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Modeling, Localization and Control of Endoscopic Capsule for Tissue Biopsy

Tolouei, Zahra | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57699 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Nejat Pishkenari, Hossein
  7. Abstract:
  8. Nowadays, endoscopic capsules are an interesting technique due to their ability to minimize patient discomfort and provide access to all parts of the gastrointestinal tract. However, they lack some capabilities of traditional methods, such as performing biopsies. An essential requirement for performing a biopsy of a specific part of the gastrointestinal tract is capsule control; in addition, localization information is required for closed-loop control. The goal of this research is the localization and control of a capsule with a biopsy module. For this purpose, an endoscopic capsule using the concept of a magnetic spring was introduced, which had different magnets so its localization and control were debatable. The actuation system consisted of three Helmholtz coils, and it was assumed that the larger magnet within the capsule would align with the external magnetic field after a short time due to the fast rotational dynamics, so controlling the magnetic field was sufficient for controlling the capsule. First, two-dimensional control of the capsule without triggering the biopsy mechanism was performed in open-loop control by rolling and adjusting the heading of the capsule using the inverse model of the coils’ magnetic field, also the biopsy mechanism was triggered using a large magnetic field at a 45-degree angle relative to the capsule’s dipole. Then, in closed-loop control, the capsule moved along triangular and sinusoidal paths with root mean square errors of 2.62 mm and 2.73 mm, respectively. Furthermore, to simulate conditions closer to reality, the capsule followed paths in the water, achieving root mean square errors of 2 mm and 2.32 mm for circular and sinusoidal paths, respectively. Magnetic localization of the capsule was done using 3-axial magnetic sensor arrays and Levenberg-Marquardt algorithm. Due to using two magnets in the capsule for the biopsy mechanism, challenges such as high sensitivity to initial conditions and significant error in orientation estimation arose; proposed solutions included finding initial conditions by assuming an equivalent moment for magnets and using two perpendicular boards, respectively. The results showed that the proposed solution for initial conditions avoided divergence, and the use of two boards significantly improved orientation estimation accuracy. Finally, six degrees of freedom in capsule localization were achieved, with accuracies of 3.2 mm for position and 4.7 degrees for orientation
  9. Keywords:
  10. Magnetic Localization ; Gastrointestinal Tract Biopsy ; Capsule Magnetic Locomotion ; Capsule Endoscopy

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