- Email: [email protected]
A pilot evaluation study of high resolution digital thermal imaging in the assessment of burn depth
burns 39 (2013) 76–81
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/burns
A pilot evaluation study of high resolution digital thermal imaging in the assessment of burn depth§ Joseph Hardwicke a, Richard Thomson a, Amy Bamford a, Naiem Moiemen a,b,* a
West Midlands Regional Burns Centre, University Hospitals of Birmingham NHS Foundation Trust, New Queen Elizabeth Hospital, Mindelsohn Way, Edgbaston, Birmingham B15 2WB, UK b Birmingham Children’s Hospital NHS Foundation Trust, Steelhouse Lane, Birmingham B4 6NH, UK
article info
abstract
Article history:
Thermal imaging is a tool that can be used to determine burn depth. We have revisited the
Accepted 28 March 2012
use of this technology in the assessment of burns and aim to establish if high resolution, real-time technology can be practically used in conjunction with clinical examination to
Keywords:
determine burn depth. 11 patients with burns affecting upper and lower limbs and the
Burns
anterior and posterior trunk were included in this study. Digital and thermal images were
Thermal imaging
recorded at between 42 h and 5 days post burn. When compared to skin temperature, full
Infrared thermography
thickness burns were significantly cooler ( p < 0.001), as were deep partial thickness burns
Assessment
( p < 0.05). Superficial partial thickness burns were not significantly different in temperature
Human
than non-burnt skin ( p > 0.05). Typically, full thickness burns were 2.3 8C cooler than nonburnt skin; deep partial thickness burns were 1.2 8C cooler than non-burnt skin; whilst superficial burns were only 0.1 8C cooler. Thermal imaging can correctly determine difference in burn depth. The thermal camera produces images of high resolution and is quick and easy to use. # 2012 Elsevier Ltd and ISBI. All rights reserved.
1.
Introduction
Establishing the difference between superficial dermal burns, that will heal spontaneously within 21 days, and deep dermal burns which can result in longer healing time and associated pathological scarring is challenging, even for experienced burn surgeons [1–4]. New National Institute for Health and Clinical Excellence (NICE) guidelines supports the use of Laser Doppler Imaging (LDI) to help guide treatment decisions for patients in whom there is doubt about the burn depth [5]. LDI image capture can be a slow process, producing low-resolution images. It requires patient to remain still for prolonged periods and in pediatric or non-compliant patients, image quality may need to be sacrificed [6]. High resolution images §
with real-time or instant image capture is now available using thermal imaging technology. Thermal imaging is a tool that can be used to determine burn depth. Lawson, originally described this technological application in 1961, by using thermal imaging to accurately predict the depth of burns in dogs [7]. Mladick et al. in 1966 found that thermograms correlated very closely with the pattern of depth of the burns in patients [8]. Hackett was a strong advocate of thermal imaging in burn assessment. In his work throughout the 1970s he assessed 109 patients, with thermal imaging and concluded that clinical examination of the burn failed to predict depth in 1/3 of cases compared to 10% failure with thermal imaging [9]. Later work by Cole imaged 23 patients (32 hand burns): Superficial and deep dermal burns were all treated conservatively and if unhealed by 2 weeks
This paper was presented at the West Midlands Plastic Surgery Meeting 2011 and was the winner of the Douglas Murray Prize. * Corresponding author at: West Midlands Regional Burns Centre, University Hospitals of Birmingham NHS Foundation Trust, New Queen Elizabeth Hospital, Mindelsohn Way, Edgbaston, Birmingham B15 2WB, UK. E-mail address: [email protected] (N. Moiemen). 0305-4179/$36.00 # 2012 Elsevier Ltd and ISBI. All rights reserved. http://dx.doi.org/10.1016/j.burns.2012.03.014
burns 39 (2013) 76–81
were excised and grafted. They then retrospectively analyzed the predictive value of the initial clinical and thermographic assessments and thermography correctly predicted the outcome and was highly significant. The authors conclude that thermography can identify a subgroup of patients with deep dermal burns that might benefit from early surgery [10– 12]. Other than a few animal studies [13,14] no further work as been published on the use of thermal imaging in burns. A major refinement of thermal imaging technology, especially in the real-time and instant image capture and processing, has seen it widely used in the military, law enforcement and industry [15,16]. We have revisited the use of this technology in the assessment of burn depth and aim to establish if this high resolution, real-time technology can be
77
practically used in conjunction with clinical examination to determine burn depth.
2.
Materials and methods
Patients admitted to the West Midlands Regional Burns Centre at the University Hospital of Birmingham NHS Foundation Trust with varying depth burns were imaged with a digital cameral (Nikon D300, Nikon Corporation, Tokyo, Japan) and a Thermal camera (FLIR SC660, FLIR Systems Inc., Wilsonville, Oregon, USA). Images were recorded after 48 h from the time of injury in a standardized ambient temperature controlled environment. Burns were assessed after 48 h in keeping with
Fig. 1 – (a) Digital image of a mixed depth burn to the posterior right flank; dotted area indicating area of clinically full thickness burn. (b) Thermal image of the burn with a calibrated colorized palate (30.1–37 8C), with overlay of full thickness burn area. (c) Grayscale image for analysis. Dotted area is analyzed for pixel content and mean thermal signal (0 = low, 255 = high), measured as arbitrary units (AU). (d) Conversion scale for calibrating grayscale arbitrary units to temperature units (8C).
78
burns 39 (2013) 76–81
current Laser Doppler Imaging (LDI) guidelines. Patients were divided into three groups: Group A included patients with isolated full-thickness burns; Group B included patients with clinically superficial burns; and Group C included patients with clinically mixed depth burns. Under advisement from the National Research Ethics Service for the West Midlands, as a service evaluation study formal ethical approval was not required. This service evaluation study was not designed to compare predictive outcome with other current imaging technologies, such as LDI, but image capture and resolution was examined.
Thermal images were selected and processed with ImageJ1 software (1.37 v; http://rsb.info.nih.gov/ij/) to extract numerical values of pixel thermal intensity (PTI; measured in arbitrary units (AU); range 0–255): Comparison with digital photography allowed the selection of areas of different burn depth (full thickness, deep partial thickness or superficial partial thickness; Fig. 1a). The colorized palate (Fig. 1b) was removed to evaluate PTI (Fig. 1c). The burn wound PTI was compared to a similar sized area of non-burnt skin PTI, to act as background skin temperature. An extrapolated skin or burn temperature was calibrated based upon in vivo skin
Fig. 2 – (a) Digital image of a typical full thickness burns affecting the right posterior leg. (b) Thermal image of a full thickness burn affecting the right posterior leg, with a calibrated colorized palate. (c) Digital image of a typical superficial partial thickness burn affecting the abdominal wall. Marker labels used for image orientation. (d) Thermal image of a superficial partial thickness burn affecting the abdominal wall, with a calibrated colorized palate.
burns 39 (2013) 76–81
temperature recording (local, non-burnt area) with a tympanic thermometer (GeniusTM 2, Covidien Plc., Dublin, Ireland). PTI in the locale of skin temperature measurement was recorded at numerous points in various patients. The mean PTI was compared to skin temperature and a linear relationship was identified (Fig. 1d), and mathematical formula calculated, to allow extrapolation of PTI (AU) to skin temperature (8C). Statistical analyses were undertaken with GraphPad Prism1, version 4.00 (GraphPad Software, La Jolle, California, USA). Data were compared using a Student’s t-test
79
(parametric methods), and ad hoc two-sample Mann Whitney U-test (non-parametric methods). Results were expressed as a mean. Statistical significance was considered at a probability of p < 0.05.
3.
Results
11 patients (13 burns) with burns affecting upper and lower limbs and the anterior and posterior trunk were included in
Fig. 3 – (a) Digital image of a mixed depth flame burn to the right leg; dotted area indicates an island of clinically non-burnt skin surrounded laterally by deep partial thickness burn. (b) Thermal image of the burn with a calibrated colorized palate (30–35.5 8C), with island of non-burnt skin with high temperature thermal signal, surrounded laterally by lower temperature deeper burn, indicated by dotted line. (c) Laser Doppler Image (LDI) of the right leg, with the location of the island of non-burnt skin indicated by the dotted line. The low-resolution LDI does not indicate blood flow in this area. (d) Intraoperative image of the burn, post test-shave, indicated punctate bleeding and good blood flow (arrow), in keeping with an area of non-burnt/superficial burn.
80
burns 39 (2013) 76–81
this study. Group A included five patients with six burns, Group B included two patients with three burns and Group C included four patients with four burns. Digital and thermal images were recorded at between 42 h and 5 days post burn. The patients included in this study had a mean age of 40 years (range 17–78 years) and included nine men and two women. There were six flame, two scald, one chemical, one contact and one electrical burn. The total body surface area (TBSA) affected included nine burns of less then five percent TBSA, one burn of between five and ten percent TBSA, and one burn of greater than ten percent TBSA. Burn image analysis sampled on average 23,633 pixels (range 2569–81,463). The extrapolated mean skin temperature away from the zone of injury was 34.6 8C (range 32.8–35.7 8C). In cases of superadded infection, mean skin temperature in the cellulitic areas was significantly increased to 35.2 8C ( p = 0.0039). Clinically assessed full thickness burns (Fig. 2a and b) had a mean calculated temperature of 32.3 8C (range 31.6–33.8 8C); deep partial thickness burns had a mean temperature of 33.4 8C (range 32.4–34.5 8C); and superficial partial thickness burns (Fig. 2c and d) had a mean temperature of 34.5 8C (range 32.6– 35.4 8C). When compared to skin temperature, full thickness burns were significantly cooler ( p < 0.001), as were deep partial thickness burns ( p < 0.05). Superficial partial thickness burns were not significantly different in temperature than non-burnt skin ( p > 0.05). Full thickness burns, when associated with superadded infection, were not significantly different in temperature than those which were clinically uninfected ( p > 0.05), and although infected skin was higher in temperature to non-infected skin, the temperature differential between burnt and non-burnt skin remained. When the infected burns were removed from the analysis, there was no significant change to the outcome data. Typically, full thickness burns were 2.3 8C cooler than non-burnt skin, deep partial thickness burns were 1.2 8C cooler than non-burnt skin, whilst superficial burns were only 0.1 8C cooler.
4.
Discussion
Thermal imaging can correctly determine difference in burn depth. The thermal camera produces images of high resolution and is quick and easy to use. Our results correlate with previous findings by Hacket [9] who found that a full thickness burn equated to a temperature drop of 2.58 or more and a deep dermal burn measured between 2.5 and 1.58 temperature drop. It is the temperature differential between burnt skin (of varying depth) and non-burnt skin that is diagnostic, rather than absolute temperature. Our work also draws a parallel with the work of Cole [10,11] finding that the thermal camera can detect the difference between superficial and deep dermal burns. Although this was a diverse cohort of patients with variable burn depth, causation, associated infection and image timing, this was a service evaluation study designed to assess image capture and quality, and the ability to assess burn depth at a point in time. This preliminary data will be used in the creation of standardized assessment protocols as are used with LDI. The increased image and thermal resolution, when compared to LDI, allows more refinement in determination
of superficial partial thickness burns, or non-burnt skin, especially when surrounded by deeper burns. A clinical example is shown in Fig. 3 with an island of clinically nonburnt skin surrounded laterally by deep partial thickness burn. The lower image resolution afforded by LDI does not match the enhanced detail produced by thermography. This allows greater tissue preservation when excising mixed depth burns, guided by thermography rather than LDI. Thermal imaging is a diverse illustrative medium that has many applications in burn and plastic surgery [17,18]. Although we imaged patients with static thermal images there is the potential to use dynamic thermal images. This could potentially be utilized intra-operatively to allow real time imaging of the burnt region providing more a precise map of areas requiring excision. The timing for imaging, between two and five days post burn, was based on LDI guidelines. However it is not yet understood if this time frame equates to the best predictive valve of the thermal images in predicting burn depth. It is hoped that future work will answer these questions and potential enable comparison with other imaging tools such as LDI. Thermal imaging has a proven role as a tool in burn surgery and is a useful addition to held determining burn depth.
Conflict of interest statement The authors have no conflict of interest.
Funding No financial support was used in the production of this article.
Acknowledgments We would like to thank Andrew Riddle of the University Hospitals of Birmingham NHS Foundation Trust Medical Illustration Department for collection of the digital and thermal images.
references
[1] Jaskille AD, Shupp JW, Jordan MH, Jeng JC. Critical review of burn depth assessment techniques: Part I. Historical review. J Burn Care Res 2009;30:937–47. [2] Jaskille AD, Ramella-Roman JC, Shupp JW, Jordan MH, Jeng JC. Critical review of burn depth assessment techniques: part II. Review of laser Doppler technology. J Burn Care Res 2010;31:151–7. [3] Kaiser M, Yafi A, Cinat M, Choi B, Durkin AJ. Noninvasive assessment of burn wound severity using optical technology: a review of current and future modalities. Burns 2011;37:377–86. [4] Monstrey S, Hoeksema H, Verbelen J, Pirayesh A, Blondeel P. Assessment of burn depth and burn wound healing potential. Burns 2008;34:761–9. [5] NICE Guidance: moorLDI2-BI: a laser Doppler blood flow imager for burn wound assessment. http:// guidance.nice.org.uk/MTG2.
burns 39 (2013) 76–81
[6] Holland AJ, Martin HC, Cass DT. Laser Doppler imaging prediction of burn wound outcome in children. Burns 2002;28:11–7. [7] Lawson RN, Wlodek CB, Webster DR. Thermographic assessment of burns and frostbite. Can Med Assoc J 1961;84:1129–31. [8] Mladick R, Georgiade N, Thorne F. A clinical evaluation of the use of thermography in determining degree of burn injury. Plast Reconstr Surg 1966;38:512–8. 1966. [9] Hackett MEJ. The use of thermography in the assessment of burn and blood supply of flaps, with preliminary reports on its use in Dupuyt-ren’s contracture and treatment of varicose ulcers. Br J Plast Surg 1974;27:311–7. [10] Cole RP, Jones SG, Shakespeare PG. Thermographic assessment of hand burns. Burns 1990;16:60–3. [11] Cole RP, Shakespeare PG, Chissell HG, Jones SG. Thermographic assessment of burns using a nonpermeable membrane as wound covering. Burns 1991;17:117–22. [12] Liddington MI, Shakespeare PG. Timing of the thermographic assessment of burns. Burns 1996;22:26–8.
81
[13] Renkielska A, Nowakowski A, Kaczmarek M, Ruminski J. Burn depths evaluation based on active dynamic IR thermal imaging—a preliminary study. Burns 2006;32:867–75. [14] Ruminski J, Kaczmarek M, Renkielska A, Nowakowski A. Thermal parametric imaging in the evaluation of skin burn depth. IEEE Trans Biomed Eng 2007;54:303–12. [15] Warmelink L, Vrij A, Mann S, Leal S, Forrester D, Fisher RP. Thermal imaging as a lie detection tool at airports. Law Hum Behav 2011;35:40–8. [16] Chiu WT, Lin PW, Chiou HY, Lee WS, Lee CN, Yang YY, et al. Infrared thermography to mass-screen suspected SARS patients with fever. Asia Pac J Public Health 2005;17:26–8. [17] Chubb D, Rozen WM, Whitaker IS, Ashton MW. Images in plastic surgery: digital thermographic photography (‘‘thermal imaging’’) for preoperative perforator mapping. Ann Plast Surg 2011;66:324–5. [18] Whitaker IS, Lie KH, Rozen WM, Chubb D, Ashton MW. Dynamic infrared thermography for the preoperative planning of microsurgical breast reconstruction: a comparison with CTA. J Plast Reconstr Aesthet Surg 2011. PMID: 21872545.
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/burns
A pilot evaluation study of high resolution digital thermal imaging in the assessment of burn depth§ Joseph Hardwicke a, Richard Thomson a, Amy Bamford a, Naiem Moiemen a,b,* a
West Midlands Regional Burns Centre, University Hospitals of Birmingham NHS Foundation Trust, New Queen Elizabeth Hospital, Mindelsohn Way, Edgbaston, Birmingham B15 2WB, UK b Birmingham Children’s Hospital NHS Foundation Trust, Steelhouse Lane, Birmingham B4 6NH, UK
article info
abstract
Article history:
Thermal imaging is a tool that can be used to determine burn depth. We have revisited the
Accepted 28 March 2012
use of this technology in the assessment of burns and aim to establish if high resolution, real-time technology can be practically used in conjunction with clinical examination to
Keywords:
determine burn depth. 11 patients with burns affecting upper and lower limbs and the
Burns
anterior and posterior trunk were included in this study. Digital and thermal images were
Thermal imaging
recorded at between 42 h and 5 days post burn. When compared to skin temperature, full
Infrared thermography
thickness burns were significantly cooler ( p < 0.001), as were deep partial thickness burns
Assessment
( p < 0.05). Superficial partial thickness burns were not significantly different in temperature
Human
than non-burnt skin ( p > 0.05). Typically, full thickness burns were 2.3 8C cooler than nonburnt skin; deep partial thickness burns were 1.2 8C cooler than non-burnt skin; whilst superficial burns were only 0.1 8C cooler. Thermal imaging can correctly determine difference in burn depth. The thermal camera produces images of high resolution and is quick and easy to use. # 2012 Elsevier Ltd and ISBI. All rights reserved.
1.
Introduction
Establishing the difference between superficial dermal burns, that will heal spontaneously within 21 days, and deep dermal burns which can result in longer healing time and associated pathological scarring is challenging, even for experienced burn surgeons [1–4]. New National Institute for Health and Clinical Excellence (NICE) guidelines supports the use of Laser Doppler Imaging (LDI) to help guide treatment decisions for patients in whom there is doubt about the burn depth [5]. LDI image capture can be a slow process, producing low-resolution images. It requires patient to remain still for prolonged periods and in pediatric or non-compliant patients, image quality may need to be sacrificed [6]. High resolution images §
with real-time or instant image capture is now available using thermal imaging technology. Thermal imaging is a tool that can be used to determine burn depth. Lawson, originally described this technological application in 1961, by using thermal imaging to accurately predict the depth of burns in dogs [7]. Mladick et al. in 1966 found that thermograms correlated very closely with the pattern of depth of the burns in patients [8]. Hackett was a strong advocate of thermal imaging in burn assessment. In his work throughout the 1970s he assessed 109 patients, with thermal imaging and concluded that clinical examination of the burn failed to predict depth in 1/3 of cases compared to 10% failure with thermal imaging [9]. Later work by Cole imaged 23 patients (32 hand burns): Superficial and deep dermal burns were all treated conservatively and if unhealed by 2 weeks
This paper was presented at the West Midlands Plastic Surgery Meeting 2011 and was the winner of the Douglas Murray Prize. * Corresponding author at: West Midlands Regional Burns Centre, University Hospitals of Birmingham NHS Foundation Trust, New Queen Elizabeth Hospital, Mindelsohn Way, Edgbaston, Birmingham B15 2WB, UK. E-mail address: [email protected] (N. Moiemen). 0305-4179/$36.00 # 2012 Elsevier Ltd and ISBI. All rights reserved. http://dx.doi.org/10.1016/j.burns.2012.03.014
burns 39 (2013) 76–81
were excised and grafted. They then retrospectively analyzed the predictive value of the initial clinical and thermographic assessments and thermography correctly predicted the outcome and was highly significant. The authors conclude that thermography can identify a subgroup of patients with deep dermal burns that might benefit from early surgery [10– 12]. Other than a few animal studies [13,14] no further work as been published on the use of thermal imaging in burns. A major refinement of thermal imaging technology, especially in the real-time and instant image capture and processing, has seen it widely used in the military, law enforcement and industry [15,16]. We have revisited the use of this technology in the assessment of burn depth and aim to establish if this high resolution, real-time technology can be
77
practically used in conjunction with clinical examination to determine burn depth.
2.
Materials and methods
Patients admitted to the West Midlands Regional Burns Centre at the University Hospital of Birmingham NHS Foundation Trust with varying depth burns were imaged with a digital cameral (Nikon D300, Nikon Corporation, Tokyo, Japan) and a Thermal camera (FLIR SC660, FLIR Systems Inc., Wilsonville, Oregon, USA). Images were recorded after 48 h from the time of injury in a standardized ambient temperature controlled environment. Burns were assessed after 48 h in keeping with
Fig. 1 – (a) Digital image of a mixed depth burn to the posterior right flank; dotted area indicating area of clinically full thickness burn. (b) Thermal image of the burn with a calibrated colorized palate (30.1–37 8C), with overlay of full thickness burn area. (c) Grayscale image for analysis. Dotted area is analyzed for pixel content and mean thermal signal (0 = low, 255 = high), measured as arbitrary units (AU). (d) Conversion scale for calibrating grayscale arbitrary units to temperature units (8C).
78
burns 39 (2013) 76–81
current Laser Doppler Imaging (LDI) guidelines. Patients were divided into three groups: Group A included patients with isolated full-thickness burns; Group B included patients with clinically superficial burns; and Group C included patients with clinically mixed depth burns. Under advisement from the National Research Ethics Service for the West Midlands, as a service evaluation study formal ethical approval was not required. This service evaluation study was not designed to compare predictive outcome with other current imaging technologies, such as LDI, but image capture and resolution was examined.
Thermal images were selected and processed with ImageJ1 software (1.37 v; http://rsb.info.nih.gov/ij/) to extract numerical values of pixel thermal intensity (PTI; measured in arbitrary units (AU); range 0–255): Comparison with digital photography allowed the selection of areas of different burn depth (full thickness, deep partial thickness or superficial partial thickness; Fig. 1a). The colorized palate (Fig. 1b) was removed to evaluate PTI (Fig. 1c). The burn wound PTI was compared to a similar sized area of non-burnt skin PTI, to act as background skin temperature. An extrapolated skin or burn temperature was calibrated based upon in vivo skin
Fig. 2 – (a) Digital image of a typical full thickness burns affecting the right posterior leg. (b) Thermal image of a full thickness burn affecting the right posterior leg, with a calibrated colorized palate. (c) Digital image of a typical superficial partial thickness burn affecting the abdominal wall. Marker labels used for image orientation. (d) Thermal image of a superficial partial thickness burn affecting the abdominal wall, with a calibrated colorized palate.
burns 39 (2013) 76–81
temperature recording (local, non-burnt area) with a tympanic thermometer (GeniusTM 2, Covidien Plc., Dublin, Ireland). PTI in the locale of skin temperature measurement was recorded at numerous points in various patients. The mean PTI was compared to skin temperature and a linear relationship was identified (Fig. 1d), and mathematical formula calculated, to allow extrapolation of PTI (AU) to skin temperature (8C). Statistical analyses were undertaken with GraphPad Prism1, version 4.00 (GraphPad Software, La Jolle, California, USA). Data were compared using a Student’s t-test
79
(parametric methods), and ad hoc two-sample Mann Whitney U-test (non-parametric methods). Results were expressed as a mean. Statistical significance was considered at a probability of p < 0.05.
3.
Results
11 patients (13 burns) with burns affecting upper and lower limbs and the anterior and posterior trunk were included in
Fig. 3 – (a) Digital image of a mixed depth flame burn to the right leg; dotted area indicates an island of clinically non-burnt skin surrounded laterally by deep partial thickness burn. (b) Thermal image of the burn with a calibrated colorized palate (30–35.5 8C), with island of non-burnt skin with high temperature thermal signal, surrounded laterally by lower temperature deeper burn, indicated by dotted line. (c) Laser Doppler Image (LDI) of the right leg, with the location of the island of non-burnt skin indicated by the dotted line. The low-resolution LDI does not indicate blood flow in this area. (d) Intraoperative image of the burn, post test-shave, indicated punctate bleeding and good blood flow (arrow), in keeping with an area of non-burnt/superficial burn.
80
burns 39 (2013) 76–81
this study. Group A included five patients with six burns, Group B included two patients with three burns and Group C included four patients with four burns. Digital and thermal images were recorded at between 42 h and 5 days post burn. The patients included in this study had a mean age of 40 years (range 17–78 years) and included nine men and two women. There were six flame, two scald, one chemical, one contact and one electrical burn. The total body surface area (TBSA) affected included nine burns of less then five percent TBSA, one burn of between five and ten percent TBSA, and one burn of greater than ten percent TBSA. Burn image analysis sampled on average 23,633 pixels (range 2569–81,463). The extrapolated mean skin temperature away from the zone of injury was 34.6 8C (range 32.8–35.7 8C). In cases of superadded infection, mean skin temperature in the cellulitic areas was significantly increased to 35.2 8C ( p = 0.0039). Clinically assessed full thickness burns (Fig. 2a and b) had a mean calculated temperature of 32.3 8C (range 31.6–33.8 8C); deep partial thickness burns had a mean temperature of 33.4 8C (range 32.4–34.5 8C); and superficial partial thickness burns (Fig. 2c and d) had a mean temperature of 34.5 8C (range 32.6– 35.4 8C). When compared to skin temperature, full thickness burns were significantly cooler ( p < 0.001), as were deep partial thickness burns ( p < 0.05). Superficial partial thickness burns were not significantly different in temperature than non-burnt skin ( p > 0.05). Full thickness burns, when associated with superadded infection, were not significantly different in temperature than those which were clinically uninfected ( p > 0.05), and although infected skin was higher in temperature to non-infected skin, the temperature differential between burnt and non-burnt skin remained. When the infected burns were removed from the analysis, there was no significant change to the outcome data. Typically, full thickness burns were 2.3 8C cooler than non-burnt skin, deep partial thickness burns were 1.2 8C cooler than non-burnt skin, whilst superficial burns were only 0.1 8C cooler.
4.
Discussion
Thermal imaging can correctly determine difference in burn depth. The thermal camera produces images of high resolution and is quick and easy to use. Our results correlate with previous findings by Hacket [9] who found that a full thickness burn equated to a temperature drop of 2.58 or more and a deep dermal burn measured between 2.5 and 1.58 temperature drop. It is the temperature differential between burnt skin (of varying depth) and non-burnt skin that is diagnostic, rather than absolute temperature. Our work also draws a parallel with the work of Cole [10,11] finding that the thermal camera can detect the difference between superficial and deep dermal burns. Although this was a diverse cohort of patients with variable burn depth, causation, associated infection and image timing, this was a service evaluation study designed to assess image capture and quality, and the ability to assess burn depth at a point in time. This preliminary data will be used in the creation of standardized assessment protocols as are used with LDI. The increased image and thermal resolution, when compared to LDI, allows more refinement in determination
of superficial partial thickness burns, or non-burnt skin, especially when surrounded by deeper burns. A clinical example is shown in Fig. 3 with an island of clinically nonburnt skin surrounded laterally by deep partial thickness burn. The lower image resolution afforded by LDI does not match the enhanced detail produced by thermography. This allows greater tissue preservation when excising mixed depth burns, guided by thermography rather than LDI. Thermal imaging is a diverse illustrative medium that has many applications in burn and plastic surgery [17,18]. Although we imaged patients with static thermal images there is the potential to use dynamic thermal images. This could potentially be utilized intra-operatively to allow real time imaging of the burnt region providing more a precise map of areas requiring excision. The timing for imaging, between two and five days post burn, was based on LDI guidelines. However it is not yet understood if this time frame equates to the best predictive valve of the thermal images in predicting burn depth. It is hoped that future work will answer these questions and potential enable comparison with other imaging tools such as LDI. Thermal imaging has a proven role as a tool in burn surgery and is a useful addition to held determining burn depth.
Conflict of interest statement The authors have no conflict of interest.
Funding No financial support was used in the production of this article.
Acknowledgments We would like to thank Andrew Riddle of the University Hospitals of Birmingham NHS Foundation Trust Medical Illustration Department for collection of the digital and thermal images.
references
[1] Jaskille AD, Shupp JW, Jordan MH, Jeng JC. Critical review of burn depth assessment techniques: Part I. Historical review. J Burn Care Res 2009;30:937–47. [2] Jaskille AD, Ramella-Roman JC, Shupp JW, Jordan MH, Jeng JC. Critical review of burn depth assessment techniques: part II. Review of laser Doppler technology. J Burn Care Res 2010;31:151–7. [3] Kaiser M, Yafi A, Cinat M, Choi B, Durkin AJ. Noninvasive assessment of burn wound severity using optical technology: a review of current and future modalities. Burns 2011;37:377–86. [4] Monstrey S, Hoeksema H, Verbelen J, Pirayesh A, Blondeel P. Assessment of burn depth and burn wound healing potential. Burns 2008;34:761–9. [5] NICE Guidance: moorLDI2-BI: a laser Doppler blood flow imager for burn wound assessment. http:// guidance.nice.org.uk/MTG2.
burns 39 (2013) 76–81
[6] Holland AJ, Martin HC, Cass DT. Laser Doppler imaging prediction of burn wound outcome in children. Burns 2002;28:11–7. [7] Lawson RN, Wlodek CB, Webster DR. Thermographic assessment of burns and frostbite. Can Med Assoc J 1961;84:1129–31. [8] Mladick R, Georgiade N, Thorne F. A clinical evaluation of the use of thermography in determining degree of burn injury. Plast Reconstr Surg 1966;38:512–8. 1966. [9] Hackett MEJ. The use of thermography in the assessment of burn and blood supply of flaps, with preliminary reports on its use in Dupuyt-ren’s contracture and treatment of varicose ulcers. Br J Plast Surg 1974;27:311–7. [10] Cole RP, Jones SG, Shakespeare PG. Thermographic assessment of hand burns. Burns 1990;16:60–3. [11] Cole RP, Shakespeare PG, Chissell HG, Jones SG. Thermographic assessment of burns using a nonpermeable membrane as wound covering. Burns 1991;17:117–22. [12] Liddington MI, Shakespeare PG. Timing of the thermographic assessment of burns. Burns 1996;22:26–8.
81
[13] Renkielska A, Nowakowski A, Kaczmarek M, Ruminski J. Burn depths evaluation based on active dynamic IR thermal imaging—a preliminary study. Burns 2006;32:867–75. [14] Ruminski J, Kaczmarek M, Renkielska A, Nowakowski A. Thermal parametric imaging in the evaluation of skin burn depth. IEEE Trans Biomed Eng 2007;54:303–12. [15] Warmelink L, Vrij A, Mann S, Leal S, Forrester D, Fisher RP. Thermal imaging as a lie detection tool at airports. Law Hum Behav 2011;35:40–8. [16] Chiu WT, Lin PW, Chiou HY, Lee WS, Lee CN, Yang YY, et al. Infrared thermography to mass-screen suspected SARS patients with fever. Asia Pac J Public Health 2005;17:26–8. [17] Chubb D, Rozen WM, Whitaker IS, Ashton MW. Images in plastic surgery: digital thermographic photography (‘‘thermal imaging’’) for preoperative perforator mapping. Ann Plast Surg 2011;66:324–5. [18] Whitaker IS, Lie KH, Rozen WM, Chubb D, Ashton MW. Dynamic infrared thermography for the preoperative planning of microsurgical breast reconstruction: a comparison with CTA. J Plast Reconstr Aesthet Surg 2011. PMID: 21872545.