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A Comparison of Wound Area Measurement
Techniques: Visitrak Versus Photography
Angela Christine Chang,aBronwyn Dearman, BSc (Hons),bJohn Edward Greenwood,
AM, BSc (Hons), MBChB, MD, FRCS (Eng), FRCS (Plast), FRACSb
aSchool of Medicine, University of Adelaide, Adelaide, South Australia; and bAdult Burn Cen-
tre, Royal Adelaide Hospital and Skin Engineering Laboratory, Hanson Institute, Adelaide, South
Australia.
Correspondence: john.greenwood@health.sa.gov.au Published April 18, 2011
Objective: To investigate whether a cheap, fast, easy, and widely available photographic
method is an accurate alternative to Visitrak when measuring wound area in cases where
a non–wound-contact method is desirable. Methods: The areas of 40 surgically created
wounds on porcine models were measured using 2 techniques—Visitrak and photogra-
phy combined with ImageJ. The wounds were photographed with a ruler included in the
photographic frame to allow ImageJ calibration. The images were uploaded to a com-
puter and opened with ImageJ. The wound outline was defined from the photographic
image using a digital pad, and the ImageJ software calculated the wound area. The
Visitrak method involved a 2-layered transparent Visitrak film placed on the wound and
the outline traced onto the film. The top layer containing the tracing was retraced onto
the Visitrak digital pad using the Visitrak pen and the software calculated the wound
area. Results: The average wound area using the photographic method was 52.264 cm2
and using Visitrak was 51.703 cm2. The mean difference in wound area was 0.560 cm2.
Using a 2-tailed paired Ttest, the Tstatistic was 1.285 and the value .206, indicating no
statistical difference between the two methods. The interclass correlation coefficient was
0.971. Conclusions: The photographic method is an accurate alternative to Visitrak for
measuring wound area, with no statistical difference in wound area measurement demon-
strated during this study. The photographic method is a more appropriate technique for
clean and uncontaminated wounds, as contact with the wound bed is avoided.
The measurement of wound dimension is an important component of successful wound
management. Monitoring changes in wound area allows assessment of treatment efficacy
and early detection of stasis or deterioration. The information can also aid in research,
communication with patients and between practitioners, evidence-based clinical decision
making, and, ultimately, an improvement in the quality of patient care. Wound surface area
calculations have been shown to be a valid and accurate indicator of wound progress.1
Although measuring wound volume may provide additional information, it has received
limited attention in the literature,2possibly due to practical difficulties incumbent with
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CHANG ET AL
volume measurement. Several series have demonstrated that wound circumference and
area directly correlate to wound volume,3,4and thus volume is not required for appropriate
wound monitoring.
There are a wide variety of devices and methods available to measure wounds. How-
ever, to be useful in routine clinical practice, the technique needs to be time- and cost-
efficient, accurate, sensitive, unbiased, comfortable for the patient, and useable by any
operator.
The simplest method of determining wound area is by measuring with a ruler. The
greatest length is multiplied by the perpendicular greatest width. This technique is quick,
inexpensive, and easy to perform but assumes that the wound is square or rectangular in
shape. This type of calculation has been shown to overestimate wound area by 10% to
44%,5,6with accuracy decreasing as wound size increases.6,7This method is imprecise and
inappropriate for wounds which are large, irregular, or cavitous.6Accuracy can be improved
by using the formula for the area of an ellipse rather than a rectangle,8or by using a formula
for a shape similar to that of the wound.9
Manual tracing, by placing a transparent film over the wound and tracing the outline
with a permanent marker allows more accurate area calculation when the wound is irregular.
From the tracing, there are several methods of determining area. The tracing can be placed
on a metric grid, and the number of squares of a known area counted. This is quick and
easy,10 but inaccuracy arises when deciding the value of partial squares.11 The outline can
also be cut out and weighed, although this may be time-consuming and error may arise
during cutting and weighing. This also requires accurate scales capable of detecting acetate
fragments of potentially very small mass. Digital planimetry involves the same process
of wound tracing, but the outline is then retraced onto a digital tablet, which calculates
the area. This has the advantage of quick, precise, and objective calculation, as well as
revealing wound circumference. However, added scope for error occurs with retracing.12
The accuracy of area measurement from wound tracings depends on correct and consistent
identification of the wound margins. Several studies have shown that the largest source of
error is when determining wound borders, rather than the process of calculating the area
traced.4,13 The reliability of this technique decreases with decreasing wound size.7The
Visitrak system (Smith & Nephew Wound Management, Inc, Largo, Florida) is an example
of a digital planimetry system developed in response to the need of an easy, fast, and
reliable tool for clinical use. The wound is traced onto a Visitrak grid sheet, which is then
retraced onto the Visitrak digital pad, which automatically completes the area calculations.
Visitrak has been shown to have excellent intra- and interoperator reliability, high validity,
and a correlation co-efficient of 0.99 compared to other systems of digital planimetry.14 Its
main advantages are the rapidity of the technique (one half to one third the time of other
systems), and its relative inexpense compared to other planimetry systems. Difficulties
using the Visitrak system are the same as those when manually tracing any wound onto
transparent film—difficulty identifying wound margins, fogging under the film impeding
vision, pressure on the wound altering the outline, stiff film unable to conform closely
to wound surface, plus the requirement of film to be in contact with the wound risking
contamination, wound bed damage, and patient discomfort and pain.3,15 The Visitrak and
many other systems requiring on-wound tracing minimize the risk of contamination by
providing a clean (although nonsterile) disposable sheet under the tracing sheet in contact
with the wound.16 Although for nonsterile venous ulcers the risk of infection from a tracing
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grid is minimal, contamination becomes a major concern for patients presenting with burns
and surgically “clean” wounds.
Photography can be used to calculate wound area. The borders of the wound are
traced from a digital photograph using a mouse or digital pen on a digital tablet. A ruler,
or other accurate scale, photographed near the wound allows the user to calibrate the
software to enable it to judge distance. An advantage of photography is that it does not
require contact with the wound. It provides a permanent record of not only wound size
but also appearance. As with other forms of wound tracing, determining wound borders
is subjective and may be problematic if edges are poorly defined or obscured by debris.
High-resolution photographs are required to properly identify epithelial growth at wound
margins.17 Important considerations when using photography are photo quality, lighting,
and camera angle. Variation in camera angle can lead to an underestimation of wound area
by up to 10%.18 Given that a 2D image is representing a 3D structure, apparent wound
size discrepancy may also occur when tracing circumferential wounds, or those on curved
body surfaces.19,20 Despite these difficulties, studies have still reported very good intra- and
interoperator reliability.6,11,21 A variation of this system is photogrammetry, such as utilized
in the VeV system (Vista Medical, Winnipeg, Mannitoba, Canada). This computerized
system consists of a video camera, frame grabber, and customized wound assessment
software. A digital photograph of the wound, including a target plate, is uploaded to the
computer. The software uses the target plate for calibration and calculates the wound area.
Computerized photogrammetry has proved to be more accurate than the manual method on
both plaster of Paris models22 and animal wounds,11 although its clinical application may
be limited by greater cost.
Sterophotogrammetry involves the use of 2 cameras and the computer to reconstruct
3D images of wounds allowing calculation of wound area and volume.19 Although steropho-
togrammetry seems to be the most accurate method22,23 of determining wound area, its use
requires additional training, the equipment is expensive, and it is time-consuming, making
it impractical for routine clinical assessment.
The aim of this study was to investigate whether a cheap, fast, easy, and widely available
photographic method is an accurate alternative to Visitrak, when measuring wound area in
cases where a non–wound-contact method is desirable.
METHODS
Animal Subjects
Porcine models with surgically created wounds already in use for alternative research
were used for this study. A total of 40 wounds (4 wounds on 2 swine measured once
a week for 5 weeks) were measured using 2 methods—Visitrak and photography com-
bined with ImageJ software. Each wound was created as an 8 ×8cm
2dissected to
the paniculus adiposus. All were located on the dorsum of the animal to minimize sur-
face curvature and allow ease of photography. During measurement, the animals were
anaesthetized to minimize movement. On each occasion, they were placed in the same
position under consistent lighting conditions. Prior to measurement and photography,
the wounds were cleaned and slough removed to provide easily visible wound margins.
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For either technique, wound border tracing was done by the same operator in every
instance.
Photographic method
The wounds were photographed using a Canon EOS 550D digital camera, with electro-
focus short back focus (EF-S) 18-55 mm lens. A “square” ruler with markings on each side
was placed around the wound and included in the photographic frame to allow calculation
of wound dimensions once uploaded to the computer. Using a visual estimate, an effort
was made to hold the camera at the zenith above the wound, and the lens parallel to the
plane of the surface. The images were uploaded to a computer and opened with ImageJ, a
Java imaging processing program available for free download from the Internet. For each
photographic image, measurements were calibrated using the ruler at the base of the image
included in the photographic frame. The wound outline was defined from the photographic
image using a digital pad. Following tracing, the ImageJ software calculated the wound
area.
Visitrak method
The wounds were also measured using Visitrak, a digital planimetry system. A 2-
layered transparent Visitrak film was placed on the wound (Fig 1), and the outline
traced onto the film using a permanent marker. The layer of the film in contact with
the wound was discarded. The top layer containing the tracing was retraced onto the
Visitrak digital pad using the Visitrak pen and the software calculated the wound
area.
Data analysis
The data was compiled and analyzed using Microsoft Excel 2007 (Microsoft, Redmond,
California).
RESULTS
Figure 2 demonstrates the individual wound area surface measurements for all 40 wounds.
The mean and variance of the surface area for both techniques are shown in Table 1.The
average wound area using the photographic method was 52.264 cm2and using Visitrak was
51.703 cm2. The mean difference in wound area between the two methods was 0.560 cm2.
Analysis of the data, using a 2-tailed paired Ttest, revealed a Tstatistic of 1.285, with a
Pvalue of .206. Thus there was no statistical difference between the two methods when
measuring wound area. The interclass correlation coefficient (ICC) was 0.971. Variance
of the Visitrak method (129.851) was slightly lower than that of the photographic method
(147.305).
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Figure 1. The method of tracing a wound outline onto a Visitrak transparent film.
Figure 2. A comparison of wound area measurement using the Visitrak and photographic
technique.
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CHANG ET AL
Table 1. Statistical Results Comparing the Visitrak and Pho-
tographic Method
Photo +ImageJ Visitrak
Mean 52.263925 51.7025
Variance 147.3046944 129.8505064
Observations 40 40
Pearson correlation 0.974376635
Hypothesized mean difference 0
Degrees of freedom 39
tStatistic 1.284814729
P(T≤t) 1-tail .103217924
tCritical 1-tail 1.684875122
P(T≤t) 2-tail .206435848
tCritical 2-tail 2.022690901
Figure 3. “Fogging” of the Visitrak film while tracing the wound outline.
DISCUSSION
The results of previous wound area measurement studies comparing photographic and
transparency tracing methods have fairly consistently shown that both yield statistically
similar wound area results.13,17,21 The majority of these studies that were performed on
patients rather than synthetic wound models have been measuring the area of venous ulcers,
which have a limited size and body region distribution. Our results concur with previous
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series, showing the photographic method to be an accurate alternative to transparency
tracings, in our case Visitrak. The high ICC of 0.971 in our study compares favorably to
other studies of similar design where an ICC of 0.9913,21 was recorded.
Figure 4. (a) The same wound photographed from varied camera angles demonstrating the
effect of angle on observed size and shape. (b) Diagrammatic representation of a wound seen
from varied angles. (c) ImageJ wound area calculations from the photographs in (a).
Wound tracing
The usefulness of both methods depends on the accuracy of wound margin identification.
Prior to tracing and photography, the wound margins were made as clear as possible. The
wounds were undressed and any debris, slough, and necrotic tissue removed. The wound
and surrounding tissue were then cleaned with saline and dried. A problem encountered
while using the Visitrak system was fogging of the Visitrak tracing grid when placed on
the wound (Fig 3). This only occurred when tracing moist wounds making identification
of wound margins difficult. We attempted to hold the camera directly above the wound as
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CHANG ET AL
camera angle affects the apparent measurable area (Fig 4). As mentioned previously, varied
camera angle can lead to underestimation of wound area by up to 10%.18 To demonstrate
this phenomenon, one of our wounds was photographed with varying camera angle and the
area calculated using ImageJ (Fig 4). As expected, the wound area decreased as the angle
from the zenith increased.
Study limitations
The results should be interpreted within the limitations of the methodology. During this
study, the two measuring methods were compared using wounds of a relatively constant
size and shape, on a body region easy to photograph. Previous studies have demonstrated
that the reliability Visitrak decreases with decreasing wound size.8Likewise, the accuracy
of photography is compromised by curved surfaces, tapering of limbs, and circumferential
wounds.24
Intra- and interoperator consistencies were not tested. For both methods, each wound
was measured only once; however, the tracings for each method were performed by the
same operator. Previous studies have demonstrated high inter- and intraoperator reliability
for Visitrak,15 but some have found considerable interoperator variability when tracing the
wound outline from a photographic image.17
CONCLUSION
The photographic method is an accurate alternative to Visitrak for measuring wound area,
with no statistical difference in wound area measurement demonstrated during this study.
The photographic method is a more appropriate technique for clean and uncontaminated
wounds as contact with the wound bed is avoided, negating the risk of wound contamination,
wound bed damage, and patient discomfort.
ACKNOWLEDGMENT
The authors would like to thank Dr David Butler, University of Adelaide, for his statistical
advice and assistance.
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