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Figure 27.1 The bleeding set -up with the EASIE -R simulator.
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Assessment of competency using
simulation models
There are not, as of yet, generally agreed upon competencies
for NOTES. As procedures mature and more experience is
achieved, a specifi c set of competencies will emerge. Through
existing animal and human experience, however, it is clear
that competencies from general surgery, minimally invasive
surgery, and fl exible endoscopy are required in a NOTES
team. Frequently, for the establishment of transvaginal
access procedures, gynecologists are consulted to assist with
the incision and closure. At present, it is prudent to insist
that a multidisciplinary NOTES team consist of members
who fulfi ll competencies and principles present in guidelines
for general surgery, minimally invasive surgery, and fl exible
endoscopy, as described by the respective authorities (i.e.,
the Accreditation Council for Graduate Medical Education
[ACGME], SAGES, and ASGE, respectively) [14–17].
The development of a NOTES assessment tool is considered a prerequisite for the credentialing process. Recently,
the Formative Intraoperative Tool for NOTES Evaluation of
Surgical Skills (FITNESS) tool has been demonstrated by
Vassiliou et al. [18] as a method of assessing competency in
NOTES. This assessment tool consists of six items scored on
a Likert scale from 1 to 5: access (A), navigation and orientation (NO), visualization and stabilization (VS), instrument
manipulation and targeting (IMT), closure (C), and application of surgical principles (SP). However, there is limited
data about the validity of this tool since the preliminary
study involved only eight participants (four novice and four
experienced). Multicenter trials are currently warranted to
establish inter -rater reliability and construct validity of
CHAPTER 27 Simulator-based Training of NOTES Procedures
FITNESS. It is currently not clear whether a team versus
individual assessment is mandatory.
The Fundamentals of NOTES Surgery (FNS) is based on
Fundamentals of Laparoscopic Surgery and Fundamentals
of Endoscopic Surgery (FLS/FES) training tools, which are
supported by the SAGES/ASGE Task Force. Prerequisites for
FNS may be FLS and FES certifi cation. FNS aims to assess
cognitive and manual skills components specifi c to NOTES
procedures and challenges related to different accesses and
evolving technology platforms. FNS may develop into
modules that are access and procedure specifi c.
Available NOTES simulation models
Prior to attempting NOTES procedures in the animal laboratory with large live animals, it is benefi cial for the multidisciplinary NOTES team to gain familiarity with the procedures,
techniques, and communication through simulated procedures. Existing trainers for laparoscopic surgery and GI
endoscopy are valuable for developing the basic skills necessary for NOTES. These trainers are especially valuable for
cross-training, such as allowing a surgeon to develop or
refi ne advanced endoscopy skills with a virtual reality (VR)
endoscopy trainer. There are currently only artifi cial tissue
and ex vivo models for NOTES available but VR training
models will become available in the near future.
Artifi cial tissue simulation models
The Endoscopic -Laparoscopic Interdisciplinary Training
Entity (ELITE) is a latex model for the training of endoscopic/
laparoscopic surgery and NOTES techniques developed
by the research group MITI (Klinikum Rechts der Isar,
Germany) and manufactured by Coburger Lehrmittelanstalt
(CLA, Coburg, Germany). It is a full -size reproduction of a
female human torso, with a skin tinted, gas -tight latex
abdominal wall. All intra -abdominal organs are based on
latex compounds with different characteristics and colors to
permit realistic mock -up of the intra -abdominal anatomy
(Figure 27.2).
The group demonstrated the construct validity of the
model in a study involving 15 novices and 15 experts (8
gastroenterologists and 22 surgeons). Participants were
asked to perform a peritoneoscopy via a trans -sigmoidal
approach in fi ve consecutive courses. The time needed to
perform the peritoneoscopy was evaluated. All participants
passed a signifi cant learning curve during the peritoneoscopy assessment (total time needed: 473.1 ± 178.5 s for
fi rst pass versus 321.9 ± 182.0 s for fi fth pass; p = 0.02, Wil-
coxon test). To demonstrate construct validity, signifi cant
differences were observed for the total time required to
perform the respective procedures between endoscopic
experts versus novices (fi rst pass: 394.3 ± 176.6 s for
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Figure 27.2 The set -up with the ELITE simulator.
Figure 27.4 The laparoscopic ports of the EASIE -R simulator. Figure 27.5 Laparoscopic view of a transgastric cholecystectomy in the
Figure 27.3 The set -up with the EASIE -R simulator.
EASIE-R simulator.
experts versus 531.9 ± 166.7 s for novices; p = 0.040, Mann Whitney test) [19].
The group also conducted a study involving a group of 30
participants (gastroenterologists, laparoscopists, and novices)
who performed a standardized NOTES cholecystectomy via
a trans -sigmoidal approach. Half of the participants performed the cholecystectomy following training with ELITE
and half without previous training. All participants showed
a signifi cant learning curve, with a total time needed on the
fi rst pass of 32 minutes versus 18 minutes for the fourth pass
(p < 0.001). For the cholecystectomy in the pig animal
model, participants with prior training needed less time to
complete the procedure than participants without training.
In the group without training, more complications/diffi culties
296
occurred than in the group with prior training (16 versus 8)
[20].
Ex vivo tissue simulation models
The EASIE -R™ simulator (Endosim, LLC, Berlin, MA, USA)
uses ex vivo porcine specimens harvested from the meat
production industry that are thoroughly cleaned, sterilized,
and surgically altered to resemble human anatomy.
The specimens are positioned into a plastic mold that
arranges the organs in a human -like anatomy. This model
is currently the only real tissue NOTES simulator available
and provides the opportunity to use commercially available
devices and prototypes (Figures 27.3–27.5).
CHAPTER 27 Simulator-based Training of NOTES Procedures
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Using the EASIE -R simulator, multiple gastrotomies or
colotomies can be performed in a single specimen. To facilitate multiple participants to train consecutively for gastrotomy or colotomy, the access sites can be closed with a
regular hand -tied suture from outside. In addition to the
endoscopic view, surgical procedures can be observed
through the clear acrylic cover or as a hybrid procedure with
laparoscopic guidance by using a domed lid with laparoscopic ports. In contrast to using live animals for NOTES
training, the use of ex vivo specimens obtained from the
meat industry does not involve ethical concerns and is not
subject to Institutional Review Board (IRB) or Institutional
Animal Care and Use Committee (IACUC) approval.
The model has been used extensively at various national
and international NOTES courses. At the Learning Center of
the SAGES 2008 and 2009 Annual Meetings, the EASIE -R
simulator was compared prospectively to the ELITE simulator for various NOTES procedures. Random participants
used both models and performed NOTES procedures such
as translumenal access/closure, NOTES appendectomy, distal
pancreatectomy, nephrectomy, and cholecystectomy. Both
models were evaluated using an evaluation form that
included twelve questions regarding various aspects of the
performance, realism, utility, and ease of use of the ex vivo
simulators, rated on a 7 -point Likert scale (1, lowest rating;
7, highest rating). The average score for all of the evaluative
questions for the plastic ELITE model, including aspects of
performance, realism, utility, and ease of use, was 5.25 ± 1.04
(median ± IQR). The average score for all of the evaluative
questions for the EASIE -R porcine ex vivo simulator, including aspects of performance, realism, utility, and ease of use,
was 5.83 ± 1.03. The EASIE -R ex vivo simulator had a signifi
cantly higher average score than the ELITE plastic simu-
lator ( p < 0.0001). Specifi cally, in visual realism of the model
compared to humans, the EASIE -R ex vivo simulator had a
signifi cantly higher user rating than the ELITE plastic simulator, 5.91 ± 0.87 versus 5.00 ± 1.07, respectively ( p = 0.02).
In tissue pliability compared to humans, the EASIE -R ex
vivo simulator had a signifi cantly higher user rating than
the ELITE plastic simulator, 5.91 ± 0.91 versus 4.60 ±
respectively ( p = 0.01). In anatomic correlation of the model
compared to humans, the EASIE -R ex vivo simulator had a
signifi cantly higher user rating than the ELITE plastic simulator, 5.68 ± 0.68 versus 4.40 ± 1.20, respectively ( p = 0.003).
There were no signifi cant differences between the simulators in individual questions specifi c to user evaluation of
utility of the simulator in improving laparo -endoscopic
skills, recommendation of the simulator to others, ability of
the workshop to improve skills, usefulness of the simulator
in teaching basic endoscopy, usefulness of the simulator in
teaching NOTES, overall realism of the simulator, usefulness
of the simulator as a teaching tool, ease of use of the simulator, and the ease of incorporation of the simulator into a
fellowship program ( p > 0.05). The results of this prospec-
1.02,
tive comparison demonstrated preferences in surgeons for
real tissue, ex vivo simulators, as opposed to plastic simulators in NOTES simulation and training [21].
Also, after the multidisciplinary NOTES team has progressed to procedures with live animals in the laboratory or
with humans in the operating room, it is useful to hone the
unique skills required in NOTES in a simulated environment. Training in the simulated environment provides a safe
environment to attempt new or refi ned procedures, and also
saves time and money that would have been spent in the
animal laboratory.
Team simulation of NOTES
Those interested in learning and training in the novel NOTES
technique should assemble a multidisciplinary team devoted
to NOTES training and procedures, composed of members
who are profi cient and experienced in general surgery, minimally invasive surgery, fl exible endoscopy, anesthesiology,
nursing, and technological support. This dedicated team
should undergo a thorough training, initially with simulation models followed by a transition to animal models, in
order to learn the premise of the procedure and master the
necessary interdisciplinary communication that is imperative to NOTES.
Furthermore, NOSCAR has created guidelines for team
development [22]:
• Multidisciplinary team, possessing skills in advanced therapeutic endoscopy and advanced laparoscopy
• Should include members of SAGES and/or ASGE
• Access to animal laboratory facilities for research and
training
• Laboratory results should be shared at semi -annual
NOSCAR group meetings
• Any and all human procedures should be performed after
IRB approval
• Human cases should be submitted to NOSCAR Registry.
Simulation training has reached the forefront of surgical
education and has also been applied to emerging techniques.
Training as part of a team is an important component of
simulation. With NOTES, new interactions between members
of teams such as endoscopists and surgeons, and merging
of endoscopic and laparoscopic surgical crews, introduces
potential confl icts and barriers to effi cient patient care.
Tsuda and colleagues developed a high -fi delity, fully
functional, mock endosuite using the EASIE -R simulator
for NOTES procedures to assess team performance in the
event of operative technical failure and bleeding crisis
during a transgastric cholecystectomy. At the 2009 SAGES
Annual Meeting Learning Center, a high -fi delity mock
endosuite with open, laparoscopic, and endoscopic capabilities, anesthesia and OR staff confederates, and a hybrid
mannequin model containing swine visceral components
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within a simulated abdominal cavity allowed practicing surgeons to perform a laparoscopic cholecystectomy via a
transgastric approach with a therapeutic gastroscope. The
procedure was videotaped following a briefi ng, and intentional scope tower malfunction followed by intralumenal
and intra -abdominal bleeding with appropriate physiologic
changes were introduced into the scenario without prior
disclosure to the participants. Time to resolution of the technical malfunction, order of troubleshooting steps, decision
to open, and time to open conversion were monitored. The
Non-Technical Skills Assessment (NOTECH) tool was used
to assess team performance, and pre - and post -surveys were
used to acquire demographic data and user impressions of
the simulation. Twelve total participants comprising fi ve surgical teams participated in the simulation; 25% (3/12) of the
participants had animal experience with NOTES compared
to no experience at all. Time to successfully diagnosis and
resolution of scope tower malfunction (loose scope cord/
camera box interface) was inversely proportional to years
in training ( p = 0.008), with all teams having participants
who disclosed less than 5 years of practice ( n = 7) able to
resolve the malfunction within 3 minutes, and all teams
with surgeons of greater than 10 years experience ( n = 4)
requiring proctor intervention at 5 minutes. Time to successful gastrotomy ranged from 3 to 9 minutes, with one
group aborting in favor of performing gastric biopsies. User
impressions on a fi ve -point Likert scale were highest for
realism, realistic response generation, and value to NOTES
training (4.55 ± 0.52, 4.5 ± 0.79, 4.67 ± 0.49, respectively)
and lowest for realism of bleeding and simulated abdominal
wall (3.75 ± 0.87, 3.18 ± 0.75, respectively) [23].
Animal laboratory experience
It is diffi cult to overemphasize the necessity of ample experience in the animal laboratory before any attempt is made to
perform human NOTES procedures. Large animals, particularly pigs, but also sheep and dogs, have been utilized in the
majority of the research that has been produced regarding
the development of NOTES as a surgical technique. Performing NOTES procedures on large animals allows the multidisciplinary team to develop acceptable techniques while
monitoring effects on physiology. It also allows the team to
become facile with the available technology, as well as the
management of complications as they arise, such as intraperitoneal bleeding. Importantly, animal laboratory studies
allow NOTES procedures to be analyzed for effi cacy, complications, and physiologic sequelae.
Although similar in many regards to humans, large
animals will never be able to reproduce perfectly the effects
of a certain procedure or technique on humans. Thus, after
multidisciplinary groups have spent a great amount of time
in the animal and simulation laboratories, and are comfort-
able in the safety and effi cacy of the procedure(s), well controlled and well -designed human studies are sought.
VR-based NOTES simulation
Background and challenges
Before NOTES can be safely introduced to humans in the
United States, several technical and physiological challenges
need to be resolved to avert the problems seen during the
maturation of laparoscopic surgery, when rapid and premature adoption of new techniques by individuals near the
beginning of their learning curves led to complications that
could have been prevented. In its highly cited White Paper
[6], NOSCAR identifi ed a number of major technical barriers, which included optimal techniques and location for
peritoneal access, evaluating the effects of pneumoperitoneum, reliable means of gastrotomy closure, maintaining
spatial orientation, novel instrumentation, and novel training regimens. NOTES procedures involve the skills of both
GI surgery and therapeutic GI endoscopy. In the short term,
a multidisciplinary team is needed to perform NOTES, before
a new kind of “NOTES surgeon ” evolves, fusing the skills of
both these professions [6]. Specialized training regimens and
objective evaluation of surgical skills are essential to ensure
smooth transition. Poor outcomes by physicians not thoroughly trained in NOTES procedures could lead to premature regulatory intervention, preventing development of a
technology that would ultimately benefi t many patients.
The question is: what testbed should be used to overcome
these barriers? Of course, testing new devices and procedures on human patients is too risky. The current paradigm
is to use animals (mostly pigs), cadavers, or the EASIE -R
NOTES simulator. Besides the fact that pig anatomy is different from human, such an approach is tedious, time consuming, requires enormous amounts of resources, and
severely delimits the number of possible alternatives that
can be explored. For example, a study comparing best gastrotomy closure practice between multiple endoscopic clips
and a proprietary device would require hundreds of animals
to begin to see small differences between the techniques.
Similarly, to design a single new tool, many prototype tools
would have to be manufactured, and the tests repeated.
A very similar hurdle in engineering has been resolved by
the advent of computer -aided design (CAD) technology.
Computational models are developed and are simulated
using a computer under various operating conditions before
a prototype, if any, is manufactured. For example, the
Boeing 777 was almost entirely designed and assembled on
the computer. Only a nose mock -up (to check critical wiring)
was built before assembly of the fi rst fl ight vehicle, which
was only 0.03 mm out of alignment when the port wing was
attached. CAD is now prevalent in most other industries,
from automobiles to microprocessors. Such computational
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CHAPTER 27 Simulator-based Training of NOTES Procedures
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tools drastically reduce the number of physical experiments
that need to be performed and signifi cantly reduce the
human resources and work hours necessary to perform
these experiments. They also allow exploration of a much
larger design space than would be possible otherwise, since
literally thousands of alternatives may be tested relatively
inexpensively within a short amount of time.
Taking advantage of recent advances in information technology, we are developing a VR -based NOTES simulator,
which will be used, much like CAD tools are used in engineering, to answer “what-if” questions related to the development of new procedures and devices. The added advantage
of such a simulator is that it will eventually serve the dual
purpose of being a training tool as the NOTES technology
matures. However, existing CAD software packages such as
ABAQUS, ADINA, and NASTRAN cannot be directly adopted
for the simulation of NOTES procedures as (i) it is not possible to interface an endoscopic tool handle to existing CAD
packages; (ii) they are developed for engineering applications and are not optimized to provide real -time interactive
performance; (iii) they lack force feedback; and (iv) the
traditional fi nite element technique is used in most of these
packages, which is slow and not suitable for very large deformations or changes in topology such as surgical cutting or
tearing. Hence, more agile physics -based algorithms are
necessary.
The VR -based simulator that we are developing will not
completely eliminate the need for animal models. Animal
models will still be necessary to study the physiological consequences of the interventional procedures, such as infection and control of intraperitoneal hemorrhage, until a more
detailed simulator that takes into account these physiologically adverse events is developed.
VR-based simulation technology for laparoscopic
surgery and GI endoscopy
While no NOTES simulator currently exists, VR -based simulators (Figure 27.6) for both GI endoscopy and laparoscopic
surgery have been developed. Leading medical organizations
such as the American Board of Medical Specialties (ABMS)
and the ACGME have also advocated their development for
obvious benefi ts, including unlimited practice material; well
planned and detailed exposure to even rare situations; signifi cant reduction in the use of animals; customization of
training regimens; and objective skill assessment. Since the
surgeon’s major tasks are observational and interventional
in nature, the challenge is to reach as high a level of visual
and haptic (touch) realism as possible in simulation. Integration of sophisticated tissue models developed by the mechanics community with medical simulators has been diffi cult
due to the requirement of real - time (i.e., interactive) performance. With the addition of haptic displays, this task
becomes even more challenging since the real -time haptic
Visual display
30 Hz
Haptic interface
1 kHz
Simulation engine
Figure 27.6 Concept of a VR -based medical simulation system.
USER
display requires much higher update rate (1 kHz) than the
visual display (30 –40Hz) [24].
In the USA and in Europe several educational institutes
and centers are involved in developing surgical simulation
technology, including the RPI Advanced Computational
Research Lab, MIT Touch Lab, Stanford University Medical
Media and Information Technologies (SUMMIT) and the
National Bio -Computation Center, Center for Integration of
Medicine and Innovative Technology (CIMIT), and Biorobotics Laboratory at University of Washington, National
Area Medical Simulation Center at Uniformed Services University (USU), the Center for Human Simulation (University
of Colorado), the Biomedical Interactive Technology Center
(Georgia Institute of Technology), the Center for Robotics
and Computer Assisted Surgery (Carnegie Mellon University); the KISMET group in Germany, the LASSO group at
ETH, Bristol Medical Simulation Centre in the UK, and the
University of Karlsruhe, Germany.
Several companies such as Boston Dynamics, Immersion
Medical, Melerit, Mentice, MedSim, METI, Mimic, Novint,
Reachin Technologies, Simbionix, and Virtual Presence have
tried or are currently trying to develop laparoscopic surgery
simulators. Immersion makes three simulators: a vascular
access simulator; AccuTouch ® Endovascular Simulation;
and AccuTouch ® Endoscopy Simulation. Mentice is a
Swedish corporation that introduced the Minimally Invasive
Surgical Trainer – Virtual Reality (MIST -VR) in the early
1990s. More recently, Mentice has collaborated with Sim Surgery A/S to develop a Key Surgical Activities (KSA)
module and a MIST Suture Module. Mentice has now introduced Procedicus ®, a platform that allows the modular addition of each of the Mentice modules with the option of
running each with haptic feedback. Simbionix is an Israel based company that uses the Xitact interface from Mentice
to provide realistic haptic feedback to its LapMentor ®
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simulator, which offers a Basic Tasks Module, a Procedural
Tasks Module, and a Virtual Patients Module created from
MRI and CT scans of real patients. Reachin Technologies AB
developed the Reachin Laparoscopic Trainer (RLT), which is
now integrated with the Procedicus MIST platform. Founded
in Berlin, Germany, Select IT VEST Systems offers the Virtual
Endoscopic Surgery Training (VEST) system, which includes
a Basic Task Training Set (BTT) and a Surgical Procedure
Training Set (SPT).
The market for GI endoscopy simulators is dominated by
two companies: Simbionix Ltd and Immersion Corporation.
Introduced in 1998 by Simbionix, the GI Mentor ® is the fi rst
commercially available VR computer simulator for GI endoscopy. In 2002, it was upgraded to GI Mentor II ®. The system
has four components: a mannequin, a real endoscope
(Pentax colonoscope for upper and lower endoscopy and a
duodenoscope for endoscopic retrograde percutaneous pancreatography, ERCP), a computer for simulating the endoscopy environment with a three -dimensional (3D) geometric
model based on video images of real endoscopic procedures,
and a monitor for displaying the VR environment. The
drawback of these simulators is that translational and rotational force feedback are not decoupled. In 1999 HT Medical
Systems, Inc., released a VR endoscopy simulator called the
PreOp Flexible Sigmoidoscopy Trainer. The company was
acquired by Immersion Corporation (San Jose, CA, USA) in
2000, and the simulator was renamed the AccuTouch
Endoscopy Simulator. The system has since been expanded
to include colonoscopy and ERCP. The AccuTouch “mannequin” is a universal platform that changes confi guration
for GI endoscopy or bronchoscopy. It is also a force -feedback
generator that uses friction brakes to deliver translational
and rotational force resistance. However, linear forces are
weak and rotational force feedback is neglected.
Issues unique to VR-based NOTES simulation
While NOTES combines features of both GI endoscopy and
surgery, it is unique in many respects. Hence, new procedures and devices must be developed and perfected before
NOTES can be transferred safely to humans. For a VR -based
NOTES simulator to be a useful clinical tool in developing
such devices and procedures, the following four unique
modeling challenges , which do not arise in the development
of laparoscopic or GI endoscopic simulators, must be
overcome:
1 Realistic modeling of multilayered hollow organs . In laparo-
scopic surgery through -thickness incisions are made in the
abdominal wall, while in GI endoscopy, the endoscope
remains inside the lumen of the GI tract. In natural orifi ce
procedures, on the other hand, the peritoneum is accessed
by perforating the walls of hollow organs. For transgastric
procedures (i.e., when the incision is made in the wall of
the stomach), for example, one way to enter the peritoneal
cavity is to make an incision in the anterior gastric wall and
then dilate the tract with a balloon dilator. Another way that
is being researched [25] is to tunnel through the submucosal
space of the gastric wall to create a fl ap valve that aids in
gastric closure. For a stomach model to behave in a physically realistic manner, the geometric as well as mechanical
response of the layers of the stomach wall must be correctly
modeled, which is challenging. First of all, the existing biomechanical data for the different layers of the GI tract is
inadequate. In the majority of existing literature [26,27] the
GI tract has been treated as a single -layer membrane rather
than a multilayered construction. The properties of the submucosa have been studied by physically separating the two
layers and using simplifying assumptions that the layers are
perfectly cylindrical [28]. Fan et al. developed a two -layered
(mucosa-submucosa and muscle layer) model of the rat
esophagus using ex vivo infl ation experiments [29]. Yang
et al. developed a two -layered fi nite element model of the
esophagus by using experimental data from ex vivo distension tests separately on the muscle and mucosal layer of
porcine esophageal specimens and using a bilinear strain
energy function [30,31]. Takeda et al. used a manometric
catheter equipped with a high compliance bag and a high
frequency intralumenal ultrasonography probe to record
esophageal pressure and images; however, properties of
individual layers have not been reported [32]. Similarly, the
vagina consists of three layers – an internal mucous lining
and a muscle coat separated by a layer of erectile tissue.
While gross mechanical properties of human cadaveric or
rat vaginal walls have been investigated [33–36], there is no
existing literature on the mechanical properties of individual
layers.
2 Realistic simulation of the interaction of fl exible surgical tools
with soft tissues . In NOTES, fl exible tools are introduced
through the endoscopic channels and are used to puncture
the stomach or other parts of the GI tract and to carry out
the surgical procedures, whereas in laparoscopic surgery,
slender rigid tools are introduced through the abdominal
wall. The interaction of slender fl exible tools with soft biological tissues poses signifi cant computational problems.
3 Evaluation of the physiology of pneumoperitoneum . Bergström
et al. measured intra -abdominal pressures during unregulated transgastric cholecystectomy and tubal ligation by
using Veress needles in fi ve pigs, and found that unacceptable levels of intra -abdominal pressures were created as the
fl ow of air from the endoscope is not pressure controlled
[37]. In actual VR -NOTES, as in the real situation, it is essential to be able to predict the intraperitoneal pressure and
air -tightness of the seal around the endoscope.
4 Evaluation of the integrity of gastrotomy closure . A variety of
approaches, from no closure to much more sophisticated
techniques, have been proposed [38]. Ryou performed an
in vitro study using whole porcine stomachs and three different closure techniques: (i) standard QuickClips; (ii) a prototype device developed by LSI Solutions; and (iii) hand -sewn
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Haptic interface
Sensors
Motors
Figure 27.7 Schematic of the VR -NOTES simulator platform.
NOTES simulation engine
Collision detection
Physics simulation
by a senior surgeon [39]. After closure, each stomach was
infl ated by an automated pressure gauge. The pressures to
achieve air leakage and liquid leakage were recorded. It was
found that the prototype device leaked air and liquid at the
highest pressure. Dray et al. performed in vivo studies for
air and liquid leakage [40]. T -bars (Wilson -Cook Medical)
were used for gastrotomy closure. For all closure devices,
the tightness of the seal must be tested to ensure leakage proof closure.
Development of a VR-NOTES simulator
Figure 27.7 shows a schematic of our VR -NOTES simulation
platform. The idea is to provide an immersive environment
in which the human user will be able to perform NOTES
procedures on 3D virtual organ models using tool handles
that are used in actual NOTES procedures. Our system consists of both hardware and software components. The hardware interface has sensors and motors to sense the movement
of the endoscope and to render the necessary forces to the
user. The main software component is the NOTES simulation engine. It takes inputs from sensors and simulates the
movement of the virtual endoscope and its interaction with
the internal organ models. The virtual endoscope and the
internal organs can be displayed on one or more display
monitors.
VR-NOTES software
The software component of the VR -based NOTES simulator
must be capable of representing realistic 3D anatomical
models, realistic tool models, fast computational algorithms,
and real -time physics -based techniques of simulating the
mechanical response of the organs to surgical intervention.
High-quality visual rendering of the organs is one of
the most important requirements for realistic surgical
simulation. Fortunately, numerous techniques have been
researched to enhance visual realism of the organs in medical
imaging and computer graphics communities. Most of the
concerned organs for NOTES simulation can be extracted
from patient -specifi c CT or MRI images. Such techniques
are standard and may be found in Lorensen and Cline [41].
The latest versions of OpenGL API and shaders enable
creation of photorealistic rendering of the 3D models for
NOTES simulation. Figure 27.8 shows an example simulation scenario created using the Visible Human Project (VHP)
dataset [42].
Models of the fl exible endoscope and surgical tools (Figure
27.9) may be developed in a software package such as SolidWorks. In NOTES simulation, virtual instruments such as
laparoscopic grasper and endoscope are manipulated through
haptic interfaces. The simulation software receives the position and orientation of the instruments and computes tool tissue interaction based on the current status of the
instrument. Rigid instruments can be easily handled by
direct transformation according to the position and orientation of the haptic device. Flexible instruments such as endoscopes have their own dynamics requiring accurate physical
models. Flexible catheters may be modeled as 1D mass spring structures [43]. An endoscope model based on a
serial-type robot is presented in [44] for simulation of colonoscopy. For an endoscope model in NOTES simulation, the
articulated rigid bodies method could be a reasonable choice.
The method allows inextensibility of the length and bendable behaviors with universal joints between the rigid bodies.
Besides, angulation of the tip can be accurately simulated
using forward kinematics of the articulated rigid bodies.
During simulation, the contact between the virtual tool
and an organ model is detected by an effi cient “contact
detection” module. That is the necessary fi rst step before one
can pick, move, or even cut tissues. Due to the high update
rate required for stable interactions, the algorithm must be
very effi cient, such as the Dynamic Point ™ algorithm developed by us for line -based contact detection between the
surgical tools and the deformable organ models [45].
Modeling methods of soft tissue due to tool -tissue interaction is an active current research area. For accurate and
effi cient simulation of volumetric soft organs such as the
liver and gallbladder, effi cient modeling techniques have
been developed including fi nite element methods (FEM)
[46–49], boundary element methods (BEM) [50], and meshless methods [51]. These methods have also been given
much attention in the computer graphics community. The
most frequently addressed issues are pre -computation
[46,48], adaptive multiresolutions [51], reduced deformation [43], and volume preservation [52].
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(a) (b)
(c)
Figure 27.8 Generation of a realistic anatomical model: (a) a slice of the VHP cryosectioned color image; (b) the same slice after segmentation and
labeling; (c) meshed organ model.
(a)
(b)
Figure 27.9 Models of (a) blades and (b) fl exible snares.
Apart from volumetric organs, modeling technique for fat
layers and membranes are also being developed for NOTES
simulation. Both mass -spring [53] and position -based
dynamics [54] methods are useful for this purpose. Numerical and structural stability issues are addressed in [55,56].
The use of a graphics processing unit (GPU) has been intro-
duced recently to vastly accelerate computational speeds on
relatively cheap personal computers and laptops [57].
In NOTES transgastric procedures, the endoscope is
inserted through the esophagus or the colon. These hollow,
cylindrical shaped organs may be simplifi ed as 1D structures.
A skeleton -driven model of the small intestine using 1D
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(b)(a)
Figure 27.10 A skeleton -driven and lattice -based deformation technique of the colon: (a) cylindrical lattice structure of the colon, and (b) global and
local deformations of the colon. (Reproduced from Ahn and Lee [59], with permission from the IEEE.)
mass-spring connection has been developed by Raghupathi
et al. [58]. The folded intestine is represented by linear
blend skinning of generalized cylinders along the centerline.
Ahn and Lee [59] adopted the skeleton -driven and lattice based deformation techniques to simulate the large and
local deformation of the colon (Figure 27.10). These techniques allow effi cient simulation of stretching, bending, and
collapsing of the colon model consisting of a large amount
of data.
Recently we conducted an expert need analysis study at
the annual NOSCAR conference held in June 2011. The
feedback obtained from experts through a questionnaire is
currently being used to steer the development of our VR NOTES simulator. The results from the study indicated that
the experts would like to see both appendectomy and cholecystectomy in our VR -NOTES simulator; 65% of the experts
opted for the transvaginal route and the rest chose transgastric simulation. The respondents also overwhelmingly indicated their preference to have a two -channel scope in the
simulator. Feeling of forces and torques were also indicated
as highly important.
VR-NOTES hardware
Specialized hardware must be developed to provide the right
interface to the computational environment using tools that
are used in actual NOTES procedures. The purpose is twofold:
(i) capture the hand motions of the user and transfer them
to the motion of the virtual tools, and (ii) provide force
feedback to the user. Though there are no VR simulators for
NOTES yet, there have been many simulators for fl exible
endoscopic procedures such as bronchoscopy, sigmoidoscopy, colonoscopy, etc. Specialized haptic (touch) interfaces
have been developed for such simulators.
A portable endoscopic visualization system was developed
by Ikuta et al. [44] in which the force feedback to the user
in linear and rotational directions was provided by the friction applied to the movement of the scope by a rubber ball
in contact and controlled by four friction rollers, two for
each of the degrees of freedom (DOF). Though this interface
had a simple drive mechanism, the main weakness was its
inability to provide suffi cient force to the users. In the work
by K örner and M änner [60], an endoscope was attached to
a carriage connected to a toothed drive belt driven by a
motor to provide force feedback. Another motor mounted
on the carriage and attached to the tip provided torque
feedback to the user. They also provided force feedback to
the user when controlling the articulated tip of the scope
using the knobs by two motors housed separately from the
scope and transmitting mechanical power through Bowden
cables threaded to the bolts attached to the knobs. Woo
et al. [61] developed a haptic interface for a colonoscopy
simulator that can provide DOF force feedback to the user.
The KAIST -Ewha system consists of an actual colonoscope
attached to a set of plates that can move on its own independent wheels mounted on a ground plate (Figure 27.11).
A wire -driven mechanism actuated by a DC motor mounted
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Rear plate
Folding guides
Colonoscope
Figure 27.11 The KAIST -Ewha colonoscopy haptic hardware mechanism. (Reproduced from Woo et al. [61], with permission from the IEEE.)
Distal tip
Guiding rods
Front plate
Ground plate
Publisher's Note:
Image not available
in the electronic edition
(a)
Figure 27.12 Colonoscopy simulator developed by Samur et al. (a) The overall set -up of the system; (b) hardware interface. (© 2011 IEEE. Reprinted,
with permission, from Samur, E.; Flaction, L.; Bleuler, H.; Experimental evaluation of a haptic interface for endoscopic simulation. World Haptics
Conference (WHC), IEEE, June 21 –24, 2011, pp. 545 –9.)
on the lower part of the rear plate provided translational
forces and the torque was provided through a timing belt,
pulley, and gear mechanism and actuated by a DC motor
attached to the front plate. The distal tip of the scope, which
was free to move, was attached with four defl ection sensors
to track the movement of the tip of the scope while controlling with the knobs. In the work by Samur et al. [62], a
haptic interface for a colonoscopy simulator was developed
with a combination of frictional rollers and mechanical
brakes to provide slip -free high -magnitude force feedback
(Figure 27.12a). The interface shown in Figure 27.12b has
a guided slotted tube through which an instrumented [63]
Olympus CF -140 or CF -160 colonoscope was inserted. The
linear force was provided by a set of friction rollers driven
by a DC motor and the torque was provided by a gear
mechanism and powered by a DC motor through a slip -ring
pair to provide full rotational freedom for the scope. A
mechanical brake augmented the motor in the linear direc-
tion when the forces exceeded 25 N and a powder brake
when the torque exceeded 0.5 Nm. Overall the haptic interface was able to provide a peak translational force of 75 N
and a peak torque of 1 Nm, which are well within the
requirements for fl exible endoscopic procedures.
A schematic diagram of a haptic hardware interface of the
fi rst VR -NOTES simulator being developed by us is shown
in Figure 27.13. The haptic hardware consists of two pairs
of friction rollers driven by two DC motors to provide slip free high linear force, and a separate torque applicator
housed on the slotted guide tube provides rotational force
through a gear mechanism actuated by a DC motor. The
rotational mechanism has two rollers to maintain fi rm
contact with the scope. The rotating knobs of the endoscope
are also instrumented with optical sensors to measure the
defl ection of the tool tip. The interface is designed to provide
nominal and peak translational force values of 25 N and 44
N, respectively, and torques in the range of 0 –1 Nm.
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