Optically pumped magnetometers disclose magnetic field components of the muscular action potential

AimAiming at analysing the signal conduction in muscular fibres, the spatio-temporal dynamics of the magnetic field generated by the propagating muscle action potential (MAP) is studied.MethodIn this prospective, proof of principle study, the magnetic activity of the intrinsic foot muscle after electric stimulation of the tibial nerve was measured using optically pumped magnetometers (OPMs). A classical biophysical electric dipole model of the propagating MAP was implemented to model the source of the data. In order to account for radial currents of the muscular tubules system, a magnetic dipole oriented along the direction of the muscle was added.ResultsThe signal profile generated by the activity of the intrinsic foot muscles was measured by four OPM devices. Three OPM sensors captured the spatio-temporal magnetic field pattern of the longitudinal intrinsic foot muscles. Changes of the activation pattern reflected the propagating muscular action potential along the muscle. A combined electric and magnetic dipole model could explain the recorded magnetic activity.InterpretationOPM devices allow for a new, non-invasive way to study MAP patterns. Since magnetic fields are less altered by the tissue surrounding the dipole source compared to electric activity, a precise analysis of the spatial characteristics and temporal dynamics of the MAP is possible. The classic electric dipole model explains major but not all aspects of the magnetic field. The field has longitudinal components generated by intrinsic structures of the muscle fibre. By understanding these magnetic components, new methods could be developed to analyse the muscular signal transduction pathway in greater detail. The approach has the potential to become a promising diagnostic tool in peripheral neurological motor impairments.     

Dose distribution correction for the influence of magnetic field using a deep convolutional neural network for online MR-guided adaptive radiotherapy

PurposeThis study aimed to develop a deep convolutional neural network (CNN)-based dose distribution conversion approach for the correction of the influence of a magnetic field for online MR-guided adaptive radiotherapy.MethodsOur model is based on DenseNet and consists of two 2D input channels and one 2D output channel. These three types of data comprise dose distributions without a magnetic field (uncorrected), electron density (ED) maps, and dose distributions with a magnetic field. These data were generated as follows: both types of dose distributions were created using 15-field IMRT in the same conditions except for the presence or absence of a magnetic field with the GPU Monte Carlo dose in Monaco version 5.4; ED maps were acquired with planning CT images using a clinical CT-to-ED table at our institution. Data for 50 prostate cancer patients were used; 30 patients were allocated for training, 10 for validation, and 10 for testing using 4-fold cross-validation based on rectum gas volume. The accuracy of the model was evaluated by comparing 2D gamma-indexes against the dose distributions in each irradiation field with a magnetic field (true).ResultsThe gamma indexes in the body for CNN-corrected uncorrected dose against the true dose were 94.95% ± 4.69% and 63.19% ± 3.63%, respectively. The gamma indexes with 2%/2-mm criteria were improved by 10% in most test cases (99.36%).ConclusionsOur results suggest that the CNN-based approach can be used to correct the dose-distribution influences with a magnetic field in prostate cancer treatment.     

Oscillations of the collisionless sheath

An Eulerian-Vlasov code is used to study the properties of a collisionless sheath with grazing incidence of the magnetic field. In the case where the ion gyroradius is large compared to the Debye length, the electrons, frozen by the magnetic field lines, have to move rapidly along the magnetic field B in their attempt to follow the ions gyrating perpendicular to B. Below a critical angle, the electrons moving parallel to B can no longer follow the gyrating ions and low-frequency oscillations appear in the system. Published in Russian in Fizika Plazmy, 2008, Vol. 34, No. 9, pp. 812–815. The text was submitted by the authors in English.     

Investigation of the temporal and spatial dynamics of muscular action potentials through optically pumped magnetometers

AimThis study aims to simultaneously record the magnetic and electric components of the propagating muscular action potential.MethodA single-subject study of the monosynaptic stretch reflex of the musculus rectus femoris was performed; the magnetic field generated by the muscular activity was recorded in all three spatial directions by five optically pumped magnetometers. In addition, the electric field was recorded by four invasive fine-wire needle electrodes. The magnetic and electric fields were compared by modelling the muscular anatomy of the rectus femoris muscle and by simulating the corresponding magnetic field vectors.ResultsThe magnetomyography (MMG) signal can reliably be recorded following the stimulation of the monosynaptic stretch reflex. The MMG signal shows several phases of activity inside the muscle, the first of which is the propagating muscular action potential. As predicted by the finite wire model, the magnetic field vectors of the propagating muscular action potential are generated by the current flowing along the muscle fiber. Based on the magnetic field vectors, it was possible to reconstruct the pinnation angle of the muscle fibers. The later magnetic field components are linked to the activation of the contractile apparatus.InterpretationMMG allows to analyze the muscle physiology from the propagating muscular action potential to the initiation of the contractile apparatus. At the same time, this methods reveals information about muscle fiber direction and extend. With the development of high-resolution magnetic cameras, that are based on OPM technology, it will be possible to image the function and structure of the biomagnetic field of any skeletal muscle with high precision. This method could be used both, in clinical medicine and also in sports science.     

A semi-analytical model for calculating the penetration depth of a high energy electron beam in a water phantom with a magnetic field

PurposeAs an electron beam is incident on a uniform water phantom in the presence of a lateral magnetic field, the depth-dose distribution of the electron beam changes significantly and forms the well-known ‘Bragg peak’, with a depth-dose distribution similar to that of heavy ions. This phenomenon has pioneered a new field in the clinical application of electron beams. For such clinical applications, evaluating the penetration depth of electron beams quickly and accurately is the critical problem.MethodsThis paper describes a model for calculating the penetration depth of an electron beam rapidly and correctly in a water phantom under the influence of a magnetic field. The model was used to calculate the penetration depths under different conditions: the energies of electron beams of 6, 8, 12 and 15 MeV and the magnetic induction intensities of 0.75, 1.0, 1.5, 2.0 and 3.0 T. In addition, the calculation results were compared with the results of a Monte Carlo simulation.ResultsThe comparison results indicate that the difference between the two calculation methods was less than 0.5 cm. Moreover, the computing time of the calculation model was less than a second.ConclusionsThe semi-analytical model proposed in the present study enables the penetration depth of the electron beam in the presence of a magnetic field to be obtained with a computational efficiency higher than that of the Monte Carlo approach; thus, the proposed model has high potential for application.     

Impact of quantization algorithm and number of gray level intensities on variability and repeatability of low field strength magnetic resonance image-based radiomics texture features

PurposeThe purpose of this work was to investigate the impact of quantization preprocessing parameter selection on variability and repeatability of texture features derived from low field strength magnetic resonance (MR) images.MethodsTexture features were extracted from low field strength images of a daily image QA phantom with four texture inserts. Feature variability over time was quantified using all combinations of three quantization algorithms and four different numbers of gray level intensities. In addition, texture features were extracted using the same combinations from the low field strength MR images of the gross tumor volume (GTV) and left kidney of patients with repeated set up scans. The impact of region of interest (ROI) preprocessing on repeatability was investigated with a test-retest study design.ResultsThe phantom ROIs quantized to 64 Gy level intensities using the histogram equalization method resulted in the greatest number of features with the least variability. There was no clear method that resulted in the highest repeatability in the GTV or left kidney. However, eight texture features extracted from the GTV were repeatable regardless of ROI processing combination.ConclusionLow field strength MR images can provide a stable basis for texture analysis with ROIs quantized to 64 Gy levels using histogram equalization, but there is no clear optimal combination for repeatability.     

Root hairs are the most important root trait for rhizosheath formation of barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)

Background and AimsRhizosheaths are defined as the soil adhering to the root system after it is extracted from the ground. Root hairs and mucilage (root exudates) are key root traits involved in rhizosheath formation, but to better understand the mechanisms involved their relative contributions should be distinguished.MethodsThe ability of three species [barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)] to form a rhizosheath in a sandy loam soil was compared with that of their root-hairless mutants [bald root barley (brb), maize root hairless 3 (rth3) and root hairless 1 (Ljrhl1)]. Root hair traits (length and density) of wild-type (WT) barley and maize were compared along with exudate adhesiveness of both barley and maize genotypes. Furthermore, root hair traits and exudate adhesiveness from different root types (axile versus lateral) were compared within the cereal species.Key ResultsPer unit root length, rhizosheath size diminished in the order of barley > L. japonicus > maize in WT plants. Root hairs significantly increased rhizosheath formation of all species (3.9-, 3.2- and 1.8-fold for barley, L. japonicus and maize, respectively) but there was no consistent genotypic effect on exudate adhesiveness in the cereals. While brb exudates were more and rth3 exudates were less adhesive than their respective WTs, maize rth3 bound more soil than barley brb. Although both maize genotypes produced significantly more adhesive exudate than the barley genotypes, root hair development of WT barley was more extensive than that of WT maize. Thus, the greater density of longer root hairs in WT barley bound more soil than WT maize. Root type did not seem to affect rhizosheath formation, unless these types differed in root length.ConclusionsWhen root hairs were present, greater root hair development better facilitated rhizosheath formation than root exudate adhesiveness. However, when root hairs were absent root exudate adhesiveness was a more dominant trait.     

Magnetic field intensified bi-enzyme system with in situ cofactor regeneration supported by magnetic nanoparticles

Efficient dynamic interactions among cofactor, enzymes and substrate molecules are of primary importance for multi-step enzymatic reactions with in situ cofactor regeneration. Here we showed for the first time that the above dynamic interactions could be significantly intensified by exerting an external alternating magnetic field on magnetic nanoparticles-supported multi-enzymatic system so that the inter-particle collisions due to Brownian motion of nanoparticles could be improved. To that end, a multienzyme system including glutamate dehydrogenase (GluDH), glucose dehydrogenase (GDH) and cofactor NAD(H) were separately immobilized on silica coated Fe₃O₄ magnetic nanoparticles with an average diameter of 105 nm, and the effect of magnetic field strength and frequency on the kinetics of the coupled bi-enzyme reaction was investigated. It was found that at low magnetic field frequency (25 Hz and 100 Hz), increasing magnetic field strength from 9.8 to 161.1 Gs led to only very slight increase in reaction rate of the coupled bi-enzyme reaction expressed by glucose consumption rate. At higher magnetic field of 200 Hz and 500 Hz, reaction rate increased significantly with increase of magnetic field strength. When the magnetic field frequency was kept at 500 Hz, the reaction rate increased from 3.89 μM/min to 8.11 μM/min by increasing magnetic field strength from 1.3 to 14.2 Gs. The immobilized bi-enzyme system also showed good reusability and stability in the magnetic field (500 Hz, 14.2 Gs), that about 46% of original activity could be retained after 33 repeated uses, accounting for totally 34 days continuous operation. These results demonstrated the feasibility in intensifying molecular interactions among magnetic nanoparticle-supported multienzymes by using nano-magnetic stirrer for efficient multi-step transformations.     

Effects of the surface wettability and zeta potential of bioceramics on the adhesiveness of anchorage-dependent animal cells

Using calcium phosphate ceramics that have high biocompatibility with the living body, the effects of the surface characteristics of the bioceramics on cell adhesiveness were investigated. In the case of carriers with contact angles from 35° to 60°, the cell adhesiveness increased according to the increase in the wettability. Measurement of the zeta potentials of HAP-TCP sinters showed that these bioceramics had negative potentials from −2 mV to −6 mV. Electrochemical analysis suggested that the initial cell anchoring ratio (R_ia) and adhesive strength (F_a,enz) were affected by the surface ionic condition of the ceramic material. To clarify the effects of the surface potential of the ceramics on cell adhesiveness, the ceramic surface was modified chemically by means of various silane coupling reagents. The surface potential was regulated from −20 mV to +24 mV. Using these ceramics, the affinity and adhesiveness of the cells to the ceramics were found to be dominantly regulated by the surface potential. A negative potential was effective in increasing the adhesiveness, even though living cells have negative charges.     

Experimental evaluation of the impact of low tesla transverse magnetic field on dose distribution in presence of tissue interfaces

PurposeAim of this study is to experimental evaluate the impact of a 0.35 T transverse magnetic field on dose distribution in presence of tissue-air and tissue-lung interfaces.MethodsThe investigation was carried out using MRIdian (ViewRay, Cleveland, Ohio) and it consisted of comparing experimental measurements performed by Gafchromic EBT3 film dosimetry, to Montecarlo simulations, carried out in the presence and, as well as, the absence of the magnetic field.A preliminary dose calibration was planned on MRIdian, arranging 3 × 3 cm² film pieces in a water slab phantom and exposing them at different beam-on times, in a dose range equal to 0.1–12.1 Gy.All experimental measurements were then carried out using the calibrated films and delivering one single beam orthogonally to three different phantoms: without inhomogeneity, with an air gap and with a lung inhomogeneity.The dose distributions measured by EBT3 films in presence of magnetic field were compared to those calculated in the presence and, as well as, the absence of the magnetic field, in terms of gamma analysis. A quantification of electron return effect (ERE) was also performed.ResultsAll the tested plans considering the magnetic field show a gamma-passing rate higher than 98% for 3%/3 mm gamma analysis.In presence of tissue-air interface, the electron return effect causes an over-dosage of +31.9% at the first interface and an under-dosage of −33% at the second interface. The dosimetric variations in presence of tissue-lung interface results to be smaller (+0.8% first interface, −1.3% second interface).ConclusionThe impact of 0.35 T magnetic field is not negligible and it can be effectively modelled by the Montecarlo dose calculation platform available in the MRIdian TPS.     

Feasibility of using a commercial collapsed cone dose engine for 1.5T MR-LINAC online independent dose verification

PurposeTo validate the feasibility and accuracy of commonly used collapsed cone (CC) dose engine for Elekta Unity 1.5T MR-LINAC online independent dose verification.Materials and MethodsThe Unity beam model was built and commissioned in RayStation treatment planning system with CC dose engine. Four AAPM TG-119 test plans were created and measured with ArcCHECK phantom for comparison, another thirty patient plans from six tumor sites were also included. The dosimetric criteria for various ROIs and 3D gamma passing rates were quantitatively evaluated, and the effects of magnetic field and dose deposition type on the dose difference between two systems were further analyzed.ResultsArcCHECK based measurement showed a clear magnetic field induced profile shift between CC with both measurement and GPUMCD. For clinical plans, gamma passing rates with criteria (3%, 3 mm) between GPUMCD and CC large than 90% can be achieved for most tumor sites except esophagus and lung cases, the mean dose difference of 3% can be satisfied for most ROIs from all tumor sites. The magnetic field caused a large dose impact on low density areas, the average gamma passing rates were improved from 85.54% to 96.43% and 87.40% to 99.54% for esophagus and lung cases when the magnetic field effect was excluded.ConclusionsIt is feasible to use CC dose engine as a secondary dose calculation tool for Elekta Unity system for most tumor sites, while the accuracy is limited and should be used carefully for low density areas, such as esophagus and lung cases.     

7-Ketocholesterol enhances the expression of adhesion molecules on human aortic endothelial cells by increasing the production of reactive oxygen species

Abstract

The aim of the present study was to assess the expression of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), monocytic adhesion of human aortic endothelial cells (HAECs), and the production of intracellular reactive oxygen species (ROS), when HAECs were stimulated by 7-ketocholesterol. 7-ketocholesterol enhances surface expression of ICAM-1 and VCAM-1 as determined by EIA, induces their mRNA expression by RT-PCR, and stimulates adhesiveness of HAECs to U937 monocytic cells. We confirmed up-regulation of ROS production of HAECs treated with 7-ketocholesterol. Although the surface expression of ICAM-1 and VCAM-1 on HAECs treated with 7-ketocholesterol increased in a time-dependent manner, α-tocopherol inhibited this increase of the surface expression of ICAM-1 and VCAM-1. In the monocytic adhesion assay, adhesion of U937 to HAECs treated with 7-ketocholesterol was enhanced, but monoclonal anti-ICAM-1 and VCAM-1 antibodies reduced the endothelial adhesiveness. In conclusion, this study suggests that the endothelial adhesiveness to monocytic cells that was increased by 7-ketocholesterol was associated with enhanced expression of ICAM-1 and VCAM-1 mediated by ROS production.     

Neural basis of the magnetic compass: interactions of visual,magnetic and vestibular inputs in the pigeon's brain

Summary Single unit electrical activity was recorded extracellularly in the lateral and superior vestibular nuclei, the vestibulo-cerebellum and the nucleus of the basal optic root (nBOR) under earth-strength magnetic stimulation. Units in the vestibular system responded with either inhibition or excitation to the magnetic stimuli only if the animal was moved out of the horizontal plane. No responses to the artificial magnetic field were observed when enucleation was performed contralateral to the recording site or when magnetic stimuli were applied in total darkness.Most of the units in the nBOR responded to slow direction changes in the magnetic field with a gradual augmentation of activity. The responses were generally weak but nevertheless statistically significant and seemed to be direction selective, i.e. different cells responded to a different distinct direction change of the magnetic field.The results indicate, that information provided by magnetic cues in the earth's strength range may be conveyed from the visual to the vestibular system via a projection from the nBOR and then related to active movements of the animal.Abbreviation nBOR nucleus of the basal optic root     

Impact of the cavity on sinus wall dose in magnetic resonance image-guided radiation therapy

PurposeThis study aims to investigate the impact of the cavity on the sinus wall dose by comparing dose distributions with and without the sinus under magnetic fields using Monte Carlo calculations.MethodsA water phantom containing a sinus cavity (Empty) was created, and dose distributions were calculated for 1, 2, and 4 irradiation fields with 6 MV photons. The sinus in the phantom was then filled with water (Full), and the dose distributions were calculated again. The sinus was set to cubes of 2 cm and 4 cm. The magnetic field was applied to the transverse and inline direction under the magnetic flux densities of 0 T, 0.35 T, 0.5 T, 1.0 T, and 1.5 T. The dose distributions were analyzed by the dose difference, dose volume histogram, and D₂ with sinus wall thicknesses of 1 and 5 mm.ResultsD₂ in the “Empty” sinus wall under transverse magnetic fields for the 1-field and 4-field cases was 51.9% higher and 3.7% lower than that in the “Full” sinus wall at 1.5 T, respectively. Meanwhile, D₂ in the Empty sinus wall under inline magnetic fields for 1-field and 4-fields was 2.3% and 2.6% lower than that in the “Full” sinus at B = 0 T, respectively, whereas D₂ was 0.9% and 0.7% larger at 1.0 T, respectively.ConclusionsThe impact of the cavity on the sinus wall dose depends on the magnetic flux density, direction of the magnetic field and irradiation beam, and number of irradiation fields.     

高压电场对A549细胞中ABCG2和V-ATPase的表达及其耐药性的影响

目的:探讨高压电场对A549细胞中ABCG2和V-ATPase表达量的影响;探讨高压电场对A549细胞耐药性的影响。方法:MTT法测细胞生长曲线,明确能导致细胞可逆性电穿孔的最高电场强度。慢病毒构建ABCG2和V-ATPase低表达的A549细胞系,并用电场处理,用q-RT-PCR和Western-blot法检测处理前后ABCG2和V-ATPase的m RNA和蛋白表达量的变化。最适强度的高压电场处理各组细胞,在处理前后的细胞中分别加入阿霉素,用高效液相色谱法检测各组细胞中阿霉素浓度。结果:当电场强度为1500 V/cm时,肿瘤细胞增殖最慢;电场强度为1500 V/cm时,肿瘤细胞中ABCG2和V-ATPase的m RNA和蛋白的表达量分别降至对照组的58%和61%,具有统计学差异;1500 V/cm强度的电场可以提高肿瘤细胞内阿霉素的浓度3-4倍。结论:高压电场可以显著降低肿瘤细胞中V-ATPase和ABCG2的m RNA和蛋白的表达量并降低肿瘤细胞的耐药性。     

The effects of pulsed magnetic field exposure on the permeability of leukemia cancer cells

Purpose: The newer methods of cancer treatment require new idea of drug delivery in cancer cells. Due to numerous researches electromagnetic field affect on cell function and cell membrane for possible therapeutic and drug delivery. In this article, we determined in vitro uptake of fluorescent dyes into the attached K562 cells due to time-varying magnetic field exposure. Method and material: The K562 cells were exposed to magnetic pulses via Magstim stimulator and double 70?mm coil. The strength and duration of pulses in all experiments were the same and three different frequencies of 0.25, 1 and 10?Hz pulses for 56, 112 and 28 numbers of pulses were applied (nine experimental groups) and uptake of Ly and PI was measured in each group. Result: Our results show that magnetic field can efficiently increase permeability. Among the treatment groups, the system gives the optimal permeabilization when cells are exposed to a train of 28 pulses with 1?Hz frequency.     

Bats Respond to Very Weak Magnetic Fields

How animals, including mammals, can respond to and utilize the direction and intensity of the Earth’s magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5^th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth’s magnetic field strength varied and the polarity reversed tens of times over the past fifty million years.     

A human source for ELF magnetic perturbations

ABSTRACT

Current models that frame consciousness in terms of electromagnetic field theory carry implications that have yet to be fully explored. Endogenous weak extremely low frequency (ELF) magnetic fields are generated by ionic charge flow in axons, dendrites and synaptic transmitters. Because neural tissues are transparent to such fields, these provide the basis for the globally unifying qualities required to properly describe consciousness as a field. At the same time, however, an electromagnetic approach predicts partial transmission of this 1–100 nT field, suggesting external interactions similar to the various ELF magnetic perturbations that are linked to homeostatic and endocrine-related physiological effects. It follows that humans may represent an additional, previously unrecognized source of weak (1–10 nT) ambient ELF magnetic fields.     

Magnetic correlates in electromagnetic consciousness

ABSTRACT

We examine the hypothesis that consciousness is a manifestation of the electromagnetic field, finding supportive factors not previously considered. It is not likely that traditional electrophysiological signaling modes can be readily transmitted throughout the brain to properly enable this field because of electric field screening arising from the ubiquitous distribution of high dielectric lipid membranes, a problem that vanishes for low-frequency magnetic fields. Many reports over the last few decades have provided evidence that living tissue is robustly sensitive to ultrasmall (1–100 nT) ELF magnetic fields overlapping the γ-frequency range often associated with awareness. An example taken from animal behavior (coherent bird flocking) lends support to the possibility of a disembodied electromagnetic consciousness. In contrast to quantum consciousness hypotheses, the present approach is open to experimental trial.     

基于磁驱动技术的空肠营养管的设计

目的:为解决目前床旁鼻肠管快速置入成功率低这一临床难题,该文提出一种基于磁驱动技术的空肠营养管的设计。方法:分析了现有空肠营养管置管过程中的动力因素,结合磁驱动技术原理,提出了通过体外旋转磁场带动体内感应磁体螺旋式前进的设计方案,以期缩短空肠营养管的飘管时间。结果:该设计包括磁性空肠营养管和体外磁力驱动装置两部分。其中磁性空肠营养管由管体和感应磁头两部分构成,感应磁头包括磁体内核和硅胶外壳。磁力驱动装置由多极磁体和手持式微型电机组成。操作时通过体外磁力驱动装置发出大旋转磁场带动空肠营养管的感应磁头做轴向旋转运动,可加速空肠营养管在肠道内的移动,达到缩短飘管时间的目的。结论:该设计基于磁驱动技术原理,设计巧妙,符合磁力学原理,操作简单,具有临床应用潜力。