 120 kV and the current parameter set at 200 mA, and the collected data were recorded in detail, and the relevant data such as the scope and degree of lung infection, as well as the impact on the surrounding tissues, etc., were collated and analysed by a professional imaging physician.

Close the doors and windows, in the room temperature of 22 ~ 25 ℃, humidity 50% ~ 65% of the closed environment without bright light using infrared thermography detection, while there is no interfering heat source, the use of non-refrigerated focal plane HYIRI-1206 non-refrigerated medical IRTI, infrared thermography can be implemented in all patients with temperature and other tests, the acquisition of the standard based on the national standard GB / T 19,665 − 2005 electronic Infrared imaging body surface thermometer general specification requirements for testing. Uncooled focal plane infrared acquisition lens 320 × 240, spectral response 8 ~ 14 μm, spatial resolution of 1.3mrad, temperature resolution of 0.05 ℃, acquisition speed of 30 frames / s, before the test, all the patients need to remove the surface clothing, the need to check the parts of the chest skin exposed, while the resting state needs to be away from the infrared lens 2 m at the same time to maintain a stable sitting position for 15 min. in standing position When taking pictures in the trunk position, the main orientation is the chest and bilateral lungs, and the operation process includes focusing, temperature calibration, image acquisition, image storage and image processing., which shows the thermal structure of the human body in the form of pseudo-colour thermograms.

Judging criteria

The distribution of infrared thermal images is usually based on the manifestation and characteristics of infrared thermal images from low to high temperatures, corresponding to the scale pseudocodes represented by different color levels, in which white is the ultra-high temperature region; red is the high temperature region; pink is the hot region; yellow is the temperature-sensitive region; green is the cool region; blue is the cold region; and black is the ultra-cold region. The sagittal line in the middle of the human body is the central axis, and the corresponding body surface part is divided according to the different levels of infrared thermal image, and the temperature value of the corresponding infrared thermal image is depicted with different temperature values from low to high temperature infrared thermal image according to the scale pseudo-code bars indicated by different colour grades, and at the same time, the temperature value of the mean temperature of the infrared thermal image of the various directions is recorded, and then the distribution of the thermal image, the change of the situation and its corresponding temperature value are qualitatively and qualitatively measured. corresponding temperature values were compared and analysed qualitatively and quantitatively. A positive IRTI finding for lung infection was defined as the presence of distinct, localized hyperthermic areas (typically appearing as red, pink, or white hotspots) over the chest/bilateral lung fields, corresponding to the regions identified on X-ray, with a measured temperature significantly higher than surrounding tissues and the corresponding area in the contralateral lung.

Statistical methods

GraphPad Prism 8.0 software was used for statistical analysis, and the measurement data conforming to normal distribution were expressed as mean ± standard deviation (x ± s), the count data were expressed by χ2 test (%), and comparisons between groups were made using independent t-tests. and the ROC curves were plotted to calculate the area under the curve (AUC), the sensitivity, the specificity and the Jordon’s index. index, and P < 0.05 indicates a statistically significant difference.

General information

Upon comparison, in the comparison of basic clinical data, there were no statistically significant differences between the two groups such as gender, age, hypertension, history of alcohol consumption and smoking history (P > 0.05); however, in the combination of underlying diseases, the patients in the infected group were higher than those in the uninfected group, and the difference was statistically significant (P < 0.05), as shown in Table 1.

Comparison of infrared radiation temperature in different parts of patients in two groups

The uninfected group exhibited consistently lower temperatures across all measured regions (Table 2). Critically, infrared radiation temperatures in the infected group were significantly elevated compared to non-infected controls in the body surface (37.98 ± 1.45 °C vs. 35.87 ± 1.32 °C; t = 5.923, P = 0.001), chest (33.45 ± 1.23 °C vs. 27.15 ± 1.06 °C; t = 38.450, P < 0.001), abdomen (32.34 ± 1.36 °C vs. 28.65 ± 1.20 °C; t = 20.180, P < 0.001), bilateral lungs (36.12 ± 1.38 °C vs. 27.56 ± 1.23 °C; t = 45.940, P < 0.001), and midpoint of breasts (39.24 ± 1.83 °C vs. 30.56 ± 1.25 °C; t = 38.480, P < 0.001).

A strong positive correlation was observed between IRTI temperature differentials (ΔT) and X-ray infiltration scores (Pearson’s r = 0.89, 95% CI [0.83–0.93], P < 0.001), where infiltration scores were graded as: 0 = no opacity, 1 = < 25% lobe involvement, 2 = 25–50%, 3 = > 50%. This suggests IRTI measurements reflect radiographic disease severity.

Infrared thermography detection rate of patients in the infection group

The positive rate of infrared thermography detection in patients in the lung infection group was 93 cases (86.11%), and the positive rate of gold standard X-ray detection was 102 cases (94.44%), as shown in Table 3.

Analysis of the efficacy of infrared thermography in the detection of acute pulmonary infections

The AUC value of infrared thermography in detecting patients with acute pulmonary infections was 0.933, the sensitivity was 90.36%, the specificity was 92.28%, and the Yoden index was 0.92, suggesting that infrared thermography has good diagnostic value in acute pulmonary infections, as shown in Fig. 1.

Case analysis

Case, male, 62 years old, emergency lung infection, the body surface (A: front; B: back) are seen infrared high temperature anomalous changes in phenomena, and the local performance, and showed irregular pieces and bands, and the colour shows abnormal, and has the distribution of the pattern of the meridian, as shown in Fig. 2.

Non-infected patients consistently showed homogeneous temperature distribution over the thorax (mean 33.5 °C ± 1.2 °C, range 32.1–35.0 °C), with < 0.5 °C variation between bilateral lung fields. This contrasts sharply with infected cases exhibiting localized hyperthermia (> 37 °C) and > 2 °C asymmetry (Fig. 2; Table 2). Representative normal thermal ranges are further documented in public repositories.

Our study demonstrates that infrared thermography (IRTI) effectively identifies significant surface temperature elevations in key anatomical regions (body surface, chest, abdomen, bilateral lungs, midpoint of breasts) among emergency patients with pulmonary infections compared to non-infected controls. These findings align with the known pathophysiology, where inflammation caused by infection increases local metabolic activity and blood flow, generating detectable heat signatures¹⁶. The observed temperature differences were substantial and statistically significant (P < 0.05, Table 2), reinforcing IRTI’s potential as a physiological indicator of infection. IRTI’s rapid turnaround and safety profile make it suitable for initial screening during outbreaks or in resource-limited settings where CT is unavailable.

The diagnostic performance metrics of IRTI were robust. An AUC of 0.933 indicates excellent discriminatory ability¹⁹. The sensitivity (90.36%) and specificity (92.28%) suggest IRTI is effective in both correctly identifying infected patients and ruling out infection in non-infected individuals. The high Youden’s index (0.92) further supports its overall diagnostic utility. While the IRTI positive rate (86.11%) was slightly lower than the X-ray gold standard rate (94.44%), the difference was statistically significant (P = 0.039, Table 3). This discrepancy warrants consideration. Potential explanations include:

Technical/Interpretation factors

Deep-seated infections or those with minimal surface temperature change might be less detectable by IRTI. Operator experience and precise interpretation criteria are crucial^11,15.

X-ray sensitivity

Chest X-ray, while our reference standard, has known limitations in sensitivity, particularly for early or subtle infiltrates¹⁸. Some X-ray positive cases might represent pathologies with minimal associated inflammation detectable by IRTI.

Timing

The stage of infection and prior treatment could influence the inflammatory response and thus the thermal signature.

While this study demonstrates IRTI’s diagnostic value through quantitative temperature analysis (Table 2), representative thermal images of non-infected patients were not included due to institutional ethical restrictions protecting control-group confidentiality. However, the homogeneous temperature distribution in non-infected individuals (< 1.5 °C variation across lung fields, Table 2) provides objective evidence of the absence of inflammatory hyperthermia, serving as a functional biomarker. Future studies with explicit consent for image sharing may further visualize this contrast.

Our findings corroborate previous research exploring IRTI in respiratory conditions. Studies have shown its ability to detect temperature changes associated with acute upper respiratory tract infections¹⁹ and its potential in monitoring inflammatory responses. The significant temperature elevations we observed over bilateral lungs and the chest midline specifically validate its relevance for pulmonary pathology detection^11,16. The case example (Fig. 2) visually demonstrates the characteristic irregular, hyperthermic patterns associated with infection, contrasting with the uniform pattern seen in a non-infected patient.

The advantages of IRTI in the emergency setting are notable: it is rapid, non-invasive, non-contact (reducing cross-infection risk)¹⁵, radiation-free, and provides a physiological correlate of inflammation. These features make it particularly suitable for initial screening, triage, monitoring treatment response, and potentially for patients where repeated radiation exposure is a concern¹⁷. However, its role is likely complementary rather than substitutive. It cannot provide the anatomical detail of X-ray or CT, nor the functional and bedside utility of lung ultrasound¹⁸.

Infrared thermography demonstrates significant value as a diagnostic tool for emergency pulmonary infections. It reliably detects localized hyperthermia associated with lung infection, showing excellent discriminatory power (AUC 0.933), high sensitivity (90.36%), and specificity (92.28%). Its non-invasive, rapid, and radiation-free nature makes it particularly suitable for the emergency department environment, offering potential for use in initial screening, triage, and monitoring therapeutic response. While not replacing anatomical imaging like X-ray or CT, IRTI provides valuable physiological information reflecting inflammatory activity. Future studies should explore its integration with other modalities like lung ultrasound and its application in specific patient subgroups or emerging pathogens.

Limitations

The reliance on X-ray as the sole gold standard is a limitation, as chest CT is more sensitive, particularly for early or subtle pneumonias. Some patients classified as non-infected based on X-ray might have had CT-detectable infections, potentially biasing the control group¹⁸.Environmental control, while standardized, can still influence surface temperatures. Strict adherence to protocol is essential.The study population was from a single center. Multi-center validation would strengthen generalizability. IRTI interpretation, while based on defined criteria, has a subjective component. While chest X-ray served as our practical reference standard, computed tomography (CT) is recognized to have higher sensitivity for detecting early or subtle pneumonias. The observed 94.44% X-ray detection rate may underrepresent true infection prevalence, potentially affecting IRTI’s apparent specificity²⁰. Further standardization of analysis protocols is beneficial. Future multicenter studies with CT correlation are needed to validate these findings. This study did not stratify patients by pneumonia type (typical/atypical). Future studies should evaluate IRTI’s performance across different etiologies.

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Author notes

1. Zuopeng Zhang and Zanfeng Cao contributed equally to this work.

Authors and Affiliations

1. Department of Emergency, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, 510120, P.R. China

   Zuopeng Zhang, Zanfeng Cao, Zhanzheng Yang & Xiaoying Chen

2. Nanshan college, Guangzhou Medical University, Guangzhou, 511400, P.R. China

   Zhixin Wu & Huiyi Nie

3. Guangzhou Institution of Respiratory Health, National Key Laboratory of Respiratory Disease, National Clinical Research Center for Respiratory Diseases, The First Affiliated Hospital of Guangzhou Medical University, 151 Yanjiang Xi Lu, Yuexiu District, Guangzhou City, 510120, Guangdong Province, P.R. China

   Fangge Deng

Contributions

Z.Z. and Z.C. (Zuopeng Zhang and Zanfeng Cao) conceptualized and designed the study. Z.W. (Zhixin Wu) and H.N. (Huiyi Nie) collected and analyzed the data. Z.Y. (Zhanzheng Yang) and X.C. (Xiaoying Chen) contributed to the interpretation of the results. F.D. (Fangge Deng) drafted the manuscript and supervised the project. All authors (Z.Z., Z.C., Z.W., Z.Y., H.N., X.C., F.D.) reviewed and edited the manuscript, and approved the final version for publication.

Corresponding author

Correspondence to Fangge Deng.

Competing interests

The authors declare no competing interests.

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