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Magma (New York, N.Y.) Aug 2021To correct for image distortions produced by standard Fourier reconstruction techniques on low field permanent magnet MRI systems with strong [Formula: see text]...
OBJECTIVE
To correct for image distortions produced by standard Fourier reconstruction techniques on low field permanent magnet MRI systems with strong [Formula: see text] inhomogeneity and gradient field nonlinearities.
MATERIALS AND METHODS
Conventional image distortion correction algorithms require accurate [Formula: see text] maps which are not possible to acquire directly when the [Formula: see text] inhomogeneities also produce significant image distortions. Here we use a readout gradient time-shift in a TSE sequence to encode the [Formula: see text] field inhomogeneities in the k-space signals. Using a non-shifted and a shifted acquisition as input, [Formula: see text] maps and images were reconstructed in an iterative manner. In each iteration, [Formula: see text] maps were reconstructed from the phase difference using Tikhonov regularization, while images were reconstructed using either conjugate phase reconstruction (CPR) or model-based (MB) image reconstruction, taking the reconstructed field map into account. MB reconstructions were, furthermore, combined with compressed sensing (CS) to show the flexibility of this approach towards undersampling. These methods were compared to the standard fast Fourier transform (FFT) image reconstruction approach in simulations and measurements. Distortions due to gradient nonlinearities were corrected in CPR and MB using simulated gradient maps.
RESULTS
Simulation results show that for moderate field inhomogeneities and gradient nonlinearities, [Formula: see text] maps and images reconstructed using iterative CPR result in comparable quality to that for iterative MB reconstructions. However, for stronger inhomogeneities, iterative MB reconstruction outperforms iterative CPR in terms of signal intensity correction. Combining MB with CS, similar image and [Formula: see text] map quality can be obtained without a scan time penalty. These findings were confirmed by experimental results.
DISCUSSION
In case of [Formula: see text] inhomogeneities in the order of kHz, iterative MB reconstructions can help to improve both image quality and [Formula: see text] map estimation.
Topics: Algorithms; Computer Simulation; Fourier Analysis; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Magnets; Phantoms, Imaging
PubMed: 33502668
DOI: 10.1007/s10334-021-00907-2 -
Biosensors & Bioelectronics Feb 2023The process of developing an end-to-end model of a magneto-immunoassay is described, simulating the agglutination effect due to the specific binding of bacteria to...
The process of developing an end-to-end model of a magneto-immunoassay is described, simulating the agglutination effect due to the specific binding of bacteria to paramagnetic particles. After establishing the properties of the dose-specific agglutination through direct imaging, a microfluidic assay was used to demonstrate changes in the magnetophoretic transport dynamics of agglutinated clusters via transient inductive magentometer measurements. End-to-end mathematical modelling is used to establish the physical processes underlying the assay. First, a modified form of Becker-Döring nucleation kinetic equations is used to establish a relationship between analyte dose and average cluster size. Next, Stokes flow equations are used to establish a relationship between cluster size and speed of motion within the fluid chamber. This predicts a cluster-size dynamic profile of concentration of PMPs versus time when the magnetic field is switched between the two actuated magnets. Finally, inductive modelling is carried out to predict the response of the magnetometer circuit in response to the dynamics of magnetic clusters. The predictions of this model are shown to agree well with the results of experiments, and to predict the shape of the dose-response curve.
Topics: Biosensing Techniques; Models, Theoretical; Magnetics; Magnets; Motion
PubMed: 36502714
DOI: 10.1016/j.bios.2022.114745 -
TheScientificWorldJournal 2013Magnetic resonance imaging is a noninvasive technique that has been developed for its excellent depiction of soft tissue contrasts. Instruments capable of ultra-high... (Review)
Review
Magnetic resonance imaging is a noninvasive technique that has been developed for its excellent depiction of soft tissue contrasts. Instruments capable of ultra-high field strengths, ≥7 Tesla, were recently engineered and have resulted in higher signal-to-noise and higher resolution images. This paper presents various subsystems of the MR imaging systems like the magnet subsystem, gradient subsystem, and also various issues which arise due to the magnet. Further, it also portrays finer details about the RF coils and transceiver and also various limitations of the RF coils and transceiver. Moreover, the concept behind the data processing system and the challenges related to it were also depicted. Finally, the various artifacts associated with the MR imaging were clearly pointed out. It also presents a brief overview about all the challenges related to MR imaging systems.
Topics: Artifacts; Equipment Design; Humans; Magnetic Resonance Imaging; Magnetics; Patient Positioning; Patient Safety; Radio Waves; Refrigeration
PubMed: 24381523
DOI: 10.1155/2013/783715 -
World Journal of Gastroenterology Apr 2017Endoscopic submucosal dissection (ESD) is a well-established, minimally invasive treatment for superficial neoplasms of the gastrointestinal tract. The universal... (Review)
Review
Endoscopic submucosal dissection (ESD) is a well-established, minimally invasive treatment for superficial neoplasms of the gastrointestinal tract. The universal adoption of ESD has been limited by its slow learning curve, long procedure times, and high risk of complications. One technical challenge is the lack of a second hand that can provide traction, as in conventional surgery. Reliable tissue retraction that exposes the submucosal plane of dissection would allow for safer and more efficient dissection. Magnetic anchor guided endoscopic submucosal dissection (MAG-ESD) has potential benefits compared to other current traction methods. MAG-ESD offers tissue retraction independent of the endoscope mimicking a surgeon's "second hand". Two types of magnets can be used: electromagnets and permanent magnets. In this article we review the MAG-ESD technology, published work and studies of magnets in ESD. We also review the use of magnetic anchor guidance systems in natural orifice transluminal endoscopic surgery and the idea of magnetic non-contact retraction using surface ferromagentization. We discuss the current limitations, the future potential of MAG-ESD and the developments needed for adoption of this technology.
Topics: Animals; Endoscopic Mucosal Resection; Equipment Design; Gastrointestinal Neoplasms; Humans; Magnetics; Magnets; Natural Orifice Endoscopic Surgery; Treatment Outcome
PubMed: 28522906
DOI: 10.3748/wjg.v23.i16.2883 -
Molecules (Basel, Switzerland) Aug 2022We developed a method of sorption determination via the atomic emission of Cu, Zr and Hf metals in the waste of samarium-cobalt magnets. This method was based on the...
We developed a method of sorption determination via the atomic emission of Cu, Zr and Hf metals in the waste of samarium-cobalt magnets. This method was based on the preconcentration of impurities using S- and N-containing heterochain sorbents, with further determination of the analytes via inductively coupled plasma atomic emission spectrometry (ICP-OES). Different sorbents such as PED (polyethelendiamine), TDA (polythiodimethanamine), PhED (-phenylpolyethediamine) and PTE (polythioether) were tested for Ti, Cu, Zr, Nb and Hf extraction. The PTE sorbent ensured the maximum extraction of the analytes (recovery 60% for Ti, 80% for Nb, 95-100% for Cu, Zr and Hf) and thus was selected for further research. Additionally, various acidities of chloride solution (0.01-1 M HCl) were investigated for metal sorption. Under the optimised sorption conditions, trace impurities of Cu, Zr and Hf were determined using ICP-OES with a relative standard deviation of less than 5%. The obtained results were confirmed by the added-found method and cross-method experiments. The detection limits (DLs) were 1.5, 2, 0.15, 2 and 0.75 µg/L for Ti, Cu, Zr, Nb and Hf, respectively. The proposed method can be successfully used for the determination of various microelements in other waste REE-magnetic materials.
Topics: Cobalt; Magnets; Metals; Samarium; Spectrum Analysis
PubMed: 36014512
DOI: 10.3390/molecules27165275 -
NMR in Biomedicine Aug 2022Prepolarized MRI (PMRI) is a long-established technique conceived to counteract the loss in signal-to-noise ratio (SNR) inherent to low-field MRI systems. When it comes...
Prepolarized MRI (PMRI) is a long-established technique conceived to counteract the loss in signal-to-noise ratio (SNR) inherent to low-field MRI systems. When it comes to hard biological tissues and solid-state matter, PMRI is severely restricted by their ultra-short characteristic relaxation times. Here we demonstrate that efficient hard-tissue prepolarization is within reach with a special-purpose 0.26 T scanner designed for ex vivo dental MRI and equipped with suitable high-power electronics. We have characterized the performance of a 0.5 T prepolarizer module, which can be switched on and off in 200 μs. To this end, we have used resin, dental and bone samples, all with times of the order of 20 ms at our field strength. The measured SNR enhancement is in good agreement with a simple theoretical model, and deviations in extreme regimes can be attributed to mechanical vibrations due to the magnetic interaction between the prepolarization and main magnets.
Topics: Magnetic Resonance Imaging; Magnetics; Magnets; Models, Theoretical; Signal-To-Noise Ratio
PubMed: 35384092
DOI: 10.1002/nbm.4737 -
Nature Communications Nov 2022High proton conductivity originated from its small size and the diffusion-free Grotthuss mechanism offers immense promise for proton-based magneto-ionic control of...
High proton conductivity originated from its small size and the diffusion-free Grotthuss mechanism offers immense promise for proton-based magneto-ionic control of magnetic materials. Despite such promise, the realization of proton magneto-ionics is hampered by the lack of proton-responsive magnets as well as the solid-state sensing method. Here, we report the proton-based magneto-ionics in molecule-based magnet which serves as both solid-state proton battery electrode and radiofrequency sensing medium. The three-dimensional hydrogen-bonding network in such a molecule-based magnet yields a high proton conductivity of 1.6 × 10 S cm. The three-dimensional printed vascular hydrogel provides the on-demand proton stimulus to enable magneto-ionics, where the Raman spectroscopy shows the redox behavior responsible for the magnetism control. The radiofrequency proton sensor shows high sensitivity in a wide proton concentration range from 10 to 1 molar under a low working radiofrequency and magnetic field of 1 GHz and 405 Oe, respectively. The findings shown here demonstrate the promising sensing application of proton-based magneto-ionics.
Topics: Protons; Hydrogen Bonding; Hydrogen-Ion Concentration; Electric Conductivity; Magnetics
PubMed: 36396649
DOI: 10.1038/s41467-022-34874-6 -
Molecules (Basel, Switzerland) Mar 2022Biomolecules participate in various physiological and pathological processes through intermolecular interactions generally driven by non-covalent forces. In the present... (Review)
Review
Biomolecules participate in various physiological and pathological processes through intermolecular interactions generally driven by non-covalent forces. In the present review, the force-induced remnant magnetization spectroscopy (FIRMS) is described and illustrated as a novel method to measure non-covalent forces. During the FIRMS measurement, the molecular magnetic probes are magnetized to produce an overall magnetization signal. The dissociation under the interference of external force yields a decrease in the magnetic signal, which is recorded and collected by atomic magnetometer in a spectrum to study the biological interactions. Furthermore, the recent FIRMS development with various external mechanical forces and magnetic probes is summarized.
Topics: Magnetics; Mechanical Phenomena; Microscopy, Atomic Force; Molecular Probes; Spectrum Analysis
PubMed: 35408471
DOI: 10.3390/molecules27072072 -
Journal (Canadian Dental Association) 2010Open-field aluminum-nickle-cobalt magnets have been used in prosthodontics for many years, but success has been limited because these magnets are susceptible to... (Review)
Review
Open-field aluminum-nickle-cobalt magnets have been used in prosthodontics for many years, but success has been limited because these magnets are susceptible to corrosion by the saliva and because their retentive force is weak relative to the initial retention offered by mechanical attachments. More recently, magnets have been made from alloys of the rare earth elements samarium and neodymium, which provide stronger magnetic force per unit size. In addition, a new generation of laser-welded containers has improved protection from salivary corrosion. The current resurgence of interest in this type of attachment appears justified because, unlike mechanical attachments, magnets have potential for unlimited durability and might therefore be superior to mechanical ball or bar attachments for the retention of removable prostheses on implants. To date, no long-term prospective trials have been conducted to confirm the clinical durability of this new generation of magnets for retaining dentures on either teeth or implants. The aim of this study was to document initial clinical experiences and levels of satisfaction among edentulous patients treated with mandibular implant-supported overdentures retained using a new generation of rare-earth magnetic attachments. At the outset, all but one of the 17 patients had had several years of experience with implant-supported overdentures. During the first year, the mean overall satisfaction among these 17 patients increased from less than 70 to over 90 out of 100 (standardized visual analogue scale). No unusual difficulties were encountered in rendering the treatment or maintaining the attachments. This report offers preliminary evidence of the excellent potential of these magnets for retaining mandibular implant-supported overdentures.
Topics: Contraindications; Corrosion; Dental Plaque; Dental Prosthesis, Implant-Supported; Dental Soldering; Denture Retention; Denture, Overlay; Humans; Lasers; Magnetic Resonance Imaging; Magnetics; Mandible; Neodymium; Patient Satisfaction; Samarium; Welding
PubMed: 20943036
DOI: No ID Found -
IUBMB Life Aug 2011Magnetic targeting has shown promise to improve the efficacy and safety of different classes of therapeutic agents by enabling their active guidance to the site of... (Review)
Review
Magnetic targeting has shown promise to improve the efficacy and safety of different classes of therapeutic agents by enabling their active guidance to the site of disease and minimizing dissemination to nontarget tissues. However, its translation into clinic has proven difficult because of inherent limitations of traditional approaches inapplicable for deep tissue targeting in human subjects and a need for developing well-characterized and fully biocompatible magnetic carrier formulations. A novel magnetic targeting scheme based on the magnetizing effect of deep-penetrating uniform fields is presented as an example of a strategy providing a potentially clinically viable solution for preventing injury-triggered reobstruction of stented blood vessels (in-stent restenosis). The design of optimized magnetic carrier formulations and experimental results showing the feasibility of uniform field-controlled targeting for site-specific vascular delivery of small-molecule pharmaceuticals, biotherapeutics, and cells are discussed in the context of antirestenotic therapy. The versatility of this approach applicable to different classes of therapeutic agents exerting their antirestenotic effects through distinct mechanisms prompts exploring the utility of uniform field-mediated magnetic stent targeting for combination therapies with enhanced efficiencies and improved safety profiles. Additional improvements in terms of site specificity and protracted carrier retention at the site of injury may be expected from the development and use of magnetic carriers exhibiting affinity for arterial wall-specific antigens.
Topics: Blood Vessels; Humans; Magnetics; Nanoparticles
PubMed: 21721100
DOI: 10.1002/iub.479