Achieving commutation control of an MRI-powered robot actuator

Actuators that are powered, imaged, and controlled by magnetic resonance (MR) scanners could inexpensively provide wireless control of MR-guided robots. Similar to traditional electric motors, the MR scanner acts as the stator and generates propulsive torques on an actuator rotor containing one or more ferrous particles. Generating maximum motor torque while avoiding instabilities and slippage requires closed-loop control of the electromagnetic field gradients, i.e., commutation. Accurately estimating the position and velocity of the rotor is essential for high-speed control, which is a challenge due to the low refresh rate and high latency associated with MR signal acquisition. This paper proposes and demonstrates a method for closed-loop commutation based on interleaving pulse sequences for rotor imaging and rotor propulsion. This approach is shown to increase motor torque and velocity, eliminate rotor slip, and enable regulation of rotor angle. Experiments with a closed-loop MR imaging actuator produced a maximum force of 9.4 N

MRI compatible miniature motor system: Proof of Concept

Master's Thesis in PhysicsPHYS399MAMN-PHY

Medical Robotics for use in MRI Guided Endoscopy

Interventional Magnetic Resonance Imaging (MRI) is a developing field that aims to provide intra-operative MRI to a clinician to guide diagnostic or therapeutic medical procedures. MRI provides excellent soft tissue contrast at sub-millimetre resolution in both 2D and 3D without the need for ionizing radiation. Images can be acquired in near real-time for guidance purposes. Operating in the MR environment brings challenges due to the high static magnetic field, switching magnetic field gradients and RF excitation pulses. In addition high field closed bore scanners have spatial constraints that severely limit access to the patient. This thesis presents a system for MRI-guided Endoscopic Retrograde Cholangio-pancreatography (ERCP). This includes a remote actuation system that enables an MRI-compatible endoscope to be controlled whilst the patient is inside the MRI scanner, overcoming the spatial and procedural constraints imposed by the closed scanner bore. The modular system utilises non-magnetic ultrasonic motors and is designed for image-guided user-in-the-loop control. A novel miniature MRI compatible clutch has been incorporated into the design to reduce the need for multiple parallel motors. The actuation system is MRI compatible does not degrade the MR images below acceptable levels. User testing showed that the actuation system requires some degree of training but enables completion of a simulated ERCP procedure with no loss of performance. This was demonstrated using a tailored ERCP simulator and kinematic assessment tool, which was validated with users from a range of skill levels to ensure that it provides an objective measurement of endoscopic skill. Methods of tracking the endoscope in real-time using the MRI scanner are explored and presented here. Use of the MRI-guided ERCP system was shown to improve the operator’s ability to position the endoscope in an experimental environment compared with a standard fluoroscopic-guided system.Open Acces

Modeling and design of an electromagnetic actuation system for the manipulation of microrobots in blood vessels

Tese de mestrado integrado em Física, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2015A navegação de nano/microdispositivos apresenta um grande potencial para aplicações biomédicas, oferecendo meios de diagnóstico e procedimentos terapêuticos no interior do corpo humano. Dada a sua capacidade de penetrar quase todos os materiais, os campos magnéticos são naturalmente adequados para controlar nano/microdispositivos magnéticos em espaços inacessíveis. Uma abordagem recente é o uso de um aparelho personalizado, capaz de controlar campos magnéticos. Esta é uma área de pesquisa prometedora, mas mais simulações e experiências são necessárias para avaliar a viabilidade destes sistemas em aplicações clínicas. O objectivo deste projecto foi a simulação e desenho de um sistema de atuação eletromagnética para estudar a locomoção bidimensional de microdispositivos. O primeiro passo foi identificar, através da análise de elementos finitos, usando o software COMSOL, diferentes configurações de bobines que permitiriam o controlo de dispositivos magnéticos em diferentes escalas. Baseado nos resultados das simulações, um protótipo de um sistema de atuação magnética para controlar dispositivos com mais de 100 m foi desenhado e construído de raiz, tendo em conta restrições de custos. O sistema consistiu num par de bobines de Helmholtz e rotacionais e um par de bobines de Maxwell dispostas no mesmo eixo. Além disso, componentes adicionais tiveram de ser desenhados ou selecionados para preencher os requisitos do sistema. Para a avaliação do sistema fabricado, testes preliminares foram realizados. A locomoção do microrobot foi testada em diferentes direções no plano x-y. As simulações e experiências confirmaram que é possível controlar a força magnética e o momento da força que atuam num microdispositivo através do campos produzidos pelas bobines de Maxwell e Helmholtz, respectivamente. Assim, este tipo de atuação magnética parece ser uma forma adequada de transferência de energia para futuros microdispositivos biomédicos.Navigation of nano/microdevices has great potential for biomedical applications, offering a means for diagnosis and therapeutic procedures inside the human body. Due to their ability to penetrate most materials, magnetic fields are naturally suited to control magnetic nano/microdevices in inaccessible spaces. One recent approach is the use of custom-built apparatus capable of controlling magnetic devices. This is a promising area of research, but further simulation studies and experiments are needed to estimate the feasibility of these systems in clinical applications. The goal of this project was the simulation and design of an electromagnetic actuation system to study the two dimensional locomotion of microdevices. The first step was to identify, through finite element analysis using software COMSOL, different coil configurations that would allow the control of magnetic devices at different scales. Based on the simulation results, a prototype of a magnetic actuation system to control devices with more than 100 m was designed and built from the ground up, taking into account cost constraints. The system comprised one pair of rotational Helmholtz coils and one pair of rotational Maxwell coils placed along the same axis. Furthermore, additional components had to be designed or selected to fulfil the requirements of the system. For the evaluation of the fabricated system, preliminary tests were carried out. The locomotion of a microdevice was tested along different directions in the x-y plane. The simulations and experiments confirmed that it is possible to control the magnetic force and torque acting on a microdevice through the fields produced by Maxwell and Helmholtz coils, respectively. Thus, this type of magnetic actuation seems to provide a suitable means of energy transfer for future biomedical microdevices

Monolithic self-supportive bi-directional bending pneumatic bellows catheter

The minimally invasive surgery has proven to be advantageous over conventional open surgery in terms of reduction in recovery time, patient trauma, and overall cost of treatment. To perform a minimally invasive procedure, preliminary insertion of a flexible tube or catheter is crucial without sacrificing its ability to manoeuvre. Nevertheless, despite the vast amount of research reported on catheters, the ability to implement active catheters in the minimally invasive application is still limited. To date, active catheters are made of rigid structures constricted to the use of wires or on-board power supplies for actuation, which increases the risk of damaging the internal organs and tissues. To address this issue, an active catheter made of soft, flexible and biocompatible structure, driven via nonelectric stimulus is of utmost importance. This thesis presents the development of a novel monolithic self-supportive bi-directional bending pneumatic bellows catheter using a sacrificial molding technique. As a proof of concept, in order to understand the effects of structural parameters on the bending performance of a bellows-structured actuator, a single channel circular bellows pneumatic actuator was designed. The finite element analysis was performed in order to analyze the unidirectional bending performance, while the most optimal model was fabricated for experimental validation. Moreover, to attain biocompatibility and bidirectional bending, the novel monolithic polydimethylsiloxane (PDMS)-based dual-channel square bellows pneumatic actuator was proposed. The actuator was designed with an overall cross-sectional area of 5 x 5 mm2, while the input sequence and the number of bellows were characterized to identify their effects on the bending performance. A novel sacrificial molding technique was adopted for developing the monolithic-structured actuator, which enabled simple fabrication for complex designs. The experimental validation revealed that the actuator model with a size of5 x 5 x 68.4 mm3 i.e. having the highest number of bellows, attained optimal bi-directional bending with maximum angles of -65° and 75°, and force of 0.166 and 0.221 N under left and right channel actuation, respectively, at 100 kPa pressure. The bending performance characterization and thermal insusceptibility achieved by the developed pneumatic catheter presents a promising implementation of flexibility and thermal stability for various biomedical applications, such as dialysis and cardiac catheterization

Innovative micro-NMR/MRI functionality utilizing flexible electronics and control systems

Das zentrale Thema dieser Arbeit ist die Entwicklung und Integration von flexibler Elektronik für Mikro-Magnetresonanz (MR)-Anwendungen. Zwei wichtige Anwendungen wurden in der Dissertation behandelt; eine Anwendung auf dem Gebiet der Magnetresonanztomographie (MRI) und die andere auf dem Gebiet der Kernspinresonanz (NMR). Die MRI-Anwendung konzentriert sich auf die Lösung der Sicherheits- und Zuverlässigkeitsaspekte von MR-Kathetern. Die NMR-Anwendung stellt einen neuartigen Ansatz zur Steigerung des Durchsatzes bei der NMR-Spektroskopie vor. Der erste Teil der Dissertation behandelt die verschiedenen Technologien die zur Herstellung flexibler Elektronik auf der Mikroskala entwickelt wurden. Die behandelten MR-Anwendungen erfordern die Herstellung von Induktoren, Kondensatoren und Dioden auf flexiblen Substraten. Die erste Technologie, die im Rahmen der Mikrofabrikation behandelt wird, ist das Aufbringen einer leitfähigen Startschicht auf flexiblen Substraten. Es wurden verschiedene Techniken getestet und verglichen. Die entwickelte Technologie ermöglicht die Herstellung einer mehrschichtigen leitfähigen Struktur auf einem flexiblen Substrat (50 $\mu$m Dicke), die sich zum Umwickeln eines schlanken Rohres (>0,5 mm Durchmesser) eignet. Die zweite Methode ist der Tintenstrahldruck von Kondensatoren mit hoher Dichte und niedrigem Verlustkoeffizienten. Zwei dielektrische Tinten auf Polymerbasis wurden synthetisiert, durch die Dispersion von TiO$_2$ und BaTiO$_3$ in Benzocyclobuten (BCB) Polymer. Die im Tintenstrahldruckverfahren hergestellten Kondensatoren zeigen eine relativ hohe Kapazität pro Flächeneinheit von bis zu 69 pFmm$^{-2}$ und erreichen dabei einen Qualitätsfaktor (Q) von etwa 100. Außerdem wurde eine Technik für eine tintenstrahlgedruckte gleichrichtende Schottky-Diode entwickelt. Die letzte behandelte Technologie ist die Galvanisierung der leitenden Startschichten. Die Galvanik ist eine gut erforschte Technologie und ein sehr wichtiger Prozess auf dem Gebiet der Mikrofabrikation. Sie ist jedoch in hohem Maße von der Erfahrung des Bedieners abhängig. Darüber hinaus ist eine präzise Steuerung der Galvanikleistung erforderlich, insbesondere bei der Herstellung kleiner Strukturen, wobei sich die Pulsgalvanik als ein Verfahren erwiesen hat, das ein hohes Maß an Kontrolle über die abgeschiedene Struktur bietet. In diesem Zusammenhang wurde eine hochflexible Stromquelle auf Basis einer Mikrocontroller-Einheit entwickelt, um Genauigkeit in die Erstellung optimaler Galvanikrezepte zu bringen. Die Stromquelle wurde auf Basis einer modifizierten Howland-Stromquelle (MHCS) unter Verwendung eines Hochleistungs-Operationsverstärkers (OPAMP) aufgebaut. Die Stromquelle wurde validiert und verifiziert, und ihre hohe Leistungsfähigkeit wurde durch die Durchführung einiger schwieriger Anwendungen demonstriert, von denen die wichtigste die Verbesserung der Haftung der im Tintenstrahldruckverfahren gedruckten Startschicht auf flexiblen Substraten ist. Der zweite Teil der Dissertation befasst sich mit interventioneller MRT mittels MR-Katheter. MR-Katheter haben potenziell einen erheblichen Einfluss auf den Bereich der minimalinvasiven medizinischen Eingriffe. Implantierte längliche Übertragungsleiter und Detektorspulen wirken wie eine Antenne und koppeln sich an das MR-Hochfrequenz (HF)-Sendefeld an und machen so den Katheter während des Einsatzes in einem MRT-Scanner sichtbar. Durch diese Kopplung können sich die Leiter jedoch erhitzen, was zu einer gefährlichen Erwärmung des Gewebes führt und eine breite Anwendung dieser Technologie bisher verhindert hat. Ein alternativer Ansatz besteht darin, einen Resonator an der Katheterspitze induktive mit einer Oberflächenspule außerhalb des Körpers zu koppeln. Allerdings könnte sich auch dieser Mikroresonator an der Katheterspitze während der Anregungsphase erwärmen. Außerdem ändert sich die Sichtbarkeit der Katheterspitze, wenn sich die axiale Ausrichtung des Katheters während der Bewegung ändert, und kann verloren gehen, wenn die Magnetfelder des drahtlosen Resonators und der externen Spule orthogonal sind. In diesem Beitrag wird die Abstimmkapazität des Mikrodetektors des Katheters drahtlos über eine Impulsfolgensteuerung gesteuert, die an einen HF-Abstimmkreis gesendet wird, der in eine Detektorspule integriert ist. Der integrierte Schaltkreis erzeugt Gleichstrom aus dem übertragenen HF Signal zur Steuerung der Kapazität aus der Ferne, wodurch ein intelligenter eingebetteter abstimmbarer Detektor an der Katheterspitze entsteht. Während der HF-Übertragung erfolgt die Entkopplung durch eine Feinabstimmung der Detektorbetriebsfrequenz weg von der Larmor-Frequenz. Zusätzlich wird ein neuartiges Detektordesign eingeführt, das auf zwei senkrecht ausgerichteten Mikro-Saddle-Spulen basiert, die eine konstante Sichtbarkeit des Katheters für den gesamten Bereich der axialen Ausrichtungen ohne toten Winkel gewährleisten. Das System wurde experimentell in einem 1T MRT-Scanner verifiziert. Der dritte Teil der Dissertation befasst sich mit dem Durchsatz von NMR-Spektroskopie. Flussbasierte NMR ist eine vielversprechende Technik zur Verbesserung des NMR-Durchsatzes. Eine häufige Herausforderung ist jedoch das relativ große Totvolumen im Schlauch, der den NMR-Detektor speist. In diesem Beitrag wird ein neuartiger Ansatz für vollautomatische NMR-Spektroskopie mit hohem Durchsatz und verbesserter Massensensitivität vorgestellt. Der entwickelte Ansatz wird durch die Nutzung von Mikrofluidik-Technologien in Kombination mit Dünnfilm-Mikro-NMR-Detektoren verwirklicht. Es wurde ein passender NMR-Sensor mit einem mikrofluidischen System entwickelt, das Folgendes umfasst: i) einen Mikro-Sattel-Detektor für die NMR-Spektroskopie und ii) ein Paar Durchflusssensoren, die den NMR-Detektor flankieren und an eine Mikrocontrollereinheit angeschlossen sind. Ein mikrofluidischer Schlauch wird verwendet, um eine Probenserie durch den Sondenkopf zu transportieren, die einzelnen Probenbereiche sind durch eine nicht mischbare Flüssigkeit getrennt, das System erlaubt im Prinzip eine unbegrenzte Anzahl an Proben. Das entwickelte System verfolgt die Position und Geschwindigkeit der Proben in diesem zweiphasigen Fluss und synchronisiert die NMR-Akquisition. Der entwickelte kundenspezifische Sondenkopf ist Plug-and-Play-fähig mit marktüblichen NMR-Systemen. Das System wurde erfolgreich zur Automatisierung von flussbasierten NMR-Messungen in einem 500 MHz NMR-System eingesetzt. Der entwickelte Mikro-NMR-Detektor ermöglicht hochauflösende Spektroskopie mit einer NMR-Empfindlichkeit von 2,18 nmol s$^{1/2}$ bei Betrieb der Durchflusssensoren. Die Durchflusssensoren wiesen eine hohe Empfindlichkeit bis zu einem absoluten Unterschied von 0,2 in der relativen Permittivität auf, was eine Differenzierung zwischen den meisten gängigen Lösungsmitteln ermöglichte. Es wurde gezeigt, dass eine vollautomatische NMR-Spektroskopie von neun verschiedenen 120 $\mu$L Proben innerhalb von 3,6 min oder effektiv 15,3 s pro Probe erreicht werden konnte

Maximising the mutual interoperability of an MRI scanner and a cancer therapy particle accelerator

The work described in this PhD thesis was undertaken as part of a much larger research project: The Australian MRI-Linac program. The goal of this program is to merge two existing medical technologies – an MRI scanner and a Linear Accelerator (Linac) – thereby creating an advanced form of cancer treatment incorporating cutting edge anatomical and physiological imaging techniques. An overview of the background information necessary to understand the work presented in this thesis is provided in chapters 1 (overview of radiotherapy) and 2 (overview of electromagnetism and accelerator physics). The work in the remainder of this thesis can be split into two distinct sections, corresponding to the two quite different (but ultimately related) projects I worked on throughout this thesis: modelling the impact of external magnetic fields on electron beam transport within the linear accelerator, and the implementation of patient rotation in radiotherapy. The former project is the focus of Chapters 3-6. In Chapter 3 a finite element model of a clinical gridded electron gun is developed based on 3D laser scanning and electrical measurements, and the sensitivity of this gun in magnetic fields characterised. The results complement the existing literature in showing that conventional linear accelerator components are very sensitive to external magnetic fields – in fact this gun is over twice as sensitive to axial magnetic fields than the less realistic models existing in the literature. A first order approach to overcoming this sensitivity is to use magnetic shielding – however magnetic shielding of the linear accelerator can negatively impact on the performance of the MRI scanner. This magnetic shielding problem is explored in Chapter 4, where the fundamental principles of passive magnetic shielding are explored, and magnetic shields are implemented for the two possible MRI-linac configurations (in-line and perpendicular) for the 1.0 Tesla MRI magnet used in the Australian MRI Linac program. The efficacy of the shielding and the impact on the MRI is quantified, with the conclusion that passive shielding could be successfully implemented to allow acceptable operation of the linac without overly degrading the magnet performance of the MRI scanner. An alternative approach to magnetic shielding which would not have any impact on the magnet is to redesign the linear accelerator such that it functions robustly in an MRI environment without the need for shielding. This approach is explored in chapter 5, where a novel electron accelerator concept based on an RF-electron gun configuration is detailed. It is shown via particle in cell simulations that such a design would be able to operate in a wide range of axial magnetic fields with minimal current loss. In chapter 6, an experimental beam line based on this concept was constructed at Stanford Linear Accelerator Center (SLAC). This project is ongoing but progress so far is described in Chapter 6. In the second part of this thesis, a completely different project is explored, patient rotation. Patient rotation would be very beneficial for MRI-Linac systems as it would eliminate the complicated engineering that is used in conventional systems to rotate the beam around the patient, and the MRI could be used to adapt in real time for the resultant anatomic deformation. Patient rotation would also minimise some of the sources of electromagnetic interference explored in chapters 3-7. The two major obstacles to patient rotation are (1) Page 11 patient tolerance to rotation, and (2) anatomical deformation due to rotation. To quantify patient rotation, a clinical study of 15 patients was carried out and is detailed in chapter 7. The results of this study suggest that patient tolerance to rotation may not be a major issue, although this result needs to be verified in larger patient cohorts. In chapter 8, the design and construction of an MRI-compatible patient rotation device is detailed. This device is the first of its kind, and will allow data on anatomic deformation under rotation to be collected, enabling strategies to adapt for this motion to be developed. Thus far, MRI compatibility has been assessed and a volunteer imaging study undertaken, in which pelvic images were acquired under rotation angles of 360⁰ every 45⁰. In summary: In chapters 3-5, the impact of magnetic fields on conventional accelerator components was quantified; and two independent approaches to compensating for these effects (magnetic shielding and bespoke accelerator design) were explored. In chapter 6, an experimental beam is constructed to verify and support the findings of chapter 6. In chapter 7, a clinical study was undertaken quantifying patient tolerance of slow, single arc rotation. Finally, in chapter 8 a unique medical device was designed, constructed and tested, and through this device MRI images of anatomical distortion under lying rotation were collected and quantified

Micro/nanoscale magnetic robots for biomedical applications

Magnetic small-scale robots are devices of great potential for the biomedical field because of the several benefits of this method of actuation. Recent work on the development of these devices has seen tremendous innovation and refinement toward ​improved performance for potential clinical applications. This review briefly details recent advancements in small-scale robots used for biomedical applications, covering their design, fabrication, applications, and demonstration of ability, and identifies the gap in studies and the difficulties that have persisted in the optimization of the use of these devices. In addition, alternative biomedical applications are also suggested for some of the technologies that show potential for other functions. This study concludes that although the field of small-scale robot research is highly innovative ​there is need for more concerted efforts to improve functionality and reliability of these devices particularly in clinical applications. Finally, further suggestions are made toward ​the achievement of commercialization for these devices

A comparison of processing techniques for producing prototype injection moulding inserts.

This project involves the investigation of processing techniques for producing low-cost moulding inserts used in the particulate injection moulding (PIM) process. Prototype moulds were made from both additive and subtractive processes as well as a combination of the two. The general motivation for this was to reduce the entry cost of users when considering PIM. PIM cavity inserts were first made by conventional machining from a polymer block using the pocket NC desktop mill. PIM cavity inserts were also made by fused filament deposition modelling using the Tiertime UP plus 3D printer. The injection moulding trials manifested in surface finish and part removal defects. The feedstock was a titanium metal blend which is brittle in comparison to commodity polymers. That in combination with the mesoscale features, small cross-sections and complex geometries were considered the main problems. For both processing methods, fixes were identified and made to test the theory. These consisted of a blended approach that saw a combination of both the additive and subtractive processes being used. The parts produced from the three processing methods are investigated and their respective merits and issues are discussed