Luc Maréchal

Optimal spatial design of non-invasive magnetic field-based localization systems

Magnetic localization systems based on passive permanent magnets (PM) are of great interest due to their ability to provide non-contact sensing and without any power requirement for the PM. Medical procedures such as ventriculostomy can benefit greatly from real-time feedback of the inserted catheter tip. While the effects of the number of sensors on the localization accuracy in such systems has been reported, the spatial design of the sensor layout has been largely overlooked. Here in this paper, a framework for determining an optimal sensor assembly for enhanced localization performance is presented and investigated through numerical simulations and direct experiments. Two approaches are presented: one based on structured grid configuration and the other derived using Genetic Algorithms. Simulation results verified by experiments strongly suggest that the layout of the sensors not only has an effect on the localization accuracy, but also has an effect far more pronounced than improvements brought by increasing the number of sensors.

Design Optimization of a Magnetic Field-Based Localization Device for Enhanced Ventriculostomy

The accuracy of many freehand medical procedures can be improved with assistance from real-time localization. Magnetic localization systems based on harnessing passive permanent magnets (PMs) are of great interest to track objects inside the body because they do not require a powered source and provide noncontact sensing without the need for line-of-sight. While the effect of the number of sensors on the localization accuracy in such systems has been reported, the spatial design of the sensing assembly is an open problem. This paper presents a systematic approach to determine an optimal spatial sensor configuration for localizing a PM during a medical procedure. Two alternative approaches were explored and compared through numerical simulations and experimental investigation: one based on traditional grid configuration and the other derived using genetic algorithms (GAs). Our results strongly suggest that optimizing the spatial arrangement has a larger influence on localization performance than increasing the number of sensors in the assembly. We found that among all the optimization schemes, the approach utilizing GA produced sensor designs with the smallest localization errors.

Using heterogeneous sensory measurements in a compliant magnetic localization system for medical intervention

In many medical intervention procedures, passive magnetic tracking technology has found favor in continuous localization of medical instruments and tools inside the human body. By utilizing a small permanent magnet as a passive source, it requires no dedicated power supply or wire connection into the body. Past researches usually adopt rigid structures to restrict the movement of sensors, as the precise positional information of the homogeneous magnetic sensors play an important role in the accuracy of traditional inverse optimization algorithms. In this paper, we investigate methods to enable the sensing system to be used for the nasogastric (NG) tube localization in a compliant setting, such that the device can conform around the patient for improved ergonomics and comfort. Such a system, which now contains additional sensors required to sense the active compliance, will contain a non-homogeneous sensor assembly producing heterogeneous sensory information. Two methods are proposed and evaluated: one is a modified inverse optimization method using a deformation model in series with the magnetic field model; the other is a direct forward Artificial Neural Network (ANN) method. The efficacy of both methods were evaluated and compared by numerical simulation and experiments. Advantages and disadvantages of both methods were discussed at the end.

Experimental Study of an Omni-Directional Wind Fluttering Energy Harvester

Wind energy harvesters based on fluttering are a valuable and efficient alternative to traditional wind turbines. The optimized drive trains of traditional wind turbines have significantly shorter life expectancy and higher fabrication costs compared to harvesting systems based on fluttering. This article presents an analysis of a novel windbelt type energy harvester designed to harvest low-speed and changing direction winds. This experimental study explores the optimal ribbon tension, length and coil position of the wind-to-vibration converter, to obtain the maximum vibration acceleration.Copyright

Design optimization of the sensor spatial arrangement in a direct magnetic field-based localization system for medical applications.

Motivated by the need for developing a neuronavigation system to improve efficacy of intracranial surgical procedures, a localization system using passive magnetic fields for real-time monitoring of the insertion process of an external ventricular drain (EVD) catheter is conceived and developed. This system operates on the principle of measuring the static magnetic field of a magnetic marker using an array of magnetic sensors. An artificial neural network (ANN) is directly used for solving the inverse problem of magnetic dipole localization for improved efficiency and precision. As the accuracy of localization system is highly dependent on the sensor spatial location, an optimization framework, based on understanding and classification of experimental sensor characteristics as well as prior knowledge of the general trajectory of the localization pathway, for design of such sensing assemblies is described and investigated in this paper. Both optimized and non-optimized sensor configurations were experimentally evaluated and results show superior performance from the optimized configuration. While the approach presented here utilizes ventriculostomy as an illustrative platform, it can be extended to other medical applications that require localization inside the body.

A compact magnetic directional proximity sensor for spherical robots

Spherical robots have recently attracted significant interest due to their ability to offer high speed motion with excellent locomotion efficiency. As a result of the presence of a sealed outer shell, its obstacle avoidance strategy has been simply “hit and run”. While this is convenient due to the specific geometry of the spherical robots, it however could pose serious issues when the robots are small and light. For portable spherical robots with on-board cameras, a high speed collision with a hard surface may damage the robot or the camera. This paper proposes a novel and compact proximity sensor that utilizes passive magnetic field to detect the ferromagnetic obstacles through perturbation of the magnetic field. Compared with the existing works that utilize the Earths weak magnetic field as a means of detection, the approach undertaken here seeks to harness the same principle but uses an intelligently designed magnetic assembly. It efficiently amplifies the perturbation and therefore improves the detection performance. The presented method is able to simultaneously determine both the distance and direction of the nearby ferromagnetic obstacles. Both simulation and experimental results are presented to validate the sensing principle and operational performance.

Real-time sensor fault detection and compensation in a passive magnetic field-based localization system

In modern mechatronic systems, due to the large number of electronic sensors employed, it is inevitable to encounter sensor faults over time. Taking the localization system for medical intervention as an illustrative example, high localization accuracy is usually the highest priority but the system should also be resilient to occasional sensor faults and failures. Presence of sensor faults, especially those irreversible ones, could greatly deteriorate the localization performance and in turn jeopardize patient safety. In this paper, inspired by current research and development of a novel real-time localization and monitoring system for nasogastric intubation, the effects of sensor faults that can occur in such magnetic field-based localization systems were first explored and classified. Three types of common sensor faults were identified, and the corresponding real-time detection methods were discussed. It focused on the two most commonly-used localization approaches, the inverse optimization method and the direct ANN method, and proposed real-time compensation remedies for both the methods in presence of such sensor faults. The feasibility and efficacy of the proposed compensation remedies were examined by numerical simulations as well as real experimental data. It is shown in presence of a single sensor fault with excessive noise, the localization performance can be deteriorated by up to 300%. But through implementation of the proposed compensation scheme, which does not sacrifice computational time (less than 1%), the inherent redundancy of the system could be used to achieve similar localization performance as that under normal conditions. The work presented in this paper aims to improve the robustness and reliability of multisensor-based localization or tracking systems.

Relax and Tighten—A Haptics-based Approach to Simulate Sphincter Tone Assessment

Digital Rectal Examination (DRE) is a physical examination performed by clinicians to diagnose anorectal and prostate abnormalities. Amongst these, sphincter tone assessment is a crucial task where a clinician asks the patient to relax or squeeze, whilst measuring its function by the amount of pressure felt on the examining finger. DRE is difficult to learn and current models fail to reproduce the dynamic function of anorectal abnormalities. We propose a haptics-based approach to incorporate sphincter tone into our current simulator by motor-controlled pulling and releasing of cables that are coiled around a silicone model of the sphincters. A range of healthy and abnormal sphincter tone cases can be modelled by controlling the motors symmetrically and asymmetrically.

Magnet array for a portable magnetic resonance imaging system

Conventional magnetic resonance imaging (MRI) scanners are bulky and heavy. It limits their applications at places, for example, in an ambulance or in a combat field hospital. The disadvantages of a conventional MRI system have led to increasing interests in the development of a portable MRI one. One of the challenges for a portable MRI scanner is to build a homogenous static magnetic field within a volume of the size of human parts, for example, human head, for imaging. In this paper, we presented the design and development of a modified permanent magnet array for a portable MRI scanner. The measurement method of the magnetic field is included.

Passive Magnetic Localization in Medical Intervention

In the past decade, with continual advancement in the magnetic field sensing technology, passive magnetic tracking has become an emerging trend in the field of medical intervention. By embedding a small permanent magnet in the medical instrument, the passive magnetic tracking approach makes the system possible to have untethered, compact and wearable, even modular design for better ergonomics and lower hardware requirements. In this chapter, an overview of the working principle and methods of the passive magnetic tracking technology was presented. Implementation of the technology in actual medical interventions were also demonstrated. Lastly, the challenges in the development of this technology were explored and discussed.