A continuous flow bioreactor system for high-throughput hyperpolarized metabolic flux analysis.

Hyperpolarized carbon-13 labeled compounds are increasingly being used in medical MR imaging (MRI) and MR imaging (MRI) and spectroscopy (MRS) research, due to its ability to monitor tissue and cell metabolism in real-time. Although radiological biomarkers are increasingly being considered as clinical indicators, biopsies are still considered the gold standard for a large variety of indications. Bioreactor systems can play an important role in biopsy examinations because of their ability to provide a physiochemical environment that is conducive for therapeutic response monitoring ex vivo. We demonstrate here a proof-of-concept bioreactor and microcoil receive array setup that allows for ex vivo preservation and metabolic NMR spectroscopy on up to three biopsy samples simultaneously, creating an easy-to-use and robust way to simultaneously run multisample carbon-13 hyperpolarization experiments. Experiments using hyperpolarized [1-13C]pyruvate on ML-1 leukemic cells in the bioreactor setup were performed and the kinetic pyruvate-to-lactate rate constants ( k PL ) extracted. The coefficient of variation of the experimentally found k PL s for five repeated experiments was C V = 35 % . With this statistical power, treatment effects of 30%-40% change in lactate production could be easily differentiable with only a few hyperpolarization dissolutions on this setup. Furthermore, longitudinal experiments showed preservation of ML-1 cells in the bioreactor setup for at least 6 h. Rat brain tissue slices were also seen to be preserved within the bioreactor for at least 1 h. This validation serves as the basis for further optimization and upscaling of the setup, which undoubtedly has huge potential in high-throughput studies with various biomarkers and tissue types.

A roadmap to high-resolution standard microcoil MAS NMR spectroscopy for metabolomics.

Current microcoil probe technology has emerged as a significant advancement in NMR applications to biofluids research. It has continued to excel as a hyphenated tool with other prominent microdevices, opening many new possibilities in multiple omics fields. However, this does not hold for biological samples such as intact tissue or organisms, due to the considerable challenges of incorporating the microcoil in a magic-angle spinning (MAS) probe without relinquishing the high-resolution spectral data. Not until 2012 did a microcoil MAS probe show promise in profiling the metabolome in a submilligram tissue biopsy with spectral resolution on par with conventional high-resolution MAS (HR-MAS) NMR. This result subsequently triggered a great interest in the possibility of NMR analysis with microgram tissues and striving toward the probe development of "high-resolution" capable microcoil MAS NMR spectroscopy. This review gives an overview of the issues and challenges in the probe development and summarizes the advancements toward metabolomics.

Exploring the Potential of Broadband Complementary Metal Oxide Semiconductor Micro-Coil Nuclear Magnetic Resonance for Environmental Research.

With sensitivity being the Achilles' heel of nuclear magnetic resonance (NMR), the superior mass sensitivity offered by micro-coils can be an excellent choice for tiny, mass limited samples such as eggs and small organisms. Recently, complementary metal oxide semiconductor (CMOS)-based micro-coil transceivers have been reported and demonstrate excellent mass sensitivity. However, the ability of broadband CMOS micro-coils to study heteronuclei has yet to be investigated, and here their potential is explored within the lens of environmental research. Eleven nuclei including 7Li, 19F, 31P and, 205Tl were studied and detection limits in the low to mid picomole range were found for an extended experiment. Further, two environmentally relevant samples (a sprouting broccoli seed and a D. magna egg) were successfully studied using the CMOS micro-coil system. 13C NMR was used to help resolve broad signals in the 1H spectrum of the 13C enriched broccoli seed, and steady state free precession was used to improve the signal-to-noise ratio by a factor of six. 19F NMR was used to track fluorinated contaminants in a single D. magna egg, showing potential for studying egg-pollutant interactions. Overall, CMOS micro-coil NMR demonstrates significant promise in environmental research, especially when the future potential to scale to multiple coil arrays (greatly improving throughput) is considered.

Canadian Association of Radiologists/Canadian Association for Interventional Radiology/Canadian Society of Thoracic Radiology Guidelines on Thoracic Interventions.

Thoracic interventions are frequently performed by radiologists, but guidelines on appropriateness criteria and technical considerations to ensure patient safety regarding such interventions is lacking. These guidelines, developed by the Canadian Association of Radiologists, Canadian Association for Interventional Radiology and Canadian Society of Thoracic Radiology focus on the interventions commonly performed by thoracic radiologists. They provide evidence-based recommendations and expert consensus informed best practices for patient preparation; biopsies of the lung, mediastinum, pleura and chest wall; thoracentesis; pre-operative lung nodule localization; and potential complications and their management.

Micro-magnetic stimulation of primary visual cortex induces focal and sustained activation of secondary visual cortex.

Cortical visual prostheses that aim to restore sight to the blind require the ability to create neural activity in the visual cortex. Electric stimulation delivered via microelectrodes implanted in the primary visual cortex (V1) has been the most common approach, although conventional electrodes may not effectively confine activation to focal regions and thus the acuity they create may be limited. Magnetic stimulation from microcoils confines activation to single cortical columns of V1 and thus may prove to be more effective than conventional microelectrodes, but the ability of microcoils to drive synaptic connections has not been explored. Here, we show that magnetic stimulation of V1 using microcoils induces spatially confined activation in the secondary visual cortex (V2) in mouse brain slices. Single-loop microcoils were fabricated using platinum-iridium flat microwires, and their effectiveness was evaluated using calcium imaging and compared with that of monopolar and bipolar electrodes. Our results show that compared to the electrodes, the microcoils better confined activation to a small region in V1. In addition, they produced more precise and sustained activation in V2. The finding that microcoil-based stimulation propagates to higher visual centres raises the possibility that complex visual perception, e.g. that requiring sustained synaptic inputs, may be achievable. This article is part of the theme issue 'Advanced neurotechnologies: translating innovation for health and well-being'.

3T high-resolution magnetic resonance imaging, conventional ultrasonography and ultrasound biomicroscopy of the normal canine eye.

BACKGROUND: Advances in MRI coil technology and increased availability of high-field MRI in veterinary medicine enable the acquisition of images of increasingly high spatial resolution while preserving signal-to-noise ratio.The purpose of the present study was to compare 3T high-resolution magnetic resonance imaging (HR-MRI) with ultrasound (US) and ultrasound biomicroscopy (UBM) in the normal canine eye, to assess its potential to depict normal ocular anatomy. RESULTS: HR-MRI was compared with US and UBM in 10 eyes from 10 healthy beagle dogs. Ocular structures (cornea, anterior chamber, iridocorneal angle, iris, lens, ciliary body, choroid, vitreous body, posterior wall of the eye, optic nerve and optic nerve sheath, extraocular muscles) were assessed subjectively and central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AQD), anteroposterior, mediolateral and dorsoventral lens diameter (APLD, MLLD, DVLD), anteroposterior diameter of the globe including and excluding the scleroretinal rim (APDSRR, APD), vitreous chamber depth (VCD) and optic nerve sheath diameter (ONSD) were measured in HR-MRI and in US. Optic nerve diameter (OND) was measured in HR-MRI. HR-MRI and UBM appearance of the anterior segment were subjectively compared. Detailed reference high-resolution MRI images of normal eyes of Beagle dogs are provided. CONCLUSIONS: HR-MRI allowed assessment of all structures identified with US and UBM. The MRI examinations were performed under general anesthesia with the addition of a neuromuscular blocking agent, while US and UBM examinations were performed in conscious animals. Visibility of the entire ocular wall, the lens, the structures caudal to the ciliary body and the optic nerve and its sheath was superior with HR-MRI. HR-MRI allowed the distinction of retina, choroid and sclera, and the delineation of structures not previously identified in canine eyes with MRI, including Tenon's capsule and the sub-Tenon's space.Plane selection was more accurate with HR-MRI compared to US. In general, the range of measurements was narrower for MRI than for US. CCT, AQD, APLD, MLLD, APD, APDSRR and ONSD differed significantly between HR-MRI and US, respectively (p = 0.005-0.027).Micro-MRI may be useful for the assessment of ocular pathologies in the future.

Hemorrhagic shock caused by preoperative computed tomography-guided microcoil localization of lung nodules: a case report.

BACKGROUND: Video-assisted thoracoscopic surgery (VATS) is an emerging technology in minimally invasive surgery, which has become recognized as standard treatments for early-stage lung cancer. Microcoil localization is considered to be a safe and effective way of preoperative localization, and is essential to facilitate VATS wedge-resection for lung nodules. CASE PRESENTATION: Here we report a rare case of a 28-year-old female who developed hemorrhagic shock caused by delayed pneumothorax after preoperative computed tomography (CT)-guided microcoil localization. The thoracic CT revealed hydropneumothorax in the right thoracic cavity at 10 h after microcoil localization, and the patient later had significant decreased hemoglobin level (87 g/L). Emergency thoracoscopic exploration demonstrated that the hemorrhagic shock was induced by delayed pneumothorax, which led to the fracture of an adhesive pleura cord and an aberrant vessel. Electrocoagulation hemostasis was then performed for the fractured vessel and the patient gradually recovered from the hypovolemic shock. CONCLUSIONS: Microcoil localization is a relatively safe and effective way of preoperative localization of lung nodules, however, hemorrhagic shock could be induced by rupture of pleural aberrant vessels subsequent to puncture related pneumothorax. Shorten the time interval between localization and thoracoscopic surgery, extend the monitoring time after localization might help to reduce the risk of these complications.

Pseudoaneurysm and arteriovenous fistula of the deep femoral artery after complete rupture of the vastus medialis muscle: endovascular treatment.

Due to its anatomical characteristics, the deep femoral artery is protected from most vascular injuries. We report a case of a soccer player with pseudoaneurysm of a perforating branch of the deep femoral artery, associated with an arteriovenous fistula and secondary to complete rupture of the vastus medialis muscle. Magnetic resonance imaging showed muscle damage associated with a pseudoaneurysm and angiotomography confirmed the presence of a pseudoaneurysm associated with a deep arteriovenous fistula of a branch of the deep femoral artery. Endovascular treatment of the fistula was performed by embolization with fibrous microcoils and surgical drainage of the muscle hematoma. The patient recovered well, was free from clinical complaints on the 30th postoperative day and also after 1 year.

Proton MRS on sub-microliter volume in rat brain using implantable NMR microcoils.

The use of miniaturized NMR receiver coils is an effective approach for improving detection sensitivity in studies using MRS and MRI. By optimizing the filling factor (the fraction of the coil occupied by the sample), and by increasing the RF magnetic field produced per unit current, the sensitivity gain offered by NMR microcoils is particularly interesting when small volumes or regions of interest are investigated. For in vivo studies, millimetric or sub-millimetric microcoils can be deployed in tissues to access regions of interest located at a certain depth. In this study, the implementation and application of a tissue-implantable NMR microcoil with a detection volume of 850 nL is described. The RF magnetic field generated by the microcoil was evaluated using a finite element method simulation and experimentally determined by high spatial resolution MRI acquisitions. The performance of the microcoil in terms of spectral resolution and limit of detection was measured at 7 T in vitro and in vivo in rodent brains. These performances were compared with those of a conventional external detection coil. Proton MR spectra were acquired in the cortex of rat brain. The concentrations of main metabolites were quantified and compared with reference values from the literature. In vitro and in vivo results obtained with the implantable microcoil showed a gain in sensitivity greater than 50 compared with detection using an external coil. In vivo proton spectra of diagnostic value were obtained from brain regions of a few hundred nanoliters. The similarities between spectra obtained with the implanted microcoil and those obtained with the external NMR coil highlight the minimally invasive nature of the coil implantation procedure. These implantable microcoils represent new tools for probing tissue metabolism in very small healthy or diseased regions using MRS.

NMR-Based Metabolomics in Cancer Research.

Nuclear magnetic resonance (NMR) spectroscopy offers reproducible quantitative analysis and structural identification of metabolites in various complex biological samples, such as biofluids (plasma, serum, and urine), cells, tissue extracts, and even intact organs. Therefore, NMR-based metabolomics, a mainstream metabolomic platform, has been extensively applied in many research fields, including pharmacology, toxicology, pathophysiology, nutritional intervention, disease diagnosis/prognosis, and microbiology. In particular, NMR-based metabolomics has been successfully used for cancer research to investigate cancer metabolism and identify biomarker and therapeutic targets. This chapter highlights the innovations and challenges of NMR-based metabolomics platform and its applications in cancer research.

Successful Treatment of Placental Chorangiomas by Ultrasound-Guided Percutaneous in utero Microcoil Embolization.

Placental chorangiomas can cause a high-output fetal state and increase neonatal morbidity and mortality. There is a paucity of data published describing the optimal treatment of these cases, and methods for occlusion to date include placement of vascular clips, bipolar cautery, injection of alcohol or surgical glue, interstitial laser, and microcoil embolization. We report 2 cases of prenatally diagnosed chorangiomas that caused a high-output fetal state and were successfully treated with microcoil embolization. This case series describes our technique and supports microcoil embolization as a potentially safe and effective antenatal treatment option in symptomatic chorangiomas.

Characterization and Miniaturization of Silver-Nanoparticle Microcoil via Aerosol Jet Printing Techniques for Micromagnetic Cochlear Stimulation.

According to the National Institute of Deafness and other Communication Disorders 2012 report, the number of cochlear implant (CI) users is steadily increasing from 324,000 CI users worldwide. The cochlea, located in the inner ear, is a snail-like structure that exhibits a tonotopic geometry where acoustic waves are filtered spatially according to frequency. Throughout the cochlea, there exist hair cells that transduce sensed acoustic waves into an electrical signal that is carried by the auditory nerve to ultimately reach the auditory cortex of the brain. A cochlear implant bridges the gap if non-functional hair cells are present. Conventional CIs directly inject an electrical current into surrounding tissue via an implanted electrode array and exploit the frequency-to-place mapping of the cochlea. However, the current is dispersed in perilymph, a conductive bodily fluid within the cochlea, causing a spread of excitation. Magnetic fields are more impervious to the effects of the cochlear environment due to the material properties of perilymph and surrounding tissue, demonstrating potential to improve precision. As an alternative to conventional CI electrodes, the development and miniaturization of microcoils intended for micromagnetic stimulation of intracochlear neural elements is described. As a step toward realizing a microcoil array sized for cochlear implantation, human-sized coils were prototyped via aerosol jet printing. The batch reproducible aerosol jet printed microcoils have a diameter of 1800 µm, trace width and trace spacing of 112.5 µm, 12 µm thickness, and inductance values of approximately 15.5 nH. Modelling results indicate that the coils have a combined depolarization-hyperpolarization region that spans 1.5 mm and produce a more restrictive spread of activation when compared with conventional CI.

Design, Analysis and Simulation of a MEMS-Based Gyroscope with Differential Tunneling Magnetoresistance Sensing Structure.

The design, analysis, and simulation of a new Micro-electromechanical System (MEMS) gyroscope based on differential tunneling magnetoresistance sensing are presented in this paper. The device is driven by electrostatic force, whereas the Coriolis displacements are transferred to intensity variations of magnetic fields, further detected by the Tunneling Magnetoresistance units. The magnetic fields are generated by a pair of two-layer planar multi-turn copper coils that are coated on the backs of the inner masses. Together with the dual-mass structure of proposed tuning fork gyroscope, a two-stage differential detection is formed, thereby enabling rejection of mechanical and magnetic common-mode errors concurrently. The overall conception is described followed by detailed analyses of proposed micro-gyroscope and rectangle coil. Subsequently, the FEM simulations are implemented to determine the mechanical and magnetic characteristics of the device separately. The results demonstrate that the micro-gyroscope has a mechanical sensitivity of 1.754 nm/°/s, and the micro-coil has a maximum sensitivity of 41.38 mOe/µm. When the detection height of Tunneling Magnetoresistance unit is set as 60 µm, the proposed device exhibits a voltage-angular velocity sensitivity of 0.131 mV/°/s with a noise floor of 7.713 × 10-6°/s/Hz in the absence of any external amplification.

Computed tomography-guided microcoil placement for localizing small pulmonary nodules before uniportal video-assisted thoracoscopic resection.

PURPOSE: The increasing number of computed tomography (CT) performed allows the more frequent identification of small, solid pulmonary nodules or ground-glass opacities. Video-assisted thoracic surgery (VATS) represents the standard in most lung resections. However, since VATS limit is the digital palpation of the lung parenchyma, many techniques of nodule localization were developed. The aim of this study was to determine the feasibility and safety of CT-guided microcoil insertion followed by uniportal VATS wedge resection (WR). MATERIALS AND METHODS: Retrospective study in a single institution, including patients undergone CT-guided microcoil insertion prior to uniportal VATS resection between May 2015 and December 2018. The lesion was identified using fluoroscopy. RESULTS: Forty-six consecutive patients were enrolled (22 male and 24 female). On CT: 5 cases of GGO, 2 cases of semisolid nodules, 39 cases of solid nodules. The median pathologic tumor size was 1.21 cm. Neither conversion to thoracotomy nor microcoil dislodgement was recorded. All patients underwent uniportal VATS WR (9/46 underwent completion lobectomy after frozen section). WR median time was 105 min (range 50-150 min). No patients required intraoperative re-resection for positive margins. After radiological procedure, 1 case of hematoma and 2 cases of pneumothorax were recorded. Four complications occurred in the postoperative period. The mean duration of chest drain and length of stay were 2.9 and 4.6 days, respectively. CONCLUSIONS: CT-guided microcoil insertion followed by uniportal VATS resection was a safe and feasible procedure having a minimal associated complications rate and offering surgeons the ease of localization of small intrapulmonary nodules.

Heterogeneous Disease Progression in a Mouse Model of Vascular Cognitive Impairment.

Recently, an asymmetric vascular compromise approach that replicates many aspects of human vascular cognitive impairment (VCI) has been reported. The present study aimed to first investigate on the reproducibility in the disease progression of this newly reported VCI model using wild-type C57BL6/J mice. The second aim was to assess how this approach will affect the disease progression of transgenic Alzheimer's disease (AD) 5XFAD mice subjected to VCI. C57BL6/J and 5XFAD mice were subjected to VCI by placing an ameroid constrictor on the right CCA and a microcoil on the left CCA. Infarcts and hippocampal neuronal loss did not appear predominantly in the right (ameroid side) as expected but randomly in both hemispheres. The mortality rate of C57BL6/J mice was unexpectedly high. Inducing VCI reduced amyloid burden in the hippocampi of 5XFAD mice. Since VCI is known to be complex and complicated, the heterogeneous disease progression observed from this current study shares close resemblance to the clinical manifestation of VCI. This heterogeneity, however, makes it challenging to test novel treatment options using this model. Further study is warranted to tackle the heterogeneous nature of VCI.

Key Factors for Simultaneous Improvements of Performance and Durability of Core-Shell Pt3 Ni/Carbon Electrocatalysts Toward Superior Polymer Electrolyte Fuel Cell.

It remains a big challenge to remarkably improve both oxygen reduction reaction (ORR) activity and long-term durability of Pt-M bimetal electrocatalysts simultaneously in the harsh cathode environment toward widespread commercialization of polymer electrolyte fuel cells (PEFC). In this account we found double-promotional effects of carbon micro coil (CMC) support on ORR performance and durability of octahedral Pt3 Ni nanoparticles (Oh Pt3 Ni/CMC). The Oh Pt3 Ni/CMC displayed remarkable improvements of mass activity (MA; 13.6 and 34.1 times) and surface specific activity (SA; 31.3 and 37.0 times) compared to those of benchmark Pt/C (TEC10E20E) and Pt/C (TEC10E50E-HT), respectively. Notably, the Oh Pt3 Ni/CMC revealed a negligible MA loss after 50,000 triangular-wave 1.0-1.5 VRHE (startup/shutdown) load cycles, contrasted to MA losses of 40 % (TEC10E20E) and 21.5 % (TEC10E50E-HT) by only 10,000 load cycles. It was also found that the SA increased exponentially with the decrease in the CO stripping peak potential in a series of Pt-M/carbon (M: Ni and Co), which predicts a maximum SA at the curve asymptote. Key factors for simultaneous improvements of performance and durability of core-shell Pt3 Ni/carbon electrocatalysts toward superior PEFC is also discussed.

Intraoperative Percutaneous Microcoil Localization of Small Peripheral Pulmonary Nodules Using Cone-Beam CT in a Hybrid Operating Room.

OBJECTIVE. Thoracoscopic surgical resection of small peripheral pulmonary nodules can be challenging, and often preoperative localization techniques are needed to avoid conversion to open thoracotomy. In this article, we show the feasibility and benefits of performing intraoperative percutaneous microcoil localization with C-arm cone-beam CT in a hybrid operating room immediately before video-assisted thoracoscopic surgery for wedge resection of a small pulmonary nodule. CONCLUSION. This technique can provide safe and accurate localization while minimizing patient discomfort and thus enhancing the patient's experience.

Image-guided thoracoscopic lung resection using a dual-marker localization technique in a hybrid operating room.

BACKGROUND: We sought to describe the feasibility and safety of a dual-marker technique-based on a combination of near-infrared (NIR) marking and microcoil localization-before image-guided video-assisted thoracoscopic surgery (iVATS) of small and/or deep pulmonary lesions in a hybrid operating room (HOR). METHODS: We retrospectively reviewed the clinical records of consecutive patients who underwent iVATS resection in a HOR using the proposed dual-marker localization technique. Patients were initially imaged with cone-beam CT, and the needle trajectory was subsequently planned with the Syngo iGuide Needle Guidance software. Using a coaxial needle technique, a microcoil was initially deployed either in the immediate proximity or within the lesion of interest followed by injection of diluted indocyanine green (ICG; quantity: 0.3-0.5 mL; dye concentration: 0.125 mg/mL) at the pleural surface. A NIR thoracoscopic camera and a C-arm portable fluoroscopic system were used to guide the subsequent resection. RESULTS: A total of 11 patients were examined. The median lesion size was 6 mm, with a median distance from the pleural surface of 4 mm. Three nodules were solid, whereas the remaining eight were GGOs. All lesions were identifiable on intraoperative cone-beam CT images. The median time required for localization was 19 min. No conversion to thoracotomy or a multi-port approach was required, and there were no clinically significant adverse events after ICG injection or microcoil placement. CONCLUSIONS: Our study indicates that iVATS with a dual-marking approach (NIR marking and microcoil localization) is safe and useful to localize difficult-to-identify pulmonary nodules.

Computed tomography-guided dual localization with microcoil and patent blue vital dye for deep-seated pulmonary nodules in thoracoscopic surgery.

BACKGROUND/PURPOSE: In video-assisted thoracic surgery (VATS) resection of small lung nodules, preoperative dye marking around the visceral pleura provides surface localization to help initiate resection, while implantation of a fiducial marker such as a microcoil can provide inner localization to aid nodule resection under fluoroscopic guidance. We aimed to determine whether dual localization with microcoil placement and dye marking is safe and useful for guiding the resection of small deep-seated lung nodules. METHODS: We retrospectively evaluated data pertaining to 39 consecutive patients (40 nodules) managed between January 2016 and December 2017 in our hospital. Dual localization with patent blue V dye and microcoil was performed preoperatively because the pulmonary nodules were expected to be difficult to visualize or palpate intraoperatively. The patients underwent computed tomography-guided dual localization in a single puncture and were then transferred to the operation room. Intraoperative fluoroscopy was used to ensure that the lung tissue resected included the microcoil. RESULTS: All 40 lesions were successfully resected using the dual localization technique followed by fluoroscopy-assisted thoracoscopic surgery. The median lesion diameter and depth were 0.9 and 1.7 cm, respectively, while the median margin/diameter ratio in the first resected specimen was 1.25. One patient had failure of localization due to partial release of the microcoil into the chest wall. Localization-related pneumothorax was detected in six of 39 patients (15.4%) and was always self-limited. CONCLUSION: Dual localization with microcoil placement and dye marking is safe and supports successful VATS resection of small deep-seated lung nodules.

Design of a Tabletop Liquid-Helium-Free 23.5-T Magnet Prototype towards 1-GHz Microcoil NMR.

We present a design study of a liquid-helium (LHe)-free 23.5-T, ϕ25-mm RT-bore REBCO magnet for high-resolution 1-GHz microcoil nuclear magnetic resonance (NMR) spectroscopy. A microcoil NMR magnet is compact and thus its cost will be less by nearly an order of magnitude than that of the standard NMR magnet, and placeable on a bench, thereby resulting in a large saving in space. In addition, LHe-free operation enables the user to be independent from a cooling source in short supply. This paper includes: 1) magnet design and conductor requirement specification; 2) conceptual design of a full-scale tabletop LHe-free 1-GHz NMR magnet; and 3) design of a 10-K operating REBCO 23.5-T magnet prototype with a ϕ20-mm cold-bore. This small-size magnet prototype will be built and tested by 2020 for validation of performance and manufacturing challenges such as splices between coils. The paper concludes with discussion of stray-field shielding methods and a screening-current-inducing field (SCF) effect.