Elsevier

Burns

Volume 32, Issue 7, November 2006, Pages 867-875
Burns

Burn depths evaluation based on active dynamic IR thermal imaging—A preliminary study

https://doi.org/10.1016/j.burns.2006.01.024Get rights and content

Abstract

Proper diagnostic assessment of burn wound depth is of the highest importance in selecting the mode of burn wound treatment. Several diagnostic methods – clinical and histopathological evaluation, as well as methods employing IR imaging – static thermography and active dynamic thermography (ADT) – are compared on the basis of in vivo experiments conducted on three domestic pigs (23 burn wounds). ADT is presented here as a new, reliable and quantitative method of assessing burn wound depth on the basis of discrimination of the thermal properties of burnt tissue.

In the case of ADT registration of thermal images was performed following thermal pulse excitation. A series of captured infrared images was used as the basis for calculating the thermal time constant τ for each pixel. The parameter values were compared with histopathological and clinical assessments of burn depth. The mean value of τ was found for burns, which heal within 3 weeks (τ = 12.08 ± 1.94 s) and for burns, which did not heal during this period (τ = 9.07 ± 0.68 s), p < 0.05. The accuracy, sensitivity and specificity of all the methods tested were compared, the best results coming from ADT. The ADT method is fast, non-invasive and relatively inexpensive, although it still requires further animal experimentation as well as clinical study to confirm the results.

Introduction

The modern approach to skin burn depth assessment tries to resolve the problem of healing and the appropriate choice of treatment—conservative or surgical [1], [2]. The traditional approach distinguishes the following grades of burn wound: I, superficial; IIa, superficial dermal; IIb, deep dermal; and III, full thickness of the skin [3]. In clinical practice even the inexperienced doctor has no difficulty in classifying first and third degree burns correctly. However, differentiation between the IIa (superficial dermal) and IIb (deep dermal) classes of wound is problematic. Clinical evaluation, mainly based on visual inspection, only insures an accurate prognosis in 50–70% of these cases [2], [3], [4], [5]. A method that enables burn wound depth to be correctly assessed and the choice of treatment to be made properly is, therefore, of the greatest importance. The aim of this paper is to present one such new objective method. The method based on IR thermal imaging of transient processes allows quantitative evaluation of burn depth and provides the answer to one of the most important questions in burn diagnostics: Will the burn heal spontaneously within 3 weeks of the burn or not?

The reference method in burn depth evaluation is histopathological assessment but as this is invasive, local and time consuming, it is not frequently used [6], [7]. Research interests have concentrated on the search for non-invasive, objective and quantitative diagnostic methods. Static thermography (ST) [8], [9], [10], ultrasonography (USG) [11], [12], spectrophotometry [13], [14], laser Doppler imaging (LDI) [15], [16], [17], [18] and indocyanine green fluorescence (ICG) [19], [20] are those most frequently cited, although none has been broadly accepted as a solution for clinical applications [2], [5].

Recently we discussed the diagnostic value of ST [21], where the basic figure of merit—ΔT, namely the difference between the mean values of skin temperature for the burn wound area and the unaffected reference skin area, is defined. The inconveniences of the method are the need for meticulous care about measurement conditions and the lack of commonly accepted temperature ranges of ΔT for particular burn wound depth classifications. However, a great advantage of the method is its non-invasive character, the possibility of assessing relatively large burn areas and the easy and objective capture of images for medical documentation [22], [23].

We propose an IR thermal imaging modality new to medical diagnostic applications, active dynamic IR thermal imaging (ADT), also termed active dynamic thermography. This is a method based on infrared detection which uses the cameras already applied in static thermography but which shows thermal tissue properties instead of changes in temperature distribution. Such an approach eliminates several of the drawbacks of traditional thermography while preserving the positive features and allowing quantitative objective assessment of burns.

Section snippets

Active dynamic IR thermal imaging (ADT)

The concept of infrared non-destructive testing (IR/NDT) has been known in industry for several years [24]. ADT may be regarded as an advanced version of IR/NDT. Analysis of heat transfer enables thermophysical material properties, such as thermal diffusivity or conductivity, to be quantified. Knowledge of these two thermal parameters allows the subsurface structure to be determined.

The general concept of the measurements performed in ADT is shown in Fig. 1. First the steady state temperature

Results

Groups of wounds were distinguished post hoc: those shallower than 60% of the dtms, which healed within 3 weeks (18 cases); and those deeper than 60% of the dtms, unhealed (five cases) (Fig. 4).

For ADT the mean value of the thermal time constant for burns shallower than 60% of the dtms (those healing within 3 weeks) was τ = 12.08 ± 1.94 s and for deeper ones (“non-healing”) it was τ = 9.07 ± 0.68 s. The difference was at the statistically significant level, (p < 0.05). We found that parameter τ had a

Discussion

We started working on model-based ADT applications in medical diagnostics in 1999 [31] and since then have published further data on the procedures applied to burn evaluation, for example in 2001 [32], [33]. Prior to these publications thermography was applied in burn depth assessment only in the traditional static form, listing only the most important positions [8], [9], [10], [22], [34], [35], [36]. Only Dickey et al. [37] made the attempt to propose an in vitro burn model using biosynthetic

Conclusions

  • 1.

    ADT examination is simple, non-contact and short. The instrumentation to be applied is based on the IR-cameras already used in hospitals and now available at reduced prices.

  • 2.

    The procedure is not as sensitive to external conditions as static thermography (ST). However, the standards valid for ST should be secured.

  • 3.

    The results of the ADT and histopathological evaluations are fully in agreement. This should not be regarded as the general rule, as the evaluation of the method was made ex post and in

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