This paper tackles the inverse problem of finding optimal configurations of magnetic gradient sources in Dipole Field Navigation (DFN), a magnetic navigation method proposed recently for the direct targeting of drugs. In DFN, a limited number of these gradient sources, called the cores, must be positioned properly around a patient in a Magnetic Resonance Imaging scanner to induce the required directional forces on the navigated therapeutic carriers. To overcome some limitations of the previous approach for solving this problem, here we propose a novel and conceptually simple multidimensional variant of the well-known Particle Swarm Optimization (PSO) algorithm. This variant, called Progressive Multidimensional PSO (PMD-PSO), enables a tradeoff between the quality and the complexity of the solutions by progressively increasing the number of dimensions in the search space. We apply this algorithm to the core placement problem using an improved fitness function for the evaluation of a core configuration given a vascular path towards a target. Experiments on simulated vasculatures show that, while the approach can effectively solve this inverse problem, PMD-PSO exhibits better performances for DFN compared with two other multidimensional PSO variants.

To achieve the effective navigation of microscale agents in the vascular network, a high magnetic field strength with high directional magnetic gradients are required. So far, the methods that have been investigated support only one of these specifications but not both. Here, we propose a new method dubbed dipole field navigation (DFN) that provides high field strength to bring magnetic agents at saturation magnetization with gradients exceeding 300 mT/m at any depth within the human body. For DFN, the high field strength is achieved by placing the patient in the tunnel of a clinical MRI scanner, while high gradients are generated by the distortions of the scanner's homogeneous field from larger ferromagnetic cores placed at specific locations outside the patient. The main challenge of DFN lies in the methods that are required to adequately place the cores in the tunnel. Here, a first method is presented to solve the inverse magnetic problem of positioning such a set of cores so that microscale agents could be guided through a desired path in the vascular network. As a first proof of concept, magnetic particles were steered successfully in three consecutive bifurcations in a 3-D in vitro network.

Cooperative localization is one of the fundamental techniques in GPS-denied environments, such as underwater, indoor, or on other planets, where teams of robots use each other to improve their pose estimation. In this paper, we present a novel schema for performing cooperative localization using bearing only measurements. These measurements correspond to the angles of pairs of landmarks located on each robot, extracted from camera images. Thus, the only exteroceptive measurements used are the camera images taken by each robot, under the condition that both cameras are mutually visible. An analytical solution is derived, together with an analysis of uncertainty as a function to the relative pose of the robots. A theoretical comparison with a standard stereo camera pose reconstruction is also provided. Finally, the feasibility and performance of the proposed method were validated, through simulations and experiments with a mobile robot setup.