A localization method using 3-axis magnetoresistive sensors for tracking of capsule endoscope

Two-Dimensional Position Tracking Using Gradient Magnetic Fields

In this work, a two-dimensional (2D) position-detection device using a single axis magnetic sensor combined with orthogonal gradient coils was designed and fabricated. The sensors used were an induction coil and a GMR spin-valve sensor GF807 from Sensitec Inc. The field profiles generated by the two orthogonal gradient coils were analyzed numerically to achieve the maximum linear range, which corresponded to the detection area of the tracking system. The two coils were driven by 1-kHz sine wave currents with a 90° phase difference to generate the fields with uniform gradients along the x- and y-axis in the plane of the tracking stage. The gradient fields were detected by a single-axis sensor incorporated with a digital dual-phase lock-in detector to retrieve the position information. A linearity correction algorithm was used to improve the location accuracy and to extend the linear range for position sensing. The mean positioning error was found to be 0.417 mm, corresponding to the relative error of 0.21% in the working range of 200 mm × 200 mm, indicating that the proposed tracking system is promising for applications requiring accurate control of the two-dimensional position.

Localization accuracy of multiple magnets in a myokinetic control interface

Magnetic localizers have been widely investigated in the biomedical field, especially for intra-body applications, because they don't require a free line-of-sight between the implanted magnets and the magnetic field sensors. However, while researchers have focused on narrow and specific aspects of the localization problem, no one has comprehensively searched for general design rules for accurately localizing multiple magnetic objectives. In this study, we sought to systematically analyse the effects of remanent magnetization, number of sensors, and geometrical configuration (i.e. distance among magnets-L_inter-MM-and between magnets and sensors-L_MM-sensor) on the accuracy of the localizer in order to unveil the basic principles of the localization problem. Specifically, through simulations validated with a physical system, we observed that the accuracy of the localization was mainly affected by a specific angle ([Formula: see text] = tan^-1(L_inter-MM / L_MM-sensor)), descriptive of the system geometry. In particular, while tracking nine magnets, errors below ~ 1 mm (10% of the length of the simulated trajectory) and around 9° were obtained if θ ≥  ~ 31°. The latter proved a general rule across all tested conditions, also when the number of magnets was doubled. Our results are interesting for a whole range of biomedical engineering applications exploiting multiple-magnets tracking, such as human-machine interfaces, capsule endoscopy, ventriculostomy interventions, and endovascular catheter navigation.

Feasibility of Tracking Multiple Implanted Magnets With a Myokinetic Control Interface: Simulation and Experimental Evidence Based on the Point Dipole Model

OBJECTIVE

The quest for an intuitive and physiologically appropriate human-machine interface for the control of dexterous prostheses is far from being completed. To control a hand prosthesis, a possible approach could consist in using information related to the displacement of forearm muscles of an amputee during contraction. We recently proposed that muscle displacement could be monitored by implanting passive magnetic markers (MMs- i.e., permanent magnets) in them. We dubbed this the myokinetic interface. However, besides the system feasibility, how much its accuracy, precision and computation time are affected by the number and distribution of both the MMs and the sensors used to record the MF was not quantified.

METHODS

Here we investigated, through simulations validated with a physical system, the performance of a system capable to track position and orientation of up to 9 MMs using information from up to 112 sensors in a volume resembling the dimensions of the human forearm.

RESULTS

The system was able to track up to 7 MMs in 450 ms, demonstrating position/orientation accuracies in the range of 1 mm/5°. The comparison with the experimental recordings demonstrated a median difference with the simulations in the order of 0.45 mm.

CONCLUSION

We were able to formulate general guidelines for the implementation of magnetic tracking systems.

SIGNIFICANCE

Our results pave the way towards the development of new human-machine interfaces for the control of artificial limbs, but they are also interesting for the whole range of biomedical engineering applications exploiting magnetic tracking.

Review of Computational Techniques for Performance Evaluation of RF Localization Inside the Human Body

Location estimation within the human body by means of wireless signals is becoming popular for a variety of purposes, including wireless endoscopy using camera pills. The precision of wireless ranging in any medium is contingent upon the methodology employed. Two of the most popular wireless tracking methods are received signal strength (RSS) and time of arrival (TOA). The scope of this study is an assessment of the precision of TOA- and RSS-based ranging in the proximity of anthropomorphic tissue by means of simulation software designed to mimic signal transmission in the human body environment. Software simulations of wireless signals traveling within a human body are exceptionally challenging and require extensive computational resources. We created a rudimentary, MATLAB script using the finite-difference time-domain (FDTD) method to simulate the signal transmission inside and outside a human body and correlated the simulation outcomes of this script with the high-end commercial finite-element method (FEM) tool, ANSYS HFSS. First, we demonstrated that the FDTD modeling produces similar outcomes. Next, we employed the script to emulate the RSS and TOA of the wide bandwidth radio transmission within the human body for wireless ranging and estimated the accuracy of each technology. The precision of both methods was also evaluated with the Cramer-Rao lower bound (CRLB), which is frequently used to estimate the ranging methodologies and the effect of human tissue and its motion.

Acoustic Sensing and Ultrasonic Drug Delivery in Multimodal Theranostic Capsule Endoscopy

Video capsule endoscopy (VCE) is now a clinically accepted diagnostic modality in which miniaturized technology, an on-board power supply and wireless telemetry stand as technological foundations for other capsule endoscopy (CE) devices. However, VCE does not provide therapeutic functionality, and research towards therapeutic CE (TCE) has been limited. In this paper, a route towards viable TCE is proposed, based on multiple CE devices including important acoustic sensing and drug delivery components. In this approach, an initial multimodal diagnostic device with high-frequency quantitative microultrasound that complements video imaging allows surface and subsurface visualization and computer-assisted diagnosis. Using focused ultrasound (US) to mark sites of pathology with exogenous fluorescent agents permits follow-up with another device to provide therapy. This is based on an US-mediated targeted drug delivery system with fluorescence imaging guidance. An additional device may then be utilized for treatment verification and monitoring, exploiting the minimally invasive nature of CE. While such a theranostic patient pathway for gastrointestinal treatment is presently incomplete, the description in this paper of previous research and work under way to realize further components for the proposed pathway suggests it is feasible and provides a framework around which to structure further work.

Joint Magnetic Calibration and Localization Based on Expectation Maximization for Tongue Tracking

BACKGROUND

Tongue tracking, which helps researchers gain valuable insights into speech mechanism, has many applications in speech therapy and language learning. The wireless localization technique, which involves tracking a small magnetic tracer within the 3-D oral space, provides a low cost and convenient approach to capture tongue kinematics. In practice, this technique requires accurate calibration of three-axial magnetic sensors used in the tracking system. The data-driven calibration depends on the trajectories of magnetic tracer and the ambient noise, which may change across time and space.

METHODS

In this paper, we model the kinematics of tracer movement and the noisy magnetic measurements in a Bayesian framework, then present a joint calibration and localization (JCL) algorithm based on expectation maximization (EM), where the unscented Rauch-Tung-Striebel smoother is employed for tracer localization and the curvilinear search algorithm is applied for sensor calibration.

RESULTS

Based on measurements conducted on our tongue tracking system with a small magnetic tracer (diameter: 6.05 mm, thickness: 1.25 mm, residual induction: 14 800 G), the JCL algorithm achieves averaged root mean square error of 0.45 mm for tracer position estimation and for tracer orientation estimation, which are significantly lower than those of the separate calibration and localization algorithms.

CONCLUSION

These results show that JCL can help improve the localization accuracy of this system.

SIGNIFICANCE

A potentially high precision tongue tracking method is demonstrated.

A compact targeted drug delivery mechanism for a next generation wireless capsule endoscope

This paper reports a novel medication release and delivery mechanism as part of a next generation wireless capsule endoscope (WCE) for targeted drug delivery. This subsystem occupies a volume of only 17.9mm3 for the purpose of delivering a 1 ml payload to a target site of interest in the small intestinal tract. An in-depth analysis of the method employed to release and deliver the medication is described and a series of experiments is presented which validates the drug delivery system. The results show that a variable pitch conical compression spring manufactured from stainless steel can deliver 0.59 N when it is fully compressed and that this would be sufficient force to deliver the onboard medication.

Novel joint TOA/RSSI-based WCE location tracking method without prior knowledge of biological human body tissues

This paper proposes a novel joint time of arrival (TOA)/received signal strength indicator (RSSI)-based wireless capsule endoscope (WCE) location tracking method without prior knowledge of biological human tissues. Generally, TOA-based localization can achieve much higher localization accuracy than other radio frequency-based localization techniques, whereas wireless signals transmitted from a WCE pass through various kinds of human body tissues, as a result, the propagation velocity inside a human body should be different from one in free space. Because the variation of propagation velocity is mainly affected by the relative permittivity of human body tissues, instead of pre-measurement for the relative permittivity in advance, we simultaneously estimate not only the WCE location but also the relative permittivity information. For this purpose, this paper first derives the relative permittivity estimation model with measured RSSI information. Then, we pay attention to a particle filter algorithm with the TOA-based localization and the RSSI-based relative permittivity estimation. Our computer simulation results demonstrates that the proposed tracking methods with the particle filter can accomplish an excellent localization accuracy of around 2 mm without prior information of the relative permittivity of the human body tissues.

Continuing challenges in the diagnosis and management of obscure gastrointestinal bleeding

The diagnosis and management of obscure gastrointestinal bleeding (OGIB) have changed dramatically since the introduction of video capsule endoscopy (VCE) followed by deep enteroscopy and other imaging technologies in the last decade. Significant advances have been made, yet there remains room for improvement in our diagnostic yield and treatment capabilities for recurrent OGIB. In this review, we will summarize the latest technologies for the diagnosis of OGIB, limitations of VCE, technological enhancement in VCE, and different management options for OGIB.

A real-time localization system for an endoscopic capsule using magnetic sensors

Magnetic sensing technology offers an attractive alternative for in vivo tracking with much better performance than RF and ultrasound technologies. In this paper, an efficient in vivo magnetic tracking system is presented. The proposed system is intended to localize an endoscopic capsule which delivers biomarkers around specific locations of the gastrointestinal (GI) tract. For efficiently localizing a magnetic marker inside the capsule, a mathematical model has been developed for the magnetic field around a cylindrical magnet and used with a localization algorithm that provides minimum error and fast computation. The proposed tracking system has much reduced complexity compared to the ones reported in the literature to date. Laboratory tests and in vivo animal trials have demonstrated the suitability of the proposed system for tracking a magnetic marker with expected accuracy.

An adaptive 6-DOF tracking method by hybrid sensing for ultrasonic endoscopes

In this paper, a novel hybrid sensing method for tracking an ultrasonic endoscope within the gastrointestinal (GI) track is presented, and the prototype of the tracking system is also developed. We implement 6-DOF localization by sensing integration and information fusion. On the hardware level, a tri-axis gyroscope and accelerometer, and a magnetic angular rate and gravity (MARG) sensor array are attached at the end of endoscopes, and three symmetric cylindrical coils are placed around patients' abdomens. On the algorithm level, an adaptive fast quaternion convergence (AFQC) algorithm is introduced to determine the orientation by fusing inertial/magnetic measurements, in which the effects of magnetic disturbance and acceleration are estimated to gain an adaptive convergence output. A simplified electro-magnetic tracking (SEMT) algorithm for dimensional position is also implemented, which can easily integrate the AFQC's results and magnetic measurements. Subsequently, the average position error is under 0.3 cm by reasonable setting, and the average orientation error is 1° without noise. If magnetic disturbance or acceleration exists, the average orientation error can be controlled to less than 3.5°.

A real-time tracking system for in vivo endofunctional capsule using magnetic sensors

This paper presents a real-time magnetic tracking system to be used for tracking an endofunctional capsule intended to aid in the delivery of biomarkers to specific areas in the gastrointestinal (GI) tract. Magnetic technology is chosen due to its significant advantages over others like RF and Ultrasonics. The tracking system is designed to be used with eight magnetic sensors making it less complex than the other proposed systems. The paper describes a new mathematical model which is more accurate than the existing ones, a linear tracking algorithm and system's performance evaluation for three sensor configurations. The algorithm copes with the problem of magnetic field strength drop due to varying orientation of magnet. The minimum average error obtained is 1.37cm/6.85% in a 20×20×20 cm(3) volume for two dimensional sensor configuration.

Wireless capsule endoscope for targeted drug delivery: mechanics and design considerations

This paper describes a platform to achieve targeted drug delivery in the next-generation wireless capsule endoscopy. The platform consists of two highly novel subsystems: one is a micropositioning mechanism which can deliver 1 ml of targeted medication and the other is a holding mechanism, which gives the functionality of resisting peristalsis. The micropositioning mechanism allows a needle to be positioned within a 22.5 ° segment of a cylindrical capsule and be extendible by up to 1.5 mm outside the capsule body. The mechanism achieves both these functions using only a single micromotor and occupying a total volume of just 200 mm (3). The holding mechanism can be deployed diametrically opposite the needle in 1.8 s and occupies a volume of just 270 mm (3). An in-depth analysis of the mechanics is presented and an overview of the requirements necessary to realize a total system integration is discussed. It is envisaged that the targeted drug delivery platform will empower a new breed of capsule microrobots for therapy in addition to diagnostics for pathologies such as ulcerative colitis and small intestinal Crohn's disease.

Capsule endoscopy: from current achievements to open challenges

Wireless capsule endoscopy (WCE) can be considered an example of disruptive technology since it represents an appealing alternative to traditional diagnostic techniques. This technology enables inspection of the digestive system without discomfort or need for sedation, thus preventing the risks of conventional endoscopy, and has the potential of encouraging patients to undergo gastrointestinal (GI) tract examinations. However, currently available clinical products are passive devices whose locomotion is driven by natural peristalsis, with the drawback of failing to capture the images of important GI tract regions, since the doctor is unable to control the capsule's motion and orientation. To address these limitations, many research groups are working to develop active locomotion devices that allow capsule endoscopy to be performed in a totally controlled manner. This would enable the doctor to steer the capsule towards interesting pathological areas and to accomplish medical tasks. This review presents a research update on WCE and describes the state of the art of the basic modules of current swallowable devices, together with a perspective on WCE potential for screening, diagnostic, and therapeutic endoscopic procedures.

Advanced technologies for gastrointestinal endoscopy

The gastrointestinal tract is home to some of the most deadly human diseases. Exacerbating the problem is the difficulty of accessing it for diagnosis or intervention and the concomitant patient discomfort. Flexible endoscopy has established itself as the method of choice and its diagnostic accuracy is high, but there remain technical limitations in modern scopes, and the procedure is poorly tolerated by patients, leading to low rates of compliance with screening guidelines. Although advancement in clinical endoscope design has been slow in recent years, a critical mass of enabling technologies is now paving the way for the next generation of gastrointestinal endoscopes. This review describes current endoscopes and provides an overview of innovative flexible scopes and wireless capsules that can enable painless endoscopy and/or enhanced diagnostic and therapeutic capabilities. We provide a perspective on the potential of these new technologies to address the limitations of current endoscopes in mass cancer screening and other contexts and thus to save many lives.

Towards a magnetic localization system for 3-D tracking of tongue movements in speech-language therapy

This paper presents a new magnetic localization system based on a compact triangular sensor setup and three different optimization algorithms, intended for tracking tongue motion in the 3-D oral space. A small permanent magnet, secured on the tongue by tissue adhesives, will be used as a tracer. The magnetic field variations due to tongue motion are detected by a 3-D magneto-inductive sensor array outside the mouth and wirelessly transmitted to a computer. The position and rotation angles of the tracer are reconstructed based on sensor outputs and magnetic dipole equation using DIRECT, Powell, and Nelder-Mead optimization algorithms. Localization accuracy and processing time of the three algorithms are compared using one data set collected in which source-sensor distance was changed from 40 to 150 mm. Powell algorithm showed the best performance with 0.92 mm accuracy in position and 0.7(o) in orientation. The average processing time was 43.9 ms/sample, which can satisfy real time tracking up to approximately 20 Hz.

A quadratic particle swarm optimization method for magnetic tracking of tongue motion in speech disorders

We have devised a new magnetic localization technique to accurately track 3-D tongue movements during speech and ingestion. A small permanent magnet secured on the tongue by tissue adhesives, is utilized as a tracer. The magnetic field variations due to tongue motion are detected by three 3-axis magneto-inductive sensor modules outside the mouth, and wirelessly transmitted to a computer for further processing. The tracer is modeled as a magnetic dipole, which position (x, y, z) and orientation (theta, y) are estimated using a quadratic particle swarm optimization (PSO) algorithm. This algorithm provides faster and more reliable computation compared to the linear PSO. Statistical analysis based on hundreds of simulation and experimental results show that using this method, calculations are accelerated by a factor of three and the tracer can be localized in real-time with approximately 1 mm resolution in position and 2 degrees in orientation.