Skin Research and Technology 2015; 21: 485–492 Printed in Singapore  All rights reserved doi: 10.1111/srt.12218

© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Skin Research and Technology

Validation of a new imaging device for telemedical ulcer monitoring B. S. B. Rasmussen1, J. Froekjaer2, L. B. Joergensen1, U. Halekoh3 and K. B. Yderstraede1 1

Department of Medical Endocrinology, Odense University Hospital, Denmark, Odense, Denmark, Department of Orthopedic Surgery, Odense University Hospital, Denmark, Odense, Denmark and 3Epidemiology, Biostatistics and Biodemography, University of Southern Denmark, Odense, Denmark

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Purpose: To clarify whether a new portable imaging device (PID) providing 3D images for telemedical use constitutes a more correct expression of the clinical situation compared to standard telemedical equipment in this case iPhone 4s. Method: We investigated intra- and interindividual variability between the new portable camera and the iPhone images vs. clinical assessment as the ‘gold standard’. The study included 36 foot ulcers. Four specialists rated the ulcers and filled out a questionnaire, which formed the basis of the evaluation. Results: We found fair to very good intra-rater agreement for the new PID and iPhone, respectively. The gold standard was evaluated by assessing the ulcer twice by two different specialists. Kappa values were moderate to very good with respect to inter-rater agreement except for two variables. The agreement

between standard and new equipment compared to the gold standard showed highest agreement with the new PID. Conclusion: The new PID is more in accordance with the clinical assessment compared to standard images. It opens for the possibility of using more advanced techniques in a telemedical approach to ulcer treatment and care, including volume measurements.

a relatively new option for monitoring ulcer healing. It allows different healthcare providers to assess ulcers via digital images at distant locations (e.g. in the patient’s own home). This approach relies on the ability to mirror the clinical situation and assessment through digital images. The clinical situation and choice of treatment options often depend on the ulcer assessment. A study by Stremitzer et al. investigated spread and variation in judgment of wounds and found an extensive inhomogeneity and variability of the results. This indicates that a simple wound assessment from different assessors could prove challenging (1). With regard to clinical assessment through an image, several studies have found the image feasible (2–6). Others conclude that the image is not ideal in all aspects and should be accompanied by clinical information. Furthermore, lack of palpation of an ulcer area is a major weakness (7,8). Recent research focus on 3D imaging and a variety of different techniques have been used

including laser scanners to rebuild digital cameras with special lenses (9). Wannous et al. present a different 3D technique and claim to assess ulcers in more detail including size and classification of the tissue (granulation, infection, and necrosis) thereby allowing monitoring of ulcer morphology in details (10). The perspective and potential of the 3D image technology applies to precise measuring techniques of area and volume (11). A review, however, concluded that some technical issues limit the potential of the 3D image technology and that incorporation of a high detailed texture image, within its 3D representation is essential (12). We present data from an innovative pilot project using a newly developed portable imaging device (PID) based on known industrial techniques applied in aviation. The purpose was to investigate PID for ulcer photographs by testing against the standard imaging device (iPhone) used in telemedical care in Denmark. A clinical assessment constituted the gold standard.

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Key words: development – gold standard – image – photo – telemedicine – ulcer care

Ó 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Accepted for publication 14 February 2015

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Aim We aimed to clarify whether the new PID, via a merged 3D mesh and a high detailed image, can provide a more valid expression of the clinical situation compared to a standard imaging device in telemedical care.

Development The PID provides a 3D image by a combination of three cameras and a projector as displayed in Fig. 1. The projector works by projecting a pattern on the surface to be measured. This pattern consists of a number of dots with an exact predefined distance between each other. The pattern is recognized by two separate cameras, which are used to adapt the basic shape of the 3D geometry. By recognizing the pattern, the software can accurately scale a point cloud (as displayed in top right corner in Fig. 1), without knowing the distance to the object. The two cameras are installed and calibrated at a certain angle focusing at the same intersection. This configuration provides the basis for 3D geometry and secures that the point clouds are assembled in the same reference point. The dots in the point cloud are integrated into the software combined with lines and then exported into a grid (mesh). The grid is then used for calculating the surface area and volume. The third camera adapts the color image to the same surface as camera one and two. This is to secure the same scale factor of the color image as the point cloud. This method thus allows calculation of area/volume on either the color images or the mesh. Details of the manufacturer can be found at http://www.teccluster.com. However, at present the PID is not commercially available.

Fig. 1. (Left) Image of the device. (Right) PID image illustrating the superimposed mesh.

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Materials and Methods This pilot study was conducted to evaluate and compare the new portable camera with standard telemedical technology and a clinical assessment. Agreement between four different raters was investigated, using the following methods:

● A clinical assessment including tools to investigate, for example investigating for fistula, was considered as the gold standard. ● The PID providing a ‘3D image’ with a resolution of 4 megapixels color image. ● A standard ‘2D image’ provided by an iPhone 4s, with a resolution of 8 megapixels color image.

Comparison Two different raters conducted a clinical assessment for each ulcer in order to ensure the validity of the gold standard. The two other raters evaluated the images. A specific schedule was designed to ensure that each rater made evaluations by all three methods. All raters completed an ulcer assessment questionnaire, which formed the basis for agreement between methods and raters. Sixteen ‘present or not present’ questions in relation to ulcer assessment were answered (e.g. ‘does the ulcer need cleansing’). The following topics addressed interpretive and observational issues: contact to bone, ulcer infection, visible tendon, wet necrosis, surrounding infection, fistula, slough, ischemia, need for cleansing, exudation, granulation, undermining, fibrin, black necrosis, dry necrosis, and yellow necrosis. Rater one to three re-evaluated the images after 1 month to allow the calculation of intrarater agreement. Four raters were selected to participate; one endocrinologist, one orthopedic surgeon, one plastic surgeon, and the head nurse of the polyclinic. All were specialists in ulcer care each with more than 10 years of experience.

Participants Thirty individuals with 36 ulcers were recruited consecutively and fulfilled the inclusion criteria: foot ulcer, age limit 18–90 years

Telemedical ulcer monitoring

and exclusion criteria: ulcer superficial and less than 0.5 cm2. Diabetic foot ulcers, venous, and traumatic ulcers were included. In the followup period, patients were provided conventional ulcer treatment according to clinical standards.

Standardization We standardized a large number of variables to ensure a fair comparison of the two devices and to identify key variables of difference. Image quality was in favor of the iPhone with respect to megapixels. However, camera performance parameters (i.e. lens parameters) were superior in the PID. With respect to photographic techniques two different approaches were needed to capture the image. However, ambient illumination was identical. Both devices used built-in illumination for optimal performance. Camera orientation was always toward the ulcers. However, the PID needed several different orientations to produce the picture as opposed to one in the iPhone camera component. A physician, not included in the study quality approved all images and ensured identical general photographic techniques. The questions posed were presented to the participating clinicians before study start in an attempt to reduce the discrepancy of the individual rater assessment. We evaluated several test-images along with the formulated questions to secure that every question was attuned within the group. All images were evaluated at the same high-end laptop thus minimizing screen quality difference.

Statistics When planning the study, we considered a design with 12, 24, 36, or 48 ulcers. Assuming a logit model for the probability of a positive rating which was additive in the normally distributed latent severity of the patients ulcer, the raters ability and the deviation of the image method from the gold standard method. We found that the standard error for the odds ratio of comparing an image method to the reference method decreased from 0.74 for 12 patients, to 0.58 for 24, 0.52 for 36 and 0.46 for 48 patients. The calculation was based on a proportion of positive results for the reference method of 0.72 and an odds ratio

between alternatives to reference method of 0.5. Intra-rater agreement

For each patient one rater rated the standard images twice and another rated the new images twice. For each method a kappa was calculated for each rater based on Fleiss et al (13). The average value across raters was reported. The confidence intervals (CI) were based on bootstrapping and the re-sampling was done with respect to ulcers based on 3000 bootstrapped samples. Inter-rater agreement gold standard

For each ulcer two raters applied the gold standard. The agreement among raters was calculated using kappa and the CIs were based on 3000 bootstrap samples from the 36 ulcers. Agreement method PID/gold standard and iPhone/gold standard

For comparisons on the agreement of the evaluation of the iPhone and the PID method with the gold standard method we calculated a kappa value to express the level of agreement between each image-based method to the gold standard method. We defined a categorical response for the iPhone rating, taking the value 1 or 2 if both evaluations from a rater on an ulcer were 0 or 1, respectively, and applying the value 3 if the two ratings differed. The same definition was used for the gold standard ratings. For these categorical responses, we calculated a kappa value. The same definition was used for the agreement between the PID and the gold standard. For interpretation, the qualitative characterization of the level of agreement was categorized as either ‘poor’ (k = 0–0.20), ‘fair’ (k = 0.21–0.40), ‘moderate’ (k = 0.41–0.60), ‘good’ (k = 0.61–0.80), or ‘very good’ (k = 0.81– 1.00), based on Altman (14). For the 16 kappa values displayed in each table the median is reported.

Statistical software For the data-manipulation and drawing of the bootstrap samples, we used the R statistical programming environment, R Core Team (2014). For the calculation of kappa values, the kappa function from Stata Statistical Software: Release 13 was used.

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Agreement method PID/gold standard and iPhone/ gold standard The agreement was calculated to evaluate whether iPhone or PID images had a higher concordance to the clinical ulcer assessment.

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We have evaluated a newly developed portable imaging device (PID) compared to a setup with an iPhone. Our results confirm a higher level of agreement of the PID with clinical assessment. Furthermore, we found a fair to very god intrarater agreement for the PID and iPhone, respectively. Involving specialists with many years of experience enforced the precision of the analysis. We thus controlled deliberately for one source of variability (i.e. examiner experience). Furthermore, we chose the best available device at present used in telemedical care at Odense University Hospital, Denmark. Although the iPhone was superior with respect to resolution, the photo optics was in favour of the PID. 1.0

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Inter-rater agreement gold standard The agreement was calculated in order to evaluate the clinical ulcer assessment as the gold standard. Figure 3 displays all values plotted. The highest agreement was obtained concerning fibrin k = 0.89, 95% CI: (0.72, 1) and the lowest concerning surrounding infection k = 0.01, 95% CI: ( 0.06, 0.01). For surrounding infection only two raters disagreed in one out of all the ulcers. Table 2 displays all results. The median kappa value was 0.64.

Discussion

1 = Blacknecrosis 2 = Bone 3 = Drynecrosis 4 = Exudation 5 = Fibrin 6 = Fistula 7 = Granulation 8 = Ischemia 9 = Needforcleansing 10 = Slough 11 = Surrounding infection 12 = Tendon 13 = Undermining 14 = Wetnecrosis 15 = Woundinfection 16 = Yellownecrosis

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Intra-rater agreement The agreement was calculated to evaluate the reproducibility of an ulcer assessment from a clinical image, iPhone and PID kappa intra-rater values showed fair to very good agreement. The highest iPhone agreement was obtained concerning bone k = 1, 95% CI: (1, 1) and fistula 1, 95% CI: (1, 1) and the lowest concerning dry necrosis k = 0.29, 95% CI: (0.24, 0.67). The highest PID agreement was obtained on five different assessments, black necrosis, bone, dry necrosis, tendon, and wound infection all with k = 1, 95% CI: (1, 1) and the lowest concerning slough, k = 0.55, 95% CI: (0.35, 1). Figure 2 displays all iPhone and PID kappa values plotted against each other for each variable. Nine in favor of PID, one with no difference, and six in favor of iPhone. This corresponds to the median value being 0.74 in iPhone and 0.88 in PID. All results are displayed in Table 1.

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Results

The highest iPhone agreement was obtained in yellow necrosis k = 0.53, 95% CI: (0.24, 0.76) and the lowest concerning surrounding infection k = 0.10, 95% CI: ( 0.18, 0.05). The highest PID agreement was obtained on tendon with k = 0.82, 95% CI: (0.47, 0.89) and the lowest concerning fistula, k = 0.05, 95% CI: ( 0.10, 0.02). Figure 4 displays all iPhone and PID kappa values plotted against each other. Thirteen variables were in favour of PID, two were equal and one in favor of iPhone. This corresponds to the median value being 0.14 in iPhone and 0.37 in PID. All results are displayed in Table 3.

Kappa (PID)

Ethics Permissions were obtained from the regional ethics committees in Denmark: NR: (s-20120145). Approved by the Danish Data Protection Agency: (case number: 2008-58-0035). Clinicaltrials.gov identifier: NCT01608425. EUDAMED CIV-DI Number: 12-08-008621. Informed consent was obtained from each patient to allow photos of their ulcers to be included in the study.

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Fig. 2. iPhone and PID intra-rater average kappa plot, line represents equality.

Telemedical ulcer monitoring TABLE 1. iPhone and PID intra-rater average kappa results with 95% confidence intervals iPhone

PID

Variables

Kappa

95% CI (2.5%, 95%)

Kappa

95% CI (2.5%, 95%)

Black necrosis Bone Dry necrosis Exudation Fibrin Fistula Granulation Ischemia Need for cleansing Slough Surrounding infection Tendon Undermining Wet necrosis Wound infection Yellow necrosis

0.91 1.00 0.29 0.65 0.71 1.00 0.87 0.51 0.45 0.86 0.76 0.87 0.83 0.67 0.38 0.65

(0.67, (1.00, (0.24, (0.29, (0.44, (1.00, (0.67, (0.24, (0.23, (0.67, (0.44, (0.67, (0.52, (0.33, (0.11, (0.41,

1.00 1.00 1.00 0.91 0.92 0.67 0.59 0.92 0.85 0.55 0.67 1.00 0.67 0.63 1.00 0.85

(1.00, (1.00, (1.00, (0.67, (0.73, (0.67, (0.42, (0.73, (0.59, (0.35, (0.67, (1.00, (0.67, (0.30, (1.00, (0.59.

1.00) 1.00) 1.00) 1.00) 1.00) 1.00) 1.00) 1.00) 1.00) 1.00) 1.00) 1.00) 1.00) 0.92) 1.00) 1.00)

Bootstrapping was applied when calculating CI to assure reliability of our results and this approach may have caused broader CI. Statistical literature suggests that the intervals could be difficult to interpret and not always qualifying the error of estimation, when creating CI in kappa statistics. The CI is always very narrow when there is complete agreement among all raters. In addition, the kappa statistics has some obvious shortcomings (e.g. the kappa value highly depends on prevalence of the phenomenon and the fact that even when the experts all agree, they may well be mistaken) (14).

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Camera performing parameters (i.e. noise, dynamic range, image compression, color balancing) were not investigated and could theoretically have influenced the results. The two devices have a different approach to the image capturing, which is more complex with the PID. Furthermore, the size is in favor of the iPhone with respect to portability. However, a smaller PID is under construction possessing the same resolution capacities, thus minimizing these practical aspects. We deliberately included ulcers of different etiologies and four different raters to reflect everyday clinical situation.

1.00) 1.00) 0.67) 0.92) 0.92) 1.00) 1.00) 0.80) 0.92) 1.00) 1.00) 1.00) 1.00) 1.00) 0.91) 0.91)

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Fig. 3. Gold standard inter-rater kappa plot, line represents transition from fair to moderate in kappa values.

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Rasmussen et al. TABLE 2. Gold standard inter-rater kappa results with 95% confidence intervals Gold standard Variables

Kappa 0.80 0.37 0.65 0.59 0.89 0.47 0.74 0.46 0.71 0.62 0.01 0.79 0.60 0.41 0.65 0.88

(0.44, ( 0.11, (0.25, (0.28, (0.72, ( 0.06, (0.45, (0.07, (0.44, ( 0.03, ( 0.06, ( 0.03, (0.11, ( 0.04, ( 0.04, (0.70,

1.00) 0.79) 0.92) 0.83) 1.00) 1.00) 0.94) 0.77) 0.93) 1.00) 0.01) 1.00) 0.91) 0.75) 1.00) 1.00)

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Black necrosis Bone Dry necrosis Exudate Fibrin Fistula Granulation Ischemia Need for cleansing Slough Surrounding infection Tendon Undermining Wet necrosis Wound infection Yellow necrosis

95%CI (2.5%, 95%)

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1 = Blacknecrosis 2 = Bone 3 = Drynecrosis 4 = Exudation 5 = Fibrin 6 = Fistula 7 = Granulation 8 = Ischemia 9 = Needforcleansing 10 = Slough 11 = Surrounding infection 12 = Tendon 13 = Undermining 14 = Wetnecrosis 15 = Woundinfection 16 = Yellownecrosis

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Kappa (gold standard − iPhone) Fig. 4. PID/gold standard and iPhone/gold standard kappa plot, line represents equality.

We used clinical judgment as the gold standard in ulcer assessment. To ensure the quality of the method, we calculated an inter-rater kappa value. Our results show that even under exactly the same conditions, an assessment often depends of the assessor in accordance with other studies (1,4). When conducting a similar research experiment, our results confirm the importance of not relying on one assessor alone as the gold standard. As for surrounding infection in the gold standard assessment we found a low kappa value of -0.01 instead of a high value due to the kappa-paradox (15). Only two raters disagreed in one of the ulcers. This

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problem only occurred when surrounding infection was evaluated. The intra-rater agreement comparison of iPhone and PID suggests that repeating an image assessment twice will provide a small advantage of the PID images compared to the iPhone images. Nearly, all kappa values were in the higher end of the scale. However, when assessing dry necrosis on the iPhone (k = 0.29) the result seems less plausible as opposed to the PID k = 1.00, similar results were observed with ‘wound infection’. This could be due to coloring issues impacting the interpretation of the assessments. Despite the few odd results, this provides some evidence that the ability to extract and interpret exactly the same assessment details from an image even a month apart is fairly good. Some of the assessments are subject to interpretation and thus impacting the agreement although the results still reflect the everyday clinical situation. Terris et al. found moderate inter-rater agreement when comparing an image against a live assessment and concluded that it may be attributed to variation in subjective perception of qualitative ulcer characteristics (4). This also seems to be the case here as shown in Fig. 4 demonstrating a cluster of assessments around 0.0, 0.3, and 0.6 indicating an interpretation issue. Fistula, ischemia and wound infection with a kappa value around 0.0 seems to be highly affected by this issue. Tsai et al. showed a high sensitivity and specificity from a clinical assessment to a remote standard image (2). Our results show a clear advantage of the PID image compared to the iPhone image. The PID has some obvious advantages by introducing motions as movement and digital zoom as opposed to only digital zoom in the iPhone image. However, many of the questions posed are purely 2D phenomenon’s and thus in theory not providing the 3D images an advantage. The results may be explained by a more natural detailed image with a more correct coloring. Other investigators have evaluated the use of imaging in clinical assessment (16,17). Our results suggest some difficulties with respect to specific assessments especially using an iPhone. In a broad perspective, the ability to extract assessment details seems to be straightforward, but transferring to the clinical situation (the gold standard) introduced some interpretation

Telemedical ulcer monitoring TABLE 3. PID/gold standard and iPhone/gold standard kappa results with 95% confidence intervals Gold standard to iPhone Variables Black necrosis Bone Dry necrosis Exudation Fibrin Fistula Granulation Ischemia Need for cleansing Slough Surrounding infection Tendon Undermining Wet necrosis Wound infection Yellow necrosis

Kappa 0.32 0.11 0.08 0.05 0.31 0.16 0.38 0.01 0.27 0.06 0.10 0.23 0.20 0.11 0.03 0.53

Gold standard to PID 95% CI (2.5%, 95%) ( 0.02, 0.6) ( 0.15, 0.45) ( 0.12, 0.25) ( 0.19, 0.27) (0.05, 0.56) ( 0.07, 0.48) (0.10, 0.63) ( 0.24, 0.25) ( 0.01, 0.53) ( 0.18, 0.31) ( 0.18, 0.05) ( 0.10, 0.64) ( 0.07, 0.46) ( 0.09, 0.32) ( 0.17, 0.14) (0.24, 0.76)

issues regardless of image or device type. We do not believe, however that clinical judgment can be fully overtaken by these modalities, emphasized by the low kappa value of wound infection. Every individual with an ulcer must be evaluated clinically and stratified accordingly, before a telemedical approach should be conceived, and even so every image should be accompanied by a clinical assessment (7). Future studies should explore the possible superiority of 3D imaging compared to 2D imaging when assessing ulcers. Studies are undertaken to apply this 3D imaging device for deeper ulcers to measure volume as opposed to the conventional surface area measurement.

Conclusion In the handling of ulcers it is essential to present a photo modality with high image quality when used in a telemedical setup. We present an evaluation of a new imaging device with a high quality clinical image. Within the limits of this feasibility study the new portable imaging device proved superior compared to an iPhone

Kappa 0.66 0.18 0.54 0.27 0.57 0.05 0.43 0.01 0.47 0.25 0.22 0.82 0.55 0.31 0.02 0.58

95% CI (2.5%, 95%) (0.33, 087) ( 0.13, 0.63) (0.21, 0.80) (0.02, 0.50) (0.30, 0.79) ( 0.10, 0.02) (0.13, 0.69) ( 0.20, 0.25) (0.23, 0.70) ( 0.03, 0.50) ( 0.05, 0.49) (0.47, 0.89) (0.21, 0.84) (0.07, 0.54) ( 0.07, 0.02) (0.34, 0.79)

in assessing ulcer details. The potential for measuring area and volume seems to be in favor of the new portable device. However, further studies are needed to substantiate this aspect.

Acknowledgements Senior physician Isa E. B. Jensen and nurse Inger Futtrup are thanked for their contributions to this study.

Funding The European Regional Development Fund, through the Commerce and Construction Authority on the recommendation of the Growth Forum. (Aid from the European Regional Development Fund): 1.5 million euro of which 788,277, – euro equity financing.

Conflicts of Interest With regard to this study, the authors have no conflicts of interest to declare.

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Validation of a new imaging device for telemedical ulcer monitoring.

To clarify whether a new portable imaging device (PID) providing 3D images for telemedical use constitutes a more correct expression of the clinical s...
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