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Design of a Laparoscopic Simulation Device for Testing and Training
by
Susan Caroline Flowers Submitted to the
Department of Mechanical Engineering
in Partial Fulfillment of the Requirements for the Degree of Bachelor of Science in Mechanical Engineering
at the
Massachusetts Institute of Technology June 2014
02014 Susan Caroline Flowers
All Rights Reserved
MASSACHUSETTS NSTITUTE OF TECHNOLOGY
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The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or
hereafter created.
Signature of Author:
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Certified by:
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Department of Mechanical Engineering May 13, 2014
Signature redacted
Alexander Slocum Pappalardo Professor of Mechanical Engineering Thesis Supervisor
Signature redacted
Accepted by:
Annette Hosoi Professor of Mechanical Engineering Undergraduate Officer
Design of a Laparoscopic Simulation Device for Testing and Training
by
Susan Caroline Flowers Submitted to the
Department of Mechanical Engineering on May 14, 2014 in Partial Fulfillment of the Requirements for the Degree of
Bachelor of Science in Mechanical Engineering
Abstract
This thesis describes the development by Caroline Flowers of two prototypes of a bench-top laparoscopy simulator that mechanically simulates access ports using outer 'tissue' samples
for port insertion and an inner cavity region where ex-vivo organs can be placed and operated on using laparoscopic tools. The alpha prototype was designed for testing tools for an MIT medical device design class, while the beta prototype was designed as a low-cost and more realistic substitute to simulators currently on the market.
Thesis Supervisor: Alexander Slocum
Acknowledgments
I want to extend my thanks: first to Professor Alexander Slocum and to Nikolai Begg for
serving as my advisors and mentors throughout this project; the doctors who provided their knowledge and feedback, including but not limited to Dr. Joan Spiegel, Dr. Denise Nebgen, Dr. Keith Reeves, and Dr. Carlos Medrano; to Ken Stone of the MIT Hobby Shop, who provided invaluable help in machining and assembling the alpha prototype; to Deb Slocum, who was there to remind me that all frustrations in a design process come to an end, and who helped keep me sane; and to Jonathan Slocum, who was there for me all the times software didn't work and equations just wouldn't come out right.
Last, I want to thank my parents, Beth and Fort Flowers, my grandparents, Dan and Jeanie Flowers, and my siblings for their unwavering support throughout the course of this project, and throughout my entire MIT career.
1. Introduction
While minimally-invasive surgeries have been recorded as being performed since the early 1900s', it was not until the development of digital cameras that it began to emerge as a commonly accepted alternative to open surgery. One particularly prominent type of minimally invasive surgery is laparoscopy, which encompasses surgeries in the chest and abdomen.
Generally, set-up for laparoscopic surgeries follows a relatively similar procedure. A Veress needle, a tool which is used to disperse gas into a body, is inserted and C02 is pumped into the abdomen until it is sufficiently insufflated. 3-5 trocars, or surgical ports, are inserted into the abdomen, one of which is used at the port for a camera, which inputs video back to the
surgical team (figure 1). Tools are inserted through the trocars, which are used to perform the surgery.
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Studies have shown many benefits of laparoscopic surgery. First, a study of time spent in surgery for a routine appendectomy showed 71.4% of laparoscopic surgeries finished in 30 minutes or less, compared to only 9.3% for open-access surgeries2. When looking at
post-operative infections (which every patient in the study experienced), 96.2% occurred for
laparoscopic surgeries in 1-2 days, while 56% occurred for open access surgery after 3-6 days.3 With that decreased risk of infection after a longer period of time, hospital stays can be shorter, resulting in saved money for both the patient and the hospital.
1.1 Testing Tools
Currently, testing new tools in a surgical-like environment requires an animal cadaver, which can be both expensive and difficult to store, or in a live animal, which, aghin, can be expensive and also requires proof that the test will not be unnecessarily painful to the animal. MIT course
2.750: Medical Device Design, a senior- and graduate-level design class, required a bench-top
laparoscopy simulator that mechanically simulates access ports using outer 'tissue' samples for port insertion and an inner cavity region where ex-vivo organs can be placed and operated on using laparoscopic tools to test new products. The alpha prototype of this simulator was designed to perform that task.
1.2 Surgical Training
Before performing laparoscopic surgeries, surgeons are required to obtain proficiency in a variety of areas, including camera and instrument navigation, grasping, cutting, suturing, precision and speed, etc. These skills are taught using simulator devices, which currently range from high-tech and incredibly expensive life-like models to 'boxes' with pre-placed ports and low-quality fixed cameras, which can still cost hundreds or thousands of dollars. The beta
prototype of the device designed for 2.750 was created to bridge that gap, providing a low-cost yet surgically realistic and portable experience for surgeons.
Figure 2: Sample simulation boxes on the market'5, which lack both a realistic surgical field and
2. Alpha Prototype
2.1 Functional Requirements
Before design began for the project, meetings were held between myself and Nikolai Begg, a MS/PhD candidate in mechanical engineering and 2.750 TA whose specialty is laparoscopic tools, to decide precisely what was desired out of the device. The following functional requirements came out of those meetings.
a. Able to clean the equipment
The primary goal behind the creation of this device was testing of laparoscopic tool in a self-contained environment, in order to keep a sterile workspace. While not all devices to be tested would require biological tissue, it was still critical for the option to be available. A design which could allow for deep and extensive cleaning, preferably with a minimal amount of work on the part of the tester, was therefore necessitated.
b. Able to change out entry ports/skin simulation
While most of the designs to be tested using the device were designed to be used internally, the capability to change out the entry ports and skin simulations is still necessary due to potential creation of a design which is focused more on port insertion, for example, or for testing where a full simulation of surgery is preferred.
c. Realistic surgical field
While during the prototyping phase of a laparoscopic device it would not be necessary to view said device and its effective outcome in a proper surgical format, at some point it would prove requisite to ensure that the device is functional in laparoscopic surgical conditions. Therefore, the
testing device required some sort of viewing apparatus, such as a camera, for a realistic surgical view.
d Geometrically accurate to human body
Although not all testing of surgical tools would require a geometrically accurate layout, the ability to see the device work to ensure, among other things, spacing could be accurate was necessary.
e. Mechanically realistic skin patches
Due to the potential for testable designs regarding external aspects of laparoscopic surgery, mechanically realistic skin patches were necessary to accurately assess the validity of the design before testing it on actual tissue. 1/8" silicone rubber was decided upon before the design began.
f
Ability to swap out types of skin patchesSince the device could be used for testing designs concerning treatment of tissue, it was necessary to be able to replace skin patches after each use, but also to be able to use different kinds of patches, including biological tissue.
g. Splatter-proof
With the prospect for biological materials to be tested on, the device had to be capable of maintaining a sterile environment.
2.2 Shape
Three concepts were finalized for creating the general shape of the device: one model with several interlocking pieces that could be taken apart and cleaned; one model where most of the device was pre-assembled, but still required some assembly; and one model that was, in
essence, a fully assembled 'box.' While the first two options would be conceivably easier to design and create, the ease of use the third offered proved to be the deciding factor.
In laparoscopic surgery, before the procedure can take place the abdomen is insufflated to allow for a greater maneuverability-creating a pneumoperitoneum. Most commonly, an instrument known as a Veress needle is placed in the patient's abdomen, which allows for the flow of C02
into the body until a pressure of 14-15 mm/Hg is obtained, which takes about 3L6.
Approximations were made about the size of the average human body to create the model, with a given length of 12". The initial volume of the device was modeled as a semicircular tube in which could fit a 6" cube, which was calculated to have a radius of approximately 6.71". Having added the 3L of C02, the new radius was calculated to be
approximately 7.5" (figure 2).
Due to the geometric functional requirement only pertaining to relative accuracy, the decision was made to have a rough appearance comparable to the human body, with straight
sides and a trapezoidal shape instead of curves. The base length of the trapezoid was decided to be the same 15".
2.2Tissue Design
2.1.1 Modeling Peritoneum
Two ways of modeling the peritoneum were discussed: small patches of 'tissue' over a mostly-solid top with specific places for holes, or tissue stretched over a frame. While the latter would provide the experience of a more realistic surgery, the necessity of keeping the silicone taut, the
cost required to provide that much silicone, and the ease of tissue-replacement found in smaller samples led to the former being decided upon.
Hole placement was modeled after generic laparoscopy rule of thumb-ports are placed approximately 10-18 cm from the point of interest, and spread out in either a semi-circle or a triangle, depending on the type of surgery and the number of ports necessary. The camera is placed around the area of the navel (figure 3).
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Figure 3: Example of port placement for laparoscopic surgery'
In an effort to keep the device easily storable and transportable, the point of interest was decided to be near one side, with the ports spread out in an arc around it (figure 4); while having a full circle of potential port placements was considered, it was decided to be unnecessarily redundant for the purpose at hand.
Figure 4: Arrangement of the tissue sites on the prototype
2.2.2 Attaching Tissue
Having chosen to use small samples of tissue, the next step was determining the best way of attaching the tissue to the device, as well as holding it in place. Instead of connecting the tissue directly to the base, a system of separators was devised to optimize cleanliness and ease of use. These separators screwed into the top of the base, aligning the holes, using o-rings to keep a water-proof boundary between the two pieces-for example, if biological tissue was used for the ports, but non-biological material was used for the inside of the device, the required post-testing cleaning would be less extensive and easier (figure 5).
Figure 5: Solid-model example of how the skin attachments fit to the base
Multiple strategies were considered in the process of finding the best way to attach the tissue samples: magnets, screws, clamps, and Velcro. Velcro was almost immediately ruled out; given the potential use of biological tissue, full cleaning was determined to be nearly impossible. For ease of use (i.e., the ability to stretch the silicone as far as could be desired), clamps were ruled out, leaving screws and magnets.
To prevent unnecessary tearing of the tissues that would occur if posts of some kind were the only things held in place, the decision was made to sandwich the tissue between two layers of
12.
Figure 6: Solid model of base and top of skin attachment pieces. The smaller two holes at 300
intervals are for the spikes, with the middle of those three is for the magnets. The vertical holes on the lower piece served to connect the attachments to the base.
While screws were originally selected as the holding mechanism, due to the cost benefit, it soon became evident that the clamping process was too lengthy to make that a viable option. Therefore, the clamping pieces were redesigned with magnets in mind, with spikes being placed along the edges to help hold the tissue in place.
---2.3 Final Design
Having decided on a general shape, the final design did not deviate much from the original plan. The port holes were decided to be 2.25" in diameter, to allow for multiple port insertions in the same location, which determined the size of the top of the 'trapezoid' that composed the simulation of the expanded abdomen (figure 7).
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Figure 7: Height and width dimensions of the prototype
Each piece was constructed out of acrylic, which allowed for both visibility and
waterproof sealing. Due to the precision requirements, the pieces were cut using a water-jet. One of the rectangular sides was designed to be a door consisting simply of a 1" edging with multiple magnets that fit with a second acrylic slab lined with silicone for sealing purposes. For ease of cleaning, the device was given 1" 'legs' and a hole was drilled into the base; when cleaning was
necessary, it could simply be placed in a sink and rinsed out, with the water and waste running out through that hole (figures 8a and 8b)
Figures 8a and 8b: Final solid-model version and final device
2.4 Feedback
Once the device was finished being built, it immediately began to be used for its intended purpose of testing new laparoscopic tools (figure 9)
Figure 9: Device in use by a 2.750 team to test their product, a new variety of grasping tool
However, it was soon recognized that this particular device could have wider-spread usages; specifically, with modifications it could be used as a low-cost laparoscopic simulation device for training surgeons.
Before the redesign began, feedback was sought to see what changes might need to be made to make the device most useful for a surgeon. Dr. Joan Spiegel of Harvard Medical School was invaluable during this process; she and her colleagues both provided feedback and access to the full-scale simulators used for official certification testing. The resulting feedback indicated a desire for a more anatomically accurate base, a specific mechanism for holding the ex-vivo organs in place inside the device, an increase in the realism of the skin samples, and changing from five separate spots for tissue samples to instead having a single sheet that would spread over the entire structure with several holes in structure itself.
The device was also presented at the Design Medical Devices conference, and a paper was published: C. Flowers, N. Begg, A. Slocum, "Laparoscopic Simulation Device for Testing and Training" ASME Journal of Medical Devices, Volume 6.1, March 2012.
Feedback from other designers and clinicians there reiterated several of the above-mentioned suggestions, but added one more significant concept-an automatic timing mechanism.
3. Beta Prototype
3.1 Shape
The general sizing was held consistent between the two prototypes, with no more than two inches difference between the widest parts of each. To both more accurately resemble the human body and to allow for ease of manufacturing, the device was separated into two halves that would fit together.
The top half, in the initial two-dimensional iteration, was the arc determined from the original calculations, with a base that was merely a box it fit into; while geometric and biological accuracy was desired, most laparoscopic surgeries concern the anterior side of the torso, and so the base did not require the same level of curvature (figure 10). A flat base was decided to be more manageable. In addition to being more stable, that also made it easier to allow for some object to the ex-vivo organs in place.
3.1.2 Design
With a more geometrically accurate and complex shape, a new method of building was required for the beta prototype, though this option would not necessarily be the same as one used
for wide-scale production.
Thermoform molding was one of the first options considered. However, while the problems inherent with requiring holes in the device could possibly be fixed by having them be cut out after the molding was complete, finite element analysis proved that the material was not
strong enough to withstand a force of 1 OON (a number decided upon relatively arbitrarily, but with the intention of representing someone accidentally leaning on the device for support).
The next strategy considered, and the one ultimately chosen, was 3-D printing. The biggest drawback of this method was the cost. This issue was dealt with by printing only the most basic framework, with the rest composed of attached acrylic. This modification proved in no way to change the functionality of the model (figure 11).
Figure 12: Geometry of the device top
A first-level analysis of the maximum force tolerated was performed. Since the failure
mode of the top was excessive deflection, a study was done of the weakest part of the structure-the minimum space between two holes (Figure 12). This area was treated as part of a beam that was pinned on both sides with a uniformly distributed load. According to beam theory, for this
scenario M = (L -x) (1) = 4 (L' - 2Lx2 + x 3) (2) 24EI h3d (3) 12 Mh (4) 21
Where M is the moment in the beam, w is the force per unit area, x is the position in the beam, L is the total length of the beam, 6 is the total deflection, E is the modulus of elasticity, I is the second area moment of inertia, h is the thickness of the beam, d is the cross-sectional width, and
taken to be the longest diagonal distance between two holes, and the beam was assumed to have the same cross-section throughout the entire length; this analysis would therefore show a lower maximum applied force than the model would actually experience. Therefore,
L=1.60"
h=0. 125"
d=0.2"
E=250ksi
Using the above equations, the maximum force spread out over the entire length was determined to be 13.5 lb, with a deflection of 0.003". These calculations, as mentioned above, were incredibly conservative, however-due to the geometry of the device, if the triangular areas are not treated as part of the beam, the effective length decreases by 2/3 and the maximum force is 30 lb.
While the model can withstand more force than these calculations have determined, if doctors feel that they require a more durable device, then the simple solution will be to make the holes smaller and allow more space between them.
Though modeling the failure mode and the forces it could withstand as a cantilevered beam was determined to be accurate, the deflection calculation was clearly off, as demonstrated
by further testing done to measure the deflection. Due to the non-linear shape of the device,
measurement was done by placing a beam across the top that was pinned at a far end, loading the beam in the middle where it hit the device, and then measuring the height change of the beam at
the far end (figure 13).
Figure 13: A is the point at which the beam on top is pinned, B is the point at which the weight is
applied to the device, and c is the point of measurement.
The device was modeled as being four partial curved beams that met in the center in a cross formation, cantilevered at one end and free at the other, where they met, and where the weight would be applied (figure 14). Given equivalent thickness and side length to the device as is, the width of each partial curved beam was calculated so that the volume of the model was equivalent to the model of the device. Each of the four partial curves could be viewed as deflecting due to one quarter of the total force.
Figure 14: Modeling of the top of the device for deflection prediction
Calculations of predicted deflection were performed using a programmed spreadsheet created by Professor Alexander Slocum in conjunction with his online textbook
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Figure 15: FUNdaMENTALS spreadsheet used to calculate deflection of the modeled system
Table 1: Comparison between measured and predicted deflections of the device and model, respectively
Force (ib) Deflection Measured (inches) Deflection Predicted (inches)
2.5 0.0187 .1332E-3
5.0 0.1224 .266E-3
7.5 0.2701 .394E-3
The calculated deflection clearly showed a wide discrepancy between predicted and measured deflection, so further work must clearly be done to develop a closed form model and
perform finite element analysis.
Since the device was now composed of two separate pieces, it was necessary to devise a mechanism for holding the two together to create a sealed environment. The original design involved a third piece-a 'lip' of sorts that press-fit to the top piece. The base would come up to meet it and be attached through some mechanism, decided eventually to be magnetic, leaving
two layers between the inside of the device and the environment. At the time, a monitor was planned to be mounted on the device itself to hook up to the 'endoscope,' so the lip would allow for that as well (figures 16a and 16b).
Figure 16a and 16b: Sketch of base with lip and prototype of base with lip.
When this first iteration of the beta prototype arrived, though, it was determined that the lip provided little benefit compared to the extra space and cost it required.
The next design reflected the same ideas of layered coverage, but this time with only one layer; the top came down to meet the base, with a male/female placement mechanism, while the base continues upward slightly. Originally, the placement mechanism was to contain magnets to
hold the two pieces together; however, testing revealed no holding mechanism was required (figure 17).
Figure 17: Full prototype
3.2 Tissue
The mechanism for holding the skin in place also had to change drastically with the beta prototype. One of the critiques of the original device was the composition of the skin sample; the tissue involved in laparoscopic surgery was compared more to a layer of rubber- and foam-style materials.
The initial decision to use 1/8" silicone rubber having been chosen before the design was begun, at this point research was begun to determine if the mechanical and elastic properties of the peritoneum had been calculated; with modulus of elasticity and quasi-static equations,
approximate materials and layers could be constructed. However, research did not prove conclusive on this subject.
Since mathematical modeling would not be applied without material constants, a compromise was struck between the original silicone rubber and some method of layered samples. The new material was chosen to be silicone foam; it had many the properties of the rubber, but in a more aerated form. Medical-grade silicone as also chosen for the sake of the users of the device; many in the medical community develop an allergy to latex due to glove use, and so this device would not trigger side-effects.
While the 'tissue' material was still being decided upon, designing began for a new holding mechanism. Originally, a similar plan to the first prototype was used, with spikes on a hinged side piece that rotated around the edge of the top half of the main device.
However, the silicone foam did not require tension to keep it in place or at a necessary tautness when pressure was applied. Therefore, to minimize the number of parts required for the device, a 'frame' of sorts was constructed instead. When the foam was draped over the top of the device, this frame press-fit over it (figure 18).
3.4 Ex-Vivo Organs
Current similar devices have two methods of holding ex-vivo organs and other training tools in place: Velcro and clips attached to the sides of the device. Velcro would destroy any chance for real biological material to be used inside the device, so that was clearly out as an option.
Alligator clips on strings was considered, until Dr. Keith Reeve of the Houston Methodist Hospital system offered a superior option that would allow greater ease of use-a series of holes into which dowels could fit. With this method, for example, the tautness of surgical tubing that would be used to practice sutures could be guaranteed instead of relying on already-placed clips, which also might move while the device was in use (figure 19).
4. Electronics
4.1 Camera
The task of finding a suitable camera and monitor was one of the most pervasive challenges of this project.
For the alpha prototype, the most important aspects were camera quality, water-resistance, and ease of use, because the focus was on testing new potential products instead of establishing an accurate as possible surgical experience. To this end, cameras that would be too large to fit in a standard trocar could be used, with adjustments made to the ports for camera use-instead of the silicone rubber, it was a solid-state piece with a PVC tube the camera could
fit through. The camera used was a Vividia 8mm USB Flexible Inspection Camera Borescope Endoscope (Figure 20).
USS Cable: 2m
Camera
Lens
LED Light
Camera head outer
diameter: 8mm
LED Light adjustable brightness
Figure 20: Sample of initial camera used for the alpha prototype'O
For the beta prototype, however, the camera was required to be a similar as possible to an endoscope while keeping the cost relatively low; one of the advantages this device has over those currently on the market is the low cost of the device combined with the realistic feel.
For the sake of portability and the ability to practice in any location, it was first decided that a monitor would be attached to the device, and a camera needed to be found to allow for that. The camera that was believed to be the solution was a category of camera known as pin-cameras. It was placed in an aluminum tube to simulate the rigidity of an endoscope. However, the camera required some kind of computing interface before the monitor would show the image, and that drove the price of the device up too much to be considered reasonable.
It was then hypothesized that a camera which could connect to a USB input on a computer would allow the device to be equally useful for on-the-go practice; this theory was confirmed after consulting with surgeons. Therefore, a new camera was chosen; a variety of pipe-inspection camera, inspection cameras having the necessarily visual quality (figure 21).
Figure 21: Camera with device
4.2 Timer
The first strategy for creating an automatic timer consisted of using sensors to tell when a tool had been placed through a trocar. Some suggested sensors were a proximity sensor, which could tell when any kind of tool had been placed through the trocar, and a magnetic sensor, which would require an additional piece of some kind to be placed on the laparoscopic tool before it was used to help the sensor detect it. However, concerns over the complexity of either of those systems, as well as the practical issue of wanting the user to be able to us the device with any laparoscopic tools that they have on hand instead of requiring new tools to be manufactured and purchased, promoted the idea of designing another method.
The second and final strategy entailed creating a flexure that could be inserted in one of the device's specifically made trocars. This flexure would have wires running down the sides
that connect to a conductive material along the flexure's base. When a tool is inserted, the connection would be broken, sending the signal that the timer should start (figure 22).
I
Figure 22: Timing flexure, with an outer radius of .98"
To allow for a natural feeling for the user, the flexure was designed to require limited force to operate. 4N was chosen, with first-order beam theory used to test the stress on and deflection of the flexure.
_FL/i 21 FL 3 3EI (5) (6)
Where F is the force, L is the length, h is the height, I is the second area moment of inertia, and E is the modulus of elasticity.
---r
mammmmmme m
For this device, F=2 lb L=.9" H=.03" E=250 ksi uyield=7.0 ksi
The specifications above produced a deflection of 13mm (laparoscopic trocars are defined by their width in millimeters, with a standard of 12mm), with a maximum stress of 6.8ksi-while that is very close to the yield stress, the tools would not require this much deflection.
The timer itself was far easier to design. After researching extensively, it was determined the easiest method was to program an Arduino board to start a timer, using 8-digit counters.
5.
Conclusion
While the device has shown to serve the purposes it was set out to accomplish, there is unquestionably more work left to be done, both on testing its use and attempting commercial production.
For testing, several avenues are currently in motion and will be completed in the summer of 2014, when residents and surgeons at the Baylor College of Medicine and the Houston
Methodist Hospital will be providing feedback for how the device compares to other simulators on the market. Questions will include, among other topics: ease of use, comfort, durability, timing mechanism, camera, accuracy of tissue, space to maneuver, ability to hold samples in place, practicality, port placement, and what could be improved upon in current devices.
Preparing for commercial production will be a slightly more abstract process, depending partially on feedback from the abovementioned users. However, one aspect that is already in the works is changing the method of building; while 3d printing worked for a single prototype, it is too time-consuming a process to be considered viable for wide-scale manufacturing. At the moment, two ideas are being considered: vacuum molding and only constructing a top piece that would be attached to a Tupperware top-the device could then be attached to any Tupperware base of appropriate size.
References
1Martin Hatzinger, S.T. Kwon, S. Langbein, S. Kamp, Axel Hacker, and Peter Alken. Journal of
Endourology. November 2006, 20(11): 848-850. doi:10.1089/end.2006.20.848
2 Mayo Foundation for Medical Education and Research
http://www.sparrow.org/HealthLibrary/MayoContent/global//images/image popup/hdg7 laparos
copy.ipvz
3 Arshad M. Malik (2012). The Laparoscopic Appendectomy - A Recent Trend, Advances in
Laparoscopic Surgery, Dr Arshad Malik (Ed.), ISBN: 978-953-307-933-2, InTech, DOI:
10.5772/25459. Available from:
http://www.intechopen.com/books/advances-in-laparoscopic- surgery/the-laparoscopic-appendectomy-a-recent-trend-4 surgery/the-laparoscopic-appendectomy-a-recent-trend-4;Portable laparoscopic trainersurgery/the-laparoscopic-appendectomy-a-recent-trend-4; by 3b scientific
5 "Portable Laparoscopic Box Trainers" by Ethicon
6 G. de Candolle and A. G. Gordon. "Training in Diagnostic Laparoscopy"
http://www.gfmer.ch/Books/Endoscopy book/Ch07 Training Lap.html
7M. Lipke and CP Sundaram, "Laparoscopic radical prostatectomy" J Minim Access Surg
(2005), http://openi.nlm.nih.gov/detailedresult.php?img-3004122 JMAS-01-196-g001&req=4
8 Alexander Slocum, PhD, May 10h, 2014 9 Alexander Slocum, PhD, "Beam Curved"
http://web.mit.edu/2.75/fundamentals/FUNdaMENTALs%2OBook%20pdf/FUNdaMENTALS% 20Design%20Spreadsheets/Topic%208%20Structures%2ODesign%20Spreadsheets/
10 Vividia "8mm USB Flexible Inspection Camera Borescope Endoscope" http://ecx.images-amazon.com/images/I/5 11 YmeC7MFL.jpg
