INTRODUCTION
Photographic documentation has been important for several medical specialties,
such as plastic surgery, dermatology, and head and neck surgery, to name a few.
Photography is used to document pre- and post-operative events and, through
measurements of distances and angles, surgical planning. 1.
Two-dimensional (2D) photography has limitations when used for capturing depth
and volume of three-dimensional (3D) structures. Procedures involving volume
changes after surgery, therefore, require other instruments to evaluate those
changes, through comparison of photographs2,3.
Several technologies have been developed for the analysis of 3D objects. These
technologies can be divided into those emitting radiation, such as computerized
tomography, and those that do not emit radiation, such as 3D cephalometry, Moire
topography, 3D laser scanning, and stereophotogrammetry4-7.
Due to advantages such as lower cost, portability, harmlessness, faster image
capturing, and storage and software processing, technologies that do not emit
radiation, especially 3D laser scanning and stereophotogrammetry, have
increasingly been used to obtain 3D images7,8.
Stereophotogrammetry has advantages over 3D laser scanning in that it is more
portable, it has the ability to capture an object’s color and texture, and there
is no need to protect the patient’s eyes during its use9. Stereophotogrammetry was first described by Thalmann in
1944, who attempted to capture a 3D image of a face. In 1967, it was improved
and simplified by Burke and Beard. In 1995, Ras and collaborators concluded that
it was adequate to obtain 3D records of changes in facial morphology.
Subsequently, Deacon et al. in 1999 improved the stereophotogrammetry technique
by using digitalized images and analysis software5.
Stereophotogrammetry uses two or more simultaneous photographs of an object to
produce a 3D geometric model, after software analysis. The software produces
3D
images based on the difference between the photographs at a known angle between
cameras. Color and texture are subsequently added.
Two types of triangulation algorithms can be used in stereophotogrammetry:
Passive and active. The active type involves projecting an unstructured light
pattern (visible or infrared) on the object’s surface, whereas the passive uses
only the natural ambient light pattern, instead of projected light1,3,5,10.
Active stereophotogrammetry, therefore, has the advantage of depending less on
external light to obtain images; however, the surroundings need to be dark when
photographs are taken. Despite depending on external light for obtaining images,
most available equipment in the market still use passive
stereophotogrammetry.
Equipment that use passive stereophotogrammetry technology have been shown to be
more flexible for use in doctors’ offices and hospitals, and it has been the
technology of choice in many companies using 3D photography. There is also a
hybrid equipment that uses both passive and active stereophotogrammetry11-14.
Stereophotogrammetry has great potential to become the standard method for
evaluating volumes and distances in facial and body anatomy. Regarding the face,
it can be used to evaluate the fill volume necessary for a given wrinkle,
post-surgery edemas or estimate volume increases obtained after aesthetic and
surgical procedures11,12.
OBJECTIVE
The objective of the present study was to perform a bibliographic review
evaluating the use and accuracy of stereophotogrammetry equipment to measure
the
volume of facial structures.
METHODS
Search strategy for study identification
A search, including studies published on or before May 2018, was performed in
the Cochrane Library and MEDLINE virtual databases.
The search in MEDLINE was performed using a combination of free terms and
MeSH keywords such as [three-dimensional imaging (MeSH Terms)],
[photogrammetry (MeSH Terms)], [face (MeSH Terms)], and the
Cochrane Sensitivity Maximizing version strategy (Figure 2, Appendix). The search in the
Cochrane Library database was performed using free
terms, following the strategy presented in Figure 3 (Appendix). No restrictions were placed on the basis of
the study language.
Inclusion and exclusion criteria:
Studies that evaluated the use of stereophotogrammetry to measure the volume
of facial structures in humans were included. Studies that used technology
unavailable commercially or studies that were reviews or response articles
were excluded. The studies retrieved were divided into two groups:
Randomized and non-randomized studies.
Two independent researchers read the titles and abstracts and then selected
the studies according to the eligibility criteria. A consensus reached by
the two researchers was used to solve disagreements on study inclusion. The
risk of bias in this study was evaluated using a similar tool to the one
used by Cochrane Collaboration.
Evaluation of the methodological quality of the randomized
studies:
A score was assigned to each study according to its methodological
quality.
RESULTS
A total of 2,213 studies were retrieved using the search strategy presented in
Figure 1. After reading the titles
and/or the abstracts, 2,051 studies were excluded based on the eligibility
criteria. A total of 162 studies were selected for full reading and, following
selection, 27 studies were included in the study, of which 21 were uncontrolled
unblinded non-randomized case studies4,8,12-29 and 6 were
randomized clinical trials10,30-34.
Figure 1 - Process of inclusion and exclusion of studies for systematic
review.
Figure 1 - Process of inclusion and exclusion of studies for systematic
review.
Figure 2 - Search strategy in Medline.
Figure 2 - Search strategy in Medline.
Figure 3 - Search strategy in the Cochrane Library.
Figure 3 - Search strategy in the Cochrane Library.
Of the 162 studies, 87 were excluded because facial parameters other than volume
were evaluated, 27 studies were excluded because they used technologies other
than stereophotogrammetry, 10 studies were excluded because they were reviews,
8
studies were excluded because they were letters to the editor or response
letters, and 3 studies were excluded because mannequins or cadavers were
used.
Of the 21 case studies, 17 used stereophotogrammetry to evaluate the differences
in facial volume before and after an intervention (surgery, fillings, fat
graph), 3 used stereophotogrammetry to evaluate the differences in facial volume
overtime (aging, monitoring of hemangioma), and 1 aimed at evaluating the
reliability of stereophotogrammetry.
A total of 703 individuals were evaluated in the case studies, of which 264
(37.55%) were men and 397 (56.47%) were women, while 42 (5.97%) did not report
their gender. The average age was 38.48 years (range; 4 months to 91 years).
The
average monitoring time was 11.07 months (range; 1 to 24 months).
A total 219 individuals (111 patients and 108 controls) were analyzed in the 6
randomized studies, of which 132 (60.27%) were women, 61 (27.85%) were men,
while 26 (11.87%) did not report their gender. The average age was 32.83 (range;
20 to 55 years) and average monitoring time was 6.59 months (range; 7 days to
18
months). These studies aimed at using stereophotogrammetry to evaluate
differences in facial volumes between a group subjected to an intervention (such
as surgery, filling, or use of devices to decrease post-operative swelling) and
control groups.
The methodological quality of the studies varied between 50 and 67%, on a grading
scale from 0 to 100% (Table 1).
Table 1 - Score of randomized trials.
Study |
A |
B |
C |
D |
Absolute |
Relative |
Hans- Joachim Niekenig 2014 |
2 |
1 |
0 |
1 |
4 |
67% |
Maieed Rana 2012 |
1 |
1 |
0 |
1 |
3 |
50% |
M. Rana 2011 |
1 |
1 |
0 |
1 |
3 |
50% |
Jeff Downie 2009 |
1 |
2 |
0 |
1 |
4 |
67% |
Kyung Suk Koh 2012 |
1 |
0 |
0 |
1 |
3 |
50% |
Majeed Rana 2011 |
1 |
1 |
0 |
1 |
3 |
50% |
Table 1 - Score of randomized trials.
DISCUSSION
Although many studies showed the use of stereophotogrammetry in medical practice,
relatively few described its usefulness for measuring facial volumes. Moreover,
many studies mentioned other 3D photography technologies, evaluated regions
other than the face, or measured parameters other than volume.
Most studies used stereophotogrammetry to evaluate volume differences before and
after an intervention, follow the evolution of diseases such as changes in
hemangioma volume, or evaluate its reliability when compared with direct volume
measurements. The scarcity of double-blinded randomized studies should be noted:
Only 6 out of the 2,213 initially retrieved studies were double-blinded.
Of the 6 double-blinded randomized trials, three studies31,32,34 compared two
methods of cooling the inferior third of the faces of patients subjected to
orthognathic or odontological procedures. In these studies, stereophotogrammetry
was used to determine which cooling method caused a lesser post-operative volume
increase, and, therefore, had a higher efficacy in decreasing post-operative
edema.
The methodology was very similar in the 3 studies in that the same facial cooling
and stereophotogrammetry equipment (FaceScan3D) was used. Only the type of
surgery performed differed. In all the three studies, subject allocation was
randomized and the observers were blinded with regards to the use of cooling
equipment.
One study used stereophotogrammetry (Di3D) to evaluate the volume gain obtained
using four different types of facial fill10. Similar to the other three studies, the subjects were allocated
randomly, and subjects and observers were blinded to the type of fill used.
Another study evaluated post-operative edema using stereophotogrammetry (CAM3D),
comparing two types of oral and maxillofacial surgical procedures30. Evaluations, done by measuring lower
facial volumes using stereophotogrammetry, were used to determine the surgical
strategy that caused less post-operative edema. Still, subjects were allocated
randomly and observers were blinded.
Finally, one study evaluated survival in subjects who underwent facial fat
grafting with or without the use of fat mesenchymal stem cells 33. Fat grafting survival was monitored by
measuring the maintenance of volume gain using stereophotogrammetry (Vectra 3D)
during post-operative follow-up. Group allocation was randomized but there was
no mention as to whether observer or patient blinding was done.
Stereophotogrammetry was observed to be more reliable for volume analysis of
inanimate objects than of living beings. It was concluded that this difference
could be explained by the effect of muscle contraction and face animation on
soft tissues. Despite this difference in reliability, there were no significant
intraclass differences in coefficients. This indicated good method
reproducibility8.
The accuracy of measurements using the equipment’s software is thought to be
dependent on the operator. To avoid this operator bias, appropriate
pre-operative volumes were obtained for proper comparison with the volumes
measured after surgery. In addition, it is important to avoid facial animation
or head rotations19; the patient should
have a neutral expression, with closed mouth and lips4,7.
The disadvantages of stereophotogrammetry include the lack of portability of some
of the equipment and the need for image analysis using a software that may not
be common users. Another disadvantage is that it is difficult to tell whether
volume variations in children are due to the intervention or due to growth.
Meanwhile, in adults, very small volume variations may be attributed to changes
such as edema that could, in reality, be unrelated to the intervention18,22,25.
Another important consideration is whether stereophotogrammetry allows for the
calculation of volume in regions with hair, cavities or depressions, such as
the
sub-nasal and submental regions. Failing to perfectly align the pre- and
post-operative photos may also cause errors. Objects that reflect light, such
as
jewels, may cause photographic artifacts. It is therefore recommended that
patients secure their hair and remove jewels and other ornaments. The high cost
of the 3D photography equipment, which may vary somewhere between U$15,000 and
U$35,0000, is a limiting factor for the availability and use of this
technology35.
As validated in previous studies, stereophotogrammetry has good accuracy and
reproducibility for the measuring of facial distances and volumes 3,26,29,36,37.
Studies have shown that the most commonly used equipment available in the market
have high accuracy. For example, 3dMD, Vectra, and Di3D systems have shown an
average error of 2%, 1.2%, and 1%, and a coefficient of reproducibility of 0.80,
1 and 0.13, respectively5,38.
A limitation of the present study is that the studies for analysis were retrieved
from only two databases (PubMed and Cochrane) and the majority
of studies were of low quality: Only 2 of the 6 studies scored higher than 50%
according to the methodological qualification used (Table 1). Also, the present review lacks reliable studies.
Of the 6 randomized studies, 3 analyzed the same facial cooling device. Worthy
of note is that the stereophotogrammetry equipment differs with regards to
software, accuracy, reproducibility, and ease of use (Table 2).
Table 2 - Characteristics of the equipaments used in articles of literature
review.
|
Geometric resolution (mm) |
Capture time (ms) |
Coverage (graus) |
Processing time (segundos) |
Number of cameras |
Software used |
Price U$ |
Company |
Vectra H1 |
0,95 |
2 |
100 |
20 |
1 |
Vectra Capture / Analysis Module |
11.000 |
Canfleld Scientific |
FaceScan 3D |
0,1 |
800 |
180 |
ND |
1 |
3D Viewer |
NA |
3D-Shape GmbH |
Di3D |
<0,2 |
1 |
180 |
60 |
4 |
Di4D Processing Software |
35.000 |
Dimension Imaging |
3dMDFace System |
<0,2 - 0,5 |
1,5 |
190 |
<8 |
6 |
3dMD Vultus Software |
27.000 |
3dMD |
Table 2 - Characteristics of the equipaments used in articles of literature
review.
CONCLUSION
Stereophotogrammetry is a promising technology that is being increasingly used to
evaluate facial volume variations in patients before and after surgery or to
monitor the evolution of facial diseases that may involve volume changes.
Measuring facial volume using this technology had high inter- and intra-operator
accuracy and reproducibility in the reviewed studies.
Although a good number of studies were retrieved, studies with better
methodological quality that evaluate stereophotogrammetry accuracy and use for
evaluation of facial volumes are still lacking.
COLLABORATIONS
REM
|
Data analysis and/or interpretation; final manuscript approval; data
collection; conceptualization; conception and design of the study;
project management; methodology; writing- preparation of the
original manuscript; writing - revision and editing; supervision;
visualization.
|
SM
|
Writing- preparation of the original manuscript; writing - revision
and editing; supervision; validation.
|
JLB
|
Data analysis and/or interpretation; data collection.
|
LHM
|
Data analysis and/or interpretation; data collection.
|
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1. Hospital das Clínicas, Faculdade de Medicina,
Universidade de São Paulo, São Paulo, SP, Brazil.
Corresponding author: Ricardo Eustachio de Miranda, Rua Bandeira
Paulista, nº 530, sala 43 - Itaim Bibi - São Paulo, SP, Brazil, Zip Code
04532-001. E-mail: ricardomiranda@hotmail.com
Article received: June 24, 2018.
Article accepted: October 4, 2018.
Conflicts of interest: none.