Thermal Imaging as a Method to Indirectly Assess Peripheral Vascular Integrity and Tissue Viability in Veterinary Medicine: Animal Models and Clinical Applications

Infrared thermography (IRT) is a technique that indirectly assesses peripheral blood circulation and its resulting amount of radiated heat. Due to these properties, thermal imaging is currently applied in human medicine to noninvasively evaluate peripheral vascular disorders such as thrombosis, thromboembolisms, and other ischemic processes. Moreover, tissular damage (e.g., burn injuries) also causes microvasculature compromise. Therefore, thermography can be applied to determine the degree of damage according to the viability of tissues and blood vessels, and it can also be used as a technique to monitor skin transplant procedures such as grafting and free flaps. The present review aims to summarize and analyze the application of IRT in veterinary medicine as a method to indirectly assess peripheral vascular integrity and its relation to the amount of radiated heat and as a diagnostic technique for tissue viability, degree of damage, and wound care.

Use of Infrared Thermography in Medical Diagnosis, Screening, and Disease Monitoring: A Scoping Review

Thermography provides non-invasive, radiation-free diagnostic imaging. Despite the extensive literature on medical thermography, a comprehensive overview of current applications is lacking. Hence, the aim of this scoping review is to identify the medical applications of passive infrared thermography and to catalogue the technical and environmental modalities. The diagnostic performance of thermography and the existence of specific reference data are evaluated, and research gaps and future tasks identified. The entire review process followed the Joanna Briggs Institute (JBI) approach and the results are reported according to PRISMA-ScR guidelines. The scoping review protocol is registered at the Open Science Framework (OSF). PubMed, CENTRAL, Embase, Web of Science, OpenGrey, OSF, and PROSPERO were searched using pretested search strategies based on the Population, Concept, Context (PCC) approach. According to the eligibility criteria, references were screened by two researchers independently. Seventy-two research articles were identified describing screening, diagnostic, or monitoring studies investigating the potential of thermography in a total of 17,314 participants within 38 different health conditions across 13 therapeutic areas. The use of several camera models from various manufacturers is described. These and other facts and figures are compiled and presented in a detailed, descriptive tabular and visual format. Thermography offers promising diagnostic capabilities, alone or in addition to conventional methods.

Radial artery pulse wave velocity: a new characterization technique and the instabilities associated with the respiratory phase and breath-holding

Objective. Pulse wave velocity (PWV) is a key diagnostic parameter of the cardiovascular system's state. However, approaches aimed at PWV characterization often suffer from inevitable drawbacks. Statistical results demonstrating how closely PWV in the radial artery (RA) and the respiration phase correlate, as well as RA PWV evolution during breath-holding (BH), have not yet been presented in the literature. The aims of this study are (a) to propose a simple robust technique for measuring RA PWV, (b) to reveal the phase relation between the RA PWV and spontaneous breathing, and (c) to disclose the influence of BH on the RA PWV.Approach.The high-resolution remote breathing monitoring method Sorption-Enhanced Infrared Thermography (SEIRT) and the new technique aimed at measuring RA PWV described in this paper were used synchronously, and their measurement data were processed simultaneously.Main results. Spontaneous breathing leaves a synchronous 'trace' on the RA PWV. The close linear correlation of the respiration phase and the phase of concomitant RA PWV changes is statistically confirmed in five tested people (Pearson's r is of the order of 0.5-0.8, P < 0.05). The BH appreciably affects the RA PWV. A phenomenon showing that the RA PWV is not indifferent to hypoxia is observed for the first time.Significance.The proposed technique for RA PWV characterization has high prospects in biomedical diagnostics. The presented pilot study deserves attention in the context of the mutual interplay between respiratory and cardiovascular systems. It may also be useful in cases where peripheral pulse wave propagation helps assess respiratory function.

Evaluating physiological progression of chronic tibial osteomyelitis using infrared thermography

Purpose

Medical infrared thermography (IRT) was used as a complementary means for the clinical evaluation of musculoskeletal trauma and progression of chronic tibial osteomyelitis.

Methods

Twenty-two adult patients with a medical diagnosis of chronic tibial osteomyelitis were followed up by IRT performed along with standard radiography. Thermal data of the affected limb were compared with those of the healthy contralateral limb based on the thermal profile of the lower limbs as per the medical thermography guideline (32 °C). Data were acquired in the following regions of the lower limb: proximal tibia, diaphysis, and distal tibia, using a FLIR infrared camera, and data were processed using MATLAB®.

Results

For patients with active infections, an increase in the average temperature of the affected limb above + 1.0 °C was observed when compared with the temperature of the contralateral. The wound region of the patients showed an increased temperature (32.3 °C) compared with the temperature of the contralateral (31.4 °C). In contrast, in latent infections, the thermal differences were small, generally below 0.3 °C, and thus were within the threshold of normality. In contrast, in areas diagnosed with reduced blood supply, the affected limb showed an average temperature up to − 5.7 °C below normal. Additionally, the initial temperature range (26.5 to 34.5 °C) decreased during the treatment to 29.8 to 34.1 °C, indicating a convergence toward normality.

Conclusion

IRT has significant potential as a complementary imaging modality in the follow-up of patients with bone lesions with a diagnosis of osteomyelitis as it does not use ionizing radiation, thus allowing repetitive use as desired. Thermal images show important physiological information related to vascularization necessary for bone repair, as well as provide a good indication of the boundary of the infected area, adjacent to the trauma, which is useful for positioning the radiography equipment. However, it should be noted that IRT cannot replace other medical imaging techniques, as it provides information about the skin and cannot directly evaluate the interior of the body.

Infrared thermography as an adjunctive tool for detection of femoral arterial thrombosis after cardiac catheterization: A prospective, pilot study

OBJECTIVES

To assess the utility of infrared thermography (IRT), to map skin temperature, in the detection of femoral arterial (FA) thrombosis after cardiac catheterization.

BACKGROUND

Ultrasound is a validated method for thrombus detection but is generally reserved as a confirmatory test for clinical suspicion due to various constraints.

METHODS

Prospective study of infants and children undergoing cardiac catheterization via FA access, comparing IRT and pulse examination. The thermograms, displayed in a color map with each pixel representing a temperature, were examined by qualitative assessment of symmetry in thermal patterns and quantitative image analysis with abnormal thermographic asymmetry defined as a difference of >10% between limbs.

RESULTS

In the 20 children enrolled, excellent agreement was found between the two methods with a Kappa value of 0.89. The median thermographic asymmetry in the nine children with pulse loss was 36 (13-76)%. Using receiver operating characteristic analysis, the asymmetrical pattern of ≥18% between limbs predicted the need for anticoagulation with a sensitivity of 100% and specificity of 89%. The area under the curve was 0.97 (95% confidence interval: 0.95-1). Children with absent pulse requiring anticoagulation showed a slower recovery in thermal asymmetry compared to those with a reduced pulse. By qualitative IRT assessment, all children with absent pulse requiring anticoagulation were correctly identified by 10 independent assessors.

CONCLUSIONS

This pilot study showed that IRT is feasible and reliable as an adjunctive tool for thrombus detection postcatheterization and treatment monitoring. Specific advantages of IRT include portability, affordability, and contactless image acquisition.

Early diagnosis of diabetic peripheral neuropathy based on infrared thermal imaging technology

AIMS

The purpose of this study was to detect and compare the surface temperature of plantar vessels in mild diabetic peripheral neuropathy (DPN) patients and healthy controls, to explore a simple, convenient and reliable method for early diagnosis of DPN, and to explore the influence of sex and age on vascular surface temperature.

MATERIALS AND METHODS

In this study, 60 mild DPN patients (30 males and 30 females) and 60 healthy volunteers were randomly recruited according to their age and sex. Intra-class correlation coefficient was used to evaluate the repeatability of skin temperature measurement in the vascular area. A general linear model was used to analyse the difference of skin temperature between mild DPN patients and healthy controls.

RESULTS

The infrared detection results of skin temperature corresponding to blood vessels showed excellent test-retest reliability. There was no significant difference in skin temperature between sex and age. But there were significant differences in skin temperature between mild DPN patients and healthy controls, except for the posterior tibial artery.

CONCLUSIONS

For mild DNP patients, in case of no obvious abnormality in the infrared detection of lower extremity arterial surface temperature, the small vessels have shown early abnormal body surface temperature, that is, the surface temperature of related vessels increased. The research conclusions of this article not only enable us to better understand the correlation between body surface temperature and hemodynamic parameters, but also provide an in vivo, non-invasive, and convenient way of thinking and methods for early diagnosis of DPN.

Thermal imaging of the fetus: An empirical feasibility study

Digital Infrared Thermal Imaging (DITI) has much potential in the field of maternal-fetal health and wellbeing research. The fact that it is totally non-invasive is particularly important in this context. The purpose of this study was, for the first time, to assess DITI’s ability to record fetal presentation and position, and other pregnancy-related physiological factors, via their superficial thermal prints. Ten healthy pregnant women (approximately 34–37 weeks of gestation) were recorded with two thermal imaging cameras (Flir C3 and i3 TE-Q1) from five different viewpoints. Participants’ views about the use of DITI in research and clinical practice were also assessed by a completion of a survey. Free hand polygon region of interests (ROIs) were drawn in order to include the entire anatomical area for investigation. The use of free hand polygon ROIs showed high reliability. Thermal images analysis revealed that fetuses presenting cephalically can be identified by the use of DITI, under specific conditions. Fetal movements influenced the thermal patterns that were produced. Future studies need to verify the heat patterns on the skin related to the placenta location, in order to understand the produced thermal recordings. Pregnant women rated the idea of using DITI in research and clinical practice very highly. This work represents a first contribution towards the use of DITI for the recording of fetal presentation and position. As it does not require direct contact and since it is completely non-invasive, it could be used to record maternal-fetal dynamic dyadic interaction in pregnancy. However, although the preliminary results are promising, further trans-disciplinary studies with a well-established protocol, more sophisticated thermal cameras, and bigger cohorts are needed.

A Pilot Study of Infrared Thermal Imaging to Detect Active Bone Lesions in Children With Chronic Nonbacterial Osteomyelitis

OBJECTIVE

Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory bone disease. An inexpensive and rapid imaging tool, infrared thermal imaging, was evaluated for its utility to detect active bone lesions in extremities of children with CNO.

METHODS

Children with suspected active CNO and healthy controls were enrolled. All subjects underwent infrared thermal imaging of the lower extremities. Patients in the CNO group also received a magnetic resonance imaging (MRI) examination. Hyperintensity within bone marrow on a fluid-sensitive T2-weighted MRI sequence was considered confirmatory for inflammation. Infrared thermal data were analyzed using custom software by dividing the leg below the knee into 3 equal segments longitudinally and adding the distal femur segment as an equal length above the knee. Median and 95th percentile temperatures were recorded for each leg segment. Temperature differences between inflamed and uninflamed segments in all subjects (both intersubject and intrasubject) were evaluated using a linear mixed-effects model.

RESULTS

Thirty children in the suspected/known CNO group and 31 healthy children were enrolled. In the healthy control group, males had significantly higher temperature in their lower extremities than females (P < 0.05). There was no difference in temperature detected between inflamed leg segments of patients with CNO versus uninflamed leg segments of the healthy control group. However, within the CNO group, significantly higher temperatures were detected for inflamed versus uninflamed distal tibia/fibula segments (P < 0.01).

CONCLUSION

Children with active CNO lesions in the distal tibia/fibula exhibited higher regional temperatures on average than healthy extremities. Larger studies are warranted to further evaluate the clinical utility of infrared thermal imaging for CNO detection.

Use of infrared thermography in the detection of superficial phlebitis in adult intensive care unit patients: A prospective single-center observational study

Common methods to detect phlebitis may not be sufficient for patients in the intensive care unit (ICU). The goal of this study was to investigate the feasibility of infrared (IR) thermography to objectively detect phlebitis in adult ICU patients. We included a total of 128 adult ICU-patients in a pilot and subsequent validation study. Median [interquartile range] age was 62 [54–71] years and 88 (69%) patients were male. Severity of phlebitis was scored using the visual infusion phlebitis (VIP)-score, ranging from 0 (no phlebitis) to 5 (thrombophlebitis). The temperature difference (ΔT) between the insertion site and a proximal reference point was measured with IR thermography. In 78 (34%) catheters early phlebitis and onset of moderate phlebitis was observed (VIP-score of 1–3). In both the pilot and the validation study groups ΔT was significantly higher when the VIP-score was ≥1 compared to a VIP-score of 0 (p<0.01 and p<0.001, respectively). Multivariate analysis identified ΔT (p<0.001) and peripheral venous catheter (PVC) dwell time (p = 0.001) as significantly associated with phlebitis. IR thermography may be a promising technique to identify phlebitis in the ICU. An increased ΔT as determined with thermography may be a risk factor for phlebitis.

Infrared thermography: a rapid and accurate technique to detect feline aortic thromboembolism

Objectives The objective of this study was to evaluate the diagnostic accuracy of infrared thermography in cats with acute pelvic paralysis to differentiate feline aortic thromboembolism (FATE) from non-ischaemic conditions. Methods Thermographic images were prospectively obtained at admission from cats presented for acute bilateral pelvic paralysis. Based on the final diagnosis, cats were divided into a FATE and a control group (ischaemic and non-ischaemic related pelvic paralysis, respectively). The maximum (Tmax), minimum (Tmin) and average (Tav) temperatures were determined for each of the four limbs within a hand-drawn region of interest on the dorsal limb extremity. Temperature differences between the forelimb (non-affected) and hindlimb (affected) with the highest temperature (ΔT), with the lowest temperature (δT) and from the right and left side (RightΔT and LeftΔT, respectively) were calculated. Results The FATE and control groups included 10 and six cats, respectively. In the FATE group, right hindlimb mean Tmax (23.6°C ± 1.9), left hindlimb mean Tmax (23.6°C ± 2.2) and mean Tav (22.7°C ± 2.2) were significantly lower than in the control group (26.6°C ± 3.5 [ P = 0.042]; 26.6°C ± 2.4°C [ P = 0.024] and 25.7°C ± 2.0 [ P = 0.020], respectively). ΔT, δT, RightΔT and LeftΔT were significantly higher in the FATE group than in the control group. A cut-off value of 2.4°C for RightΔTmax and LeftΔTmax allowed discrimination between the FATE and control groups with a sensitivity of 80% and 90%, respectively, a specificity of 100% for both, a positive predictive value of 100% for both, and a negative predictive value of 75% and 86%, respectively. Conclusions and relevance A minimal difference of 2.4°C between ipsilateral affected and non-affected limbs has an excellent specificity and high sensitivity for FATE diagnosis. Infrared thermography seems to be a promising, useful, easy, non-invasive and rapid method for detecting aortic thromboembolism in cats, particularly in emergency situations.

Development of a high-resolution infrared thermographic imaging method as a diagnostic tool for acute undifferentiated limp in young children

Acute limp is a common presenting condition in the paediatric emergency department. There are a number of causes of acute limp that include traumatic injury, infection and malignancy. These causes in young children are not easily distinguished. In this pilot study, an infrared thermographic imaging technique to diagnose acute undifferentiated limp in young children was developed. Following required ethics approval, 30 children (mean age = 5.2 years, standard deviation = 3.3 years) were recruited. The exposed lower limbs of participants were imaged using a high-resolution thermal camera. Using predefined regions of interest (ROI), any skin surface temperature difference between the healthy and affected legs was statistically analysed, with the aim of identifying limp. In all examined ROIs, the median skin surface temperature for the affected limb was higher than that of the healthy limb. The small sample size recruited for each group, however, meant that the statistical tests of significant difference need to be interpreted in this context. Thermal imaging showed potential in helping with the diagnosis of acute limp in children. Repeating a similar study with a larger sample size will be beneficial to establish reproducibility of the results. Graphical abstract A young child with an acute undifferentiated limp undergoes thermal imaging and the follow on image analysis assists the limp diagnosis.

Detection of cervical lymph node metastasis from oral cavity cancer using a non-radiating, noninvasive digital infrared thermal imaging system

This study aimed to evaluate the diagnostic performance of a non-radiating, noninvasive infrared (IR) thermal imaging system in the detection of cervical lymph node metastasis from oral cavity cancer. In this prospective clinical trial, a total of 90 oral cavity cancer patients suspected of having cervical lymph node metastasis underwent IR imaging of the neck prior to neck dissection. Analysis of the IR images was performed by two methods: manual qualitative analysis and automatic analysis by an entropy-gradient support vector machine (EGSVM). The efficacies of the EGSVM-based infrared thermal imaging system and contrast-enhanced computed tomography (CT) were compared by using the Noninferiority Testing. Compared with manual qualitative analysis, the EGSVM-based automatic analysis had a higher sensitivity (84.8% vs. 71.7%), specificity (77.3% vs. 72.7%), accuracy (81.1% vs. 72.2%), positive predictive value (79.6% vs. 73.3%) and negative predictive value (82.9% vs. 71.1%). The EGSVM-based infrared thermal imaging system was noninferior to contrast-enhanced CT (P < 0.05). The EGSVM-based infrared thermal imaging system showed a trend of higher sensitivity, whereas contrast-enhanced CT showed a trend of higher specificity. The EGSVM-based infrared thermal imaging system is a promising non-radiating, noninvasive tool for the detection of lymph node metastasis from oral cavity cancer.

There's an app for that: A handheld smartphone-based infrared imaging device to assess adequacy and level of aortic occlusion during REBOA

BACKGROUND

Advances in thermal imaging devices have made them an appealing noninvasive point-of-care imaging adjunct in the trauma setting. We sought to assess whether a smartphone-based infrared imaging device (SBIR) could determine presence and location of aortic occlusion in a swine model. We hypothesized that various levels of aortic occlusion would transmit significantly different heat signatures at various anatomical points.

METHODS

Six swine (35-50 kg) underwent sequential zone 1 (Z1) aortic cross clamping as well as zone 3 (Z3) aortic balloon occlusion (resuscitative endovascular balloon occlusion of the aorta [REBOA]). SBIR images and readings (FLIR One) were taken at five anatomic points (axilla [A], subcostal [S], umbilical [U], inguinal [I], medial malleolar [M]) and were used to determine significant thermal trends 5 minutes to 10 minutes after Z1 and Z3 occlusion. Significant (p ≤ 0.05) thermal ratio patterns were identified and compared among groups, and images were reviewed for obvious qualitative differences at the various levels of occlusion.

RESULTS

Body temperatures were similar during control (CON), Z1 occlusion, and Z3 occlusion, ranging from 94.0 °F to 100.9 °F (p = 0.126). No significant temperature differences were found among A, S, U, I, M points prior to and after aortic occlusions. Among the anatomical 2-point ratios evaluated, A/M and S/M ratios were the best predictors of aortic occlusion, whether at Z1 (8.2 °F, p < 0.01; 10.9 °F, p < 0.01) or Z3 (7.3 °F, p < 0.01; 8.4 °F, p < 0.01), respectively. The best predictor of Z1 versus Z3 level of occlusion was the S/I ratio (5.2 °F, p < 0.05 vs. 3.4 °F, p = 0.27). SBIR generated qualitatively different thermal signatures among groups.

CONCLUSION

SBIR was capable of detecting thermal trends during Z1 and Z3 aortic occlusion by using an anatomical 2-point thermal ratio. There were also easily recognized qualitative differences between control and occlusion images that would allow immediate determination of adequate occlusion of the aorta. SBIR represents a potential inexpensive and accurate tool for assessing perfusion, adequate REBOA placement, and even the aortic level of occlusion.

Infrared thermal imaging and Doppler vessel pressurization ultrasonography to detect lower extremity deep vein thrombosis: Diagnostic accuracy study

BACKGROUND AND OBJECTIVE

Infrared thermal imaging (IRTI) is a new technique for detecting deep vein thrombosis (DVT) based on DVT's infrared presentation and distribution characteristics (PDCs). A method that is singularly sensitive to DVT is needed. They, therefore, enrolled 157 subjects with suspected lower extremity DVT in a double-blind, controlled clinical trial using IRTI, and Doppler compression ultrasonography (CPUS) to verify the clinical value of IRTI.

METHODS

An IRTI system could precisely measure and store real-time thermal images. A double-blind, controlled clinical study using IRTI and detection on 157 patients with suspected DVTs, evaluating the following parameters: sensitivity, specificity, positive prescreening, negative prescreening, false positivity, false negativity, and diagnostic accordance of IRTI with CPUS for detecting DVT were conducted.

RESULTS

Of 140 subjects who underwent screening both IRTI and CPUS detect were included for analyses. According to their IRTI DVT's presentation and distribution characteristics, patients were divided into IRTI- negative (n = 59) and IRTI-positive (including suspicious IRTI positive) (n = 81) groups. CPUS identified 80 DVT-negative and 60 DVT-positive patients. The sensitivity of IRTI for detecting DVT was 88.33%, specificity 65.00%, false-positive diagnosis 11.67%, false-negative diagnosis 35.00%, positive prescreening 65.43%, negative prescreening 88.14%, diagnostic accordance rate 75.00%. IRTI results accorded with CPUS results (P = .001) except for the positivity incidence (χ²  = 39.997, P < .001).

CONCLUSIONS

IRTI could be used to supplement CPUS detection for detecting DVTs and adjunctive diagnostic screening.