Effect of static magnetic field exposure of up to 8 Tesla on sequential human vital sign measurements

PURPOSE: To determine if increasing static magnetic field strength exposures up to 8 Tesla (T) affect vital signs or electrocardiograms (ECGs) in normal human volunteers. MATERIALS AND METHODS: We studied 25 normal subjects, consisting of 19 men and six women, ages 24-53 years. The vital signs and ECGs of the subjects were measured 14 times inside and outside the magnetic field. This included the heart rate, respiratory rate, systolic and diastolic blood pressures, finger pulse oxygenation levels, core body temperature via the external auditory canal temperature, and fiber optic core body sublingual temperatures. Inside the magnetic field the vital signs were measured sequentially at field strengths of 8, 6, 4.5, 3, and 1.5 T. RESULTS: The only statistically significant effect of magnetic field strength was observed with systolic blood pressure. An average increase of 3.6 mm Hg in systolic blood pressure was seen with 8 T exposure. ECG rhythm strip analysis demonstrated no significant changes post-exposure. CONCLUSIONS: Normal subjects exposed to varying magnetic field strengths of up to 8 T demonstrated no clinically significant changes in vital signs. Transient ECG artifacts were noted to increase with the field strength.     

Toward direct mapping of neuronal activity: MRI detection of ultraweak, transient magnetic field changes.

A novel method based on selective detection of rapidly changing DeltaB(0) magnetic fields and suppression of slowly changing DeltaB(0) fields is presented. The ultimate goal of this work is to present a method that may allow detection of transient and subtle changes in B(0) in cortical tissue associated with electrical currents produced by neuronal activity. The method involves the detection of NMR phase changes that occur during a single-shot spin-echo (SE) echo-planar sequence (EPI) echo time. SE EPI effectively rephases all changes in B(0) that occur on a time scale longer than the echo time (TE) and amplifies all DeltaB(0) changes that occur during TE/2. The method was tested on a phantom that contains wires in which current can be modulated. The sensitivity and flexibility of the technique was demonstrated by modulation of the temporal position and duration of the stimuli-evoked transient magnetic field relative to the 180 RF pulse in the imaging sequence-requiring precise stimulus timing. Currently, with this method magnetic field changes as small as 2 x 10(-10) T (200 pT) and lasting for 40 msec can be detected. Implications for direct mapping of brain neuronal activity with MRI are discussed.     

Daily exposure to inhomogeneous static magnetic field significantly reduces blood glucose level in diabetic mice

Purpose:?The present study was designed to reveal, whether the 30?min daily full body exposure of mice to an inhomogeneous static magnetic field (SMF) has a statistically significant effect on diabetic neuropathy.

Materials and methods:?Three different doses (100, 150, or 200 mg/kg) of streptozotocin (STZ) were administered intraperitoneally in groups of mice to induce diabetes. Body weight, blood glucose level and the nociceptive temperature threshold of mice were monitored for a period of 12 weeks. The group treated with 200 mg/kg i.p. STZ produced manifest diabetic neuropathy. Results were compared to non-treated (no SMF, no STZ) and SMF exposure without STZ-treatment group (SMF, no STZ) group. The inhomogeneous SMF was in the range of 2.8–476.7 mT peak-to-peak magnetic flux density.

Results:?Whereas SMF exposure did not seem to affect body weight and nociceptive temperature threshold, it statistically significantly (p?<?0.001) reduced blood glucose level in the 200 mg/kg STZ (n?=?6) group.

Conclusions:?Daily SMF exposure repeated for several weeks is protective against the development of high blood glucose level in diabetic mice.     

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.     

Induced magnetic force in human heads exposed to 4 T MRI

Purpose:

To map the distribution of the magnetic force induced in the human head during magnetic resonance imaging (MRI) at 4 T for a large group of healthy volunteers.

Materials and Methods:

The magnetic field distribution in the head of 100 men and 18 women was mapped using phase mapping techniques. Statistical parametric mapping methods using a family‐wise error (FWE) corrected threshold P < 0.05 and region‐of‐interest analyses were used to assess the significance of the results.

Results:

Eyeballs, orbitofrontal and temporal cortices, subcallosal gyrus, anterior cingulate, midbrain, and brainstem (pons) are the brain regions most susceptible to magnetic force. The strength of the magnetic force density in the head was lower than 11.5 ± 5.3 N/m³ (right eyeball). The strength of the magnetic force density induced in occipital cortex varied linearly with the x‐rotation (pitch) angle.

Conclusion:

We found that the induced magnetic force is highly significant in the eyeballs, orbitofrontal and temporal cortices, subcallosal gyrus, anterior cingulate as well as midbrain and brainstem (pons), regardless of subjects' age or gender. The maximum induced magnetic force was 6 × 10⁵ times weaker than the gravitational force; thus, biological effects of the magnetic force during imaging are not expected to be significant. J. Magn. Reson. Imaging 2010;31:815–820. ©2010 Wiley‐Liss, Inc.     

Combination of static magnetic field and cisplatin in order to reduce drug resistance in cancer cell lines

Abstract

Purpose: In this study, the effects of different intensities of Static Magnetic Fields (SMFs) (10, 15 and 25?mT) and different concentrations of cisplatin drug were investigated on the viability percent and IC₅₀ of the A2780 and A2780-CP cell lines at 24, 48 and 96?h to show useful potential of SMF as a physical agent to enhance the effectiveness of common therapeutic approaches and decrease of drug resistance to cisplatin anticancer drug.

Materials and methods: Magnetic field exposure was performed using a locally designed generator. The cell viability percent, IC₅₀ and cisplatin uptake in treated cells were evaluated by MTT assay and inductively coupled plasma (ICP), respectively.

Results: Increasing of concentration and time of cisplatin drug showed a noticeable decrease in viability percent in sensitive and resistant cell lines compared with control group. These decreases were more significant in resistant cells compared with sensitive cells. The obtained IC₅₀ values for resistant were greater than the values obtained for A2780 cells. ICP analysis demonstrated an increased uptake of cisplatin after treatment for 48 and 96?h relative to untreated groups in both resistant and sensitive cells.

Conclusion: Results showed that A2780 cells were more sensitive to cisplatin than A2780-CP. Studies have shown that SMF can increase the effect of cisplatin on cell viability percent and decrease the resistance of A2780-CP cells by producing large, verruca shaped structures at the surface of the cell membrane.     

Safety of human MRI at static fields above the FDA 8 T guideline: sodium imaging at 9.4 T does not affect vital signs or cognitive ability

PURPOSE: To assess whether exposure to a 9.4 T static magnetic field during sodium imaging at 105.92 MHz affects human vital signs and cognitive function. MATERIALS AND METHODS: Measurements of human vital signs and cognitive ability made before and after exposure to a 9.4 T MR scanner and a mock scanner with no magnetic field are compared using a protocol approved by the U.S. Food and Drug Administration (FDA). RESULTS: Exposure to a 9.4 T static magnetic field during sodium imaging did not result in a statistically significant change in the vital signs or cognitive ability of healthy normal volunteers. CONCLUSION: Vital sign and cognitive ability measurements made before and after sodium imaging at 9.4 T suggest that performing human MRI at 105.92 MHz in a 9.4 T static magnetic field does not pose a health risk.     

Magnetic field correlation as a measure of iron‐generated magnetic field inhomogeneities in the brain

The magnetic field correlation (MFC) at an applied field level of 3 Tesla was estimated by means of MRI in several brain regions for 21 healthy human adults and 1 subject with aceruloplasminemia. For healthy subjects, highly elevated MFC values compared with surrounding tissues were found within the basal ganglia. These are argued as being primarily the result of microscopic magnetic field inhomogeneities generated by nonheme brain iron. The MFC in the aceruloplasminemia subject was significantly higher than for healthy adults in the globus pallidus, thalamus and frontal white matter, consistent with the known increased brain iron concentration associated with this disease. Magn Reson Med 61:481–485, 2009. © 2009 Wiley‐Liss, Inc.     

Magnetic field changes in the human brain due to swallowing or speaking

Variations in the magnetic field in the human brain caused by the processes of swallowing or speaking are measured. In both processes, motion of the pharyngeal muscles, especially the tongue and jaw, alter the susceptibility-induced magnetic field distribution at the brain slice being imaged. This leads to image warping, compromising the analysis of a time series of images, such as in functional magnetic resonance imaging (fMRI). These dynamic changes are assessed by acquiring a time series of images using a gradient-echo asymmetric-spin-echo sequence (GREASE), a technique in which two images are acquired for each excitation–one during the gradient echo, and one during the latter part of the spin echo. The NMR phase difference between the two images is a measure of the magnetic field distribution. A series of brain images, acquired with this sequence while the subject either swallows or speaks, indicated negative magnetic field changes of up to O.087 ppm in the inferior region of the brain for both speaking and swallowing, and in some speech, additional positive changes of up to O.056 ppm in the frontal region of the brain were indicated.     

B1 transmission‐field inhomogeneity and enhancement ratio errors in dynamic contrast‐enhanced MRI (DCE‐MRI) of the breast at 3T

Purpose:

To quantify B₁ transmission‐field inhomogeneity in breast imaging of normal volunteers at 3T using 3D T₁‐weighted spoiled gradient echo and to assess the resulting errors in enhancement ratio (ER) measured in dynamic contrast‐enhanced MRI (DCE‐MRI) studies of the breast.

Materials and Methods:

A total of 25 volunteers underwent breast imaging at 3T and the B₁ transmission‐fields were mapped. Gel phantoms that simulate pre‐ and postcontrast breast tissue T₁ were developed. The effects of B₁‐field inhomogeneity on ER, as measured using a 3D spoiled gradient echo sequence, were investigated by computer simulation and experiments on gel phantoms.

Results:

It was observed that by using the patient orientation and MR scanner employed in this study, the B₁ transmission‐field field is always reduced toward the volunteer's right side. The median B₁‐field in the right breast is reduced around 40% of the expected B₁‐field. For some volunteers the amplitude was reduced by more than 50%. Computer simulation and experiment showed that a reduction in B₁‐field decreases ER. This reduction increases with both B₁‐field error and contrast agent uptake.

Conclusion:

B₁ transmission‐field inhomogeneity is a critical issue in breast imaging at 3T and causes errors in quantifying ER. These errors would be sufficient to reduce the conspicuity of a malignant lesion and could result in reduced sensitivity for cancer detection. J. Magn. Reson. Imaging 2010;31:234–239. © 2009 Wiley‐Liss, Inc.     

Evaluation of mutagenicity and co-mutagenicity of strong static magnetic fields up to 13 Tesla in Escherichia coli deficient in superoxide dismutase

Purpose:

To evaluate the biological effects of static magnetic fields (SMFs) up to 13 Tesla (T), with respect to superoxide behavior, by determining the effect on mutagenicity in superoxide dismutase (SOD)‐deficient Escherichia coli strain QC774, and its parental strain GC4468.

Materials and Methods:

Experimental strains were exposed to a 5, 10, or 13T SMF for 24 h at 37°C in Luria‐Bertani medium. To evaluate mutagenicity after SMF exposure, the mutation frequency in thymine synthesis genes was determined. The effect of exposure to a 5 or 13T SMF on mutagenicity induced by plumbagin was also investigated.

Results:

No statistically significant differences in the mutation frequency in thymine synthesis genes were observed between SMF‐exposed cells and unexposed cells at any of the applied magnetic flux densities. Furthermore, exposure to SMFs up to 13T did not affect mutagenicity induced by plumbagin.

Conclusion:

Exposure to SMFs up to 13T caused neither mutagenicity nor co‐mutagenicity in the SOD‐deficient E. coli strain QC774 or in its parental strain GC4468, suggesting that exposure to strong SMFs does not affect the behavior of superoxides in these microorganisms. J. Magn. Reson. Imaging 2012;35:731‐736. © 2011 Wiley Periodicals, Inc.     

Correction of spatial distortion in EPI due to inhomogeneous static magnetic fields using the reversed gradient method

PURPOSE: To derive and implement a method for correcting spatial distortion caused by in vivo inhomogeneous static magnetic fields in echo-planar imaging (EPI). MATERIALS AND METHODS: The reversed gradient method, which was initially devised to correct distortion in images generated by spin-warp MRI, was adapted to correct distortion in EP images. This method provides point-by-point correction of distortion throughout the image. EP images, acquired with a 3 T MRI system, of a phantom and a volunteer's head were used to test the correction method. RESULTS: Good correction was observed in all cases. Spatial distortion in the uncorrected images ranged up to 4 pixels (12 mm) and was corrected successfully. CONCLUSION: The correction was improved by the application of a nonlinear interpolation scheme. The correction requires that two EP images be acquired at each slice position. This increases the acquisition time, but an improved signal-to-noise ratio (SNR) is seen in the corrected image. The local SNR gain decreases with increasing distortion. In many EPI acquisition schemes, multiple images are averaged at each slice position to increase the SNR; in such cases the reversed gradient correction method can be applied with no increase in acquisition duration.