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2011 Michiel van den Bosch

MRI-guided robot for needle interventions in the prostate

Magnetic resonance imaging (MRI) is applied to non-invasively visualize patient’s anatomy and tumour suspicious regions with superior soft tissue contrast. Amongst others, online MRI is valuable in the diagnostic and treatment techniques for prostate cancer. Clinical MR scanners are suitable to perform MRI-guided needle interventions, such as biopsies and brachytherapy, but the access to the patient in the narrow MR bore is limited. Therefore, robotic devices have to be developed to execute these diagnostic and treatment techniques. This thesis describes the development and quality assurance of the University Medical Center Utrecht (UMCU) robot. Furthermore, it reports the first in vivo experiences with this robot and discusses its possible future applications. Chapter 1 is a general introduction to this research. In Chapter 2, the results are presented of a feasibility study on the dose coverage in low-dose rate brachytherapy using divergent needle insertion methods, as could theoretically be established inside the MR scanner applying the UMCU robot. The study revealed that with the divergent needle methods adequate dose distributions in the prostate can be achieved. Chapter 3 describes a new method to detect undesired situations with risk of tissue heating around the needle tip caused by the radiofrequency (RF) waves needed to generate MR images during interventional procedures. The method is based on the RF induced image artefacts and quantifies the induced current inside the needle. The method is effective for detecting potentially dangerous situations non-invasively. In Chapter 4, development considerations and quality assurance methods of MRI-guided robotic devices dedicated for needle interventions are listed. It provides background information on how to deal with the MRI-related challenges, such as accessibility, MR compatibility, needle placement accuracy and safety, before the devices can be safely applied on patients. Chapter 5 reports the proof of principle of our robot. Four fiducial gold markers were placed under MRI guidance inside the prostate of a prostate cancer patient using the UMCU robot. The needle could automatically be inserted and tracked using fast MR scans. Despite an advanced needle insertion technique (tapping), prostate deformations up to 7 mm were measured, which implies that improvement of the tapping device for further reduction of tissue deformation is needed. In Chapter 6, it is investigated whether single shot MR tagging can be used to quantify local prostate deformations due to the needle insertion. Single shot MR tagging creates artificial landmarks in the prostate which deform with the actual tissue deformations. The method can for example be used to better position the needle during the intervention or to assure the needle insertion quality of robotic devices. Chapter 7 summarizes the various studies of this thesis and discusses the future applications of the UMCU robot, such as online MRI-guided prostate brachytherapy and biopsies. To our knowledge, the UMCU robot is the first and up-to-now the only robotic device in the world that performed a needle insertion in patients inside an MR scanner, while tracking the needle using online MRI.