The feasibility for in vivo navigation of untethered devices or robots is demonstrated with the control and tracking of a 1.5 mm diameter ferromagnetic bead in the carotid artery of a living swine using a clinical magnetic resonance imaging ͑MRI͒ platform. Navigation is achieved by inducing displacement forces from the three orthogonal slice selection and signal encoding gradient coils of a standard MRI system. The proposed method performs automatic tracking, propulsion, and computer control sequences at a sufficient rate to allow navigation along preplanned paths in the blood circulatory system. This technique expands the range of applications in MRI-based interventions.
Medical nanorobotics exploits nanometer-scale components and phenomena with robotics to provide new medical diagnostic and interventional tools. Here, the architecture and main specifications of a novel medical interventional platform based on nanorobotics and nanomedicine, and suited to target regions inaccessible to catheterization are described. The robotic platform uses magnetic resonance imaging (MRI) for feeding back information to a controller responsible for the real-time control and navigation along pre-planned paths in the blood vessels of untethered magnetic carriers, nanorobots, and/or magnetotactic bacteria (MTB) loaded with sensory or therapeutic agents acting like a wireless robotic arm, manipulator, or other extensions necessary to perform specific remote tasks. Unlike known magnetic targeting methods, the present platform allows us to reach locations deep in the human body while enhancing targeting efficacy using real-time navigational or trajectory control. The paper describes several versions of the platform upgraded through additional software and hardware modules allowing enhanced targeting efficacy and operations in very difficult locations such as tumoral lesions only accessible through complex microvasculature networks.
This paper shows that even a simple proportional-integral-derivative (PID) controller can be used in a clinical MRI system for real-time navigation of a ferromagnetic bead along a predefined trajectory. Although the PID controller has been validated in vivo in the artery of a living animal using a conventional clinical MRI platform, here the rectilinear navigation of a ferromagnetic bead is assessed experimentally along a two-dimensional (2D) path as well as the control of the bead in a pulsatile flow. The experimental results suggest the likelihood of controlling untethered microdevices or robots equipped with a ferromagnetic core inside complex pathways in the human body.
A dedicated software architecture for a novel interventional method allowing the navigation of ferromagnetic endovascular devices using a standard real-time clinical MRI system is shown. Through a specially developed software environment integrating a tracking method and a real-time controller algorithm, a clinical 1.5T Siemens Avanto MRI system is adapted to provide new functionality for potential automated interventional applications. The proposed software architecture was successfully validated through in vivo controlled navigation inside the carotid artery of a swine. Here we present how this MRI-upgraded software environment could also be used in more complex vasculature models through the real-time navigation of a 1.5 mm diameter chrome steel bead in two different MR-compatible phantoms with flowless and quiescent flow conditions. The developed platform and software modules needed for such navigation are also presented. Real-time tracking achieved through a dedicated positioning method based on an off-resonance excitation technique has also been successfully integrated in the software platform while maintaining adequate real-time performance. These preliminary feasibility experiments suggest that navigation of such devices can be achieved Because MR imaging offers many advantages in term of spatial resolution and safety for the patient, modern interventional medicine is now considering this imaging modality as an alternative for upcoming interventional applications. Many standard fluoroscopy catheter procedures can now be executed in an MRI environment (1-3), providing enhanced visual precision for the medical team without patient exposure limitations due to radiation emission. However, all catheter-based procedures, whether offering or not a better quality in visualization, face the same limitations with regard to accessibility and flexibility. Many actual medical interventions would require enhanced targeting of specific organs or physiological sites for the delivery of drug or contrast agents (4 -7). Although catheters can reach some of these specific sites without much complication, many sites remain inaccessible and cannot be reached without involving major invasive surgeries. Moreover, these interventional applications rely on MRI capabilities only for the imaging modality provided by the system without considering using an MRI system as a fully integrated and automated endovascular navigation environment.A recent breakthrough in interventional MRI-guided in vivo procedures demonstrated that real-time MRI systems can offer a well-suited integrated environment for the propulsion, tracking, and control of a ferromagnetic device, which was done in the carotid artery of a living swine (8). The standard imaging environment, however, must be adapted in order to provide such new capabilities. Timing and integration constraints must be overcome to permit the use of a standard MRI system as a new endovascular navigation platform. Unlike some other methods that simply use a DC field flux to create a torque on ...
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