Assessment of time required to reach plantar thermal acclimatisation in patients with diabetes.

Technical Summary: Assessment of Time Required to Reach Plantar Thermal Acclimatisation in Patients with Diabetes

Problem Statement
Infrared thermography (IRT) is a non-invasive tool used to detect pre-ulcerative changes in diabetic feet by identifying abnormal plantar temperature patterns, specifically inter-foot temperature asymmetry exceeding 2.2 °C. Current clinical guidelines, established by bodies such as the American Academy of Thermology (AAT) and the International Academy of Clinical Thermology (IACT), recommend a minimum 15-minute acclimatisation period to allow skin temperature to reach thermal equilibrium with the ambient environment. However, this duration is based on the stabilisation of absolute skin temperature rather than the stability of inter-foot asymmetry, which is the primary diagnostic metric for diabetic foot risk. This lack of standardisation regarding the specific metric of interest (absolute vs. relative temperature) and the variability in practice (ranging from 5 to 60 minutes) acts as a barrier to the clinical adoption of diabetic-foot thermography. Furthermore, existing literature has largely examined whole-body or regional skin temperatures, leaving foot-specific acclimatisation dynamics unexamined.

Methodology
This was a single-centre, prospective, repeated-measures methodological study conducted at King Salman Hospital in Riyadh, Saudi Arabia. The study recruited 41 adult patients with diabetes mellitus (Type 1 or Type 2) undergoing routine foot screening. Participants were excluded if they had active foot ulceration, acute infection, prior lower-extremity amputation, or Charcot neuroarthropathy.

Thermographic data were collected in a temperature-controlled environment (21–24 °C) using the TFScan thermal imaging system (incorporating a FLIR ONE Edge Pro camera). Images were captured at 30-second intervals over a 15-minute period while participants sat with their feet stationary. Temperature data were extracted from four predefined plantar regions of interest (angiosomes) for both feet: lateral calcaneal artery (LCA), medial calcaneal artery (MCA), lateral plantar artery (LPA), and medial plantar artery (MPA).

Stabilisation was assessed using three distinct metrics:

1. Categorical Inter-foot Asymmetry: Defined as a temperature difference >2.2 °C between corresponding regions of the left and right feet. Stabilisation was defined as the earliest time point where the presence or absence of this asymmetry remained constant for the remainder of the recording.
2. Absolute Plantar Temperature: Stabilisation was determined using a reference-value approach, where the mean of the final five measurements served as the reference. Stabilisation occurred when the temperature entered and remained within a ±5% tolerance of this reference.
3. Inter-foot Temperature Difference (Delta): Stabilisation was defined as the earliest time point where the delta value entered and remained within a ±1.0 °C tolerance of the reference value (mean of the final five measurements).

Statistical analysis included descriptive statistics and repeated-measures ANOVA, with stabilisation times calculated on a per-participant basis.

Key Results
The study found that thermal stabilisation occurred significantly earlier than the standard 15-minute recommendation for the majority of participants, particularly when focusing on asymmetry.

• Categorical Asymmetry: 75% of participants (31 of 41) showed a stable asymmetry status from the initial measurement (0 seconds). The median stabilisation time was 0 seconds. The 80th percentile of participants stabilised within 60 seconds, and the 90th percentile within 270 seconds (4.5 minutes).
• Absolute Temperature: Median stabilisation times for absolute plantar temperatures (whole-foot and regional) were between 0 and 75 seconds. Approximately 75% of participants reached stability within 3.5 minutes.
• Inter-foot Delta Measures: Similar to categorical asymmetry, the median stabilisation time for inter-foot temperature differences was 0 seconds across all regions. The 75th percentile for most variables was 0 seconds, indicating that relative temperature differences stabilised almost immediately for most participants.

While a small subset of participants exhibited prolonged stabilisation times (up to 870 seconds for asymmetry), the data demonstrated that the clinically relevant signal (asymmetry) stabilised much faster than absolute temperature values.

Significance and Claims
The paper claims that the diagnostic signal most relevant to diabetic foot screening—inter-foot temperature asymmetry—stabilises earlier than absolute temperature-based measures. The authors argue that because asymmetry is a relative measure, it is intrinsically robust to global thermal drift; when both feet cool or warm in parallel, the temperature gap between them is preserved even while absolute values continue to change.

Consequently, the study suggests that the conventional 15-minute acclimatisation period may be a conservative safety margin that is often unnecessary for detecting inter-foot abnormalities. The authors propose that re-examining fixed acclimatisation protocols through an "asymmetry-centred lens" could lead to shorter, more practical screening times. This adjustment has the potential to improve workflow efficiency, reduce appointment bottlenecks, and enhance the feasibility of thermographic screening in routine clinical practice without compromising diagnostic integrity. The paper concludes that these findings provide an empirical basis for exploring shorter acclimatisation approaches, though it acknowledges the need for further validation in larger, multi-centre cohorts.