A novel method for real-time magnetic marker monitoring in the gastrointestinal tract

Location-aware ingestible microdevices for wireless monitoring of gastrointestinal dynamics

Localization and tracking of ingestible microdevices in the gastrointestinal (GI) tract is valuable for the diagnosis and treatment of GI disorders. Such systems require a large field-of-view of tracking, high spatiotemporal resolution, wirelessly operated microdevices and a non-obstructive field generator that is safe to use in practical settings. However, the capabilities of current systems remain limited. Here, we report three dimensional (3D) localization and tracking of wireless ingestible microdevices in the GI tract of large animals in real time and with millimetre-scale resolution. This is achieved by generating 3D magnetic field gradients in the GI field-of-view using high-efficiency planar electromagnetic coils that encode each spatial point with a distinct magnetic field magnitude. The field magnitude is measured and transmitted by the miniaturized, low-power and wireless microdevices to decode their location as they travel through the GI tract. This system could be useful for quantitative assessment of the GI transit-time, precision targeting of therapeutic interventions and minimally invasive procedures.

Addressing the Directionality Challenge through RSSI-Based Multilateration Technique, to Localize Nodes in Underwater WSNs by Using Magneto-Inductive Communication

The deployment and efficient use of wireless sensor networks (WSNs) in underwater and underground environments persists to be a difficult task. In addition, the localization of a sensor Rx node in WSNs is an important aspect for the successful communication with the aforementioned environments. To overcome the limitations of electromagnetic, acoustic, and optical communication in underwater and underground wireless sensor networks (UWSNs), magneto-inductive (MI) communication technology emerged as a promising alternative for usage in UWSNs with a wide range of applications. To make the magneto-inductive underwater wireless sensor networks (MI-UWSNs) more efficient, recently, various research studies focused on the optimization of the physical layer, MAC layer, and routing layer, but none of them has taken into account the effect of directionality. Despite the directionality issue posed by the physical nature of a magnetic field, the unique qualities of MI communication open up a gateway for several applications. The directionality issue of MI sensors is a critical challenge that must be taken into account while developing any WSN protocol or localization algorithm. This paper highlights and discusses the severity and impact of the directionality issue in designing a localization algorithm for magneto-inductive wireless sensor networks (MI-WSNs). A received signal strength indicator (RSSI)-based multilateration localization algorithm is presented in this paper, where a minimum of 2 and maximum of 10 anchor Tx nodes are used to estimate the position of the sensor Rx nodes, which are deployed randomly in a 15 m × 15 m simulation environment. This RSSI-based multilateration technique is the most suitable option that can be used to quantify the impact of directionality on the localization of a sensor Rx node.

Application of In Vivo MRI Imaging to Track a Coated Capsule and Its Disintegration in the Gastrointestinal Tract in Human Volunteers

Oral specially coated formulations have the potential to improve treatment outcomes of a range of diseases in distal intestinal tract whilst limiting systemic drug absorption and adverse effects. Their development is challenging, partly because of limited knowledge of the physiological and pathological distal gastrointestinal factors, including colonic chyme fluid distribution and motor function. Recently, non-invasive techniques such as magnetic resonance imaging (MRI) have started to provide novel important insights. In this feasibility study, we formulated a coated capsule consisting of a hydroxypropyl methylcellulose (HPMC) shell, coated with a synthetic polymer based on polymethacrylate-based copolymer (Eudragit®) that can withstand the upper gastrointestinal tract conditions. The capsule was filled with olive oil as MRI-visible marker fluid. This allowed us to test the ability of MRI to track such a coated capsule in the gastrointestinal tract and to assess whether it is possible to image its loss of integrity by exploiting the ability of MRI to image fat and water separately and in combination. Ten healthy participants were administered capsules with varying amounts of coating and underwent MRI imaging of the gastrointestinal tract at 45 min intervals. The results indicate that it is feasible to track the capsules present in the gastrointestinal tract at different locations, as they were detected in all 10 participants. By the 360 min endpoint of the study, in nine participants the capsules were imaged in the small bowel, in eight participants in the terminal ileum, and in four in the colon. Loss of capsule integrity was observed in eight participants, occurring predominantly in distal intestinal regions. The data indicate that the described approach could be applied to assess performance of oral formulations in undisturbed distal gastrointestinal regions, without the need for ionizing radiation or contrast agents.

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.

A new development in magnetic particle tracking technology and its application in a sheared dense granular flow

This paper presents a new development in the magnetic particle tracking (MPT) technology that measures the translational and rotational motions of a small particle. A main advantage of MPT is that it is able to track objects in an opaque environment without using radioactive material or X-rays. In addition, it can provide information about the orientation and rotation of the object, which is difficult to obtain using other technologies. However, the reconstruction process of MPT using standard optimization approaches is very time consuming and, therefore, limits its applications. In this work, two new MPT reconstruction algorithms are examined and the results are compared with the optimization approach. The extended Kalman filter (EKF) algorithm has the same accuracy as the optimization method but is orders of magnitude faster. The speed of the sequential importance sampling approach is between those of the above two methods. The accuracy of position obtained using EKF is about 0.6%, and the uncertainty of orientation is less than 1.5°. The MPT is applied to measure a dense granular shear flow to investigate the spatial distribution of a tracer particle.

Polymer adhesion predictions for oral dosage forms to enhance drug administration safety. Part 3: Review of in vitro and in vivo methods used to predict esophageal adhesion and transit time

The oral cavity is frequently used to administer pharmaceutical drug products. This route of administration is seen as the most accessible for the majority of patients and supports an independent therapy management. For current oral dosage forms under development, the prediction of their unintended mucoadhesive properties and esophageal transit profiles would contribute for future administration safety, as concerns regarding unintended adhesion of solid oral dosage forms (SODF) during oro-esophageal transit still remain. Different in vitro methods that access mucoadhesion of polymers and pharmaceutical preparations have been proposed over the years. The same methods might be used to test non-adhesive systems and contribute for developing safe-to-swallow technologies. Previous works have already investigated the suitability of non-animal derived in vitro methods to assess such properties. The aim of this work was to review the in vitro methodology available in the scientific literature that used animal esophageal tissue to evaluate mucoadhesion and esophageal transit of pharmaceutical preparations. Furthermore, in vivo methodology is also discussed. Since none of the in vitro methods developed are able to mimic the complex swallowing process and oro-esophageal transit, in vivo studies in humans remain as the gold standard.

The myokinetic control interface: tracking implanted magnets as a means for prosthetic control

Upper limb amputation deprives individuals of their innate ability to manipulate objects. Such disability can be restored with a robotic prosthesis linked to the brain by a human-machine interface (HMI) capable of decoding voluntary intentions, and sending motor commands to the prosthesis. Clinical or research HMIs rely on the interpretation of electrophysiological signals recorded from the muscles. However, the quest for an HMI that allows for arbitrary and physiologically appropriate control of dexterous prostheses, is far from being completed. Here we propose a new HMI that aims to track the muscles contractions with implanted permanent magnets, by means of magnetic field sensors. We called this a myokinetic control interface. We present the concept, the features and a demonstration of a prototype which exploits six 3-axis sensors to localize four magnets implanted in a forearm mockup, for the control of a dexterous hand prosthesis. The system proved highly linear (R² = 0.99) and precise (1% repeatability), yet exhibiting short computation delay (45 ms) and limited cross talk errors (10% the mean stroke of the magnets). Our results open up promising possibilities for amputees, demonstrating the viability of the myokinetic approach in implementing direct and simultaneous control over multiple digits of an artificial hand.

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.

Development of an AMR-ACB array for gastrointestinal motility studies

The association between anisotropic magnetoresistive (AMR) sensor and AC biosusceptometry (ACB) to evaluate gastrointestinal motility is presented. The AMR-ACB system was successfully characterized in a bench-top study, and in vivo results were compared with those obtained by means of simultaneous manometry. Both AMR-ACB and manometry techniques presented high temporal cross correlation between the two periodicals signals . The contraction frequencies using AMR-ACB were 73.9 ± 7.6 mHz and using manometry were 73.8 ± 7.9 mHz during the baseline . The amplitude of contraction using AMR-ACB was 396 ± 108 μT·s and using manometry were 540 ± 198 mmHg·s during the baseline. The amplitudes of signals for AMR-ACB and manometric recordings were similarly increased to 86.4% and 89.3% by neostigmine, and also decreased to 27.2% and 21.4% by hyoscine butylbromide in all animals, respectively. The AMR-ACB array is nonexpensive, portable, and has high-spatiotemporal resolution to provide helpful information about gastrointestinal tract.

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.

Gastric transit and small intestinal transit time and motility assessed by a magnet tracking system

Background

Tracking an ingested magnet by the Magnet Tracking System MTS-1 (Motilis, Lausanne, Switzerland) is an easy and minimally-invasive method to assess gastrointestinal transit. The aim was to test the validity of MTS-1 for assessment of gastric transit time and small intestinal transit time, and to illustrate transit patterns detected by the system.

Methods

A small magnet was ingested and tracked by an external matrix of 16 magnetic field sensors (4 × 4) giving a position defined by 5 coordinates (position: x, y, z, and angle: θ, ϕ). Eight healthy subjects were each investigated three times: (1) with a small magnet mounted on a capsule endoscope (PillCam); (2) with the magnet alone and the small intestine in the fasting state; and (3) with the magnet alone and the small intestine in the postprandial state.

Results

Experiment (1) showed good agreement and no systematic differences between MTS-1 and capsule endoscopy when assessing gastric transit (median difference 1 min; range: 0-6 min) and small intestinal transit time (median difference 0.5 min; range: 0-52 min). Comparing experiments (1) and (2) there were no systematic differences in gastric transit or small intestinal transit when using the magnet-PillCam unit and the much smaller magnetic pill. In experiments (2) and (3), short bursts of very fast movements lasting less than 5% of the time accounted for more than half the distance covered during the first two hours in the small intestine, irrespective of whether the small intestine was in the fasting or postprandial state. The mean contraction frequency in the small intestine was significantly lower in the fasting state than in the postprandial state (9.90 min^-1 vs. 10.53 min^-1) (p = 0.03).

Conclusion

MTS-1 is reliable for determination of gastric transit and small intestinal transit time. It is possible to distinguish between the mean contraction frequency of small intestine in the fasting state and in the postprandial state.

A novel device with 36 channels for imaging and signal acquisition of the gastrointestinal tract based on AC biosusceptometry

The alternate current biosusceptometry (ACB) is a biomagnetic technique used to study some physiological parameters associated with gastrointestinal (GI) tract. For this purpose it applies an AC magnetic field and measures the response originating from magnetic marks or tracers. This paper presents an equipment based on the ACB which uses anisotropic magnetoresistive (AMR) sensors and an inexpensive electronic support. The ACB-AMR developed consists of a square array of 6×6 sensors arranged in a first-order gradiometer configuration with one reference sensor. The equipment was applied to capture magnetic images of different phantoms and to acquire gastric contraction activity of healthy rats. The results show a reasonable sensitivity and spatial-temporal resolution, so that it may be applied for imaging of phantoms and signal acquisition of the GI tract of small animals.

Understanding gastric forces calculated from high-resolution pill tracking

Although other methods exist for monitoring gastrointestinal motility and contractility, this study exclusively provides direct and quantitative measurements of the forces experienced by an orally ingested pill. We report motive forces and torques calculated from real-time, in vivo measurements of the movement of a magnetic pill in the stomachs of fasted and fed humans. Three-dimensional net force and two-dimensional net torque vectors as a function of time data during gastric residence are evaluated using instantaneous translational and rotational position data. Additionally, the net force calculations described can be applied to high-resolution pill tracking acquired by any modality. The fraction of time pills experience ranges of forces and torques are analyzed and correlate with the physiological phases of gastric digestion. We also report the maximum forces and torques experienced in vivo by pills as a quantitative measure of the amount of force pills experience during the muscular contractions leading to gastric emptying. Results calculated from human data are compared with small and large animal models with a translational research focus. The reported magnitude and direction of gastric forces experienced by pills in healthy stomachs serves as a baseline for comparison with pathophysiological states. Of clinical significance, the directionality associated with force vector data may be useful in determining the muscle groups associated with gastrointestinal dysmotility. Additionally, the quantitative comparison between human and animal models improves insight into comparative gastric contractility that will aid rational pill design and provide a quantitative framework for interpreting gastroretentive oral formulation test results.

Capsule endoscope localization based on computer vision technique

To build a new type of wireless capsule endoscope with interactive gastrointestinal tract examination, a localization and orientation system is needed for tracking 3D location and 3D orientation of the capsule movement. The magnetic localization and orientation method produces only 5 DOF, but misses the information of rotation angle along capsule's main axis. In this paper, we presented a complementary orientation approach for the capsule endoscope, and the 3D rotation can be determined by applying computer vision technique on the captured endoscopic images. The experimental results show that the complementary orientation method has good accuracy and high feasibility.

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.

Study on gastric interdigestive pressure activity based on phase space reconstruction and FastICA algorithm

To investigate the features of the gastric interdigestive pressure activity under normal physiological conditions, we have developed the wireless radiotelemetry capsule based on a telemetry technique. Twelve healthy volunteers participated in this study. Pressure activity data which are an important index of gastric motility can be obtained from the wireless radiotelemetry capsule. But the capsule only records single-dimensional pressure time series which may contain a few interdependent components simultaneously. Automated embedding phase space reconstruction algorithm is employed to reconstruct multi-dimensional phase space. Then the dominant and separated component of the gastric contractions is identified using FastICA algorithm. Finally the use of Hilbert Huang transform method for analyzing the characters of gastric motility is investigated. The results show that the proposed method is an effective approach for the analysis of the gastric pressure series.

A novel biomagnetic instrumentation with four magnetoresistive sensors to evaluate gastric motility

A novel instrumentation using anisotropic magnetoresistive (AMR) sensors associated with magnetic coils excitation was developed to evaluate gastrointestinal tract motility parameters. The susceptometer has four sensors that were used to measure the gastric activity contractions (GAC) in anaesthetized dogs, its performance was evaluated by manometry with good results.

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

In this paper, we propose a non-invasive tracking method, which has the potential to be used for localization of the capsule endoscope. The tracking system consists of a magnetic marker, a sensor array, amplifiers, data acquisition devices and a signal processing unit. The marker is modeled as a magnetic dipole to simplify the theoretical expression of the magnetic field distribution. By minimizing the squared error of the field values between the calculation and measurements using Levenberg-Marquardt optimization method, the 5 localization parameters of the dipole can be determined. Real time experiments were carried out to test the feasibility of the method. It is demonstrated that, the accuracy of the localization is related to the number of sensors. For the sensor array including 16 3-axis magnetoresistive sensors, the average position error is 3.3 mm and the average orientation error is about 3 degrees, when the magnetic marker is 100 mm above the sensor array plane.

A novel magnetic method for examination of bowel motility

In contrast to the well-developed methods for morphological diagnosis of the gastrointestinal tract, there is no comparatively satisfying technique for functional disorders. One important example is irritable bowel syndrome (IBS), a disorder that affects a high percentage of all individuals. It can only be diagnosed by excluding organic diseases and by considering symptom criteria. In this case, the examination of the motility of the bowel may be a promising way to differentiate between the two major mechanisms of IBS: increased sensitivity of the intestine and altered gastrointestinal motility. To this aim, a recently developed method for monitoring magnetic markers in the gastrointestinal tract was utilized that works without the use of ionizing radiation. We give a short description of this method, showing a spatial resolution of 3-4 mm and a temporal resolution of 330 ms, and report on examples of the first in vivo experiments. Typical monitoring results are shown for the esophagus, the stomach, and the duodenum. The motility behavior is described for the lower parts of the gut as well. The advantages and drawbacks of this type of magnetic marker monitoring are discussed with special consideration of the noninvasive examination of the motility in different sections of the gut.

Magnetic pill tracking: a novel non-invasive tool for investigation of human digestive motility

A new minimally invasive technique allowing for anatomical mapping and motility studies along the entire human digestive system is presented. The technique is based on continuous tracking of a small magnet progressing through the digestive tract. The coordinates of the magnet are calculated from signals recorded by 16 magnetic field sensors located over the abdomen. The magnet position, orientation and trajectory are displayed in real time. Ten young healthy volunteers were followed during 34 h. The technique was well tolerated and no complication was encountered. The information obtained was 3-D configuration of the digestive tract and dynamics of the magnet displacement (velocity, transit time, length estimation, rhythms). In the same individual, repeated examination gave very reproducible results. The anatomical and physiological information obtained corresponded well to data from current methods and imaging. This simple, minimally invasive technique permits examination of the entire digestive tract and is suitable for both research and clinical studies. In combination with other methods, it may represent a useful tool for studies of GI motility with respect to normal and pathological conditions.

A non-invasive method for gastrointestinal parameter monitoring

AIM: To propose a new, non-invasive method for monitoring 24-h pressure, temperature and pH value in gastrointestinal tract.

METHODS: The authors developed a miniature, multi-functional gastrointestinal monitoring system, which comprises a set of indigestible biotelemetry capsules and a data recorder. The capsule, after ingested by patients, could measure pressure, temperature and pH value in the gastrointestinal tract and transmit the data to the data recorder outside the body through a 434 MHz radio frequency data link. After the capsule passed out from the body, the data saved in the recorder were downloaded to a workstation via a special software for further analysis and comparison.

RESULTS: Clinical experiments showed that the biotelemetry capsules could be swallowed by volunteers without any difficulties. The data recorder could receive the radio frequency signals transmitted by the biotelemetry in the body. The biotelemetry capsule could pass out from the body without difficulties. No discomfort was reported by any volunteer during the experiment. In vivo pressure and temperature data were acquired.

CONCLUSION: A non-invasive method for monitoring 24-h gastrointestinal parameters was proposed and tested by the authors. The feasibility and functionality of this method are verified by laboratory tests and clinical experiments.