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Foot Thermography Background Information


Key Features in Thermal Assessment

Two different colour scales

The Colour Scale

It is important to note that a contact making device such as Podium is not thermometric, i.e. it does not measure the absolute temperature of the foot. On contact with the thermal sheet the foot cools (if the sheet is colder than the foot) or warms (if it is warmer). As a result the absolute foot temperature changes. This is often advantageous, e.g. when cooling provides a mild "cold stress" that can serve to highlight areas of inflammation. Relative temperature patterns are thus preserved or emphasised which may be helpful when interpreting the resulting thermograms.

The Histogram

As outlined above Podium thermograms are non-thermometric by design. The numbers on the histogram scale are therefore provided as relative indications and do not represent absolute temperature values.

Image of a thermal histogram
The normal foot: average and standard deviation

The Healthy Foot

The image shows the average plantar foot temperature of 103 healthy subjects who were resting at 22℃ for 10 minutes after taking their socks and shoes off. Reproduced from Kluwe B., Early detection of diabetic foot ulcers using thermal imaging, PhD Thesis, University of South Wales, July 2018

Thermal Variability

The image shows the variation of tempertures in the 103 healthy individuals within a 1 standard deviation interval. It is noticeable that the temperature at the toes is far more variable between individuals than that of the medial arch. Reproduced from Kluwe B., Early detection of diabetic foot ulcers using thermal imaging, PhD Thesis, University of South Wales, July 2018

Variability in foot temperature
Foot symmetry graph

Thermal Symmetry

The figure shows a histogram of the left-right differences at 33 distinct points in the feet of 103 healthy subjects (resulting in 3,399 data points). The width of the interquartile range (IQR) is 0.9℃, i.e. 50% of all aspects in one foot differ by less than 0.45℃ from those of the other foot, 99% less than 1.8℃. Reproduced from Macdonald A., Petrova N. et al.

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