Effects of exposure of CHO-K1 cells to a 10-T static magnetic field

PURPOSE: To evaluate whether exposure to strong static magnetic fields (SMFs), of up to 10 T, affects the growth and cycle distribution of and the micronucleus formation in monolayered Chinese hamster ovary CHO-K1 cells. MATERIALS AND METHODS: The authors developed a system to expose cultured cells to strong SMFs immediately after the cells are seeded. Cell growth rate was evaluated according to cell number count. Cell cycle distribution experiments were performed by using flow cytometric analysis. In these experiments, the cells were exposed to SMFs for up to 4 days. The frequency of micronucleus formation with only SMF exposure at x-ray irradiation was analyzed at microscopic observation. RESULTS: Long-term exposure to a 10-T SMF for up to 4 days did not affect cell growth rate or cell cycle distribution. Exposure to SMFs alone did not affect micronucleus frequency. In x-ray-irradiated cells, exposure to a 1-T SMF did not affect micronucleus frequency, but exposure to a 10-T SMF resulted in a significant (P <.05) increase in micronucleus frequency. CONCLUSION: Strong (10-T) SMFs have no effect on cell growth, cell cycle distribution, or micronucleus frequency, but they may cause an increase in the micronucleus formation induced by 4-Gy x rays.     

Exposure to a 1.5-T static magnetic field does not alter body and skin temperatures in man

The literature has conflicting reports concerning the effect of static magnetic fields on body and skin temperatures in mammals. Since temperature changes induced by static magnetic fields would have important safety implications for clinical magnetic resonance imaging body (sublingual pocket) and skin (abdomen, forehead, chest, upper arm, forearm, thigh, and calf) temperatures were determined in six normal subjects using a fluoroptic thermometry system during a 20-min exposure to a 1.5-T static magnetic field. Ambient conditions were controlled and held constant. An analysis of variance for repeated measures revealed that there were no statistically significant changes in body or any of the skin temperatures recorded. We conclude that exposure for 20 min to a 1.5-T static magnetic field does not alter body and skin temperatures in man.     

Three-dimensional mapping of the static magnetic field inside the human head

Finite element analysis was used to calculate the static magnetic field within the three-dimensional head model. Localized field distributions were evaluated by using the magnetic field histogram technique. Experimental field maps and histograms of the human head were also obtained to validate the simulation results. Field deviations and gradients inside the human head cause NMR signal frequency shifts and line broadening, respectively. Voxels 2 × 2 × 0.5 cm may have frequency differences of more than 2.0 ppm. The linewidth of a single voxel may be broadened by more than 0.5 ppm. Calculated and experimental field maps are in excellent agreement. The global field distortion in the human head is primarily due to the susceptibility difference between air and tissues and their corresponding geometrical shapes.     

Magnetic resonance in hepatic lesions. Experience with a 1.5-T magnetic field

Forty-one patients with histologically proven hepatic lesions (6 cysts, 6 hemangiomas, 8 hepatomas, 19 metastases and 2 negative cases) were studied with Magnetic Resonance (MR) imaging at 1.5 T, and with US and CT. This prospective study was aimed at evaluating: the comparative accuracy of MR, US and CT; the sensitivity and specificity of spin-echo (SE) vs FISP pulse sequences; the efficacy of T1 and T2 relaxation time values in differentiating hemangiomas from hepatomas and metastases. MR diagnostic accuracy was 94.7% vs 89.4% of CT and 84.2% of US. FISP sequences provided 60% sensitivity and 66% specificity. T2 relaxation time values were statistically significant (p less than 0.05) in differentiating hemangiomas (T2 range: 80.9-218.9 ms) from hepatomas (T2 range: 59.4-83.2 ms). The differences in mean T2 values between hemangiomas and metastases (T2 range 54.3-177.3 ms) were not statistically significant (p greater than 0.25).     

Movement of steel-jacketed projectiles in biological tissue in the magnetic field of a 3-T magnetic resonance unit

Purpose

The fact that ferromagnetic bullets can move in air or gelatine when subjected to magnetic resonance (MR) units is well known. A previous study showed that the movement of 7.5-mm GP 11 Suisse bullets also depends on their orientation toward the gantry. In order to compare the movement in gelatine to that in real tissue, we decided to measure the movement of these bullets, as well as 9-mm Luger bullets, in the brain and liver.

Methods

The GP 11 and 9-mm Luger bullets were inserted into the fresh calf brain or pig liver either vertically or horizontally in the x- or z-axis to the gantry. Before and after exposure to a 3-T MR unit, their position was documented by CT.

Results

GP 11 bullets rotated more readily and in general proved to be more mobile than the 9-mm Luger. All GP 11 bullets and a large amount of the 9-mm Luger bullets exited the brain. Sliding toward the gantry was easier for 9-mm Luger bullets in the brain than in the liver.

Conclusions

The orientation of a ferromagnetic object influences its mobility in a strong magnetic field. Tipping is easier than sliding for longish ferromagnetic projectiles, probably due to the lesser tissue resistance. The bullets moved more readily in biological tissue, especially brain tissue, compared to gelatine, thus implying that gelatine is not a suitable substitute for soft tissues when examining the movement of ferromagnetic objects in MR units.

     

Safety of strong, static magnetic fields

Issues associated with the exposure of patients to strong, static magnetic fields during magnetic resonance imaging (MRI) are reviewed and discussed. The history of human exposure to magnetic fields is reviewed, and the contradictory nature of the literature regarding effects on human health is described. In the absence of ferromagnetic foreign bodies, there is no replicated scientific study showing a health hazard associated with magnetic field exposure and no evidence for hazards associated with cumulative exposure to these fields. The very high degree of patient safety in strong magnetic fields is attributed to the small value of the magnetic susceptibility of human tissues and to the lack of ferromagnetic components in these tissues. The wide range of susceptibility values between magnetic materials and human tissues is shown to lead to qualitatively differing behaviors of these materials when they are exposed to magnetic fields. Mathematical expressions are provided for the calculation of forces and torques.     

Long-term continuous exposure to static magnetic field reduces popolysaccharide-induced cytotoxicity of fibroblasts

PURPOSES: Lipopolysaccharide (LPS) is one of the major substances initiating the immune host response in microbial infections that results in cytotoxicity. In terms of treatment of the immune response, research has been conducted on physical environments that can reduce LPS-induced damage. In this experiment, a long-term continuous static magnetic field (SMF) was used as a physical resource to reduce LPS-induced immune host response. MATERIALS AND METHODS: Cultured fibroblasts were challenged with LPS to initiate an inflammatory reaction. Cell viability and various proinflammatory cytokine levels were detected and compared between SMF and sham-exposed groups. RESULTS: Our in vitro study revealed that, with LPS challenge, fibroblasts continuously exposed to a 0.4-T SMF for 12 h demonstrated higher cell viability compared to unexposed analogs. From cytokine test, the levels of LPS-induced interleukin-1beta (IL-1beta) in the SMF-exposed groups were significantly lower relative to their unexposed counterparts (p < 0.05). By contrast, SMF exposure tended to increase the level of LPS-induced IL-1 receptor antagonist (IL-1Ra) and IL-6. CONCLUSIONS: Our results suggest that SMF stimulation inhibits LPS-induced cytotoxicity through reduction of proinflammatory cytokines and increase in anti-inflammatory cytokines of NIH-3T3 cells.     

Long-term continuous exposure to static magnetic field reduces popolysaccharide-induced cytotoxicity of fibroblasts

Purposes:?Lipopolysaccharide (LPS) is one of the major substances initiating the immune host response in microbial infections that results in cytotoxicity. In terms of treatment of the immune response, research has been conducted on physical environments that can reduce LPS-induced damage. In this experiment, a long-term continuous static magnetic field (SMF) was used as a physical resource to reduce LPS-induced immune host response.

Materials and methods:?Cultured fibroblasts were challenged with LPS to initiate an inflammatory reaction. Cell viability and various proinflammatory cytokine levels were detected and compared between SMF and sham-exposed groups.

Results:?Our in vitro study revealed that, with LPS challenge, fibroblasts continuously exposed to a 0.4-T SMF for 12 h demonstrated higher cell viability compared to unexposed analogs. From cytokine test, the levels of LPS-induced interleukin-1β (IL-1β) in the SMF-exposed groups were significantly lower relative to their unexposed counterparts (p < 0.05). By contrast, SMF exposure tended to increase the level of LPS-induced IL-1 receptor antagonist (IL-1Ra) and IL-6.

Conclusions:?Our results suggest that SMF stimulation inhibits LPS-induced cytotoxicity through reduction of proinflammatory cytokines and increase in anti-inflammatory cytokines of NIH-3T3 cells.     

A spiral volume coil for improved RF field homogeneity at high static magnetic field strength

Biological samples have a high dielectric constant that can shorten RF wavelengths by a factor of 8 relative to the vacuum. At high field strengths, finite wavelength effects within larger samples are the dominant cause of RF field nonunifor-mity. A coil design is presented that can reduce and even eliminate this inhomogeneity; 4-T images in phantoms and in the head of a normal volunteer are presented, which demonstrate improved homogeneity relative to a standard coil. This coil design should aid in realizing the potential advantages of imaging large samples at high field strengths.     

Short communication: assessment of environmental disturbances to the static magnetic field in magnetic resonance installations

The static magnetic field of MRI scanners can be affected by environmental factors. Magnetic resonance spectroscopy and functional imaging with single-shot echo-planar imaging (EPI) are particularly vulnerable to the movement of lifts, vehicles, trains and other large metallic masses in the vicinity. This work investigates the sensitivity of two different imaging techniques to assess disturbances of the static magnetic field: (i) phase changes in gradient-echo images of a uniform test object; and (ii) image displacement along the phase encoding direction in single-shot EPI images. For the latter a hexane sample was used, and the separation between CH2 and CH3 signals was taken as a reference. Both techniques were evaluated in a site known to be free of any significant environmental disturbances and validated by inducing a magnetic field disturbance. Both techniques provide valuable information in acceptance tests, allowing MRI users to evaluate and manage the environmental conditions surrounding a scanner. The single-shot EPI technique was found to be highly sensitive, being expected to detect magnetic field fluctuations down to 0.005 parts per million (ppm). The phase images method was found to be less sensitive (0.02 ppm) but is more easily available. The single-shot EPI technique was used in acceptance tests and environmental disturbances to the magnetic field of the order of 0.04 ppm were measured at the isocentre on two separate occasions.     

Effect of a 1.5 T static magnetic field on body temperature of man

Reports in the literature concerning the effect of static magnetic fields on the body temperature of mammals have been contradictory and confusing. A significant increase in body temperature in human subjects exposed to the static magnetic fields used in magnetic resonance imaging (MRI) would have important safety implications. Therefore, in two separate studies we determined body temperature in 20 subjects exposed to a 1.5 T static magnetic field. One group of subjects (Group I, N = 9) had sublingual pocket temperature measured immediately before and after a 60 min exposure, while another group of subjects (Group II, N = 11) had esophageal temperature determined at 2 min intervals during a 20 min exposure. No statistically significant changes in body temperature were observed in either Group I or II subjects during exposure to the 1.5 T static magnetic field. We conclude that a relatively intense static magnetic field has no effect on body temperature of normal human subjects.     

Effect of orthodontic brackets and different wires on radiofrequency heating and magnetic field interactions during 3-T MRI

Objectives:

To evaluate the heating and magnetic field interactions of fixed orthodontic appliances with different wires and ligaments in a 3-T MRI environment and to estimate the safety of these orthodontic materials.

Methods:

40 non-carious extracted human maxillary teeth were embedded in polyvinyl chloride boxes, and orthodontic brackets were bonded. Nickel–titanium and stainless steel arch wires, and elastic and stainless steel ligaments were used to obtain four experimental groups in total. Specimens were evaluated at 3 T for radiofrequency heating and magnetic field interactions. Radiofrequency heating was evaluated by placing specimens in a cylindrical plastic container filled with isotonic solution and measuring changes in temperature after T₁ weighted axial sequencing and after completion of all sequences. Translational attraction and torque values of specimens were also evaluated. One-way ANOVA test was used to compare continuous variables of temperature change. Significance was set at p < 0.05.

Results:

None of the groups exhibited excessive heating (highest temperature change: <3.04 °C), with the maximum increase in temperature observed at the end of the T₁ weighted axial sequence. Magnetic field interactions changed depending on the material used. Although the brackets presented minor interactions that would not cause movement in situ, nickel–titanium and stainless steel wires presented great interactions that may pose a risk for the patient.

Conclusions:

The temperature changes of the specimens were considered to be within acceptable ranges. With regard to magnetic field interactions, brackets can be considered “MR safe”; however, it would be safe to replace the wires before MRI.     

Investigation of higher-order cognitive functions during exposure to a high static magnetic field

Purpose:

To test for potential changes in higher‐order cognitive processes related to the exposure to a high static magnetic field.

Materials and Methods:

Twenty‐four healthy volunteers participated in two experimental sessions inside a 3 Tesla (T) magnetic resonance imaging (MRI) magnet. During one session the magnetic field was ramped down. The tasks consisted of six well‐established paradigms probing a variety of cognitive functions. Reaction times (RT) and accuracies (AC) were recorded for statistical analysis.

Results:

The overall performance was very similar in both sessions. Strong task‐specific effects (all P < 0.006) were consistent with previously published results. Direct comparisons of task‐specific effects between the two sessions (magnetic field on or off) remained insignificance for all paradigms (RT: all P > 0.196; AC: all P > 0.17; no corrections for multiple comparisons).

Conclusion:

The results did not indicate any apparent safety concerns with respect to cognitive performance in a static magnetic field of a typical whole‐body magnet. In addition, comparisons of cognitive effects from testing situations with and without exposure to high static magnetic fields can be considered valid. J. Magn. Reson. Imaging 2012;36:835–840. © 2012 Wiley Periodicals, Inc.     

A computer simulation of the static magnetic field distribution in the human head

Distortion of the static magnetic field inside the human head is dependent on regional tissue susceptibility variations and geometrical shape. These effects result in resonance line broadening and frequency shifts and consequently, intensity and spatial errors in both magnetic resonance imaging (MRI) and magnetic resonance (MR) spectroscopy. To calculate the field distortion due to the susceptibility's geometry, two dimensional (2D) finite element analysis was applied to simulate the field distribution in a 2D model of the human head, placed in a uniform magnetic field. The model contains air-filled cavities and sinuses, and the remainder is treated as water. The magnetic field deviation was evaluated using gray scale plots and histograms of the magnetic field. The shifts in parts/ million and broadening of the histograms correspond to the NMR of the sampled region. The field distribution of the human head was also experimentally mapped using the DANTE tagging sequence. The calculated and experimental field maps are in good agreement. Thus, geometric considerations with uniform susceptibilities are sufficient to explain most of the static magnetic field distribution in the human head.     

Recording of electrical brain activity in a magnetic resonance environment: Distorting effects of the static magnetic field

The technical limitations of electroencephalography (EEG) and flashed visually-evoked potentials (VEP) recordings in the static magnetic field of the MR system were systematically studied. A main artifact occurring in the magnetic field was found to be correlated with the heart cycle and had amplitudes in the range of EEG and VEP signals. For VEP recordings, a substantial reduction of this effect was achieved by subtraction of the averaged artifact from the averaged composed signal (VEP and artifact) resulting in the VEP signal alone. However, for continuous EEG recordings, there is no such solution, since the observed effect is not sufficiently constant in amplitude, and the standard deviation of the amplitude of the effect is often larger than the EEG amplitude.     

Subchronic exposure to static magnetic field differently affects zinc and copper content in murine organs

Purpose Static magnetic fields (SMF) have been widely used in research, medicine and industry. Since zinc and copper play an important role in biological systems, we studied the effects of the subchronic continuous SMF exposure on their distribution in murine tissues.

Materials and methods For 30 days, mice were exposed to inhomogeneous, vertical, downward or upward oriented SMF of 1?mT averaged intensity with spatial gradient in vertical direction.

Results SMF decreased the amount of copper and zinc in liver. In brain, zinc levels were increased and copper levels were decreased. In spleen, zinc content was reduced, while copper amount remained unchanged.

Conclusions Subchronic exposure to SMF differently affected copper and zinc content in examined organs, and the changes were more pronounced for the downward oriented field. The outcome could be attributed to the protective, rather than the harmful effect of SMF.