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PubMed2000

Comparison of left ventricular ejection fraction and volumes in heart failure by echocardiography, radionuclide ventriculography and cardiovascular magnetic resonance; are they interchangeable?

AIMS: To prospectively compare the agreement of left ventricular volumes and ejection fraction by M-mode echocardiography (echo), 2D echo, radionuclide ventriculography and cardiovascular magnetic resonance performed in patients with chronic stable heart failure. It is important to know whether the results of each technique are interchangable, and thereby how the results of large studies in heart failure utilizing one technique can be applied using another. Some studies have compared cardiovascular magnetic resonance with echo or radionuclude ventriculography but few contain patients with heart failure and none have compared these techniques with the current fast breath-hold acquisition cardiovascular magnetic resonance. METHODS AND RESULTS: Fifty two patients with chronic stable heart failure taking part in the CHRISTMAS Study, underwent M-mode echo, 2D echo, radionuclude ventriculography and cardiovascular magnetic resonance within 4 weeks. The scans were analysed independently in blinded fashion by a single investigator at three core laboratories. Of the echocardiograms, 86% had sufficient image quality to obtain left ventricular ejection fraction by M-mode method, but only 69% by 2D Simpson's biplane analysis. All 52 patients tolerated the radionuclude ventriculography and cardiovascular magnetic resonance, and all these scans were analysable. The mean left ventricular ejection fraction by M-mode cube method was 39+/-16% and 29+/-15% by Teichholz M-mode method. The mean left ventricular ejection fraction by 2D echo Simpson's biplane was 31+/-10%, by radionuclude ventriculography was 24+/-9% and by cardiovascular magnetic resonance was 30+/-11. All the mean left ventricular ejection fractions by each technique were significantly different from all other techniques (P<0.001), except for cardiovascular magnetic resonance ejection fraction and 2D echo ejection fraction by Simpson's rule (P=0.23). The Bland-Altman limits of agreement encompassing four standard deviations was widest for both cardiovascular magnetic resonance vs cube M-mode echo and cardiovascular magnetic resonance vs Teichholz M-mode echo at 66% each, and was 58% for radionuclude ventriculography vs cube M-mode echo, 44% for cardiovascular magnetic resonance vs Simpson's 2D echo, 39% for radionuclide ventriculography vs Simpson's 2D echo, and smallest at 31% for cardiovascular magnetic resonance-radionuclide ventriculography. Similarly, the end-diastolic volume and end-systolic volume by 2D echo and cardiovascular magnetic resonance revealed wide limits of agreement (52 ml to 216 ml and 11 ml to 188 ml, respectively). CONCLUSION: These results suggest that ejection fraction measurements by various techniques are not interchangeable. The conclusions and recommendations of research studies in heart failure should therefore be interpreted in the context of locally available techniques. In addition, there are very wide variances in volumes and ejection fraction between techniques, which are most marked in comparisons using echocardiography. This suggests that cardiovascular magnetic resonance is the preferred technique for volume and ejection fraction estimation in heart failure patients, because of its 3D approach for non-symmetric ventricles and superior image quality.

Echocardiography↗
PubMed1996

Tissue response to space closure in monkeys: a comparison of orthodontic magnets and superelastic coil springs.

Interest in using magnets for generating orthodontic forces started with the widespread availability of rare earth magnetic alloys. In vivo studies have indicated that a static magnetic field and/or corrosion products from the magnetic materials may induce biological effects when in close contact with cells or tissues. In the clinical situation, orthodontic magnets are often situated some distance away from the gingiva and bone. Consequently, the previously observed biological effects may not be found in an experimental situation mimicking the clinical setting. Thus, the present experimental study was undertaken to test this hypothesis using commercially available cobalt-samarium magnets for orthodontic treatment in comparison to treatment with Sentalloy closed coil springs with respect to possible side effects on alveolar bone growth, gingival epithelial thickness as well as rate of space closure. Corrosion of the uncovered areas of the magnets was already evident after 6 weeks. No statistical differences were found between the magnet and coil spring specimens with respect to rate of space closure, bone formation or epithelial thickness. The only two variables that differed significantly between magnet and coil spring specimens was that there were more resorption and more tetracycline labelled osteocyte lacunae under the magnets. In conclusion, although some marginal statistical differences were found between the magnet and coil spring specimens with respect to cell and tissue reactions, the near lack of cell and tissue effects of the magnets in the present clinical experimental situation compared to previous studies in which the magnets were positioned in close contact with the tissue under study, indicate limited adverse clinical effects.

Alveolar Process↗
PubMedDate not supplied

Image analysis of bioparticles accumulation and diamagnetic alignment in high-gradient magnetic field.

Magnetic properties of biological particles are measured in high-gradient magnetic separation (HGMS) analysis, revealing the concentrating process of nucleoprotein particles, ferritin, red blood cells, and eggs. A magnetic force acting on micrometer and submicrometer biological particles having diamagnetic or paramagnetic susceptibility with respect to the solution causes their movement and accumulation in gradient magnetic fields dependent on the values of the magnetic moments. The methods developed enable us to obtain the magnetic moments values of single particles and their assembly directly from magnetic separation and image analyses without assuming the detection of sizes. Our precision methods for the measurement of the capture traveling (magnetic diffusion) time and the accumulation (magnetic sedimentation) radius in HGMS show that it is really possible to determine the weak dia- or paramagnetic shifts of magnetic susceptibility up to 0.7x10(-10) (SI units). HGMS analysis of the concentrating process of nucleoprotein granules (microcells, DNA granules, or nucleosome core particles) with polarization microscopy reveals phase transitions for DNA in granules, and separation accumulation of particles enables the determination of the diamagnetic susceptibility and anisotropy properties. Magnetic concentration effects always occur in living systems because micrometer-located gradient magnetic fields inside an organism are strong enough to cause drifts of cellular complexes and organelles of micrometer and submicrometer sizes. We report the appearance of superparamagnetic contamination inside developing shrimp eggs. In the developing shrimps eggs, ferritin aggregates are observed under weak gradient magnetic fields and diaparaferromagnetic changes are detected. A significant interruption of egg development is revealed in such fields.

Animals↗
PubMed1989

Comparison of magnetic resonance imaging and computed tomography in suspected lesions in the posterior cranial fossa.

OBJECTIVE: To compare computed tomography and magnetic resonance imaging in investigating patients suspected of having a lesion in the posterior cranial fossa. DESIGN: Randomised allocation of newly referred patients to undergo either computed tomography or magnetic resonance imaging; the alternative investigation was performed subsequently only in response to a request from the referring doctor. SETTING: A regional neuroscience centre serving 2.7 million. PATIENTS: 1020 Patients recruited between April 1986 and December 1987, all suspected by neurologists, neurosurgeons, or other specialists of having a lesion in the posterior fossa and referred for neuroradiology. The groups allocated to undergo computed tomography or magnetic resonance imaging were well matched in distributions of age, sex, specialty of referring doctor, investigation as an inpatient or an outpatient, suspected site of lesion, and presumed disease process; the referring doctor's confidence in the initial clinical diagnosis was also similar. INTERVENTIONS: After the patients had been imaged by either computed tomography or magnetic resonance (using a resistive magnet of 0.15 T) doctors were given the radiologist's report and a form asking if they considered that imaging with the alternative technique was necessary and, if so, why; it also asked for their current diagnoses and their confidence in them. MAIN OUTCOME MEASURES: Number of requests for the alternative method of investigation. Assessment of characteristics of patients for whom further imaging was requested and lesions that were suspected initially and how the results of the second imaging affected clinicians' and radiologists' opinions. RESULTS: Ninety three of the 501 patients who initially underwent computed tomography were referred subsequently for magnetic resonance imaging whereas only 28 of the 493 patients who initially underwent magnetic resonance imaging were referred subsequently for computed tomography. Over the study the number of patients referred for magnetic resonance imaging after computed tomography increased but requests for computed tomography after magnetic resonance imaging decreased. The reason that clinicians gave most commonly for requesting further imaging by magnetic resonance was that the results of the initial computed tomography failed to exclude their suspected diagnosis (64 patients). This was less common in patients investigated initially by magnetic resonance imaging (eight patients). Management of 28 patients (6%) imaged initially with computed tomography and 12 patients (2%) imaged initially with magnetic resonance was changed on the basis of the results of the alternative imaging. CONCLUSIONS: Magnetic resonance imaging provided doctors with the information required to manage patients suspected of having a lesion in the posterior fossa more commonly than computed tomography, but computed tomography alone was satisfactory in 80% of cases...

Brain Diseases↗
PubMedDate not supplied

Diagnostic performance of clinical examination and selective magnetic resonance imaging in the evaluation of intraarticular knee disorders in children and adolescents.

To determine the diagnostic performances of clinical examination and selective magnetic resonance imaging in the evaluation of intraarticular knee disorders in children and adolescents we compared them with arthroscopic findings in a consecutive series of pediatric patients (< or = 16 years old). Stratification effects by patient age and magnetic resonance imaging center were examined. There were 139 lesions diagnosed clinically, 128 diagnosed by magnetic resonance imaging, and 135 diagnosed arthroscopically. There was no significant difference between clinical examination and magnetic resonance imaging with respect to agreement with arthroscopic findings (clinical examination, 70.3%; magnetic resonance imaging, 73.7%), overall sensitivity (clinical examination, 71.2%; magnetic resonance imaging, 72.0%), and overall specificity (clinical examination, 91.5%; magnetic resonance imaging, 93.5%). Stratified analysis by diagnosis revealed significant differences only for sensitivity of lateral discoid meniscus (clinical examination, 88.9%; magnetic resonance imaging, 38.9%) and specificity of medial meniscal tears (clinical examination, 80.7%; magnetic resonance imaging, 92.0%). For magnetic resonance imaging, children younger than 12 years old had significantly lower overall sensitivity (61.7% versus 78.2%) and lower specificity (90.2% versus 95.5%) compared with children 12 to 16 years old. There was no significant effect of magnetic resonance imaging center. In conclusion, selective magnetic resonance imaging does not provide enhanced diagnostic utility over clinical examination, particularly in children, and should be used judiciously in cases where the clinical diagnosis is uncertain and magnetic resonance imaging input will alter the treatment plan.

Adolescent↗
PubMed2006

Calibration of magnetic and celestial compass cues in migratory birds--a review of cue-conflict experiments.

Migratory birds use multiple sources of compass information for orientation, including the geomagnetic field, the sun, skylight polarization patterns and star patterns. In this paper we review the results of cue-conflict experiments designed to determine the relative importance of the different compass mechanisms, and how directional information from these compass mechanisms is integrated. We focus on cue-conflict experiments in which the magnetic field was shifted in alignment relative to natural celestial cues. Consistent with the conclusions of earlier authors, our analyses suggest that during the premigratory season, celestial information is given the greatest salience and used to recalibrate the magnetic compass by both juvenile and adult birds. Sunset polarized light patterns from the region of the sky near the horizon appear to provide the calibration reference for the magnetic compass. In contrast, during migration, a majority of experiments suggest that birds rely on the magnetic field as the primary source of compass information and use it to calibrate celestial compass cues, i.e. the relative saliency of magnetic and celestial cues is reversed. An alternative possibility, however, is suggested by several experiments in which birds exposed to a cue conflict during migration appear to have recalibrated the magnetic compass, i.e. their response is similar to that of birds exposed to cue conflicts during the premigratory season. The general pattern to emerge from these analyses is that birds exposed to the cue conflict with a view of the entire sunset sky tended to recalibrate the magnetic compass, regardless of whether the cue conflict occurred during the premigratory or migratory period. In contrast, birds exposed to the cue conflict in orientation funnels and registration cages that restricted their view of the region of sky near the horizon (as was generally the case in experiments carried out during the migratory season) did not recalibrate the magnetic compass but, instead, used the magnetic compass to calibrate the other celestial compass systems. If access to critical celestial cues, rather than the timing of exposure to the cue conflict (i.e. premigratory vs migratory), determines whether recalibration of the magnetic compass occurs, this suggests that under natural conditions there may be a single calibration reference for all of the compass systems of migratory birds that is derived from sunset (and possibly also sunrise) polarized light cues from the region of sky near the horizon. In cue-conflict experiments carried out during the migratory season, there was also an interesting asymmetry in the birds' response to magnetic fields shifted clockwise and counterclockwise relative to celestial cues. We discuss two possible explanations for these differences: (1) lateral asymmetry in the role of the right and left eye in mediating light-dependent magnetic compass orientation and (2) interference from the spectral and intensity distribution of skylight at sunset with the response of the light-dependent magnetic compass.

Animal Migration↗
PubMed2001

Magnetic compass orientation in the blind mole rat Spalax ehrenbergi.

The blind mole rat Spalax ehrenbergi is a solitary, subterranean rodent that digs and inhabits a system of branching tunnels, with no above-ground exits, which it never leaves unless forced to. To survive, the mole rat must be able to orient efficiently in its tunnel system. The sensory channels available for spatial orientation in the subterranean environment are restricted in comparison with those existing above ground. This study examined the possibility that the mole rat is able to perceive and use the earth's magnetic field to orient in space. Experiments were performed using a device constructed from a pair of electromagnetic 'Helmholtz coils', which create a magnetic field whose direction and strength can be altered. In the first experiment, we tested a group of mole rats (N=33) in an eight-armed maze under the earth's natural magnetic field to determine whether they have directional preferences for the location of their sleeping nest, food chamber and toilet site. A second group of mole rats (N=30) was tested for their directional preference after the earth's magnetic field had been experimentally shifted by 180 degrees. We found that the first group exhibited a significant preference (P<0.001) to build both their sleeping nest and their food store in the southern sector of the maze, whereas the second group shifted the location of their nests (P<0.01) and food store (P<0.05), to the northern sector of the maze, corresponding to the shift in the magnetic field. In the second experiment, we tested whether the magnetic compass orientation found in the first experiment depends on a light stimulus by testing a group of mole rats in the eight-armed maze under total darkness. No significant difference in directional preference between light and dark test conditions was observed. It can be concluded, therefore, that, in contrast to some amphibians and birds, magnetic compass orientation in the mole rat is independent of light stimulation. In the third experiment, we examined whether mole rats (N=24) use the earth's magnetic field as a compass cue to orient in a labyrinth. In the first stage (trials 1-13), the animals were trained to reach a goal box at the end of a complex labyrinth until all individuals had learned the task. In the second stage (trial 14), half the trained mole rats underwent another labyrinth trial under the earth's natural magnetic field, while the other half were tested under a magnetic field shifted by 180 degrees. We found a significant decrease (P<0.001) in performance of the mole rats tested under the shifted magnetic field compared with the group tested under the natural magnetic field. The findings from these experiments prove that the mole rat is able to perceive and use the earth's magnetic field to orient in space.

Animals↗
PubMed2003

Radiographic findings before and after oral administration of a magnet in cows with traumatic reticuloperitonitis.

OBJECTIVE: To evaluate by use of radiography the efficacy of oral administration of magnets in the treatment of traumatic reticuloperitonitis in cows. ANIMALS: 90 cows referred because of indigestion. PROCEDURE: Radiography of the reticulum was performed. In all cows, radiographic findings revealed a metal foreign body in the reticulum. A magnet was administered orally, and the reticulum was again radiographed to assess the position of the magnet and to determine whether the foreign body was attached to the magnet. RESULTS: The magnet was observed in the reticulum in 75 cows and in the cranial aspect of the dorsal sac of the rumen in 9 cows; in 6 cows, the magnet was not observed. The foreign body was fully attached to the magnet in 49 cows. In 6 cows, the foreign body was in contact with the magnet but still penetrated the reticulum. In 24 cows, the foreign body did not contact the magnet, and in 11 cows, it was not clear whether the foreign body was attached to the magnet. A foreign body at an angle to the ventral aspect of the reticulum of > 3 degrees was less likely to become attached to a magnet, compared with a foreign body situated horizontally on the ventral aspect of the reticulum. A foreign body with no contact to the ventral aspect of the reticulum or a perforating foreign body was also less likely to become attached to a magnet. CONCLUSIONS AND CLINICAL RELEVANCE: Position of the foreign body within the reticulum greatly influences the efficacy of treatment with a magnet.

Animals↗
PubMed2002

Comparison of static and placebo magnets on resting forearm blood flow in young, healthy men.

STUDY DESIGN: Prospective, randomized, double-blind, placebo-controlled crossover design. OBJECTIVES: To examine the effects of static magnets on resting forearm blood flow and vascular resistance. BACKGROUND: Despite little scientific evidence indicating benefits of wearing static magnets, recent reports have indicated a dramatic increase in the usage of magnets to treat a variety of medical conditions. Magnet manufacturers have proposed that one mechanism for pain reduction involves magnet-related blood flow alterations to the affected area. METHODS AND MEASURES: Twenty young, healthy men (mean age +/- SD = 25 +/- 2 years) wore commercially available static magnets and placebos for 30 minutes on 2 separate occasions. Resting forearm blood flow was assessed in triplicate at minutes 10, 20, and 30, using venous occlusion plethysmography. Forearm vascular resistance was estimated by dividing mean arterial pressure by blood flow. RESULTS: The average blood flow over the 30-minute measurement period was not significantly different between the magnet and placebo sessions (mean +/- SD for magnet session = 1.40 +/- 0.63 ml blood x 100 ml tissue(-1) x min(-1); mean +/- SD for placebo session = 1.36 +/- 0.46 ml blood x 100 ml tissue(-1) x min(-1); P = 0.66). Blood flow measurements at minutes 10, 20, and 30 were also not significantly different between the magnet and placebo sessions, and forearm vascular resistance was not different between the magnet and placebo sessions at any time (P > 0.05). CONCLUSION: Exposure to static magnets for up to 30 minutes had the same effect on resting forearm blood flow and vascular resistance as placebo magnets. These data suggest that static magnets do not result in significant alterations in resting blood flow.

Adult↗
PubMed2002

[Preparation of surface functional magnetic microspheres and their application in nucleic acid separation and enzyme immobilization].

OBJECTIVE: To Prepare surface functional magnetic microspheres for the separation of vascular endothelial growth factor (VEGF) nucleic acid and lactase enzyme immobilization. METHODS: Using suspension polymerization methods to copolymerize MA-styrene containing magnetite nanoparticles and GMA-styrene also containing magnetite nanoparticles, respectively. Both the carboxyl-modified magnetic microspheres and epoxy-modified magnetic microspheres were obtained. In addition, the chloromethyl-modified magnetic microspheres were prepared by seedy microemulsion. The magnetic microspheres bound with b-gamma IgG were determined by radioimmunoassay (RIA), and the separation of VEGF nucleic acid and lactase enzyme immobilization were performed by carboxyl-modified magnetic microspheres. RESULTS: Transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and infrared (IR) spectra showed that the products of polymer magnetic microspheres were monodispersed and that the magnetic particles were uniformly distributed in the microsphere with special functional group on the surface of the microsphere. RIA showed that three kinds of magnetic microspheres could be bound with b-gamma IgG and the absorption of b-gamma IgG reached 75 micrograms/mg, especially for the carboxyl-modified magnetic microspheres. The carboxyl-modified magnetic microspheres can be used for the separation of VEGF nucleic acid by coupling with corresponding primer. Moreover, the immobilized enzyme was proportional to the amount of the carboxyl-modified magnetic microspheres. CONCLUSIONS: The surface functional magnetic polymer microspheres can be bound with active bio-substance, and have a wide application prospect in the fields of biology and medicine.

Adsorption↗
PubMed1994

[The effect of magnetic application for primary dysmenorrhea].

There was necessary to study that the magnetic application is effective to menstrual pain based on rogers theory about energy exchange. The purpose of this study was to examine the effectiveness of magnetic application in primary dysmenorrhea and so this study provide the basic information about nursing intervention of pain relief. The data was gathered from 23 student nurses at S University during the period of June 1. 1992 to October 5. 1992. This study was designed with control group pretest-posttest design to examine the effectiveness of magnetic application in primary dysmenorrhea. The subjects were experiencing self-reported dysmenorrhea above 5 scores measured by GRS during menstruation. The subjects were assigned randomly to one of two groups: 1) an experimental group (n = 11) that applied magnet (800-1299 gauss) or 2) a control group (n = 12) that applied nonmagnet. Both groups' pain level was assessed using the GRS (Graphic Rating Scale) which was developed by Scott and Huskisson (1976), and the ALPRSR (Adjective Labor Pain Rating Scale Rank) and ALPRSS (Adjective Labor Pain Rating Scale Score) which was developed by Park and Hur (1984). The pain level of experimental group was measured first 9 a.m. after beginning of dysmenorrhea, Md (3 hours after applied magnet) and 3 p.m. (3 hours after detached magnet). The pain level of control group was measured first 9 a.m. after beginning of dysmenorrhea, MD (3 hours after applied nonmagnet) and 3 p.m. (3 hours after detached nonmagnet). The both group applied magnet or nonmagnet on the suprapubic area, the bilateral lumbar 3 and above 4FB of the medial malleolus of tibial bilaterally. The research data was analyzed by SPSS/PC+. The results of this study were as follows: 1) 3 hours after applying magnet or nonmagnet (MD), The GRS mean rank was significant difference statistically (p = 0.0001). 2) 3 hours after applying magnet or nonmagnet (MD), the ALPRSR mean rank was significant difference statistically (p = 0.0106). 3) 3 hours after applying magnet or nonmagnet (MD), The ALPRSS mean rank was significant difference statistically (p = 0.0086). 4) 3 hours after detached magnet or nonmagnet (3 p.m.), the GRS mean rank was significant difference statistically (p = 0.0070). 5) 3 hours after detached magnet or nonmagnet (3 p.m.), the ALPRSR mean rank was significant difference statistically (p = 0.0317). 6) 3 hours after detached magnet or nonmagnet (3 p.m.), The ALPRSS mean rank was significant difference statistically (p = 0.0374).(ABSTRACT TRUNCATED AT 400 WORDS)

Dysmenorrhea↗
PubMed1997

Effect of magnetic resonance imaging on a new electromagnetic implantable middle ear hearing device.

OBJECTIVE: A 1.5-T magnetic resonance imager has been shown to be contraindicated for use in patients with pacemakers, cochlear implants, and neurostimulators. Our semi-implantable middle ear device uses a new adhesive bone cement. 4-META/MMA-TBB, for cementation of a 29-mg titanium-encased neodymium-iron-boron (NdFeB) magnet to the incus. METHODS: Five NdFeB magnets and four solid titanium cylinders were cemented onto the incus of five preserved human temporal bones and two cadaver heads. They were all inserted into a magnetic resonance imager and evaluated for possible disruption. RESULTS: Owing to the magnetic torque, the three magnets on the temporal bone were disrupted from the incus. The two cylinders on the temporal bones and the two cylinders and two magnets on the whole heads were not affected. The magnetic resonance imaging field did not affect the coercive force of the NdFeB magnets. CONCLUSION: The large torque produced by a magnetic resonance imager may disrupt the magnet-cement and cement-incus interfaces, causing dislodgement. We postulate that patients with implantable magnets on the incus should not undergo magnetic resonance imaging testing.

Cochlear Implants↗
PubMed2005

No effect of 85 mT permanent magnets on laser-Doppler measured blood flow response to inspiratory gasps.

Although no effects of permanent magnets on resting skin blood flow (SBF) in humans have yet been demonstrated, the possibility that magnet related effects might modify dynamic SBF changes has not been previously studied. We hypothesized that magnets may alter local neurovascular mechanisms to cause changes in normal SBF vasoactive responses. To test this, we studied the effects of a magnet on SBF reductions induced by sympathetic reflexes associated with deep inspirations. SBF was continuously monitored by a dual channel laser-Doppler flowmeter with probes on the middle finger dorsum of both hands of 24 healthy subjects. In the first of two successive intervals, each of the fingers rested on sham ceramic magnets (control interval). Subsequently, one finger rested on an active magnet and the other finger on a sham (experimental interval). Skin temperatures were also measured. The magnet was a 37 mm diameter x 14 mm thick ceramic magnet with a surface field strength of 85 mT measured in the geometrical center of the magnet. Field strength at the finger dorsum, 13 mm above magnet, was 31.5 mT. During each interval, three deep breaths were used to elicit SBF reductions. Responses were calculated as the percent reduction in SBF from its prior 20 s average. Breaths in each interval were spaced 3 min apart to permit full recovery between responses. The experimental interval started after an active magnet was in place for 20 min. Results showed no significant difference in either vasoconstrictive responses or skin temperature due to the magnet. We conclude that magnets of the type, strength and duration used, have no significant effect on vasoconstrictive processes associated with this sympathetic reflex in this group of healthy subjects.

Adult↗
PubMed1994

Magnetophoresis: I. Detection of magnetically labeled cells.

A new method for the detection of magnetically labeled cells in suspension using an optical microscope is presented. The movement of individual cells in a nonuniform magnetic field (magnetophoresis) can be studied and the direction and velocity of their movement can be determined. Cell-associated magnetic particles (e.g., attached magnetic immunomicrospheres) influence these parameters. We developed a magnetophoresis chamber for measuring the movement of single cells in a high-gradient magnetic field. Paramagnetic erythrocytes were used to monitor the level of magnetic force in the chamber. Bw6 antigen-positive REH cells were used as a biological model. Magnetic microspheres coupled with anti-Bw6 antibody were used as magnetic labels. The movement of magnetically labeled REH cells was investigated versus the intensity of magnetic field. The magnetization of microspheres was experimentally determined by the Faraday balance method. Experimental and theoretical results substantiate the feasibility of detecting a single cell associated with a single magnetic microsphere. Thus, magnetophoresis provides a sensitive biometrical system for magnetically labeled entities.

Humans↗
PubMed1998

The genotoxic potential of electric and magnetic fields: an update.

We review 23 studies on the potential genotoxicity of electric and magnetic fields that have appeared in the published literature since our 1993 review of 55 published studies (McCann et al., Mutat. Res. 297 (1993) 61-95) and six additional studies published prior to 1993, which were not previously reviewed. As in our previous review, internal electric fields present in media (for in vitro experiments) and in the torso (for in vivo experiments) were estimated. Individual experiments are evaluated using basic data quality criteria. The potential for genotoxicity of electric and magnetic fields is discussed in light of the significant body of genotoxicity data that now exists. Three unsuccessful attempts to replicate previously reported positive results have appeared since our previous review. We conclude that, in spite of the 34 studies reviewed in this and our previous publication that report positive genotoxic effects, none satisfy all of three basic conditions: independent reproducibility, consistency with the scientific knowledge base, and completeness according to basic data quality criteria. As we discuss, these criteria are satisfied for several groups of negative studies in several exposure categories (ELF magnetic fields, 150 microT-5 mT, combined ELF electric and ELF magnetic fields, approx. 0.2 mT, 240 mV/m, and static magnetic fields, 1-3.7 T). The evidence reviewed here strengthens the conclusion of our previous review, that the preponderance of evidence suggests that ELF electric or magnetic fields do not have genotoxic potential. Nevertheless, a pool of positive results remains, which have not yet been tested by independent replication. Among the 12 studies reviewed here, which report statistically significant or suggestive positive results, we point particularly to results from five laboratories [J. Miyakoshi, N. Yamagishi, S. Ohtsu, K. Mohri, H. Takebe, Increase in hypoxanthine-guanine phosphoribosyl transferase gene mutations by exposure to high-density 50-Hz magnetic fields, Mutat. Res. 349 (1996) 109-114; J. Miyakoshi, K. Kitagawa, H. Takebe, Mutation induction by high-density, 50-Hz magnetic fields in human MeWo cells exposed in the DNA synthesis phase, Int. J. Radiat. Biol. 71 (1997) 75-79; H. Lai. N.P. Singh, Acute exposure to a 60-Hz magnetic field increases DNA strand breaks in rat brain cells, Bioelectromagnetics, 18 (1997) 156-165; H. Lai, N.P. Singh, Melatonin and N-tert-butyl-alpha-phenylnitrone block 60-Hz magnetic field-induced DNA single and double strand breaks in rat brain cells, J. Pineal Res. 22 (1997) 152-162; T. Koana, M. Ikehata, M. Nakagawa, Estimation of genetic effects of a static magnetic field by a somatic cell test using mutagen-sensitive mutants of Drosophila melanogaster, Bioelectrochem. Bioenergetics 36 (1995) 95-100; F.L. Tabrah, H.F. Mower, S. Batkin, P.B. Greenwood, Enhanced mutagenic effect of a 60-Hz time-varying magnetic field on numbers of azide-induced TA100 revertant colonies, Bioelectromagnetics 15 (1994) 85-93; S. Tofani, A. Ferrara, L. Anglesio, G. Gilli, Evidence for genotoxic effects of resonant ELF magnetic fields, Bioelectrochem. Bioenergetics, 36 (1995) 9-13], which satisfy most basic data quality criteria and may be of interest.

Animals↗
PubMed2006

Giant reduction in dynamic modulus of kappa-carrageenan magnetic gels.

Effects of magnetization on the complex modulus of kappa-carrageenan magnetic gels have been investigated. The magnetic gel was made of a natural polymer, kappa-carrageenan, and a ferrimagnetic particle, barium ferrite. The complex modulus was measured before and after magnetization of the gel by dynamic viscoelastic measurements with a compressional strain. The gels showed a giant reduction in the storage modulus of approximately 10(7) Pa and also in the loss modulus of approximately 10(6) Pa due to magnetization. The reduction increased with increasing volume fraction of ferrite, and it was nearly independent of the frequency. It was also found that the change in the modulus was nearly independent of the magnetization direction and irradiation time of the magnetic fields to the gel. The magnetic gels demonstrating the giant reduction in the dynamic modulus showed a large nonlinear viscoelastic response. It was observed that the magnetic gel was deformed slightly due to magnetization. The observed giant complex modulus reduction could be attributed to the nonlinear viscoelasticity and deformation caused by magnetization. Magnetism, nonlinear viscoelasticity, and effects of magnetization on the morphological and shape changes were discussed.

Journal Article↗
PubMed2007

Calculation of static and dynamic linear magnetic response in approximate time-dependent density functional theory.

We report implementations and results of time-dependent density functional calculations (i) of the frequency-dependent magnetic dipole-magnetic dipole polarizability, (ii) of the (observable) translationally invariant linear magnetic response, and (iii) of a linear intensity differential (LID) which includes the dynamic dipole magnetizability. The density functional calculations utilized density fitting. For achieving gauge-origin independence we have employed time-periodic magnetic-field-dependent basis functions as well as the dipole velocity gauge, and have included explicit density-fit related derivatives of the Coulomb potential. We present the results of calculations of static and dynamic magnetic dipole-magnetic dipole polarizabilities for a set of small molecules, the LID for the SF6 molecule, and dispersion curves for M-hexahelicene of the origin invariant linear magnetic response as well as of three dynamic polarizabilities: magnetic dipole-magnetic dipole, electric dipole-electric dipole, and electric dipole-magnetic dipole. We have also performed comparison of the linear magnetic response and magnetic dipole-magnetic dipole polarizability over a wide range of frequencies for H2O and SF6.

Journal Article↗
PubMed2001

Nonlinear turbulent magnetic diffusion and mean-field dynamo.

The nonlinear coefficients defining the mean electromotive force (i.e., the nonlinear turbulent magnetic diffusion, the nonlinear effective velocity, the nonlinear kappa tensor, etc.) are calculated for an anisotropic turbulence. A particular case of an anisotropic background turbulence (i.e., the turbulence with zero-mean magnetic field) with one preferential direction is considered. It is shown that the toroidal and poloidal magnetic fields have different nonlinear turbulent magnetic diffusion coefficients. It is demonstrated that even for a homogeneous turbulence there is a nonlinear effective velocity that exhibits diamagnetic or paramagnetic properties depending on the anisotropy of turbulence and the level of magnetic fluctuations in the background turbulence. The diamagnetic velocity results in the field being pushed out from the regions with stronger mean magnetic field, while the paramagnetic velocity causes the magnetic field to be concentrated in the regions with stronger field. Analysis shows that an anisotropy of turbulence strongly affects the nonlinear turbulent magnetic diffusion, the nonlinear effective velocity, and the nonlinear alpha effect. Two types of nonlinearities (algebraic and dynamic) are also discussed. The algebraic nonlinearity implies a nonlinear dependence of the mean electromotive force on the mean magnetic field. The dynamic nonlinearity is determined by a differential equation for the magnetic part of the alpha effect. It is shown that for the alphaOmega axisymmetric dynamo the algebraic nonlinearity alone (which includes the nonlinear alpha effect, the nonlinear turbulent magnetic diffusion, the nonlinear effective velocity, etc.) cannot saturate the dynamo generated mean magnetic field while the combined effect of the algebraic and dynamic nonlinearities limits the mean magnetic field growth.

Journal Article↗