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PubMed2002

Magnetic resonance imaging characterization of hemorrhagic transformation of embolic stroke in the rat.

Intracranial hemorrhage is a critical factor when considering efficacy and safety of thrombolytic intervention after thromboembolic stroke. This study tested whether magnetic resonance imaging could identify tissue for hemorrhagic transformation after the onset of embolic stroke. Rats subjected to embolic stroke with and without recombinant tissue-type plasmogen activator (rt-PA) treatment were followed-up with magnetic resonance imaging using the inverse of the apparent forward transfer rate for magnetization transfer (k(inv)), gadolinium-chelate contrast-enhanced magnetic resonance imaging, and diffusion-, perfusion-, and T2-weighted imaging. Rats with embolic stroke either were treated with rt-PA 1 (n = 16) or 4 hours (n = 13) after stroke onset or were not treated (n = 15). From these groups, at total of 17 rats had intracerebral hemorrhage. Tissue progressing to hemorrhage and adjacent to the site of hemorrhage was analyzed to identify magnetic resonance imaging markers that characterize hemorrhagic transformation. The parameter maps of k(inv) and contrast-enhanced magnetic resonance imaging showed greater sensitivity in the detection of tissue destined for hemorrhagic transformation compared with the apparent diffusion coefficient of water (ADCw) and CBF. In tissue not destined to undergo hemorrhagic transformation, k(inv) maps and contrast-enhanced magnetic resonance imaging exhibited small increases in k(inv) and contrast-enhanced magnetic resonance imaging signal intensity in the area encompassing the territory supplied by the middle cerebral artery. In contrast, large increases in k(inv) and in signal intensity in the contrast-enhanced magnetic resonance images were detected in the region where gross hemorrhage was confirmed histologically. The values of k(inv), T2, and signal intensity in the contrast-enhanced magnetic resonance images were significantly higher in the region destined for hemorrhagic transformation (k(inv), P < or = 0.033 3-24 hours after embolization; T2, P < or = 0.037 24-48 hours; contrast-enhanced magnetic resonance imaging, P < 0.05 4-7 hours) compared with the nonhemorrhagic transformation ischemic region or in the contralateral homologous regions after onset of ischemia. Of these methods, k(inv) shows the most sensitivity in the detection of hemorrhagic transformation soon after embolization. The authors' data suggest that k(inv) and contrast-enhanced magnetic resonance imaging are potentially important methodologies for detecting tissue destined for hemorrhagic transformation.

Animals↗
PubMed1997

Transcutaneous pressure-adjustable valves and magnetic resonance imaging: an ex vivo examination of the Codman-Medos programmable valve and the Sophy adjustable pressure valve.

OBJECTIVE: We investigated the compatibility of magnetically adjustable cerebrospinal fluid valves with clinical magnetic resonance imaging. Torque acting on the valves, subjective sensations of valve-carrying volunteers, extension of artifacts on acquired images, changes in valve pressure setting, and accurate valve function after repeated exposure to the magnetic field were tested. METHODS: Two externally adjustable differential pressure valves, i.e., the Codman-Medos programmable valve (Medos S.A., Le Locle, Switzerland) (n = 5) and the Sophy programmable pressure valve (Sophysa, Orsay, France) (Model SP3, n = 4; Model SU8, n = 3; and Model SM8, n = 2) were exposed to the magnetic fields of 1.5-T clinical scanners. Ferromagnetic properties were investigated according to an established protocol. Subjective sensations during positioning and scanning and image artifacts were investigated using standard clinical imaging protocols. Changes in opening pressure setting during repeated magnetic field exposure were examined using valves affixed to a dummy. RESULTS: Deflection forces measured 117 dynes in the Medos valve, and 2439 (Model SP3), 2172 (Model SU8) and 1914 (Model SM8) dynes in the Sophy valves. Torque during positioning and during imaging was reported for the Sophy valves. Distortion of the magnetic field with artifacts on acquired images ranged 6 x 6 x 12 cm around the Sophy valve and 4 x 4 x 4 cm around the Medos valves. Artifact extension increased with longer TE times on T2-weighted images and when using gradient-echo sequences. The pressure setting of the Medos valves did not change in 31 of 88 tests. Below 170 mm H2O, the maximal disadjustment was 60 mm H2O in each direction. Minor changes of the pressure setting were observed at 50 and 30 mm H2O. In 11 of 15 tests at 200 mm H2O, the setting after magnetic field exposure was below 30 mm H2O. One Medos valve could no longer be programmed after being exposed four times to the static magnetic field. Sophy valves remained at or changed to "high" in 68 of 81 tests and to "low" in 9. All Sophy valves exhibited paramagnetic behavior after the tests. All remained programmable. Observed changes always occurred within the safety area of the magnet. CONCLUSION: Subjective disturbances resulting from paramagnetic valve behavior are absent in Medos valves and are minor in Sophy valves. Image artifacts require careful planning of valve position. Artifacts observed in magnetic resonance imaging are less disturbing than those observed in computed tomography. Medos valves are more stable regarding disadjustment than are Sophy valves. Radiological control of valve setting after exposure to the magnetic field is mandatory in both. The 0.5-mT safety line encircling the area that patients with pacemakers should not enter is a useful safety borderline for patients with pressure-adjustable valves. Failure of the programming mechanism of one Medos valve after several exposures to the magnetic field requires clarification.

Artifacts↗
PubMed2003

The role of magnetic resonance imaging in the management of vascular malformations of the trunk and extremities.

Vascular malformations can usually be diagnosed on clinical grounds. They have a well-defined appearance on magnetic resonance imaging, which can effectively determine their tissue and flow characteristics. However, the role of cross-sectional imaging in the management of vascular malformations is not well defined. Most reviews suggest that magnetic resonance imaging should be reserved for cases in which the extent of the lesion cannot be estimated on physical examination. However, to date no group has compared the accuracy of physical examination alone to that of magnetic resonance imaging in determining this extent. A review was performed of all the patients evaluated for vascular malformations at the New York University Trunk and Extremity Vascular Anomalies Conference between July of 1994 and August of 1999. Patients who underwent magnetic resonance evaluation at other institutions and whose images were not available for review were excluded. All study patients either underwent magnetic resonance imaging examination at New York University Medical Center or had outside films reviewed at the center. The physical examination findings were compared with the magnetic resonance findings and the surgeon and radiologist made a joint decision about whether there was a correlation between the magnetic resonance and physical examination findings. Fifty-eight patients met the study criteria, 44 (76 percent) of whom were found to have more extensive disease on magnetic resonance examination than appreciated on physical examination. Of the 51 patients with low-flow vascular malformations (venous vascular malformations, lymphatic malformations, and capillary malformations), 39 (76 percent) had more extensive disease on magnetic resonance examination than on physical examination. Of the seven patients with high-flow arteriovenous malformations, five had more extensive disease on magnetic resonance. In all of the 44 patients whose magnetic resonance imaging findings did not correlate with those of the physical examination, therapeutic decision making was affected. Contrary to the conventional wisdom of published reviews, physical examination findings significantly underestimated the extent of vascular malformations in the majority of cases. Magnetic resonance imaging should be performed in all patients with vascular malformations of the trunk and extremities before therapy is planned. In an age when physicians are asked to justify their decisions, especially where the use of expensive diagnostic modalities is concerned, the situations in which these tests are indispensable must be clearly defined or else patients will be denied access to them.

Adolescent↗
PubMed2006

MR-guided radiofrequency ablation: do magnetic fields influence extent of coagulation in ex vivo bovine livers?

PURPOSE: To prospectively determine if static magnetic fields of magnetic resonance (MR) imagers affect radiofrequency (RF) ablation coagulation volume and shape. MATERIALS AND METHODS: Ex vivo RF ablations of bovine livers were performed with magnetic field strengths of 0.2, 1.5, and 3.0 T and were compared with ablations performed outside the magnetic field in a control group. Two MR-compatible monopolar RF devices (internally cooled single and cluster electrodes) were systematically tested. Length of long axis (y-axis), length of two short axes (x- and z-axes), and coagulation volume and shape measured outside and inside different magnetic fields were compared with the Dunnett test. Significance level was set to .05. RESULTS: For the single electrode, no significant difference was observed between length of short axes and coagulation volume and shape measured inside and outside the magnetic field. Mean x- and z-axis lengths were 2.3 and 2.6 cm, respectively, outside the magnetic field; 2.4 and 2.4 cm, respectively, at 0.2 T; 2.5 and 2.6 cm, respectively, at 1.5 T; and 2.2 and 2.5 cm, respectively, at 3.0 T. Differences between length of long axis, length of short axis perpendicular to static magnetic field, and coagulation volume and shape achieved with the cluster electrode inside and outside the magnetic field were not significant. Mean x- and z-axis lengths were 3.9 and 3.9 cm, respectively, outside the magnetic field; 3.7 and 3.8 cm, respectively, at 0.2 T; 4.0 and 4.3 cm, respectively, at 1.5 T; and 3.8 and 3.8 cm, respectively, at 3.0 T. Differences between ablations performed at 1.5 T and those performed in the control group with the cluster electrode were significant (P = .026). In this case, a difference of 4 mm in the length of the short axis parallel to the magnetic field was detected, but there was no significant difference in coagulation volume. CONCLUSION: No significant differences in coagulation volume and shape could be recorded between RF ablations performed outside and those performed inside the static magnetic field.

Animals↗
PubMed1997

[Development and transition of magnetic attachments--a literature review].

In the 1950 s, a new method of using magnets for the retainers of removable partial dentures (RPDs) was developed. It utilized magnetic attractive force instead of mechanical friction. However, the magnets used in those days were Alnico, Ferrite and/or Pt-Cobalt magnets and their retentive force was not strong enough to stabilize the dentures. Therefore, they gradually went out of use. In the middle of the 1970 s, Samarium Cobalt magnets, which have strong magnetic characteristics, were developed and introduced into dental field. In 1976, Sasaki first applied the samarium cobalt magnets to the retainers of PPDs. While in 1981, Mizutani, et al. first used well-fitted ferromagnetic alloy and the magnet for the purpose of stabilizing the RPD. Since then, many researchers have developed devices such as the magnetic retainer and the closed field magnetic attachment placed on the market in 1992. Now, as for the popular retainer of RPD, one can easily use a smaller yet stronger magnetic attachment which uses Neodium rather than Samarium Cobalt magnet.

Dental Alloys↗
PubMed2003

Behavioral effects of high-strength static magnetic fields on rats.

Advances in magnetic resonance imaging are driving the development of more powerful and higher-resolution machines with high-strength static magnetic fields. The behavioral effects of high-strength magnetic fields are largely uncharacterized, although restraint within a 9.4 T magnetic field is sufficient to induce a conditioned taste aversion (CTA) and induce brainstem expression of c-Fos in rats. To determine whether the behavioral effects of static magnetic fields are dependent on field strength, duration of exposure, and orientation with the field, rats were restrained within the bore of 7 or 14 T superconducting magnets for variable durations. Behavioral effects were assessed by scoring locomotor activity after release from the magnetic field and measuring CTA acquisition after pairing intake of a palatable glucose and saccharin (G+S) solution with magnetic field exposure. Magnetic field exposure at either 7 or 14 T suppressed rearing and induced tight circling. The direction of the circling was dependent on the rat's orientation within the magnetic field: if exposed head-up, rats circled counterclockwise; if exposed head-down, rats circled clockwise. CTA was induced after three pairings of taste and 30 min of 7 T exposure or after a single pairing of G+S and 1 min of 14 T exposure. These results suggest that magnetic field exposure has graded effects on rat behavior. We hypothesize that restraint with high-strength magnetic fields causes vestibular stimulation resulting in locomotor circling and CTA acquisition.

Animals↗
PubMedDate not supplied

Magnetization transfer MR of the normal adult brain.

PURPOSE: To establish a normal baseline of the percent magnetization transfer of gray (cortical and deep) and white matter structures in the brain in healthy adults and to determine whether there are adult age-related differences in these measurements. METHODS: Axial T1-weighted scans (800/20 [repetition time/echo time]) with and without magnetization transfer were prospectively performed on a 1.5-T MR imaging unit on 68 healthy patients (aged 20 to 76 years). Presaturation and postsaturation magnetization transfer images were obtained using an on-resonance binomial pulse. All patients had normal MR scans on all pulse sequences. A calculated "difference" image was used to calculate the percent magnetization transfer in multiple specific regions of the brain. In each hemisphere, 9 discrete areas of cortical and deep gray matter and 29 areas of white matter were measured in 68 patients to generate age-related changes in percent magnetization transfer in these anatomic regions. Ranges of normal percent magnetization transfer in each of the 38 measures were established. RESULTS: The percent magnetization transfer of the gray matter (28% +/- 2%) was lower than that of the white matter (36% +/- 2%). There was no statistically significant difference in the percent magnetization transfer in different areas of gray matter. Deep white matter in the different lobes (percent magnetization transfer, 31% to 38%) also showed no differences by age. Percent magnetization transfer was the highest in the genu of the corpus callosum (42%), and this was statistically significant compared with other white matter measurements. CONCLUSION: There were no statistically significant age-related variations in the percent magnetization transfer in healthy adults in gray or white matter. These percent magnetization transfer measurements provide baseline normative data, which can be used to measure the extent and severity of white matter changes in disease states.

Adult↗
PubMed2003

Testing the cytotoxicity of metal alloys used as magnetic prosthetic devices.

Technical magnetic materials are increasingly used for the development of magnetic retained dental prosthetic and orofacial epithetic devices. Since most of the magnets based on rare earth metals, such as samarium-cobalt based alloys have a high tendency for corrosion they were first coated by tin and then encapsulated by titanium. However, the high mechanical load particularly on dental devices may cause a rupture of the titanium capsule and the alloys contact directly biological fluids. Hence, it is important to know the cytotoxicity of these magnets to assess their potential effects on the surrounding tissue. In this study, the cytotoxicity of neodymium-iron-boron and samarium-cobalt (plain, tin and titanium coated) magnets was tested. First, magnets were incubated up to 7 days in culture medium to prepare extracts for cytotoxicity measurements. Changes in the surface morphology due to corrosion were visualized by scanning electron microscopy and analysis of the elemental composition. 3T3 mouse fibroblasts were cultured in the presence of extracts and their viability measured by neutral red and metabolic assays. To learn more about a possible toxic activity of the main components of magnets, salt solutions of different concentrations resembling those elements, which are main constituents of the magnets, were used. 3T3 fibroblasts were also cultured in direct contact with the materials and material induced effects on cell morphology and growth monitored by microscopy. As a result of this study it was found that samarium-cobalt magnets have a strong tendency for corrosion and exert a considerable cytotoxicity. Neodymium-iron-boron magnets have a lesser tendency for corrosion and are only moderate cytotoxic. Coating of samarium-cobalt magnets with tin or titanium makes the materials non-toxic. Application of salt solutions shows that cobalt has a tendency to be cytotoxic at higher concentrations, but enhances cell metabolism and proliferation at lower concentrations while the other magnet constituents had a lower or negligible cytotoxic potential.

Journal Article↗
PubMed2007

High-temperature metal-organic magnets.

For over two decades there have been intense efforts aimed at the development of alternatives to conventional magnets, particularly materials comprised in part or wholly of molecular components. Such alternatives offer the prospect of realizing magnets fabricated through controlled, low-temperature, solution-based chemistry, as opposed to high-temperature metallurgical routes, and also the possibility of tuning magnetic properties through synthesis. However, examples of magnetically ordered molecular materials at or near room temperature are extremely rare, and the properties of these materials are often capricious and difficult to reproduce. Here we present a versatile solution-based route to a new class of metal-organic materials exhibiting magnetic order well above room temperature. Reactions of the metal (M) precursor complex bis(1,5-cyclooctadiene)nickel with three different organics A-TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)--proceed via electron transfer from nickel to A and lead to materials containing Ni(II) ions and reduced forms of A in a 2:1 Ni:A ratio--that is, opposite to that of conventional (low Curie temperature) MA(2)-type magnets. These materials also contain oxygen-based species within their architectures. Magnetic characterization of the three compounds reveals spontaneous field-dependent magnetization and hysteresis at room temperature, with ordering temperatures well above ambient. The unusual stoichiometry and striking magnetic properties highlight these three compounds as members of a class of stable magnets that are at the interface between conventional inorganic magnets and genuine molecule-based magnets.

Journal Article↗
PubMed2005

Analysis of magnetization in nanocomposite Nd4.5(Fe,Cr)77B18.5 by electron holography and simulation.

Magnetization distribution in nanocomposite Nd4.5(Fe,Cr)77B18.5 was studied by electron holography and computer simulation. In order to understand the detailed magnetization distribution, the magnetic flux distribution was calculated taking into account the magnetic charge or the stray field on the basis of magnetization models consisting of small magnetic dipoles and was compared with that in reconstructed phase images experimentally observed. Through the comparison, the characteristic feature in the distribution of the magnetization distribution in the nanocomposite magnetic materials was clarified, and the distribution was found to well correspond to their magnetic properties. It is pointed out that for understanding magnetization, the interpretation of reconstructed phase images should be done through computer simulation just as the analysis of high-resolution electron microscope images. Eventually, it was demonstrated that electron holography with computer simulation is quite useful to analyze detailed magnetization distribution in nanocrystalline magnetic materials at the nanometer scale.

Journal Article↗
PubMedDate not supplied

Best quality patient care: a historical perspective on Magnet hospitals.

Donabedian's Structure-Process-Outcome paradigm is used to analyze the evolution and research on the concept of magnetism through 4 phases. The identifying foci of the original 1983 study were 4 outcomes. A large number and array of structural features were derived from the identified Magnet hospitals. The quest for excellence in nursing care continued with the Gold Standard of Magnetism case studies utilizing all identified Magnet structures, processes, and outcomes. The advent of the American Nurses Credentialing Center Magnet Recognition Program stimulated much valuable and insightful research related to outcomes associated with the large group of magnetic structures. Magnet hospital staff nurses (SNs) identification of processes/functions most essential to quality patient care highlights the Process phase. Many of the vast array of structural features attributed to Magnet hospital in 1983 are outdated and differentially defined and have not been tested for their relationship to either processes or outcomes. Identification of magnetism from an SN perspective has lagged. Recommendations include updating and clarifying structural criteria; increasing focus on the SN perspective of magnetism by continuing identification of processes; and challenging leadership in Magnet hospitals to initiate multisite evidence-based practice initiatives to link structures with process-enabling outcomes. Now may well be the time for nursing to exert leadership in expanding the Magnet concept to the total patient-care operation in a hospital.

Awards and Prizes↗
PubMed1993

Assessing human exposure to power-frequency electric and magnetic fields.

This paper reviews published literature and current problems relating to the assessment of occupational and residential human exposures to power-frequency electric and magnetic fields. Available occupational exposure data suggest that the class of job titles known as electrical workers may be an effective surrogate for time-weighted-average (TWA) magnetic-field (but not electric-field) exposure. Current research in occupational-exposure assessment is directed to the construction of job-exposure matrices based on electric- and magnetic-field measurements and estimates of worker exposures to chemicals and other factors of interest. Recent work has identified five principal sources of residential magnetic fields: electric power transmission lines, electric power distribution lines, ground currents, home wiring, and home appliances. Existing residential-exposure assessments have used one or more of the following techniques: questionnaires, wiring configuration coding, theoretical field calculations, spot electric- and magnetic-field measurements, fixed-site magnetic-field recordings, personal- exposure measurements, and geomagnetic-field measurements. Available normal-power magnetic-field data for residences differ substantially between studies. It is not known if these differences are due to geographical differences, differences in measurement protocols, or instrumentation differences. Wiring codes and measured magnetic fields (but not electric fields) are associated weakly. Available data suggest, but are far from proving, that spot measurements may be more effective than wire codes as predictors of long-term historical magnetic-field exposure. Two studies find that away-from-home TWA magnetic-field exposures are less variable than at-home exposures. The importance of home appliances as contributors to total residential magnetic-field exposure is not known at this time. It also is not known what characteristics (if any) of residential electric and magnetic fields are determinants of human health effects.

Electric Wiring↗
PubMed1992

Detection of extraordinary large bio-magnetic field strength from human hand during external Qi emission.

It is generally accepted that more than 10(-6) gauss order magnetism was not detected in normal human condition. However, we detected 10(-3) gauss (mGauss) order bio-magnetic field strength from the palm in special persons who emitted External Qi ("Chi" or "Ki"). This detection was possible by special arranged magnetic field detection system, consisted of a pair of 2 identical coils with 80,000 turns and a high sensitivity amplifier. Each of the coils were rolled 80,000 turns accurately, and were connected in series in opposite direction, actuating as a gradiometer. We measure bio-magnetic field strength in 37 subjects with this detection system. The only 3 subjects of them exhibited strong bio-magnetic field of 2 to 4 mGauss in frequency range of 4 to 10 Hz. This magnetic field strength was greater than that of normal human bio-magnetism by 1,000 times at least. A simultaneous measurement of bio-magnetic field strength and its corresponding bio-electric current was examined in one subject. During exhibiting such strong bio-magnetism, its corresponding electric current was not detectable. Therefore, the extra-ordinary large bio-magnetic field strength can not derive from internal body current alone, hence the origin of the large bio-magnetism is still unknown. We suppose that the extraordinary large bio-magnetic field strength might be originated from "Qi" energy in the oriental medicine or in the oriental traditional philosophy.

Electromagnetic Fields↗
PubMed1999

NTP Toxicology and Carcinogenesis Studies of 60-HZ Magnetic Fields IN F344/N Rats and B6C3F1 Mice (Whole-body Exposure Studies).

Electric and magnetic fields (EMF) are associated with the production, transmission, and use of electricity; thus, the potential for human exposure is high. These electric and magnetic fields are predominantly of low frequency (60 Hz in the United States and 50 Hz in Europe) and generally of low intensity. Epidemiology studies have suggested a potential for increased breast cancer, brain cancer, and leukemia rates with increasing magnetic field exposure. Therefore, given the widespread exposure to low-intensity, 60-Hz magnetic fields in industrialized societies, standard toxicology studies and long-term carcinogenesis studies were conducted using traditional rodent models. Male and female F344/N rats and B6C3F1mice were exposed to 60-Hz magnetic fields by whole-body exposure for 2 years. 2-YEAR STUDY IN RATS: Groups of 100 male and 100 female rats were exposed to 60-Hz magnetic fields at intensities of 0.02, 2, or 10 G for 18.5 hours per day, 7 days per week, for 106 weeks. Groups of 100 male and 100 female control rats were housed in the same exposure chambers without applied magnetic fields. Additional groups of 100 male and 100 female rats were intermittently exposed (1 hour on and 1 hour off) to a 10 G 60-Hz field 18.5 hours per day, 7 days per week, for 106 weeks. The highest field intensity (10 G) is approximately 5,000-fold greater than what was considered high intensity for homes in epidemiology studies in humans. Survival and Body Weights: Survival and mean body weights of exposed groups of male and female rats was similar to those of the control groups. Pathology Findings: The incidences of thyroid gland C-cell adenoma and carcinoma in 0.02 G male rats, adenoma in 2 G males, and adenoma or carcinoma (combined) in 0.02 and 2 G males were significantly greater than in the control group. The incidence of mononuclear cell leukemia in males in the 10 G intermittent group was significantly less than in the control group. 2-YEAR STUDY IN MICE: Groups of 100 male and 100 female mice were exposed to 60-Hz magnetic fields at intensities of 0.02, 2, or 10 G for 18.5 hours per day, 7 days per week, for 106 weeks. Groups of 100 male and 100 female control mice were housed in the same exposure chambers without applied magnetic fields. Additional groups of 100 male and 100 female mice were intermittently exposed (1 hour on and 1 hour off) to a 10 G 60-Hz field 18.5 hours per day, 7 days per week, for 106 weeks. Survival and Body Weights: Survival of male mice exposed to 10 G was significantly less than that of control mice after 2 years; survival of all other exposed groups of mice was similar to that of control mice. Mean body weights of exposed groups of male and female mice were similar to those of the control groups throughout the study. Pathology Findings: The incidences of alveolar/bronchiolar adenoma were significantly decreased in 0.02 and 2 G male mice and 2 G female mice relative to the control groups; the incidences of alveolar/bronchiolar adenoma or carcinoma (combined) were significantly less in males and females exposed to 2 G than in the control groups. In female mice, the incidence of malignant lymphoma in the 10 G intermittent group was significantly less than in the controls. CONCLUSIONS: Under the conditions of these 2-year whole-body exposure studies, there was equivocal evidence of carcinogenic activity of 60-Hz magnetic fields in male F344/N rats based on increased incidences of thyroid gland C-cell neoplasms in the 0.02 and 2G groups. There was no evidence of carcinogenic activity in female F344/N rats or male or female B6C3F1 mice exposed to 0.02, 2, or 10 G, or 10 G intermittent 60-Hz magnetic fields. In exposed rats and mice there were no increased incidences of neoplasms at sites for which epidemiology studies have suggested an association with magnetic fields (brain, mammary gland, leukemia).

Journal Article↗
PubMed1986

A gross morphologic, histologic, hematologic, and blood chemistry study of adult and neonatal mice chronically exposed to high magnetic fields.

Six sets of Charles River CD-1 mice (3 sets of adults and 3 sets of offspring: 156 mice total) were raised for varying times (360 h over 1 month to 624 h over 3 months) in a 1.89-T magnetic field. Each set was divided into 3 groups: control group raised in the animal facility (Control); control group raised in the magnet room but not in the magnet (Magnet-Controls); experimental group raised in the magnet (Magnet). At the end of each predefined exposure period, the mice were euthanized and studied. Body and organ weights were lower in 3 of 6 sets in the Magnet groups when compared to Control groups, but they were not significantly different from age matched, sex matched Magnet-Controls. This seems to indicate that the decreased growth of mice was due to the laboratory environment surrounding the magnet, when compared to the animal facility environment, rather than to magnetic field effects. No consistent differences were found in gross and microscopic morphology, hematocrit and white blood cell counts, plasma creatine phosphokinase, lactic dehydrogenase, cholesterol, triglyceride, or protein concentrations in Magnet groups compared to the two control groups.

Animals↗
PubMed2006

Dynamics of paramagnetic agents by off-resonance rotating frame technique in the presence of magnetization transfer effect.

The simple method for measuring the rotational correlation time of paramagnetic ion chelates via off-resonance rotating frame technique is challenged in vivo by the magnetization transfer effect. A theoretical model for the spin relaxation of water protons in the presence of paramagnetic ion chelates and magnetization transfer effect is described. This model considers the competitive relaxations of water protons by the paramagnetic relaxation pathway and the magnetization transfer pathway. The influence of magnetization transfer on the total residual z-magnetization has been quantitatively evaluated in the context of the magnetization map and various difference magnetization profiles for the macromolecule conjugated Gd-DTPA in cross-linked protein gels. The numerical simulations and experimental validations confirm that the rotational correlation time for the paramagnetic ion chelates can be measured even in the presence of strong magnetization transfer. This spin relaxation model also provides novel approaches to enhance the detection sensitivity for paramagnetic labeling by suppressing the spin relaxations caused by the magnetization transfer. The inclusion of the magnetization transfer effect allows us to use the magnetization map as a simulation tool to design efficient paramagnetic labeling targeting at specific tissues, to design experiments running at low RF power depositions, and to optimize the sensitivity for detecting paramagnetic labeling. Thus, the presented method will be a very useful tool for the in vivo applications such as molecular imaging via paramagnetic labeling.

Algorithms↗
PubMed1994

Empirical test of an ion parametric resonance model for magnetic field interactions with PC-12 cells.

A companion paper describes a predictive ion parametric resonance (IPR) model of magnetic field interactions with biological systems based on a selective relation between the ratio of the flux density of the static magnetic field to the AC magnetic field and the charge-to-mass ratio of ions of biological relevance. Previous studies demonstrated that nerve growth factor (NGF)-stimulated neurite outgrowth (NO) in PC-12 cells can be inhibited by exposure to magnetic fields as a function of either magnetic field flux density or AC magnetic field frequency. The present work examines whether the PC-12 cell response to magnetic fields is consistent with the quasi-periodic, resonance-based predictions of the IPR model. We tested changes in each of the experimentally controllable variables [flux densities of the parallel components of the AC magnetic field (Bac) and the static magnetic field (Bdc) and the frequency of the AC magnetic field] over a range of exposure conditions sufficient to determine whether the IPR model is applicable. A multiple-coil exposure system independently controlled each of these critical quantities. The perpendicular static magnetic field was controlled to less than 2 mG for all tests. The first set of tests examined the NO response in cells exposed to 45 Hz Bac from 77 to 468 mG(rms) at a Bdc of 366 mG. Next, we examined an off-resonance condition using 20 mG Bdc with a 45 Hz AC field across a range of Bac between 7.9 and 21 mG(rms). Finally, we changed the AC frequency to 25 Hz, with a corresponding change in Bdc to 203 mG (to tune for the same set of ions as in the first test) and a Bac range from 78 to 181 mG(rms). In all cases the observed responses were consistent with predictions of the IPR model. These experimental results are the first to support in detail the validity of the fundamental relationships embodied in the IPR model.

Animals↗
PubMed1995

Hypothesis: the risk of childhood leukemia is related to combinations of power-frequency and static magnetic fields.

We present a hypothesis that the risk of childhood leukemia is related to exposure to specific combinations of static and extremely-low-frequency (ELF) magnetic fields. Laboratory data from calcium efflux and diatom mobility experiments were used with the gyromagnetic equation to predict combinations of 60 Hz and static magnetic fields hypothesized to enhance leukemia risk. The laboratory data predicted 19 bands of the static field magnitude with a bandwidth of 9.1 microT that, together with 60 Hz magnetic fields, are expected to have biological activity. We then assessed the association between this exposure metric and childhood leukemia using data from a case-control study in Los Angeles County. ELF and static magnetic fields were measured in the bedrooms of 124 cases determined from a tumor registry and 99 controls drawn from friends and random digit dialing. Among these subjects, 26 cases and 20 controls were exposed to static magnetic fields lying in the predicted bands of biological activity centered at 38.0 microT and 50.6 microT. Although no association was found for childhood leukemia in relation to measured ELF or static magnetic fields alone, an increasing trend of leukemia risk with measured ELF fields was found for subjects within these static field bands (P for trend = 0.041). The odds ratio (OR) was 3.3 [95% confidence interval (CI) = 0.4-30.5] for subjects exposed to static fields within the derived bands and to ELF magnetic field above 0.30 microT (compared to subjects exposed to static fields outside the bands and ELF magnetic fields below 0.07 microT). When the 60 Hz magnetic fields were assessed according to the Wertheimer-Leeper code for wiring configurations, leukemia risks were again greater with the hypothesized exposure conditions (OR = 9.2 for very high current configurations within the static field bands; 95% CI = 1.3-64.6). Although the risk estimates are based on limited magnetic field measurements for a small number of subjects, these findings suggest that the risk of childhood leukemia may be related to the combined effects of the static and ELF magnetic fields. Further tests of the hypothesis are proposed.

Calcium↗