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3D HD versus 2D HD: surgical task efficiency in standardised
phantom tasks
Pirmin Storz
•
Gerhard F. Buess
•
Wolfgang Kunert
•
Andreas Kirschniak
Received: 27 June 2011 / Accepted: 3 November 2011 / Published online: 17 December 2011
Springer Science+Business Media, LLC 2011
Abstract
Background Common video systems for laparoscopy
provide the surgeon a two-dimensional image (2D), where
information on spatial depth can be derived only from
secondary spatial depth cues and experience. Although the
advantage of stereoscopy for surgical task efficiency has
been clearly shown, several attempts to introduce three-
dimensional (3D) video systems into clinical routine have
failed. The aim of this study is to evaluate users’ perfor-
mances in standardised surgical phantom model tasks using
3D HD visualisation compared with 2D HD regarding
precision and working speed.
Methods This comparative study uses a 3D HD video sys-
tem consisting of a dual-channel laparoscope, a stereoscopic
camera, a camera controller with two separate outputs and a
wavelength multiplex stereoscopic monitor. Each of
20 medical students and 10 laparoscopically experienced
surgeons (more than 100 laparoscopic cholecystectomies
each) pre-selected in a stereo vision test were asked to perform
one task to familiarise themselves with the system and sub-
sequently a set of five standardised tasks encountered in typ-
ical surgical procedures. The tasks were performed under
either 3D or 2D conditions at random choice and subsequently
repeated under the other vision condition. Predefined errors
were counted, and time needed was measured.
Results In four of the five tasks the study participants
made fewer mistakes in 3D than in 2D vision. In four of the
tasks they needed significantly more time in the 2D mode.
Both the student group and the surgeon group showed
similarly improved performance, while the surgeon group
additionally saved more time on difficult tasks.
Conclusions This study shows that 3D HD using a state-
of-the-art 3D monitor permits superior task efficiency, even
as compared with the latest 2D HD video systems.
Keywords Laparoscopy High definition Stereoscopy
3D monitor Standardised phantom tasks
Several studies have shown stereoscopic endoscopic video
to have more or fewer advantages as compared with
monocular endoscopic video [1–7]. To date, the efficacy of
high-definition (HD) resolution in endoscopy has not been
definitively proven [8], although it is commonly assumed,
and every new available laparoscopy system on the market
is equipped with HD technology.
Spatial depth information loss in a 2D image can be
compensated to a high degree by experience on the one
hand [9], and by the ability of the human brain to interpret
secondary spatial depth cues, such as shadows and parallax
movement for estimation of spatial proportions [10–14], on
the other hand. The benefit of secondary spatial depth cues
focussing on shading was shown by Arrezzo et al. [15].
As early as the 1980s, Prof. G.F. Buess stated that ste-
reoscopic vision is important in minimally invasive sur-
gery. He developed a bi-channel optical system for his
transanal endoscopic microsurgery (TEM) procedure [16].
Moreover, the surgical microscopes used in ophthalmo-
logic, neurosurgical and ear–nose–throat (ENT) depart-
ments provide a binocular view. Attempts to use camera
and monitor systems via microscopes have failed, because
surgeons prefer the good spatial impression and direct view
Gerhard F. Buess—deceased.
P. Storz G. F. Buess W. Kunert (&) A. Kirschniak
Department of General, Visceral and Transplant Surgery,
Workgroup Experimental Minimally Invasive Surgery
and Training, University Hospital Tuebingen,
Waldhoernlestrasse 22, 72072 Tuebingen, Germany
e-mail: wolfgang.kunert@uni-tuebingen.de
123
Surg Endosc (2012) 26:1454–1460
DOI 10.1007/s00464-011-2055-9
and Other Interventional Techniques
that oculars provide. In the meantime, several experiments
have investigated the efficacy of 3D in a surgeon’s work
using various 3D systems. Because these early prototypes
entailed several technical flaws, 3D was always seen to be
a compromise that includes a loss in image quality.
Mu
¨
ller-Richter et al. [17] concluded that only half of the
published studies show a real advantage when using 3D.
However, the latest technical developments ensure high-
definition 3D visualisation with the same quality that cur-
rent 2D systems provide.
This study is designed to proof that users’ performances
in a revised standardised surgical task setting differ
between using 3D HD visualisation and standard 2D HD
visualisation regarding precision and working speed.
For 3D HD visualisation a novel wavelength multi-
plexing monitor is used.
Materials and methods
The applied stereovision system consists of the following:
• 10-mm 25 angulated dual-channel rod lens laparo-
scope (prototype; Richard Wolf GmbH, Knittlingen,
Germany)
• 6CCD stereo endoscopic camera head (functional
model; R. Wolf GmbH, Toshiba HD-CCDs)
• Camera controller with two separate digital XGA video
outputs, one for each eye (functional model; R. Wolf
GmbH)
• Wavelength multiplex stereoscopic monitor (functional
model; INFITEC GmbH, Ulm, Germany)
• Wavelength multiplex stereo glasses (passive; INFI-
TEC GmbH)
For 3D HD visualisation the monitor shows two separate
images, one for the left eye and one for the right eye, which
are presented to the corresponding eye by special filter
glasses. The 3D HD system used separates the two images
by means of wavelength multiplexing. Here, both images
are composed of partial spectra of the three primary colours
red, green and blue. These partial spectra used for the left
image are different from those of the right image and are
generated with the aid of interference filters. By these
means the images are coded and can be assigned to the
corresponding eye via the mentioned glasses.
For 2D HD visualisation, only one HD chip of the
system is used and presented in 2D mode to ensure iden-
tical images apart from the stereoscopic effect.
Stereo vision test
Many studies show that the ability to perform stereoscopic
image fusion differs from person to person. Especially
people with strabismus are sometimes not able to extract
spatial information from two simultaneously perceived
images, each with a slightly different angle of view (ste-
reoscopic video stream) [18]. To ensure that only study
participants with stereo vision were enrolled in the study,
each subject had to pass a stereo vision test. This test was
based on the random dots principle by Julesz [19] that is
used in the common Randot, Lang and Titmus stereo tests.
In our test the stereoscopic information included six cir-
cular slices with one quarter missing from each slice. The
potential study participants were asked to enter the location
of the missing quarter (left, right, top or bottom) in a pre-
printed form. The two partial images were presented
simultaneously on the stereo monitor using a personal
computer (PC).
In a pre-evaluation, 2 out of 40 medical students failed
the test and were therefore excluded from analysis of the
pre-study. All 20 students who wanted to participate in the
main study passed the stereo vision test.
Adaption to the stereo effect (adaption task)
Depending on the quality of the stereoscopic display, the
user needs an adaption period until the full 3D effect is
experienced. To quantify the adaption time, an independent
pre-study was performed with 34 medical students. A
simple manual adaption task with negligible learning effect
was repeated four times using the 3D system including the
wavelength multiplexing monitor. The adaption task was
similar to a simple sorting task as used in several studies. It
included bi-manual grasping and positioning steps using an
endoscopic grasping forceps and an endoscopic Maryland
dissector (R. Wolf GmbH) in order to sort pins into two
small buckets.
On average, the second repetition was completed more
quickly than the first. Further repetitions did not show any
statistically relevant improvement. We concluded that one
run through this adaption task was sufficient to learn the
manual procedure and fully adapt to the stereo effect. In the
main study all participants performed the adaption task
twice to ensure its full effect.
Improved standardised task course
The phantom tasks used in our study represent typical basic
surgical tasks and were partially based on the setups used
in previous studies [2, 3, 15]. The tasks were derived from
typical surgical procedures such as electro-coagulation of
individual spots as well as complex movements around
anatomical structures and suturing. For reasons of repro-
ducibility, these procedures were abstracted and task setups
were constructed of artificial materials. Each task setup was
mounted on a board that slid into a training box, where it
Surg Endosc (2012) 26:1454–1460 1455
123
was fixed in a precisely defined position. The top of the
training box was fitted with a rubber plate with two
openings for the trocars for the laparoscopic instruments
and another central opening for the stereoscopic rigid
endoscope. The stereoscope was guided by a metal tube
and could be precisely fixed in position and angle to
guarantee reproducible vision conditions. The distance
between monitor and study participant was standardised at
1.20 m. The time required for task completion and the
number of electronically counted predefined errors were
measured as indicators of task efficiency. The electronic
components were integrated in the training box. No direct
error feedback was given to the study participants. Instead
of using endoscopic illumination, two halogen light sources
were placed in the training box together with a large con-
cave white reflection screen fixed between the back plane
and the top face to reduce shading (a secondary spatial
depth cue) in the endoscopic viewing field by means of
indirect illumination.
Study design
This study is a randomised comparative study in a stand-
ardised experimental setup.
The course of action of the study is shown in Fig. 1.
After passing the stereoscopy test, the student group and
the surgeon group were randomly divided into two sub-
groups each. The first subgroup started by doing a complete
set of tasks under 2D vision, and the second subgroup
under 3D vision. Then each subgroup performed the same
set of tasks again, but under the other vision condition. The
student group had to wait a minimum of 48 h before the
second run-through. All these steps were taken to ensure
that residual learning effects would not influence the sta-
tistical analysis.
Instruction and adaption
Before each stage the study participants were shown an
introduction video explaining the phantom tasks in order to
guarantee the reproducibility of instruction. They were
instructed to not unnecessarily lose time, but to focus on
precision. Next they took the instruments in hand and were
given time to familiarise themselves with them without
using the phantom model.
In order to familiarise themselves with the 3D system,
study participants performed an adaption task twice. This
was a simple grasping and moving task, in which four pins
had to be picked up with the left-hand instrument (forceps),
passed to the right-hand Maryland dissector and put down
again.
Tasks 1–5
This was followed by the five tasks explained below and in
Fig. 2.
Task 1 was a one-handed flat shape positioning task.
Eight black circular target spots (Ø 3 mm) had to be tou-
ched once each with a Maryland dissector using the right
hand and moving in a counter-clockwise sequence. Each
time the surrounding brown surface was touched was
counted as an error.
Task 2 was similar to task 1, but the targets were placed
on a relief surface. Seven circular target spots (Ø 3 mm)
had to be touched 20 times in a randomly defined order
using a Maryland dissector and the right hand. Touching
the outer metal ring counted as an error.
Task 3 involved a complex 3D movement. A wire was
bent in all three spatial directions and threaded through a
metal loop, with both ends of the wire fixed to a board. The
metal loop had to be grasped with a lockable endoscopic
needle holder and touched to an electronic contact at the
upper end of the wire. Then the loop was guided along the
wire, without touching it, to the lower end of the wire.
After touching the electronic contact at the wire’s lower
end, the loop was moved back along the wire to the top
end. Accidental touches between loop and wire were
counted as errors.
Task 4 consisted of precise straight stitching done
bi-manually. Five straight stitching channels (3 mm) had to
be pierced from right to left using a straight needle held
with a needle holder in the right hand, moving from the top
one downwards. The needle was received by a needle
grasping forceps, guided by the left hand and then returned
to the needle holder.
Task 5 called for continuous suturing using a circular
needle. Four stitch-in and four stitch-out marks (Ø 1.5 mm)
were printed in ideal orientation on a disposable glove
pulled over a sponge block. A continuous suture had to be
Fig. 1 Overview of procedure sequence
1456 Surg Endosc (2012) 26:1454–1460
123
executed at the given marks. The deviations between the
actual puncture points and the corresponding marks were
measured on a photo using a computer.
Statistical analysis
For statistical analysis SAP JMP software was used, and
Wilcoxon signed-rank tests for related samples were per-
formed to compare both time and errors. In this way we
were not only able to compare the results of all 2D and 3D
performances, but also to take each participant’s individual
improvement or deterioration between the tasks under the
two vision conditions into account.
We consider calculation of error rates to be inappro-
priate, because the type of correlation between time and
errors is not proven.
The data collected were also tested for an effect of the
sequence in which 2D and 3D were used in order to
investigate for learning effects.
In addition, performance was examined with the Mann–
Whitney U test for differences between students and
surgeons.
For p values, two-tailed test results were considered.
Results
Figure 3 shows a comparison of 2D HD and 3D HD
visualisation. For clearer understanding the graph shows
the relative change between tasks performed under 3D HD
vision and those performed under 2D HD. Thus, values in
the lower half demonstrate better performance under 3D
HD vision and those in the upper half poorer performance
when using 3D HD. Table 1 shows the study participants’
performance in detail.
Student group (n = 20)
For task 1 no statistically relevant difference in precision
was seen between 2D and 3D vision conditions. However,
under 3D vision the task was completed in 28.0% less time
than under 2D vision (median; p = 0.0003).
The student group completed task 2 29.8% more
quickly (p = 0.0002) and made 45.0% fewer mistakes
(p = 0.0204) when using 3D than when using 2D vision.
With regard to task 3, by median 11 fewer mistakes
were made (-73.5%; p \ 0.0001). Task performance
under 3D vision permitted time savings of 15.6% by
median (p = 0.0153).
Fig. 2 All five tasks seen endoscopically
Surg Endosc (2012) 26:1454–1460 1457
123
Performance of task 4 showed 25% fewer errors
(p = 0.0023) while working at the same speed.
Task 5 also showed better precision under 3D vision
(0.5 mm/stitch; 29.3%; p \ 0.0001) and substantial time
savings of 31.5% (p = 0.0042).
In summary, obviously difficult tasks were completed
with greater precision when working under 3D vision.
Moreover, with one exception, the amount of time needed
for task performance was also shorter.
Regarding the effect of the sequence in which 2D and
3D were used, the statistics showed no relevant difference.
Surgeon group (n = 10)
The results calculated for the advanced laparoscopic sur-
geons were similar.
In task 1 the surgeons achieved slightly greater precision
when using 3D, although it was not statistically significant.
Again, already in task 1 a time saving of 14.1% by median
(p = 0.0020) was observed.
Task 2 was performed with 33.8% fewer mistakes
(p = 0.0078), but the amount of time needed was about the
same.
Fig. 3 Statistics summary
Table 1 Study participants’ performances
Task 1 Task 2 Task 3 Task 4 Task 5
Errors Time (s) Errors Time (s) Errors Time (s) Errors Time (s) Deviation
(mm)
Time (s)
Student
group
Median 2D 5 71.04 3 98.085 14.5 46.455 3 120.13 6.2 411.64
Median 3D 4 44.33 2 70.265 4 35.445 2 103.655 4.41 283.235
Median
3D–2D
0.5 -29.08 -1 -29.81 -11 -8.185 -1 -16.17 -1.95 -126.33
p 0.0003 0.0204 0.0002 \0.0001 0.0153 0.0023 NS \0.0001 0.0042
Surgeon
group
Median 2D 5.5 37.54 5.5 55.66 13 40.17 3 114.32 6.36 150.10
Median 3D 5.5 30.41 3.5 53.21 3.5 25.83 2 76.88 5.23 112.33
Median
3D–2D
-1 -5.14 -2 -2.62 -9 -14.18 -1 -21.44 -0.97 -32.58
p 0.0020 0.0078 0.0020 0.0020 0.0156 one-sided
0.0322
0.0020 0.0195
NS not significant
1458 Surg Endosc (2012) 26:1454–1460
123
Task 3 showed increased precision (74.6%; p = 0.0020)
and time savings of 33.4% (p = 0.0020).
On task 4, precision was increased by 45% (p = 0.0156)
and the time saving was 18.0% (one-sided p = 0.0322).
On task 5, also precision was greater under 3D vision
(0.24 mm/stitch; 16.1%; p = 0.0020), and the time saving
was 25.8% as compared with 2D vision (p = 0.0195).
No statistically relevant effect of sequence was
observed.
Comparison of students versus surgeons
In our experimental setup students and surgeons achieved
similar precision under 2D vision and 3D vision. Precision
did not differ significantly throughout all five tasks.
In tasks 1, 2 and 5, performance by surgeons was sta-
tistically significantly faster under 2D vision (p
1
= 0.0001;
p
2
= 0.0001; p
5
\ 0.0001). Under 3D vision surgeons
were faster in tasks 1 and 5 (p
1
= 0.0002; p
5
= 0.0001)
but in task 2 the students achieved the same working speed.
While there was no difference in working speed between
the two groups in tasks 3 and 4 under 2D vision, the sur-
geon group was faster than the student group in both tasks
under 3D vision (p
3
= 0.0064; p
4
= 0.0311).
Discussion
Our results show a significant benefit when using 3D HD
visualisation as compared with 2D HD visualisation. In the
student group this positive 3D effect had the greatest
impact on precision in difficult tasks, while it permitted
faster task performance for simple tasks.
The surgeon group showed a similar gain in precision
for 3D visualisation, both in absolute numbers of errors and
in relative improvement with regard to their 2D perfor-
mance. With regard to time needed, 3D permitted the
surgeons to also achieve a greater improvement in working
speed in the difficult tasks than the students.
A look at the various studies on the effect of 3D in
minimally invasive surgery [2, 3, 5, 7, 17] reveals the
inhomogeneity of their results.
By contrast, our clear results can be ascribed to the
idealised setting.
The synthetic phantom task setup simulates only surgi-
cal partial procedures and was designed for the purpose of
statistical analysis. It does not reflect the complexity of
clinical conditions.
In clinical routine, in teaching settings using animal
organs placed in phantoms and in setups using corpses,
multiple disturbance variables are encountered that con-
stitute a major obstacle to obtaining objective data on
surgical task efficiency as well as isolated exploration of
the 3D effect.
Most secondary spatial depth cues were reduced in our
setup (by means of diffuse illumination, very few shadows
and blank surfaces without textures). However, high-defi-
nition vision itself emphasises the outlines of instruments
and therefore especially supported the important secondary
spatial depth cue of overlapping objects.
Arezzo et al. showed that visible shadows in the oper-
ative field can improve task efficiency [15], especially
when approaching an organ surface with an instrument tip.
This visual support can be expected to work even better
under HD vision and therefore help compensate the lack of
stereoscopic information, which would then diminish the
isolated effect of 3D. However, in the mentioned study, a
special shadow telescope was used to create relevant
shading.
In clinical practice as compared with the static inani-
mate phantom environment of our study some further dif-
ferences can be expected. Here, the telescope can be moved
to achieve motion parallaxes, which also provides sec-
ondary spatial depth information [13, 14] (e.g. when per-
forming a diagnostic overview).
A closer look at the study participants’ performance,
especially that of the students, shows that on simple tasks
3D vision produced only little improvement in precision,
while performance time was better.
Probably, in most operations performed today, 3D HD
offers the possibility to merely work faster without causing
damage. However, in complex operations it increases
patient safety. As attempts increase to use 3D HD for more
complex operations that are still done in open procedures,
this effect will at least gain in relevance.
The influence of this additional visual information, and
maybe additional strain, on the human brain of course
remains to be examined.
Persons with 3D blindness will unfortunately not be able
to take advantage of a 3D system, as they derive their
spatial impression only from secondary spatial depth cues.
They are, in a manner of speaking, optimally adapted to 2D
image reproduction. Use of 3D furthermore eliminates the
handicap that stereoscopic persons presently have when
working laparoscopically.
Conclusions
Use of 3D visualisation not only improves task efficiency
as compared with standard-resolution 2D as previous
studies show. High-definition 3D is superior to up-to-date
2D HD systems.
Use of 3D might be of minor importance in simple tasks
and indeed remains a cost factor, but it still increases
Surg Endosc (2012) 26:1454–1460 1459
123
surgical task efficiency, especially when performing diffi-
cult surgical tasks, even in the age of HD video.
Acknowledgments The 3D HD TV project was funded by the
German Federal Ministry of Economics and Technology. The ste-
reoscopic laparoscope with the 6CCD endocam was a purpose-built
item devised by Richard Wolf GmbH, Knittlingen, Germany. The 3D
wavelength multiplex monitor is patented and constructed by INFI-
TEC GmbH, Ulm, Germany.
Disclosures Authors P. Storz, W. Kunert, G.F. Buess and
A. Kirschniak have no conflicts of interest or financial ties to disclose.
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