ABSTRACT

From the world of scopes “Colonoscope” is the best equipment for the diagnosis as well as for the biopsy of diseases inside the colon. One of the most common and ongoing challenge during the colonoscopy procedure with this equipment is the formation of loop, that forms between the colon and colonoscope. Due to the loop formation, the further insertion of the colonoscope towards the area of interest would become quite impossible. As a result, the risk towards the perforation of the colon increased and stimulate pain to the patient. Whereas on the other hand the time duration of the procedure will also get effected due to the loop formation. Currently there are some manufacturers that addressed the loop formation problem and modified their colonoscope according to it, which are available in the clinical work places. However, experimental evaluation comes up with the results that these introduced modifications in colonoscope does not work up to that extent which is required practically. This is the main motivation for the research presented in this project report.

This project is about the interfacing and embedding a system with the colonoscope that will help doctors and colonoscopist to perform successful colonoscopy procedure without facing any looping problem, if any problem occurs system will help to identify problem. The embedded system will have a Colonoscope Force Monitor (CFM) to monitor the applied Force and Torque, whereas the resultant Friction Force will be observed by the Force/Pressure Sensors. The data (force and friction) will then forwarded by the interfacing system to the computer that will make a comparison display between applied force and resultant friction force on the colonoscope.

INTRODUCTION

To diagnose and evaluate the colorectal diseases of the lower Gastrointestinal (GI) area, colonoscopy is one of the best system designed. The colonoscopy system is designed in such a way that it is not only used for the diagnosis purpose, but for the treatment purpose as well. Like the removal of the polyps is done through the instrument section commonly known as biopsy wire guide (Obstein & Valdastri, 2013). While performing colonoscopy the failure rate is about 10% (Park, et al. 2013), the biggest challenge among these failure is the loop formation of the colonoscope shaft that creates obstruction to visualize the entire colon and it is also responsible for the colonic wall injuries and perforation.  (Sato, et al. 2006) (Mitchell, et al. 2002).

Colon Anatomy:

The “Colon” commonly known as “large intestine” is a long flexible organ of about 1.5 meters (5 feet) that extends from Cecum to the Anus of the lower gastrointestinal tract (Jones, 2017). The digested food from the small intestine is forwarded to the colon, where the process of water and ions absorption take place to finally form the feces. Based on the definition of anatomy, the colon is divided into four parts which are known as Ascending Colon, Transverse Colon, Descending Colon and Sigmoid Colon.

The track of the colon starts from the ascending colon section which has retroperitoneal structure (fixed to the retroperitoneum) that rises in the upward direction from the cecum. At the right lobe of the liver, ascending colon make the turn of 90 degree to the horizontal direction and meet with the transverse colon. This turning is known as Hepatic Flexure.

The transverse colon which has intraperitoneal structure, starts from the hepatic flexure, travels over the abdomen and extends to the spleen where colon turns again at an angle of 90 degree vertically downwards and join with the descending colon and that turning is known as Splenic Flexure.

The colon travels from the splenic flexure towards the downwards direction for that reason this section is known as descending colon. Just like ascending colon, it is also retroperitoneal in structure located in front of the left kidney and ends at the Sigmoid Flexure. The sigmoid colon is the last section of the gastrointestinal tract, which is located at the lower left quadrant of the abdomen.

Figure 01. Anatomy of the Colon

(Retrieved from: http://www.yoursurgery.com/ProcedureDetails.cfm?Proc=17)

Colonoscopy System:

The general colonoscopy system consists of major sections like LCD monitor for the real-time display, the Video System section where the video processor converts the electrical signals from the scope into video signals and transfer them to LCD for display, the Light Generation Source section uses a xenon lamp to produce light similar to natural light which is transferred to the scope’s distal end, the Suction System section incorporates a pump for supplying water and air to the scope and finally the Scope Section.

The scope section (colonoscope) itself can divided in four sections – the universal Cord and Plug Section, Control section, Insertion Section (commonly known as Shaft) and Bending Section. The control section of the scope contains all the hand controls that is required for the navigation, instrument (biopsy), air & water controls and bending of the distal end of the scope.

The above described sections are shown in the following figure 02. Furthermore, the scope section will be discussed more in detail as this is the only part which is the area of interest of this report.

Figure 02: Olympus Corporation, USA Colonoscopy System (Ottawa Endoscopy & Day Surgery Centre, 2011)

Retrieved from: (http://www.ottawaendoscopy.ca/services.htm)

Colonoscope:

The length of the insertion tube (containing the insertion and bending sections) is about 130 centimeters (51 inches), that is composed of major components like digital wires channel for camera, optical fibers channel for light, instrument (biopsy) channel, air channel, water supply & suction channels and the Bowden cable for flexible movement (Jechart, 2004). At the tip side (distal end of the scope) for the camera channel, a lens is present with the lens cover along with a video chip that produces the image (Jechart, 2004).

Figure 03: Tip of the Colonoscope and its cross-section (Gastroenterology and Hepatology, 2015)

Retrieved from: (https://clinicalgate.com/how-endoscopes-work/)

The bending section is composed of the last 15 centimeters (6 inches) of the insertion tube and made specifically flexible for bending in all four direction that allows exclusively better steering during the use in gastrointestinal tract (Jechart, 2004). Therefore, the operator could bend the tip of the colonoscope about 160 degrees to right/left sides and 180 degrees to up/down direction (Jechart, 2004).

The control head section of the scope contains all the necessary functions that are highlighted in the following figure 04.

Figure 04: Hand control unit of the colonoscope (Fujifilm Europe Gmbh, Expo21xx online exhibition)

Retrieved from: (http://www.expo21xx.com/news/fujifilm-eluxeo-endoscopy-system/)

Procedure of Colonoscopy: 

The process of colonoscopy initiates with the intubation of a colonoscope from the anus via the colon to the cecum, which is considered as the least invasive procedure for detecting the colorectal diseases. Throughout a comprehensive colonoscopy procedure, the insertion shaft is inserted into the anus then pushed forward through the rectum, sigmoid colon, descending colon, transverse colon, ascending colon and to the cecum (Hoff, et al. 2011).

The colorectal diseases would be just a simple polyp (depends on the condition the simple polyp could be remove from the colon via biopsy instrument) or might be the related to the colon cancer (Cheng, 2013). Following figure 05 illustrate some examples of the colon diseases diagnose by colonoscope.

Figure 05: Different types of colorectal diseases (Messmann, 2006, Atlas of colonoscopy)

Retrieved from: (http://www.colonoscopy.ru/books/rar/Atlas%20of%20Colonoscopy.pdf)

To perform the colonoscopy procedure, two methods are commonly used in clinical practice known as one – person and two – person colonoscopy procedure (Cheng, 2013).

In the one – person colonoscopy, the colonoscopist performs the investigation alone, handling the controls of angulation and options of the hand control by one hand and inserting, push/pull or twisting the scope’s shaft with the other hand. During the procedure, it is commonly observed that the colonoscopist uses the right hand to insert the scope where as the scope’s distal end orientation and angulation is control with the left hand (Hoff, et al. 2011).

In the two – person colonoscopy, a colonoscopist (considered as first person) and an assistant (considered as second person) performs the examination, the colonoscopist or gastroenterologist has the hand control section of the scope, while the assistant pulls and pushes the colonoscope according to the commands given by the first person (Hoff, et al. 2011).

By comparing the two methods, during the two – person procedure the perfect coordination is difficult to accomplish. Therefore, the one – person method usually provides the best results due to the strong coordination achieved for the two operations performed by a single person (Cheng, 2013). Furthermore, the procedure caused abdominal pains and injuries are reported more in two – person rather than one – person method (Hoff, et al. 2011).

Loop formation during colonoscopy procedure:

Despite of the fact that colonoscopy system is the major tool in clinics for the diagnosis of colorectal diseases, the failure rate of the procedure is still more than 10 % means among the one of the ten procedures the scope is unable to reach to the last section of the colon (cecum), and the main reason behind the unsuccessful procedures is the formation of scope’s loop in the colon (Church, 1993).

Naturally the colon shape is deformable, therefore the formation of the loop arises when the colonoscope encounters the colon wall and results in the generation of the resistive force of friction. The further advancement of the scope with the frictional resistance along with the factor of the existing shape of the shaft and colon, this leads towards the formation of loop and eventually the distal tip of the colonoscope will not able to move further, whereas in some cases the resistive force will forces the shaft in backwards direction (Moser, et al. 2012).

Formation of loop in colon are of different types among them alpha – loops and N –  loops are the most common one, while U – loops, gamma – loops, reverse alpha – loops and reverse gamma – loops are also the types of loop formation in colon. According to the study done by Koichiro Sato and his team, 60% of the colonic loop formation occur in the sigmoid colon section with the forming of alpha or N – type loop, whereas transverse colon section contributes 33% with the U – loop formation. Creation of reverse alpha – loop is 8%, whereas the contribution of gamma and reverse gamma – loop is only 1% (Sato, et al. 2006).

Figure 06: Alpha and N type loop formation (Overcoming the Sigma – part 2, Endoscopy colon explorer)

Retrieved from: (http://www.endoscopy-colon-explorer.com/overcoming-the-sigma-part-2/#lightbox [1107] prettyPhoto[gallery1]/7/)

James M. Church explained the four ways for countering and minimizing the loop formation during the procedure that are: exerting abdominal pressure, holding the patient’s breath, turning the patient to the right side and turning to the left side (Church, 1993). The different combinations of these techniques are used to successfully resolve the loops.

Effects of loop formation:

One study reflects that 91 out of 100 patients that goes under the procedure of colonoscopy have experienced the looping problem (Shah, et al. 2000). During the procedure patients are provided anesthesia but due to the loop formation the patient gets uncomfortable therefore for that reason the level of anesthesia must be raised, and prolongs the colonoscopy procedure time of duration that in turns increases the risk associated due to the time exposure to anesthesia (Sato, et al. 2006).

Looping also causes pain to the patient because of the stretching the mesentery of colon, which is the set of tissues that is formed between the wall of colon to the wall of the abdomen (Eickhoff, et al. 2010).

The colonoscopist or gastroenterologist will exert force by twisting inwards and outwards direction to the colonoscope shaft that will enhance the risk level of damaging mucosa and inner tissue lining of the colon (Park, et al. 2007), while in few cases the Splenic injuries has been reported (Shankar & Rowe, 2011). It is also reported that due to the additional force exerted by the tip of the scope along with the colon wall stretching, the outer lining of the colon called Serosal get damaged or injured (Livstone & Kerstein, 1979).

Research Objective:

When we analyze different colonoscope in the market then we realize that there are various colonoscopies are available by different manufactures that addressed the loop formation problem in there colonoscope system and they are now adapted by the clinics and hospitals for medical examinations as well. Among them some are as follows:

• Over – tube Colonoscope
• Capsule Endoscope
• Virtual Colonoscopy
• Aer – O – Scope
• Neo Guide Endoscopy System
• Image Guided Colonoscopy

However, clinical analysis and experimental assessment reveals that the above mentioned colonoscope models does not up to expectation of Gastroenterologists in terms of overcoming loop formation (Cheng, et al. 2012). Analysis done by Cheng and his team discloses that the solutions that are available in market have missed the important factor of engineering perception known as self-locking of the colonoscope and colon (Moser, et al. 2012).

To overcome these issues, the suggested model must be fulfilling the definition of operator-assisted colonoscopy. In this new paradigm, the operator or gastroenterologist would be able to get some additional parameters on display such as the exerted force by the operator, resultant friction force (between colon and colonoscope) and their comparison.

From the aforementioned research analysis and suggestions, following two objectives will be proposed in this report:

1. Analyse and evaluate the available colonoscope devices and their solutions for eliminating the loop formation from the prospective of engineering design methodology.

2. To develop an idea of an operator – assisted colonoscopy model that would be embedded on the shaft of the colonoscope and interface with the computer to monitor the force angle and compares it with the friction angle. The display of these angles will help the operator to assist him to keep the driving force greater than the friction force for avoiding the loop formations.

Organization of the report:

The report will be composed of different chapters, the organization of the report will be described as under:

1. Basic introduction of Colonoscopy system and its procedure, problems related to colonoscope and effect of loop formation.

2. Analysis and evaluation of the colonoscope devices for looping elimination available in the market through the concept of Engineering Design Theory and Methodology.

3. Idea of a new equipment, modelling and designing methodology to get proper idea pertaining to new designed procedure.

4. Simulation of the introduced idea.

5. Future work

6. Conclusion

7. References

CAUSES OF LOOP FORMATION AND EVALUATION THE EXISTING COLONOSCOPY DEVICES

In this section, the evaluation will be done of the available design and devices that focuses the looping elimination issue during the colonoscopy procedure. Before the evaluation the causes related loop formation will be explain with its mathematical explanation. For the evaluation of the devices, first we need to establish criteria whose structure is based on the theory presented in Advance Engineering Design and Methodology (ME886) course known as Axiomatic Design Theory (ADT). 

Causes of loop formation:

Generally, loop formation initializes when the colonoscope shaft reaches to the sigmoid colon. Where the experienced physician or gastroenterologist can resolve the formed loop and able to pass into the adjacent descending section of the colon. Once the scope reaches at the splenic flexure of the colon which has a sharp turn, the scope experiences looping once again. Furthermore, another formation of loop has been observed at the sharp turn of the hepatic flexure. The formation of the loop in the colon can be explained by the self-locking mechanism (Moser, et al. 2012). 

Self-locking Mechanism:

When the colon and colonoscope meet at contact point they will experiences force of friction because both the objects are deformable, that results may be either static or dynamic friction. At the point of contact between colon and colonoscope generally two states are formed in the tangential contact which are defined as slip state and stick state (Cheng, et al. 2012).

Slip state occurs when tangential force is greater than the limit of static friction force, which is defined as the product of the normal force with the static frictional coefficient. In the slip state, there will be a possible slip occurs between the colon and the colonoscope. Therefore, for that reason the shaft of the colonoscope has the possibility to move forward along with the friction force.

Stick state is the displacement of two contact points when both are equal to zero. This stick state usually occurs in sigmoid colon, as a result the colonoscope remains stationary and unable to move forward.

This friction force can be determined by the multiplication of dynamic frictional coefficient and normal applied force to the point (Dequidt, et al. 2009).

Mathematical analysis of Stick and Slip states:

Figure 07: Analysis of the force contact between colonoscope and colon near sigmoid colon.

Let us consider the above figure 07 to establish the mathematical analysis of Stick and Slip states. Suppose there is a contact between colonoscope and colon at point P and this point frame is represented as Xp, Yp and Zp. Where Xp is a normal direction and its force component is F(nor). Whereas Yp and Zp are the two component directions representing the tangential direction of the colonoscope at the point of contact which are perpendicular to each other (Cheng). The force component F1 and F2 are the respectively representing forces along these component directions.

Now consider the general equation of the force of friction:

F friction = μ  ×  N                  Eq. (1.0)

Where µ is known as coefficient of friction and N is the normal force.

By applying Eq. (1.0) on the figure 07, the state of frictional force can be defined as follows (Dequidt, et al. 2009):

F1 × F2Fnor < μ         a

F1 × F2F(nor) ≥ μ        b

Where the (a) is the mathematical explanation for occurring of Sticking Friction and (b) indicates the occurrence of Slip Friction.

Let us consider

α

(alpha) as driving force angle and

β

(beta) as friction angle.

Therefore defining

F1 × F2Fnor =tan⁡α

and on the bases of the definition of friction angle:

tan⁡β = μ

This results in the following relationship:

tan⁡α  < tan⁡β                     c

tan⁡α  ≥ tan⁡β                     d

Where (c) represents the Sticking State and (d) directs the Slip State. On the bases of the above equations if the condition occurred when

α < β

then the shaft of the colonoscope will not move forward and remain stationary, this event is known as Self-locking.

Due to the formation of the self-locking state, the physician will apply an additional unwanted increase in the driving force to drive colonoscope forward and this would result the swelling of the colon internal tissues.

On the bases of the above analysis it is been concluded that for avoiding loop formation and for the smooth procedure of colonoscopy, the Driving Force Angle must be remaining greater than the Friction Force Angle.

Evaluation of existing devices for loop elimination:

Advanced Engineering Design and Methodology is a subject which is point of interest for every organization, especially for those who are having an immense research in this area related to innovation, designing of engineering products, modelling and enhancement or modifications related to engineering design and various processes.

Dr. Suh Nam Pyo introduced the concept of axiomatic design theory for systems and developed the relation between “What we want to achieve?” and “How we want to achieve?” (Suh, 1998). The following table can explain this concept in more detail:

The constraint requirement can be described as the limitation or restriction of a system, and it provides the conditions criteria for the system where the functional requirements are achieved. In short, the design theory could be defined as “the design process to develop the design parameters (DPs) for achieving or fulfilling the functional requirements (FRs) under the defined constraint requirements (CRs)” (Suh, 1998).

The structure of the evaluation criteria for the devices that provides the solution of looping of the colonoscope could be defined by the following check points:

• The causes of loop formation are considered as Functional Requirements (FRs) along with Constraint Requirements (CRs).
• The available or existing design and their solution are considered as Design Parameters (DPs)

Axiomatic Design Theory (ADT) will evaluate the design parameters DPs of the given system by providing the FRs and CRs (Suh, 1998). The Axiomatic Design uses two Axioms defined in the following table:

The validity and reliability of a design is explained by the Axiom 1, whereas the Axiom 2 describe the best possible design among the different design options with respect to its material availability, manufacturing cost etc (Suh, 1998).

Now we need to develop the parameters of DP, FR and CR for the colonoscopy system that we need to design for the loop elimination, through which the Axiomatic Design Theory will compare the parameters of the existing devices. As we have already defined in the self-looking mechanism section that for the prevention of the loop formation is only be occur when the driving force angle must be kept higher than the friction angle, therefore the Functional Requirement (FR) is defined as: