An overview of multiple DoF magnetic actuated micro-robots.

International audienceThis paper reviews the state of the art of untethered, wirelessly actuated and controlled micro-robots. Research for such tools is being increasingly pursued to provide solutions for medical, biological and industrial applications. Indeed, due to their small size they o er both high velocity, and accessibility to tiny and clustered environments. These systems could be used for in vitro tasks on lab-on-chips in order to push and/or sort biological cells, or for in vivo tasks like minimally invasive surgery and could also be used in the micro-assembly of microcomponents. However, there are many constraints to actuating, manufacturing and controlling micro-robots, such as the impracticability of on-board sensors and actuators, common hysteresis phenomena and nonlinear behavior in the environment, and the high susceptibility to slight variations in the atmosphere like tiny dust or humidity. In this work, the major challenges that must be addressed are reviewed and some of the best performing multiple DoF micro-robots sized from tens to hundreds m are presented. The di erent magnetic micro-robot platforms are presented and compared. The actuation method as well as the control strategies are analyzed. The reviewed magnetic micro-robots highlight the ability of wireless actuation and show that high velocities can be reached. However, major issues on actuation and control must be overcome in order to perform complex micro-manipulation tasks

Navigation multi-bifurcations de corps ferromagnétiques avec un scanner d’imagerie par résonance magnétique

RÉSUMÉ Le nombre de personnes atteintes par le carcinome hépatocellulaire (CHC), un type de cancer du foie, est en progression croissante. Mondialement, le CHC est la seconde cause de mortalité chez les patients atteints par le cancer, à cause du taux de survie extrêmement faible. Le pronostic du CHC est très mauvais : aux USA et au Canada, le taux de survie à cinq ans est de 12% et 20% respectivement. Pour les personnes à un stade très avancé, les traitements possibles sont très limités. Un des traitements possibles est la chimioembolisation hépatique qui consiste à injecter des microparticules médicamenteuses dans le foie. L’objectif de ces particules est double : d’une part, elles embolisent les vaisseaux sanguins qui nourrissent les cellules tumorales et, d’autre part, libèrent des médicaments anti-cancer qui vont détruire les cellules malades. Malheureusement, en l’absence de tout contrôle, ces vecteurs thérapeutiques détruisent aussi des cellules saines de l’organe, en général en nombre limité. Pour ainsi améliorer les soins de ces patients, nous proposons d’utiliser le scanner d’imagerie à résonance magnétique (IRM) pour diriger ces microparticules dans la circulation sanguine dans le but de cibler uniquement les cellules malades. Les retombées de ce projet sont multiples pour le patient : entre-autres, diminution des effets secondaires, et procédures moins invasives et plus efficaces. Pas uniquement limitée au foie, la navigation par résonance magnétique (NRM) a réellement le potentiel de révolutionner certaines pratiques médicales et d’améliorer grandement la prise en charge et les soins pour les patients touchés par le cancer. Cette thèse décrit les stratégies à mettre en place afin de réaliser la NRM sur plusieurs canaux consécutifs afin de rendre les procédures de navigation plus ciblées et plus localisées. Pour atteindre cet objectif, plusieurs expériences ont été menées. Tout d’abord, nous avons prouvé qu’il était possible de guider une bille de 1 mm sur 4 canaux consécutifs à l’aide d’une bobine imagerie. Nous avons donc conçu un prototype microfluidique (fantôme) sous la forme d’un arbre, où chaque canal père se divise en deux canaux fils. Nous obtenons alors huit chemins possibles avec trois bifurcations (deux choix possibles à chaque jonction). Nous avons ainsi démontré que le guidage d’une bille sur trois bifurcations était possible, avec des gradients magnétiques inférieurs à 40 mT/m et donc équivalents à ceux utilisés par des IRM cliniques. Des vitesses de déplacement de 14 cm/s ont été mesurées. Suite à ces expériences de guidage, nous avons présenté quelques résultats sur la problématique de l’augmentation de la température : en effet, les bobines de gradient, lorsqu'utilisées pour faire de la navigation, chauffent rapidement et nécessitent des temps de refroidissement. Le ratio durée de guidage sur durée de refroidissement peut ainsi être faible sans stratégie de guidage adaptée. Ainsi, nous suggérons d’utiliser le temps de refroidissement de la bobine de propulsion afin de réaliser des séquences d’imagerie pour, par exemple, évaluer la dose injectée et réévaluer les paramètres de guidage. Expérimentalement, les séquences d'imagerie n'ont pas induit d'augmentation de la température et peuvent donc être exécutées sans perte de performance.----------ABSTRACT The number of new cases of Hepatocellular Carcinoma (HCC), one type of liver cancer, is on the rise. HCC is the second leading cause of cancer death worldwide, due to extremely low survival rate. Prognosis is very poor: the overall 5-year relative survival rate is 12% in the USA and 20% in Canada. The number of available treatments for patients diagnosed at distant stages of the disease is low. A possible treatment is the transarterial chemoembolization (TACE). TACE consists in a combined injection of embolic material and chemotherapeutic drugs. The benefit of TACE is two-fold: embolisation of tumor feeding arteries and local release of anti-cancer drugs directly to the tumoral cells. Unfortunately, without any control, these vectors may reach and kill surrounding healthy liver cells. To increase patient care, we propose to use the Magnetic Resonance Imaging scanner (MRI) as an actuator to navigate therapeutic microparticules into the bloodstream toward liver lesions. Potential outcomes for the patient are, among others, a reduction of side effects and a less invasive intervention. Not restricted to liver, Magnetic Resonance Navigation (MRN) shows promises to drastically change some medical procedures and to increase cancer patient care and management. This thesis decribes strategies to achieve MRN along multiple consecutive channels. In this objective, several experiments have been conducted. Firstly, we showed that a 1-mm bead can be navigated along four consecutives microfluidic channels using an imaging coil. A microfluidic phantom has been designed to obtain eight paths with three bifurcations (two possible choices at every junction). Using magnetic gradient amplitudes lower than 40 mT/m, which are equivalent to clinical MR scanners performance, we successfully steered a bead in all the eight paths. The velocity of the bead reached 14 cm/s. Following these experiments, we worked on potential issues regarding heat rise in the coil. Indeed, imaging coils heats up very quickly when used for MRN and therefore require some time to cool. Without any temperature management strategies, the navigation time over cooling time ratio can be low and thus the procedure duration may be longer. We therefore suggested using the cooling deadtime to apply imaging sequences and acquire information about injected dose or to re-assess navigation parameters. Experimentally, since no temperature rise was measured during the imaging sequences, there is no performance loss. From these observations, more characterisation tests were conducted on the imaging coil to find the most critical parameters regarding the heat rate. We measured an average time of two minutes before the coil reaches its critical temperature. In the worst-case scenario, where at least two gradients are applied simultaneously, less than one minute of propulsion at maximum power is available. From these results, a temperature model has been derived to predict heat rise according to the characteristics of the propulsion sequence. These equations will be integrated within a broad MRN model. Lastly, the inherent design of MRI only allows the application of a single force vector upon all magnetic bodies within a volume. It is therefore impossible to steer a continuous stream of particles along multiple consecutive vessels. One requirement for multiple-bifurcation navigation is therefore to create a discrete injection of particles (bolus) such that only one bolus is navigated at a time. Furthermore, a second requirement for multiple-bifurcation navigation is the synchronisation of the release of the bolus from the catheter with the start of the propulsion sequence

MRI magnetic signature imaging, tracking and navigation for targeted micro/nano-capsule therapeutics

International audienceThe propulsion of nano-ferromagnetic objects by means of MRI gradients is a promising approach to enable new forms of therapy. In this work, necessary techniques are presented to make this approach work. This includes path planning algorithms working on MRI data, ferromagnetic artifact imaging and a tracking algorithm which delivers position feedback for the microdevice and a propulsion sequence to enable interleaved magnetic propulsion and imaging. Using a dedicated software environment integrating path-planning methods and real-time tracking, a clinical MRI system is adapted to provide this new functionality for potential controlled interventional targeted therapeutic applications. Through MRI-based sensing analysis, this paper aims to propose a framework to plan a robust pathway to enhance the navigation ability to reach deep locations in human body. The proposed approaches are validated with different experiments