Validation of low-cost smartphone-based thermal camera for diabetic foot assessment
Introduction
Ulceration and infection are frequently occurring foot complications in people with diabetes and peripheral neuropathy, and these complications increase morbidity and mortality [1], [2]. If not treated quickly, the consequences can be devastating. Therefore, early detection of diabetic foot complications is critical. However, detection by self-examination may be impeded by health impairments related to diabetes and other comorbidities, like bad eyesight, limited mobility or social impairment [3]. An alternative is frequent examination by health professionals, but this is costly and may be meddlesome for the patient. An advanced home assessment tool to monitor the foot in people with diabetes is desirable, and for this measurement of foot skin temperature is a promising modality [4], [5], [6], [7], [8], [9], [10], [11].
Temperature assessment is built on the notion that the heating up of the skin is a predictor for a diabetic foot ulcer (DFU) [12], [13]. Before skin breaks down, it heats up due to inflammation and enzymatic autolysis of tissue resulting from mild to moderate repetitive stresses on the foot that go unnoticed due to neuropathy [12], [13]. Such inflammation is only present in the affected side. This makes detection possible, by determining the temperature difference between the affected location and the same location on the contralateral foot. Using this principle, three randomized controlled trials have shown that diabetic foot ulceration can be prevented when contralateral foot temperature differences are monitored, followed by preventative actions when a temperature increase >2.2 °C is found in specific plantar foot regions on one foot [8], [9], [10]. In addition, further research has confirmed this threshold, and additionally indicated that the most optimal cut-off value for determining urgency of treatment is a 1.35 °C difference between average temperatures of the entire plantar foot [7]. Despite the promising findings from these RCTs and the clear and objectively measurable cut-off values, temperature monitoring to prevent diabetic foot ulcers is hardly used in daily practice [14].
Originally, temperature assessment in the seminal RCTs was done with simple handheld infrared thermometers [8], [9], [10]. The reason why this method is not implemented in daily foot care is not clear, but may have to do with reimbursement, a lack of confirmation of trial results in other geographical settings, and with participant barriers in the daily use of the thermometer [11]. Recent studies have exploited thermal infrared (IR) cameras. With IR, temperature profiles of the foot can be studied in more detail than with handheld thermography, and the identification of (pre-signs of) DFU may become automated with these devices, reducing the effort by the participants and the clinician to acquire and assess images [6], [7], [11], [15].
However, broad implementation of thermal assessment is still obstructed. A major reason are the costs of IR-cameras, as well as the need for complex data analysis. With newly available low-cost smartphone-based IR-cameras, the price barrier disappears and development of smartphone applications focused on DFU assessment to improve usability of data analysis and implementation in diabetes clinical practice becomes feasible [16], [17], [18]. However, it is unknown if the quality of these low-cost cameras is sufficient to reliably depict clinical outcomes. A smartphone-based IR-camera has been compared to a high-end camera in one pilot study [19]. They reported promising results, but in a small sample (5 DFUs) and only the intra- and interrater reliability was researched, with unknown cut-off points; validity and reliability of the smartphone-based IR-camera itself were not investigated. It remains therefore unknown whether this low-cost IR-camera can be safely applied for DFU detection. In this study, we aim to validate a smartphone-based IR-camera in a daily setting against high-end IR-cameras for DFU assessment.
Section snippets
Study design
In this single-centre prospective clinical study, a convenience sample of 32 consecutive participants with diabetes mellitus who visited the multidisciplinary outpatient diabetic foot clinic of Hospital Group Twente (Almelo, The Netherlands) was included. Every participant had a current, or recently healed (<4 weeks), diabetic foot ulcer. People with a major amputation (i.e. above the ankle) were excluded.
The Medical Ethical Committee Twente approved the study protocol (K17-45), and informed
Study population
Characteristics of the 32 participants included are shown in Table 1. All participants had peripheral neuropathy, no participant had a major amputation, the population was predominantly male and around 67 years of age. Four participants had a recently healed DFU, all other participants had an existing DFU, most often (n = 13) classified as University of Texas 1A.
Plantar foot temperature
The left-right temperature assessment of the entire plantar foot was completed for 30 participants; the remaining two participants
Discussion
To bring home monitoring for diabetic foot ulcer assessment towards diabetes clinical practice, we compared plantar foot temperatures of people with diabetes acquired with a smartphone-based IR-camera and a high-end IR-camera. The resulting intra-class correlation and Bland-Altman plots of the contralateral foot temperature differences showed high agreement between the two cameras. The clinical applicability of the smartphone-based IR camera for accurate (impending) DFU detection showed a
Conclusion
The low-cost smartphone-based thermal infrared camera showed excellent reliability and validity for the assessment of temperature differences between contralateral feet in people with diabetic foot complications. For this reason, the smartphone based IR-camera can be used as assessment tool for monitoring and preventing diabetic foot ulcers in daily clinical practice.
Funding source
PIONEERS IN HEALTH CARE INNOVATION FUND.
Conflict of interest
None.
Acknowledgments
We thank the physician assistants and wound care consultants at the diabetic foot clinic in Hospital Group Twente (Almelo and Hengelo) for their assistance in participant inclusion.
This study was financially supported by an unrestricted research grant from the Pioneers in Health Care Innovation Fund, a fund established by the University of Twente, Saxion University of Applied Sciences, Medisch Spectrum Twente, ZiekenhuisGroep Twente and Deventer Hospital.
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Present addresses: Jaap van Netten changed to Amsterdam UMC, University of Amsterdam, Dept. of Rehabilitation, Amsterdam Movement Sciences, Amsterdam, the Netherlands and Ziekenhuisgroep Twente, Almelo and Hengelo, the Netherlands.