Assessment of burn depth: a prospective, blinded comparison of laser Doppler imaging and videomicroscopy

INTRODUCTION AND AIMS: There is a need, both in clinical and research settings, for an affordable, objective method of assessing burn depth. This study compares burn depth assessment by videomicroscopy with laser Doppler imaging (LDI) in patients with dermal burns. The videomicroscope is inexpensive compared to LDI, and can visualise the dermal capillary structure, therefore potentially allowing objective assessment of dermal burn injuries. METHODS: Patients admitted <72 h post-injury were included in the trial. Blinded LDI and videomicroscopy assessments were carried out. The patients were then followed up to one of three end-points: primary healing without surgery; early surgery; delayed healing and subsequent split skin grafting. The incidence of infection was also noted. RESULTS: Twenty-seven burn wounds were examined. In superficial partial thickness injuries, the videomicroscope reliably demonstrated an intact or nearly intact dermal vascular structure, progressing through to large amounts of capillary destruction and haemoglobin deposition in deep partial thickness injuries and complete destruction in full thickness injuries. The videomicroscope findings correlated strongly with both those of the LDI (p<0.001) and with clinical outcome (p<0.001). DISCUSSION: The videomicroscope is capable of accurately and objectively assessing burn depth. The results correlated well with both the clinical outcome and the laser Doppler findings. In addition, videomicroscopy is significantly cheaper than LDI and avoids several of the disadvantages of LDI.     

Prospective comparative evaluation study of Laser Doppler Imaging and thermal imaging in the assessment of burn depth

Introduction

The accurate assessment of burn depth is challenging but crucial for surgical excision and tissue preservation. Laser Doppler Imaging (LDI) has gained increasing acceptance as a tool to aid depth assessment but its adoption is hampered by high costs, long scan times and limited portability. Thermal imaging is touted as a suitable alternative however few comparison studies have been done.

Burn imaging with a whole field laser Doppler perfusion imager based on a CMOS imaging array

Laser Doppler perfusion imaging (LDPI) has been proven to be a useful tool in predicting the burn wound outcome in an early stage. A major disadvantage of scanning beam LDPI devices is their slow scanning speed, leading to patient discomfort and imaging artifacts. We have developed the Twente Optical Perfusion Camera (TOPCam), a whole field laser Doppler perfusion imager based on a CMOS imaging array, which is two orders of magnitude faster than scanning beam LDPI systems. In this paper the first clinical results of the TOPCam in the setting of a burn centre are presented. The paper shows perfusion images of burns of various degrees. While our system encounters problems caused by blisters, tissue necrosis, surface reflection and curvature in a manner similar to scanning beam imagers, it poses a clear advantage in terms of procedure time. Image quality in terms of dynamic range and resolution appears to be sufficient for burn diagnosis. Hence, we made important steps in overcoming the limitations of LDPI in burn diagnosis imposed by the measurement speed.     

Burn wound healing time assessed by laser Doppler imaging. Part 2: validation of a dedicated colour code for image interpretation

Introduction

Laser Doppler imaging (LDI) has been investigated and used since 1993 for the assessment of burn wounds. Here we describe tests that validate use of the dedicated colour palette, derived in Part 1, for a standardised interpretation of LDI images for prediction of healing time (<14 days, 14-21 days or >21 days). We also describe clinical and technical factors to be taken into account during LDI imaging and during image interpretation.

Methods

(1) A cohort of images, selected at random, were assessed, according to strict rules of interpretation, by 6 clinicians against photographs of healing, for accuracy of healing time prediction and clinical usefulness using five-point scales. (2) All images were assessed technically in a similar way for accuracy and the accuracy was further studied by analysing the data by ordinal logistic regression to predict the dependence of burn healing time on demographic variables (age, sex, race, %TBSA, burn cause and site). (3) Where average LDI blood flow could be determined, regression analysis was used to assess the potential accuracy of the technique.

Results

(1) Clinical accuracy was found to be 93% and usefulness was 89%; (2) technical accuracy was found to be 96%; (3) regression analysis found that a potential accuracy of 90.9% could be achieved using LDI results alone, increasing to 92% if gender was also considered; no other parameters had an influence on healing time prediction.

Conclusion

LDI can be used in a standardised way as a valid tool for improving on clinical assessment of burn wounds. This can enable earlier appropriate management.     

Ultrasound assessed thickness of burn scars in association with laser Doppler imaging determined depth of burns in paediatric patients

This study describes the ultrasound assessment of burn scars in paediatric patients and the association of these scar thickness with laser Doppler imaging (LDI) determined burn depth. A total of 60 ultrasound scar assessments were conducted on 33 scars from 21 paediatric burn patients at 3, 6 and 9 months after-burn. The mean of peak scar thickness was 0.39 ± 0.032 cm, with the thickest at 6 months (0.40 ± 0.036 cm). There were 17 scald burn scars (0.34 ± 0.045 cm), 4 contact burn scars (0.61 ± 0.092 cm), and 10 flame burn scars (0.42 ± 0.058 cm). Each group of scars followed normal distributions. Twenty-three scars had original burns successfully scanned by LDI and various depths of burns were presented by different colours according to blood perfusion units (PU), with dark blue <125, light blue 125–250, and green 250–440 PU. The thickness of these scars was significantly different between the predominant colours of burns, with the thinnest scars for green coloured burns and the thickest for dark blue coloured burns. Within light blue burns, grafted burns healed with significantly thinner scars than non-grafted burns. This study indicates that LDI can be used for predicting the risk of hypertrophic scarring and for guiding burn care. To our knowledge, this is the first study to correlate the thickness of burns scars by ultrasound scan with burn depth determined by LDI.     

Accuracy of laser speckle contrast imaging in the assessment of pediatric scald wounds

Background

Changes in microvascular perfusion in scalds in children during the first four days, measured with laser speckle contrast imaging (LSCI), are related to the time to healing and need for surgical intervention. The aim of this study was to determine the accuracy (sensitivity and specificity) of LSCI on different days after injury in the prediction of healing outcome and if the accuracy can be improved by combining an early and a late measurement. Also, the accuracy of LSCI was compared with that of clinical assessment.

Relationship between healing time and mean perfusion units of laser Doppler imaging (LDI) in pediatric burns

Background

Laser Doppler imaging (LDI) is a noninvasive technique used to assess burn depth. However, there have been no studies regarding the use of LDI in predicting burn healing time.

Objectives

The aims of this study are to evaluate the relationship between healing time and the amount of perfusion seen on LDI and to determine a cut-off value for LDI that predicts if a burn will heal within 14 days.

Study design

Consecutive patients younger than 15 years old with partial-thickness burns were recruited from May to November 2006 for this prospective observational study. The mean number of perfusion units (PU) as determined by LDI (Periscan PIM 3 system) was obtained within 2–3 days following injury. Healing time was estimated clinically by two physicians and marked by the observation of reepithelization. The mean PU was compared between the early (healed with 14 days) and late healing groups (healed later than 14 days). The usefulness of the mean PU in predicting healing time within 14 days was estimated by receiver operating characteristic curve analysis.

Results

A total of 103 patients with 181 partial-thickness burn wounds were enrolled in this study. The mean PU from LDI was higher in the early healing group compared to the late healing group (380.2 ± 157.8 vs. 185.8 ± 115.8, p < 0.001). When using 250 PUs as a cut-off value to predict early healing, the sensitivity and specificity were 80.6% and 76.9%, respectively. The area under the ROC curve was 0.844 (p < 0.001, 95% CI = 0.780–0.908).

Conclusions

This study suggests the mean PU as determined by LDI can be used as a valuable tool in predicting the healing time of burn wounds.     

Cutaneous microcirculatory assessment of the burn wound is associated with depth of injury and predicts healing time

Rationale

Current trends for the treatment of deep partial thickness and full-thickness burns include early excision and skin grafting. In this study we retrospectively evaluated the ability of Laser Doppler Flowmetry (LDF), taken within 24 h of the burn to predict: (1) burn wound depth and (2) wounds which would heal in less than 21 days.

Method

The Laser Doppler Flowmeter (O2C, LEA Medizintechnik, Germany) was employed to non-invasively measure the cutaneous microcirculation of 173 selected areas on 28 patients who suffered burns.

Results

A distinct association between initial flow (<24 h after burn injury) and the clinical assessment of depth of burn wounds was observed. Wounds demonstrating an initial blood flow of >100 AU were, in 93.1% of cases, correctly (positively) predicted for spontaneous healing within 21 days. A blood flow of <100 AU (negatively) predicted in 88.2%, those wounds which would not go on to heal within 21 days. Sequential measurement analysis (<24 h, 3 days after injury and 6 days after injury) revealed no significant decrease in skin perfusion velocity or flow rate.

Conclusion

LDF can provide immediate results for early determination of burn wound depth and is useful in selecting patients for conservative treatment of their burn wounds.     

Assessment of burn depth and burn wound healing potential

The depth of a burn wound and/or its healing potential are the most important determinants of the therapeutic management and of the residual morbidity or scarring. Traditionally, burn surgeons divide burns into superficial which heal by rapid re-epithelialization with minimal scarring and deep burns requiring surgical therapy. Clinical assessment remains the most frequent technique to measure the depth of a burn wound although this has been shown to be accurate in only 60-75% of the cases, even when carried out by an experienced burn surgeon. In this article we review all current modalities useful to provide an objective assessment of the burn wound depth, from simple clinical evaluation to biopsy and histology and to various perfusion measurement techniques such as thermography, vital dyes, video angiography, video microscopy, and laser Doppler techniques. The different needs according to the different diagnostic situations are considered. It is concluded that for the initial emergency assessment, the use of telemetry and simple burn photographs are the best option, that for research purposes a wide range of different techniques can be used but that, most importantly, for the actual treatment decisions, laser Doppler imaging is the only technique that has been shown to accurately predict wound outcome with a large weight of evidence. Moreover this technique has been approved for burn depth assessment by regulatory bodies including the FDA.     

Evaluation of hyperspectral imaging as a modern aid in clinical assessment of burn wounds of the upper extremity

The most common burn wound assessment continues to be the clinical inspection and the tactile examination, which are subjective and remain challenging even for experienced burn surgeons. Recently, hyperspectral imaging camera systems have been increasingly used to support the evaluation of burn wounds. The aim of our study was to determine if hyperspectral imaging analysis differentiates and objectifies the assessment of burn wounds in burns of the upper extremities.We included 97 superficial partial, deep partial dermal burns, and full thickness burns. Hyperspectral imaging analysis was performed for all burns using proprietary software. The software recorded parameters for tissue oxygenation (StO2), tissue hemoglobin index, and near-infrared perfusion. These values were compared with the recordings for healthy, non-burned skin.We found that hyperspectral imaging analysis effectively differentiates burn wounds and shows the ability to distinguish even superficial partial burns from deep partial burns in the near-infrared perfusion analysis feature. Although, it was not possible to differentiate burn wounds in all features.Currently, it is important to optimize the respective reference values of the individual burn degrees for an objectified assessment.     

A new,fast LDI for assessment of burns: A multi-centre clinical evaluation

IntroductionLaser Doppler imaging (LDI) provides early accurate determination of wound healing potential. LDI can scan large areas of up to 2500 cm² within 2 min. This duration may require additional sedation in a mobile, uncooperative child. In five burn centres a faster Laser Doppler Line Scanner (LDLS) was assessed. This new imager scans 300 cm² in 4 s with potential benefit for patients and operators. The aim of this study was to assess the accuracy and convenience of the LDLS and to compare this with an established LDI imager.MethodsOutpatients and admitted patients were included. LDI and LDLS images were obtained between 2 and 5 days post burn (PB). Photographs and records of wound and healing were obtained on day of scan and at 14 and 21 days PB. This provided data on three categories of burn wounds: healing within 14 days, 14–21 days and not healed within 21 days.ResultsThe analysis included 596 burn areas from 204 burns patients. An accuracy of 94.2% was found with use of the LDLS compared with 94.4% for the original LDI imager.ConclusionsThe high accuracy of the new line-scan imager was comparable to that of the traditional LDI. Its size and mobility enabled easier ward and outpatient use. The higher scan speed was particularly beneficial for scans in paediatric patients.     

3D-perfusion analysis of burn wounds using hyperspectral imaging

BackgroundDetermination of the depth of burn wounds is still a challenge in clinical practise and fundamental for an optimal treatment. Hyperspectral imaging (HSI) has a high potential to be established as a new contact-free measuring method in medicine. From hyperspectral spectra 3D-perfusion parameters can be estimated and the microcirculatory of burn wounds over the first 72 h after thermal injury can be objectively described.MethodsWe used a hyperspectral imaging camera and extended data processing methods to calculate 3D-perfusion parameters of burn wounds from adult patients. The data processing results in the estimation of perfusion parameters like volume fraction and oxygenation of haemoglobin for 6 different layers of the injured skin. The parameters are presented as depth profiles. We analyzed and compared measurements of wounds of different degrees of damage and present the methodology and preliminary results.ResultsThe depth profiles of the perfusion parameters show characteristic features and differences depending on the degree of damage. With Hyperspectral Imaging and the advanced data processing the perfusion characteristics of burn wounds can be visualized in more detail. Based on the analysis of this perfusion characteristics, a new and better reliable classification of burn degrees can be developed supporting the surgeon in the early selection of the optimal treatment.     

Real-time burn depth assessment using artificial networks: a large-scale,multicentre study

IntroductionEarly judgment of the depth of burns is very important for the accurate formulation of treatment plans. In medical imaging the application of Artificial Intelligence has the potential for serving as a very experienced assistant to improve early clinical diagnosis. Due to lack of large volume of a particular feature, there has been almost no progress in burn field.Methods484 early wound images are collected on patients who discharged home after a burn injury in 48 h, from five different levels of hospitals in Hunan Province China. According to actual healing time, all images are manually annotated by five professional burn surgeons and divided into three sets which are shallow(0–10 days), moderate(11–20 days) and deep(more than 21 days or skin graft healing). These ROIs were further divided into 5637 patches sizes 224 × 224 pixels, of which 1733 shallow, 1804 moderate, and 2100 deep. We used transfer learning suing a Pre-trained ResNet50 model and the ratio of all images is 7:1.5:1.5 for training:validation:test.ResultsA novel artificial burn depth recognition model based on convolutional neural network was established and the diagnostic accuracy of the three types of burns is about 80%.DiscussionThe actual healing time can be used to deduce the depth of burn involvement. The artificial burn depth recognition model can accurately infer healing time and burn depth of the patient, which is expected to be used for auxiliary diagnosis improvement.     

Reflection-optical multispectral imaging method for objective determination of burn depth

We present a noninvasive imaging method for objective determination of the depth of burn wounds. The method is easy to use and enables even the nonspecialized physician to determine the burn depth at a very early time and to make available an objective documentation for quality management.     

Laser Doppler imaging of paediatric burns: burn wound outcome can be predicted independent of clinical examination

This study sought to assess the validity of independent, blinded reporting of Laser Doppler Imaging (LDI) prediction of burn wound outcome in children. Two experienced paediatric burn consultants were invited to report on LDI scans performed routinely within 3 days of burn. They were provided with the LDI flux image, a low-resolution colour digital photograph of the burnt area and a basic history. Report predictions were correlated with outcome. Reports were compiled on 50 scans performed on 31 patients at a mean of 54h post burn. Of the 100 reports generated, mean correlation with outcome was 97%. If the LDI predicted a deep burn, it was always correct. Non-correlations were due to a number of factors including inadequate scanning of the affected area, excessive movement and residual wound debris. Accurate prediction of burn wound outcome could be made via the standard information generated by LDI and appeared more reliable than clinical prediction. The correlation improved with increasing experience with LDI.     

Interobserver reliability of laser speckle contrast imaging in the assessment of burns

ObjectivesLaser speckle contrast imaging (LSCI) is an emerging technique for the assessment of burns in humans and interobserver differences have not been studied. The aim of this study was to compare assessments of perfusion images by different professional groups regarding (i) perfusion values and (ii) burn depth assessment.MethodsTwelve observers without LSCI experience were included. The observers were evenly recruited from three professional groups: plastic surgeons with experience in assessing burns, nurses with experience in treating burns, and junior doctors with limited experience of burns. Ten cases were included. Each case consisted of one digital photo of the burn with a pre-marked region of interest (ROI) and two unmarked perfusion images of the same area. The first and the second perfusion image was from 24 h and 72–96 h after injury, respectively. The perfusion values from both perfusion images were used to generate a LSCI recommendation based on the perfusion trend (the derivative between the two perfusion values). As a last step, each observer was asked to estimate the burn depth using their clinical experience and all available information. Intraclass correlation (ICC) was calculated between the different professional groups and among all observers.ResultsPerfusion values and perfusion trends between all observers had an ICC of 0.96 (95% CI 0.91–0.99). Burn depth assessment by all observers yielded an ICC of 0.53 (95% CI: 0.31–0.80) and an accuracy of 0.53 (weighted kappa). LSCI recommendations generated by all observers had an ICC of 0.95 (95% CI: 0.90–0.99).ConclusionObservers can reliably identify the same ROI, which results in observer-independent perfusion measurements, irrespective of burn experience. Extensive burn experience did not further improve burn depth assessment. The LSCI recommendation was more accurate in all professional groups. Introducing LSCI measurements would be likely improve early assessment of burns.     

The impact of laser Doppler imaging on the early decision-making process for surgical intervention in adults with indeterminate burns

Objective

We aimed to analyze whether laser Doppler imaging (LDI) can lead to earlier decision-making regarding the need for surgery in adults with indeterminate burns.

Methods

In a retrospective cohort study, we developed a prediction model for surgery in adults with indeterminate burns. Patient data (n = 101) from January 2007 to December 2009 were used for model development, and those (n = 40) from January 2010 to October 2010 for external validation.

Results

Between non-surgical and surgical groups, there were significant differences for mean age (p = 0.009), % total body surface area burn (p = 0.016), site of burn wound (p = 0.033), and mean perfusion units (PU) (p < 0.001). Multiple logistic regression showed that only the mean PU differed significantly between the groups. The area under the curve (AUC) of the equation derived from multiple logistic regression was 0.938, which did not differ from that of the mean PU alone (0.931; p = 0.453). Using a cut-off point of 154.7PU, the sensitivity of LDI was 78.3% and the specificity was 92.7%. This cut-off point also yielded a sensitivity of 77.8% and specificity of 95.5% in the external validation dataset.

Conclusion

LDI can help make a decision for surgery in the early stages of care for adults with indeterminate burns.     

Burn depth assessment using hyperspectral imaging in a prospective single center study

BackgroundThe assessment of thermal burn depth remains challenging. Over the last decades, several optical systems were developed to determine burn depth. So far, only laser doppler imaging (LDI) has been shown to be reliable while others such as infrared thermography or spectrophotometric intracutaneous analysis have been less accurate. The aim of our study is to evaluate hyperspectral imaging (HSI) as a new optical device.MethodsPatients suffering thermal trauma treated in a burn unit in Germany between November 2019 and September 2020 were included. Inclusion criteria were age ≥18 years, 2^nd or 3^rd degree thermal burns, written informed consent and presentation within 24 h after injury. Clinical assessment and hyperspectral imaging were performed 24, 48 and 72 h after the injury. Patients in whom secondary wound closure was complete within 21 days (group A) were compared to patients in whom secondary wound closure took more than 21 days or where skin grafting was indicated (group B). Demographic data and the primary parameters generated by HSI were documented. A Mann Whitney-U test was performed to compare the groups. A p-value below 0.05 was considered to be statistically significant. The data generated using HSI were combined to create the HSI burn index (BI). Using a logistic regression and receiver operating characteristics curve (ROC) sensitivity and specificity of the BI were calculated. The trial was officially registered on DRKS (registration number: DRKS00022843).ResultsOverall, 59 patients with burn wounds were eligible for inclusion. Ten patients were excluded because of a poor data quality. Group A comprised 36 patients with a mean age of 41.5 years and a mean burnt body surface area of 2.7%. In comparison, 13 patients were allocated to group B because of the need for a skin graft (n = 10) or protracted secondary wound closure lasting more than 21 days. The mean age of these patients was 46.8 years. They had a mean affected body surface area of 4.0%. 24, 48, and 72 h after trauma the BI was 1.0 ± 0.28, 1.2 ± 0.29 and 1.55 ± 0.27 in group A and 0.78 ± 0.14, 1.05 ± 0.23 and 1.23 ± 0.27 in group B. At every time point significant differences were demonstrated between the groups. At 24 h, ROC analysis demonstrated BI threshold of 0.95 (sensitivity 0.61/specificity 1.0), on the second day of 1.17 (sensitivity 0.51/specificity 0.81) and on the third day of 1.27 (sensitivity 0.92/specificity 0.71).ConclusionChanges in microcirculation within the first 72 h after thermal trauma were reflected by an increasing BI in both groups. After 72 h, the BI is able to predict the need for a skin graft with a sensitivity of 92% and a specificity of 71%.     

Review of methodological developments in laser Doppler flowmetry

Laser Doppler flowmetry is a non-invasive method of measuring microcirculatory blood flow in tissue. In this review the technique is discussed in detail. The theoretical and experimental developments to improve the technique are reviewed. The limitations of the method are elaborated upon, and the research done so far to overcome these limitations is critically assessed.