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CHAPTER 1
AIM OF THE WORK
Endoscopy is a medical procedure used to examine and inspect the interior of human body through a flexible endoscope. In particular, when the investigation regards the colon, that is the last portion of gastrointestinal tract, the procedure is called colonoscopy. There are some diseases that interfere with the normal colon functioning. For example colorectal cancer (CRC) is a major cause of mortality in the western world (>200.000/year in Europe). Identification and removal of precancerous adenomatous polyps in colonoscopy demonstrated to be effective in preventing CRC, but the application of CRC screening is low. In fact, despite such technique enables reliable diagnosis, its application is considered traumatic and frequently poor tolerate by patients. The examination requires to insufflate with air the colon to extend the tissue and it causes discomfort to the patient during the procedure. Furthermore, the rigidity and the diameter of the probe and the need for a good level of practice by the physician to move the endoscope in appropriate manner, are the other limitations of this traditional technique. As consequence, these aspects reduce the compliance at the exam and the participation to the patients at screening programs.
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Wireless capsule endoscopy is a new medical treatment technology and it is a significant step to develop an effective endoscopy technique that overcomes the inconveniences, above mentioned.
However, it brings some new problems. In fact commercial capsule, which has to be located inside the human body, cannot be driven by the physician to move towards a specific site to get more information or images because it is propelled passively by peristalsis forces of the gastrointestinal tract (passive endoscopy capsule).
To solve this drawback, researchers have proposed several methods for the capsule locomotion (active endoscopy capsule), such as using piezoelectric drive, shape memory alloy and micro motors, that have to be inserted inside the capsule itself (internal locomotion system). These active propulsions allow the control of the device, operating in areas of interest. But also this solution has some limitations, due to the difficulty to integrate these locomotion technologies into the capsule body, because of required small dimensions.
A possible idea to overcome this disadvantage is to consider a control method of the capsule based on magnetic field, generated by a source outside the human body (external locomotion system). Since magnetic fields have static and low frequencies, they can pass through human body tissue without any attenuation.
For this reason, an internal permanent magnet (IPM) is inserted inside the capsule and it can interact with a magnetic field, generated by an external magnetic source. This combination creates a magnetic force and torque that provides locomotion and orientation of the capsule.
The current state of the art about electromagnetic locomotion uses bulky equipments not compatible with a low-cost and outpatient environment.
SUPCAM project (FP7-SME-315378 ) [1] develops a new cost effective and minimally invasive system, which is composed by a new mechanical configuration of the wireless capsule endoscopy (SUPCAM capsule or WCE) and by an external electromagnetic system (ESS) with cylindrical form. The
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capsule will have the appearance of a small spherical shape and it will allow the medical examination of the colon’s mucosa through EES.
In particular the aim of work, described in the present thesis, addresses, inside SUPCAM system, the design and the develop of the external magnetic control system that allows, outside the human body, to have the propulsion of a SUPCAM capsule along lumen of the colon.
The electromagnetic controller will have a simple structure, it will be inexpensive and compact, with reduced bulk. In fact this external device should be suitable for transport and to be used in normal outpatient settings. For these reasons, EES is composed by a single electromagnet (also indicated as solenoid and coil), that, applying a current, creates an appropriate magnetic field to control SUPCAM capsule inside an enclosed environment.
EES has to be capable to maneuver SUPCAM capsule along five degrees of freedom, three for the translation and two for the orientation. To achieve these WCE movements, EES design takes in account to use it in two different configurations: one, called C1, in which EES is positioned perpendicular to the abdomen of the patient and one, called C2, in which the EES is rotated of 90° degrees from C1 to be parallel to the abdomen of the patient. These are the working conditions that are able to examine the colonic lumen.
As a consequence, the thesis describes all the steps that have been necessary to design and develop the required electromagnet, taking in account the following requirements and constraints:
- based on the chosen IPM dimensions and magnetic features (in order to balance size and high magnetization capability) and the total SUPCAM capsule weight, it is necessary to compute the magnetic torque and force to have the required magnetic field and gradient, that EES has to generate to control SUPCAM capsule, as described above. In fact, the magnetic field gradient allows SUPCAM capsule translation, in terms of attraction and
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locomotion, instead the magnetic field allows the capsule orientation (yaw and pitch rotation as explained later on);
- the strength of magnetic field created by an electromagnet depends on the input current and the coil parameters, like height, external diameter, internal diameter, iron core (with cylindrical form which will have the diameter equal to EES internal diameter), wire copper dimension, number of windings. Coil dimensioning has to take into account that EES size has not to be too large because one requirement is to have a compact device; - in order to generate a stronger magnetic field in the space outside the
electromagnet, in the internal part of EES, it will be inserted an iron core. EES internal dimension is influenced by iron core required size;
- EES current density has to be lesser than a limit value, to avoid a heating, caused by Joule effect. Therefore, it will be necessary to consider an appropriate wire diameter and a suitable current intensity.
In order to perform EES design in accordance with the above listed requirements and constraints, it is necessary to identify some models that allow to make magnetic field and gradient simulations, based on EES size, iron core, current intensity and so on. To make a double check about simulation correctness, it was chosen two different tools: one is based on finite element method (FEM), using a software simulation platform (COMSOL Multiphysics 4.3a, Inc., Sweden), and the other one is based on an analytical model.
Of course, before to have designed the final EES, some experimental measures were performed to verify the reliability of the simulation modeling.
