ORIGINAL ARTICLE

T. T. Carpenter Æ A. S. H. Kent

A new method of quantifying endometriosis using digital photography

Received: 19 December 2004 / Accepted: 18 February 2005 / Published online: 13 May 2005
� Springer-Verlag Berlin / Heidelberg 2005

Abstract The revised American Fertility Society scoring
system for quantifying endometriosis is a relatively
insensitive tool when assessing peritoneal endometriosis.
We describe a new technique that can be used to
quantify endometriosis which uses digital photography
and a specifically designed computer analysis package to
calculate lesion surface area. Using this we were able to
demonstrate good intra-observer reproducibility, al-
though inter-observer variability was relatively poor.

Keywords Endometriosis Æ Quantification

Introduction

Despite the fact that the revised American Fertility
Society scoring system (rAFS) [1–3] is the standard
technique for classifying endometriosis, it is rather lim-
ited in its discriminatory powers when dealing with
peritoneal disease. By virtue of the fact that it was
developed as a scoring system aimed to correlate with
fertility, points are allocated heavily for disease affecting
the fallopian tubes and ovaries with very little points
being available for peritoneal disease. In fact, for peri-
toneal disease alone the highest possible score is six,
which places it in the mild category. Thus if one is spe-
cifically interested in change in peritoneal disease the
rAFS is a rather blunt tool.

In view if this, we undertook a pilot study to assess
the feasibility and reproducibility of using digital imag-
ing to assess the surface area of specific endometriotic
lesions.

Method

Subjects

This was a three-centre study with multicentre regional
ethics committee approval. Six patients were recruited
(two from each site). Inclusion criteria were patients
who were due to undergo a laparoscopy for suspected
or known endometriosis, were over 18 years old, had
all gynaecological organs present and had given in-
formed consent. There was no limitation on stage of
disease.

Image capture

All patients underwent laparoscopy in the proliferative
phase of the cycle. Laparoscopic entry was carried out
in the usual way as per the practice of the gynaecolo-
gist, with particular care being taken when the uterus
was instrumented not to be too vigorous with bimanual
examination. On entry, the abdominopelvic cavity was
inspected in the usual way, at which time an endome-
triotic ‘‘index’’ lesion was selected. This was a lesion
that was anatomically relatively easy to photograph
with no/minimal manipulation needed, next to which
could be placed a needle. The operating camera system
was then detached from the laparoscope and replaced
by a Nikon COOLPIX 4500 digital camera with a
special adaptor to allow attachment of the camera to
the end of the laparoscope. The camera had 4.0
megapixel resolution.

Camera set-up

A straight 13 mm surgical needle (with 2.0 vicryl at-
tached) was introduced via a second port and placed as
close to the lesion as possible in the same plane. The
light setting on the camera was set to incandescent with
a light intensity of zero (range �3 to +3).

T. T. Carpenter (&) Æ A. S. H. Kent
Dept. of Gynaecology, Royal Surrey County Hospital,
Egerton Road, Guildford, GU2 7XX, UK
E-mail: t.carpenter@doctors.org.uk

T. T. Carpenter
7 Pointout Road, Southampton, SO16 7DL, UK

Gynecol Surg (2005) 2: 119–125
DOI 10.1007/s10397-005-0095-7



Using auto focus, supplemented by manual focus
where necessary, the lesion was photographed close-up,
ensuring that the whole lesion and needle was in view.
The laparoscope was then pulled back, the camera
refocused, and a wide-angle picture taken to allow the
location of the lesion to be demonstrated.

The laparoscope and needle were then removed and
the camera system detached. Following this, the whole
process was then repeated to obtain a second set of
images on the same lesion. The remainder of the lap-
aroscopy was completed by the laser ablation of all
visible endometriosis and closure of the abdominal port
sites was by the usual practice of the operating
gynaecologist.

Images captured on the digital flash card where then
downloaded onto the hard drive of a Compaq Evo
computer and copies of each pair (close-up and wide
angle) of images were stored on individual compact discs.

Image analysis

The images were analysed independently by two
gynaecologists using a specifically-prepared software
package produced by Virtualscopics, Rochester, NY,
USA. The 12 individual close-up images were presented
in random order for each assessor to quantify. The
surface area was calculated by first defining the needle
for scale. The individual components of each le-
sion—red, black and white (as defined by the rAFS
definition) [1]—were then circumscribed by the investi-
gators using any combination of the various functions.
Functions available were:

Filters:

Red, Green, Blue, Black, White

Delineators:
Live wire mode Allows you to optimise the path

drawn between successively user-
defined points.

Shrink-wrap mode Allows you to define a structure by
roughly tracing the outside perim-
eter of a well-defined structure.

Region growth
mode

Allows you to identify, with one
mouse click, an entire well-defined
structure.

3-D region growth
mode

Similar to the Region Growth
Mode, but the growth will proceed
in three dimensions.

Geometrically
constrained region
growth (GEORG)
mode

Allows you to define the shape of
the geometric model. The model is
used to smooth region boundaries
and limit growth outside a struc-
ture of interest.

3-D GEORG
mode

Operates on the same principle as
GEORG, with the additional
functionality of growth proceeding
in three dimensions.

Add mode Allows you to use free hand
tracking to modify a currently
finalized (red) contour by adding a
new area.

Adjust mode The Adjust Mode allows you to
modify the active contour. Each
time the left mouse button is
clicked, the contour is forced to
pass through the clicked point.

Continuous trace
mode

Allows you to perform free hand
tracing of structure boundaries.

Erase mode Allows you to modify the currently
finalized contour by using free
hand tracing to delete the un-
wanted portion of the region.

Polygon mode Allows you to manually trace
structure boundaries by connecting
points that the user made in the
Image window. Straight lines are
used to connect points defined by
successive mouse clicks.

Rectangle mode Allows you to define a rectangle.
Select mode Allows you to convert a finalized

(red) contour to an active (blue)
contour.

When the investigator was happy with the defined
area, the image was finalised and the computer calcu-
lated the surface area using the needle as a reference.

Statistical analysis

Intra- and inter-observer reproducibility was assessed by
variance, coefficient of variation, and subjectively using
plots.

Results

The total lesion area and the breakdown of red, black
and white components as assessed by the two assessors
are shown in Table 1.

The range in sizes of the index lesions selected for
assessment is wide (0.5–69 mm

2
). The index lesions for

three out of the six subjects contained only red tissue
and had no black or white component. These were also
the three smallest lesions. The remaining three lesions
had all three component areas, with the largest compo-
nent being white scar tissue.

Plots of the lesion areas for the duplicate assessments
made on each subject are presented by area type in
Figs. 1, 2, 3 and 4.

The within- and between-subject variance compo-
nents of the index lesion assessments are shown in
Table 2 and the within-subject coefficient of variations
(SD/mean) are shown in Table 3.

120



Discussion

The ranges in lesion size and lesion components in these
patients are quite wide, with some small lesions having
only red components and other larger lesions being
dominated by white areas.

To assess the reproducibility of a test there is no
standard single ‘‘test’’ that can be applied. Instead one
must use a combination of quantitative and qualitative
assessments. In this experiment we used the coefficient of
variation (CV) to quantitatively assess variability; how-
ever, this should be interpreted with great caution as the
number of assessments is small and as such will be
markedly influenced by any outlying values. As a general
rule, a CV of 100 is used as the cut-off for an acceptable
lack of variation, but the figure is obviously a contin-
uum, with lower figures indicating less variability. The
CVs obtained in this study for both assessors show good
reproducibility for within-subject analysis, with all
figures being below 100. Variability in all cases was less
for assessor one than for assessor two, with the within-T

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Fig. 1 Plots of total lesion surface area for each pair of lesions and
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121



subject variation contributing between only 0.7 and
3.6% of the total variance of assessor 1 compared to a
within-subject variance for assessor 2 of between 6.7 and
34%. However, it is important to note that the per-
centage variance figures given in Table 2 are percent-
ages, so the figures are proportions. Therefore, if the
between-subject variance component is high, as in the
case of assessor 1, then proportionately, and thus as a
percentage, the within-subject variance will be low. This
can therefore give an artificial impression of a smaller
within-subject variance than is actually the case. Look-
ing at the true figures for variance, it is still clear that
assessor 1 gave consistently less within-subject variabil-
ity than assessor 2, although to a lesser extent than is
apparent from the percentage values.

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sors, assessor 1 used significantly more manual tracing
of the regions via the live wire mode than user 2, who
predominantly used the more automated functions of
regional growth and geometrically constrained regional
growth modes. This would imply that, although more

time-consuming, semi-automated manual drawing of the
lesions is a more reproducible technique.

In both cases the most reproducible component of
analysis was the red area. This is encouraging, as red
areas are considered most active [4], and thus if one were
to test any new treatment for active endometriosis, one
would expect these areas to respond first and possibly to
a greater extent.

The total CVs for the two assessors were clearly far
less reproducible. As a function of both between-subject
variance and within-subject variance, this would be ex-
pected due to the wide ranges in lesion sizes and com-
positions. When assessing the efficacy of any treatment
(or indeed a simple change in disease) one is interested in
the changes in individual lesions or components of
individual lesions, not the changes in total areas of le-
sions in a combined set of patients. As such this varia-
tion is unimportant.

As explained earlier, assessment of reproducibility is
enhanced by the combination of both quantitative and
qualitative methods. Thus the plots of lesion size are
equally important when drawing conclusions on

Fig. 2 Plots of red lesion surface area for each pair of lesions and
for each assessor

Fig. 3 Plots of black lesion surface area for each pair of lesions
and for each assessor

122



reproducibility and they also allow us to assess intra-
and inter-observer variability. From Tables 1 to 3 and
Figs. 1, 2, 3 and 4, the intra-observer reproducibility of
the red and black areas appears very good in both
observers. Note, however, that assessor 1 found no black
areas in three of the subjects and assessor 2 found no
black areas in two subjects, thereby making the plots of
the black areas for the six subjects look better than
perhaps is truly the case. Red areas, however, were
present in all subjects, and the reproducibility is good
throughout. The total lesion areas and white lesion areas
do seem to show greater variability, with the greatest
variability being apparent in the larger lesions. The re-
duced reproducibilities of these areas compared to the
red and black areas are probably related to the fact that
the red and black areas have more obvious borders and
thus confines. We are looking at lesions on a back-
ground of peritoneum which itself has a white/greyish
appearance. Identifying a border between a white area
of endometriosis and normal peritoneum is therefore
considerably harder, and hence more prone to error,
than defining a border between a red or black area and

Fig. 4 Plots of white lesion surface area for each pair of lesions
and for each assessor

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123



normal peritoneum. The greater variability seen in the
larger lesions is most likely to be as a consequence of
size. The potential for error is going to increase with
lesion size since the border to be defined is longer. In
addition, we show actual lesion size in the plots rather
than relative differences between plots. Thus, a 20%
difference in actual surface area between plots in a small
lesion will be markedly smaller than a 20% difference in
a larger lesion. In reviewing plots of the two assessments,
the larger lesion will have a much steeper slope between
the two plots than the smaller lesion, despite the relative
difference in the two assessments being the same.

Assessment of inter-observer variability is best made
by viewing Figs. 1, 2, 3 and 4. The more horizontal the
line, the lower the intra observer variability, and
the closer each pair of lines lie to each other, the lower
the inter observer variability. From all plots it is clear
that the reproducibility of analysis is significantly worse
between assessors. The differences between the assessors
when assessing the black areas does not seem great;
however, as previously mentioned this is because no
black areas were present in two of the subjects (as as-
sessed by both assessors), and with the exception of
subject 3 the black areas in the other subjects were very
small. The lesion from subject 3 showed wide variation
in all areas of assessment between the two assessors. On
review, this lesion is a very complex lesion, with a
potentially large chance of error.

There was no consistent difference between the
assessors, although it is interesting to note that whilst
the red area was most reproducible in within-observer
analysis, it was in fact the area that showed most vari-
ation between observers. Thus it would appear that,
although borders of these areas are easier than other
areas to elucidate, the subjective decision as to whether
an area is red, black or white still remains to be made by
the assessor, and this appears to show more variability.

When assessing reproducibility one must be aware of
the components contributing to the variability. The ta-
bles and figures concentrate on the variability within and
between the two assessors. In fact the pairs of lesions
analysed in each case are not the same image of the lesion
but two different images of the same lesion taken at
different times (albeit the same operation). Thus the
within-subject variation is not only a function of
the variability of the assessor but also the variability of
the image taken. Whilst efforts have been made to min-
imise the variability between the images, inevitably the
photographs will not be taken at exactly the same angle,

the needle will not be in exactly the same position for
each photograph, and other variables will be slightly
different between them too. It is important to be aware of
these differences, as they are likely to be minimised in this
study by the fact that the images were captured during
the same operation a short duration apart. In studies
assessing the efficacy of a treatment over time, the images
will be captured during separate operations some time
apart, almost certainly increasing the variability.

The aim of developing new analysis techniques is to
facilitate the detection of clinically-significant effects of a
treatment on a disease, which in this case means that we
would like to detect a clinically-significant difference in
endometriotic lesions. In endometriosis, whilst one can
make assumptions as to what would be a clinically-sig-
nificant reduction in pain for example, because of the
lack of correlation of symptoms with disease, it is not
possible to logically select a value for clinically-signifi-
cant change (with the exception of total disease irradi-
ation) in lesion surface area. This technique is therefore
most useful as a research tool. For ethical and economic
reasons it is not possible to run long, large-scale trials of
new treatments without some indication of the efficacy
to begin with. Research tools such as this will allow
investigators to detect changes, which may be relatively
small, over a short period of time, which may then be
used to justify a larger, more pragmatic study of a par-
ticular treatment.

What is important, however, is to be aware of the
ability, or limitations, of a test used to detect a differ-
ence. A test that has a relatively high variability is going
to be unable to detect small differences between two
groups because the difference will be ‘‘masked’’ by the
background intrinsic variability. From the results ob-
tained using this technique, assessor 1 should be able to
detect a within-subject variance of more than 3.6%, and
assessor 2 a within-subject variance of more than 34%.
These figures should be kept in mind when interpreting
the results. Because of the relatively small number of
lesions used in this study and the differences between
each pair of lesions examined, it was not possible to
assess whether there was a ‘‘learning curve’’ with this
technique.

One criticism of this technique is that it only mea-
sures the diseased surface and takes no account of
depth of invasion and volume of disease. This would be
particularly applicable to patients with relatively ad-
vanced disease or those in areas such as the uterosacral
ligaments, which often have little visible disease at the

Table 3 Coefficients of
variation for each assessor Lesion area Overall mean CV (Total) CV (Within-Subject)

Assessor 1 Assessor 2 Assessor 1 Assessor 2 Assessor 1 Assessor 2

Total 23.08 14.77 107.8 80.93 13.4 47.1
Red 9.32 5.48 106.0 72.4 9.0 22.9
Black 1.96 1.58 194.8 180.9 18.4 46.9
White 11.80 7.71 118.0 151.9 22.5 82.2

124



surface but have deep deposits within. At present, the
most likely route to quantifying this sort of disease
would be via other means of imaging, such as magnetic
resonance imaging. While work has been undertaken in
this area, a reproducible technique has not been found
to date [5].

Conclusions

This technique demonstrates acceptable intra-observer
variability for both assessors; however, there is signifi-
cant operator dependence for reproducibility. The
intra-observer reproducibility is relatively poor. This
technique allows us to estimate an observers variability,
thereby highlighting what might be considered a clini-
cally-significant change when power calculations are
performed for future studies.

Acknowledgments We would like to acknowledge Pfizer UK for
provision of the digital equipment and statistical analysis. We
would also like to acknowledge Mr. S. Ewen and Mr. A. Pooley
who undertook the digital photography at two of the sites.

References

1. American Society for Reproductive Medicine (1997) Revised
American Society for Reproductive Medicine classification of
endometriosis. Fertil Steril 67(5):817–821

2. American Fertility Society (1985) Revised American Fertility
Society classification of endometriosis. Fertil Steril 43(3):351–
352

3. American Fertility Society (1979) American Fertility Society for
Classification of endometriosis. Fertil Steril 32(6):633–634

4. Khan KN et al (2004) Higher activity by opaque endometriotic
lesions than nonopaque lesions. Acta Obstet Gynecol Scand
83(4):375–382

5. Kinkel K et al (1999) Magnetic resonance imaging characteris-
tics of deep endometriosis. Hum Reprod 14(4):1080–1086

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