University of Twente Student Theses


Design of a control strategy for a robotically assisted ultrasound guided biopsy

Pantelis, D. (2019) Design of a control strategy for a robotically assisted ultrasound guided biopsy.

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Abstract:Breast cancer is one of the most common forms of cancer today that is negatively affecting the lives of many people. One very important step in the diagnostics step is performing a biopsy procedure. During a biopsy, the radiologist inserts a needle inside the breast tissue and under ultrasound guidance he moves it towards the target lesion, to extract a sample. The extracted cells are then further examined for a diagnosis to be reached. However, the biopsy can be timeconsuming and uncomfortable for patients. Additionally, the accuracy of the result is heavily dependent on the experience of the practitioner who is performing the process. These same practitioners also tend to suffer from fatigue and work-related musculoskeletal pain. Many of these problems can be alleviated by using a robotic system that would assist the radiologists. Robotics is more capable at performing tasks that require repeatability and precision, compared to humans. This could result in improving the patient’s experience, reduce the time of the entire diagnosis process, have a better accuracy rate, and benefit radiologists’ working conditions. The MURAB project is one such attempt to create this kind of robotic system. An end-effector for this specific application has already been designed. It consists of an ultrasound probe holder and a needle guiding mechanism. This end-effector is mounted on the 7 DOF KUKA LBRMed articulated robotic arm. In this thesis, a control strategy is designed that moves the end-effector to the appropriate position, as to allow the ultrasound probe to have a visual of the target and so that the needle orientation mechanic can guide the biopsy needle into the correct direction. For this to happen, what is referred to as the "Initialization Phase" was first created. Furthermore, to ensure that the target would be hit, the tissue located at the target position was tracked through the ultrasound images. This was achieved by designing a tracking algorithm, with optical flowas its core. Additionally, a controller that would guide the needle, using this tracking algorithm, was designed and implemented. This controller relied on controlling the actuators of the needle orientation mechanism. However, the controller cannot compensate inaccuracies presented by needle bending. For that reason, the possibility of directly tracking the needle using the Hough transformation was examined. Lastly, it could be argued that an issue that the above controller has is that it does not give the radiologist any control since the needle orientation mechanism is manipulated with position control. For that reason, an impedance controller was designed that would allow the radiologist to controller the degree in which the robotic system and the user has control over the direction of the needle. This design was then simulated in 20-sim, as to determine its correct behavior. It was shown that the presented tracking algorithm was able to achieve sub-millimeter accuracy. Combing it with the needle orientation controller, also presented near sub-millimeter accuracy. The needle detection algorithm was able to compensate for big offsets of the needle orientation mechanism but was not able to reduce the error to the degree that the needle orientation controller was able. Furthermore, simulations of the impedance controller, show it can be used to allow the radiologist to manually adjust the needle’s orientation if that is desired. The results of the experiments are promising. They show that the proposed control strategy has the potential of being the bases of a robotic system that can improve the quality of the biopsy process.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology, 54 computer science
Programme:Systems and Control MSc (60359)
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