An international comparison of field deployed radiometers for sea surface skin temperature (SSTskin) retrieval was conducted in June 2022. The campaign comprised a laboratory comparison and a field comparison. In the laboratory part, the radiometers were compared with reference standard blackbodies, while the same was done with the blackbodies used for the calibration of the radiometers against a transfer standard radiometer. Reference values were provided by the National Physical Laboratory (NPL), traceable to the primary standard on the International Temperature Scale of 1990. This was followed by the field comparison at a seaside pier on the south coast of England, where the radiometers were compared against each other while viewing the closely adjacent surface of the sea. This paper reports the results of the laboratory comparison of radiometers and blackbodies. For the blackbody comparison, the brightness temperature of the blackbody reported by the participants agreed with the reference value measured by the NPL transfer standard radiometer within the uncertainties for all temperatures and for all blackbodies. For the radiometer comparison, the temperature range of most interest from the SSTskin retrieval point of view is 10 degrees-30 degrees C, and in this temperature range, and up to the maximum comparison temperature of 50 degrees C, all participants' reported results were in agreement with the reference. On the other hand, below 0 degrees C the reported values showed divergence from the reference and the differences exceeded the uncertainties. The divergence shows there is room for improvement in uncertainty estimation at lower temperatures, although it will have limited implication in the SSTskin retrieval.

Quantitative thermal imaging, the measurement of temperature by use of thermal imaging devices, is reviewed here from a metrological perspective with a focus on measurement confidence and system application to fields such as condition monitoring and healthcare diagnostics. Thermal imaging has seen greatly increased application for the measurement of temperature following dramatic improvements in practicality and price. Selected thermal imaging systems are reviewed here by providing some example measurements outputs from devices, highlighting their outcomes on measurement confidence and impact on practical use, such as in condition monitoring and healthcare diagnostics.

The ground testing of satellites necessitates the validation of their thermal model whilst operational in vacuum.Thermocouples are widely used for this testing, but they are only able to provide a point temperature measurement so a large number are used.A low-cost, in vacuum thermal imaging system however could determine the temperature of a large area.Such an approach can be used to supplement contact temperature measurements, thereby reducing the number of thermocouples required.NPL has completed the de-risking of such a thermal imager that can operate in thermal vacuum from -40 °C to 60°C and has a low instrument uncertainty of ± 1°C (k=2).

There has been a marked rise in the number of avoidable deaths in health services around the world. At the same time there has been a growing increase in antibiotic resistant so-called "superbugs." We examine here the potential role of body temperature measurement in these adverse trends. Electronic based thermometers have replaced traditional mercury (and other liquid-in-glass type) thermometers for reasons of safety rather than superiority. Electronic thermometers are in general less robust from a measurement perspective than their predecessors. We illustrate the implications of unreliable temperature measurement on the diagnosis and management of disease, including COVID-19, through statistical calculations. Since a return to mercury thermometers is both undesirable and impractical, we call for better governance in the current practice of clinical thermometry to ensure the traceability and long-term accuracy of electronic thermometers and discuss how this could be achieved.

Welcome to this focus collection of Physiological Measurement on Thermal Imaging in Medicine. Thermal imaging had its origins in the Second World War, where scientists were trying to measure infrared signatures for target identification and recognition. In the decades immediately following the war, thermal imaging was almost exclusively confined to military applications. However, as the technology rapidly developed, system miniaturisation followed, and then, through the introduction of un-cooled focal plane detector arrays, the cost of thermal imagers quickly decreased. This resulted in thermal imaging becoming increasingly pervasive in non-destructive testing and other research disciplines, including a rapid uptake in the field of medicine. Thermal imaging is now routinely used in a variety of clinical and clinically related research settings; for example, it is now utilised in identifying and tracking the course of Raynaud’s phenomenon and other vasospastic disorders (Wilkinson et al 2018), and there has been a lot of interest in the widespread deployment of thermal imaging to help prevent diabetic foot ulceration (Machin et al 2017, MacDonald et al 2017). This focus collection of Physiological Measurement showcases, through ten papers, the diversity of contemporary clinical and clinically related applications for thermal imaging. These papers are a selection based on presentations given at the 14th European Association of Thermology (www.eurothermology.org/) Congress held at the UK’s National Physical Laboratory (www.npl.co.uk/), 4–7 July 2018. The scene is set by the review paper of Machin et al (2019) discussing the importance of standardisation and calibration in the context of clinical thermometry, not just for thermal imaging but for a variety of techniques including more exotic approaches such as magnetic resonance imaging spectroscopy (Babourina-Brooks et al 2015). Blackbody sources that can be used for the calibration and validation of thermal imagers in medicine have been described elsewhere (Machin et al 2009). Papers by MacDonald et al (2019) ‘Between visit variability of thermal imaging of feet in people attending podiatric clinics with diabetic neuropathy at high risk of developing foot ulcers’ and Seixas et al (2019) ‘Relationship between skin temperature and soft tissue hardness in diabetic patients: an exploratory study’ both relate to the deployment of thermal imaging to the feet of diabetic patients, with the aim of reducing and preventing ulceration and hence the many deleterious consequences that follow. The paper by Pokorná et al (2019) ‘Intestinal resection of the porcine model under thermographic monitoring’ demonstrates the use of thermal imaging as an essential adjunct to improving the outcome of surgical procedures. This has been powerfully demonstrated, for example, through the improved outcomes in breast reconstruction surgery by Weum, Mercer and de Weerd (2016), after thermal imaging was introduced into the clinical pathway. There is a growing interest in the deployment of thermal imaging in monitoring and optimising athletic performance and sports science more generally. This was reflected by the three contributions, by da Silva et al (2018) ‘Can exercise-induced muscle damage be related to changes in skin temperature?’, Pérez-Guarner et al (2019) ‘Association between physiological stress and skin temperature response after a half marathon’ and Gil-Calvo et al (2019) ‘Effects of prefabricated and custom-made foot orthoses on skin temperature of the foot soles after running’. The use of thermal imaging to monitor the presence of infection is discussed by Benavent Casanova et al (2019) in the ‘Application of infrared thermography in diagnosing peripherally inserted central venous catheter infections in children with cancer’. The use of thermal imaging to detect infection is of wider importance. For example, thermal imaging is widely deployed, especially in East Asia, to detect febrile individuals passing through airports (IEC/FDIS 80601-2-59 2017). The objective in this case is to try to prevent the spread of highly infectious diseases such as avian flu in potentially pandemic situations. Hence the paper by Vardasca et al (2019), ‘Bilateral assessment of body core temperature through axillar, tympanic and inner canthi thermometers in a young popuG Machin et al

Objective: People with diabetic neuropathy who have previously ulcerated are at high risk of re-ulceration. They should regularly attend podiatry clinics for surveillance and routine protective podiatric treatment. It has been suggested that inflammation prior to skin breakdown shows up as a hotspot on a thermal image even in the absence of clinical signs. The aim of this study is to quantify inter-patient and intra-patient thermal variations presented by diabetic feet at high risk of ulceration. Approach: Whole foot and spot temperatures were recorded for 96 patients who attended two successive podiatry appointments without ulceration 28 [28, 31] days apart, median [interquartile range]. This was a part of a longer study into whether thermal imaging in clinic can reduce the rate of re-ulceration. Main results: The variation in spot temperature right/left differences for single patients between visits was comparable to the variation observed between patients (0.8 [0.3, 1.5] °C compared with 0.9 [0.4, 1.7] °C). Similarly, whole foot temperature variation for a single patient between visits was comparable to the variation observed between patients (0.6 [0.2, 1.1] °C compared with 0.8 [0.2, 1.3] °C). Significance: Thresholds which depend on thermal differences from visit to visit are unlikely to have sufficient specificity to effectively target treatment designed to prevent the development of foot ulcers.

Infrared (IR) modalities represent the only currently viable mass fever screening approaches for outbreaks of infectious disease pandemics such as Ebola virus disease and severe acute respiratory syndrome. Non-contact IR thermometers (NCITs) and IR thermographs (IRTs) have been used for fever screening in public areas such as airports. While NCITs remain a more popular choice than IRTs, there has been increasing evidences in the literature that IRTs can provide great accuracy in estimating body temperature if qualified systems are used and appropriate procedures are consistently applied. In this study, we addressed the issue of IRT qualification by implementing and evaluating a battery of test methods for objective, quantitative assessment of IRT performance based on a recent international standard (IEC 80601-2-59). We tested two commercial IRTs to evaluate their stability and drift, image uniformity, minimum resolvable temperature difference, and radiometric temperature laboratory accuracy. Based on these tests, we illustrated how experimental and data processing procedures could affect results, and suggested methods for clarifying and optimizing test methods. Overall, the insights into thermograph standardization and acquisition methods provided by this study may improve the utility of IR thermography and aid in comparing IRT performance, thus improving the potential for producing high quality disease pandemic countermeasures.

Non-contact infra-red skin thermometers (NCITs) are becoming more prevalent for use in medical diagnostics. Not only are they used as an alternative means of estimating core body temperature but also to assess the diabetic foot for signs of inflammation prior to ulceration. Previous investigations have compared the performance of NCITs in a clinical setting against other gold standard methods. However, there have been no previous investigations comparing the performance of NCITs in assessing temperature measurement capability traceable to the International Temperature Scale of 1990 (ITS-90). A metrological assessment of nine common NCITs was carried out over the temperature range of 15-45 °C using the National Physical Laboratory's blackbody reference sources to identify their accuracy, repeatability, size-of-source and distance effects. The results are concerning in that five of the NCITs fell far outside the accuracy range stated by their manufacturers as well as the medical standard to which the NCITs are supposed to adhere. Furthermore, a 6 °C step change in measurement error over the temperature range of interest for the diabetic foot was found for one NCIT. These results have implications for all clinicians using NCITs for temperature measurement and demonstrate the need for traceable calibration to ITS-90.

Quantitative thermal imaging has the potential of reliable temperature measurement across an entire field-ofview. This non-invasive technique has applications in aerospace, manufacturing and process control. However, robust temperature measurement on the sub-millimetre (30 mu m) length scale has yet to be demonstrated. Here, the temperature performance and size-of-source (source size) effect of a 3-5 mu m thermal imaging system have been assessed. In addition a technique of quantifying thermal imager non-uniformity is described. An uncertainty budget is constructed, which describes a measurement uncertainty of 640 mK(k = 2) for a target with a size of 10 mm. The results of this study provide a foundation for developing the capability for confident quantitative sub-millimetre thermal imaging.

Thirty participants with healthy feet were imaged in the same way on two separate occasions (an average of 4 weeks apart). Overall, feet were found to be thermally symmetric although absolute temperature could vary considerably between visits. Temperature differences at specific sites on the foot sometimes exceeded the threshold of 2.2 degrees C regarded as clinically significant when looking for evidence of inflammation prior to skin breakdown in diabetes. At least one site exceeded this threshold in nine (30%) participants (the same figure for both visits). However, when looking for significant thermal asymmetry it is important to rule out transient changes by repeated imaging and to refer to baseline images.

Early identification of areas of inflammation may aid prevention of diabetic foot ulcers. A new bespoke thermal camera system has been developed to thermally image feet at risk. Hotspots (areas at least 2.2 °C hotter than the contralateral site) may indicate areas of inflammation prior to any apparent visual signs. This article describes the thermal pattern and symmetry of 103 healthy pairs of feet. 68% of participants were thermally symmetric at the 33 foot sites measured. 32% of participants had at least one hotspot, but hotspots overall only accounted for 5% of the measurements made. Refinements to the definition of hotspots are proposed when considering feet at risk of ulceration.

This paper will consider how to improve confidence in the use of thermal imagers quantitatively, that is for actual temperature measurement. The proposed route will be through the implementation of best international measurement practice via calibration, traceability and accreditation. Reference blackbody standards that have been rigorously qualified will be described, with emphasis on developments in clinical thermography.

The paper describes the comparison method and analyses the results of comparison in terms of agreement between the blackbody of the National Physical Laboratory (NPL), United Kingdom and four different blackbody cavities of the Laboratory of Metrology and Quality (LMK), at the University of Ljubljana, Faculty of Electrical Engineering (FE), Slovenia. Three cavity shapes are suggested in different standards as suitable for calibration of infrared ear thermometers (IRETs), while one cavity shape was proposed by the LMK. The agreement between blackbody cavities was determined with the help of platinum resistance thermometers. Two reference IRETs were used to check their stability and level of agreement between calibration results at different institutes and against different blackbody cavities. Measurements were performed with two IRETs, at the NPL in one cavity and at the LMK in four different cavities. The comparison was initiated to solve the problem of assuring proper traceability for IRETs and to present the solution to their users.