Humans are exposed daily to artificial and naturally occurring magnetic fields that originate from many different sources. We review recent studies that examine the biological effects of and medical applications involving electromagnetic fields, review the properties of static and pulsed electromagnetic fields that affect biological systems, describe the use of a pulsed electromagnetic field in combination with an anticancer agent as an example of a medical application that incorporates an electromagnetic field, and discuss the recently updated safety guidelines for static electromagnetic fields. The most notable modifications to the 2009 International Commission on Non-Ionizing Radiation Protection guidelines are the increased exposure limits, especially for those who work with or near electromagnetic fields (occupational exposure limits). The recommended increases in exposure were determined using recent scientific evidence obtained from animal and human studies. Several studies since the 1994 publication of the guidelines have examined the effects on humans after exposure to high static electromagnetic fields (up to 9.4 tesla), but additional research is needed to ascertain further the safety of strong electromagnetic fields.

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We evaluated radiofrequency (RF) heating of various implants embedded in a gel phantom during magnetic resonance (MR) procedures. We examined the dependence of RF heating on variation in specific absorption rate (SAR) and angle between the implant and the static magnetic field (B₀) and on the displacement of the phantom in the irradiation coil using a 1.5-tesla MR system, and we compared the influence of RF heating on the same implant using a 3.0T MR system.
Our results support the occurrence of RF heating of implants made of non-magnetizing metal. We observed greater RF heating when the implant was set parallel to B₀, embedded at a shallower depth, and placed at the center of the RF irradiation coil. We also confirmed that the rise in temperature was proportionate to the increase in SAR. We considered the difference in temperature elevation on depth of embedding to reflect the skin-depth effect of RF intensity for both the 1.5- and 3.0-T MR systems.

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Purpose: We assessed whether magnetic resonance (MR) imaging evaluation of portosystemic collateral shunts can aid prediction of therapeutic effectiveness and complications after creation of a transjugular portosystemic shunt (TIPS), and technical difficulty during the TIPS procedure.
Materials and Methods: We retrospectively reviewed 32 patients (27 men, 5 women; mean age, 56.4 years) who underwent TIPS creation following gadolinium-enhanced MR examination. We measured the diameters of pre-existing portosystemic collateral shunting vessels, added the measurements together to generate a shunting collateral score for each patient, and divided patients into 2 groups by score of 4 or greater or less than 4. We then compared therapeutic effectiveness, technical difficulty and complications of the TIPS procedure, and portal venous (PV) pressure, PV-inferior vena cava (IVC) pressure gradient, and PV diameter between the groups.
Results: The patients with a pre-existing large portosystemic shunt showed insignificant trends toward higher technical difficulty of the shunt procedure and rate of shunt dysfunction. The 2 groups showed no significant difference in early mortality rate, onset or worsening rate of hepatic encephalopathy after TIPS creation, PV pressure, PV-IVC pressure gradient, or PV diameter.
Conclusion: Gadolinium-enhanced MR imaging may help in predicting technical difficulty and complications of TIPS.

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Purpose: The distal dural ring (DDR) is an anatomical landmark used to distinguish intra- and extradural aneurysms. We investigated identification of the DDR using 2 three-dimensional (3D) magnetic resonance (MR) cisternography sequences-3D constructive interference in steady state (CISS) and 3D sampling perfection with application optimized contrasts using different flip angle evolutions (SPACE)-at 3.0 tesla.
Methods: Ten healthy adult volunteers underwent imaging with 3D-CISS, 3D-SPACE, and time-of-flight (TOF) MR angiography (TOF-MRA) sequences at 3.0T. We analyzed DDR identification and internal carotid artery (ICA) signal intensity and classified the shape of the carotid cave.
Results: We identified the DDR using both 3D-SPACE and 3D-CISS, with no significant difference between the sequences. Visualization of the outline of the ICA in the cavernous sinus (CS) was significantly clearer with 3D-SPACE than 3D-CISS. In the CS and petrous portions, signal intensity was lower with 3D-SPACE, and the flow void was poor with 3D-CISS in some subjects.
Conclusion: We identified the DDR with both 3D-SPACE and 3D-CISS, but the superior contrast of the ICA in the CS using 3D-SPACE suggests the superiority of this sequence for evaluating the DDR.

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Purpose: We investigated the characteristics of hyperpolarized (HP) ¹²⁹Xe magnetic resonance (MR) imaging obtained from balanced steady-state free precession (SSFP) measurement of mouse lungs, especially under spontaneous breathing, and compared the results with those obtained using traditional spoiled gradient echo (SPGR) method, focusing on improved signal-to-noise ratio (SNR) and reduced total acquisition time.
Methods: We calculated magnetization response of the HP ¹²⁹Xe gas for the balanced SSFP sequence under spontaneous breathing to derive optimal conditions for the imaging experiment. We then placed an anesthetized mouse in the magnet (9.4T) supplied with oxygen gas and a mixture of HP ¹²⁹Xe gas supplied from a continuous-flow hyperpolarizing system. We obtained an axial plane image of the lung through balanced SSFP and SPGR sequences, changing the various magnetic resonance (MR) imaging parameters, and measured the SNR of these images.
Results: We demonstrated the clear dependence of image intensity on flip angle and number of shots. The SNR was higher in balanced SSFP than in SPGR and 2.3-fold higher compared at each maximum. In contrast, total acquisition time in balanced SSFP was shortened to about one-eighth that of SPGR using a one-shot acquisition mode.
Conclusion: In HP ¹²⁹Xe MR imaging of the lung of a spontaneously breathing mouse, balanced SSFP sequence with multi-shot and centric order acquisition provides higher SNR in a shorter acquisition time than SPGR.

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Purpose: We evaluated and compared the reproducibility, diagnostic accuracy, and sequence dependency of the fat fraction (FF) determined by 3-point Dixon (DIXON) and multi-echo gradient-echo (MEGE) methods to those of the FF determined by magnetic resonance spectroscopy (MRS).
Methods: Our study included 98 volunteers, ten of whom underwent scanning twice to evaluate sequence reproducibility. We compared the FFs determined by the DIXON and MEGE methods to that by MRS as the gold standard, calculated sensitivity and specificity for each image analysis method at a threshold value of 6.25% of spectroscopic value, and used Pearson's correlation coefficient and Bland-Altman analysis to compare agreement among the repeated measurements and FF values with the 3 methods, in 98 volunteers.
Results: There was no significant difference in repeated scans in any sequence with Wilcoxon's t-test. Each correlation coefficient (r) exceeded 0.930 for the repeated measurements of all 3 sequences. Sensitivity of DIXON was 82% and specificity, 96%; sensitivity of MEGE was 70% and specificity, 99%. The FFs determined by DIXON and MEGE correlated well with that by MRS (r=0.920) but showed significant difference (paired t-test, P<0.001). The mean difference between the FF determined by DIXON and that by MEGE were 0.93 and −1.16, respectively. The slope of the regression lines as determined by DIXON was −0.655 (P<0.001) and that by MEGE was −0.527 (P<0.001). When the FF by MRS was less than 6.25%, the FF values by DIXON and MEGE were significantly higher; when the spectroscopic value was greater than 6.25%, their values were significantly lower.
Conclusion: We demonstrated the high reproducibility of each FF measurement using MRS, DIXON, and MEGE. Compared to MRS, both DIXON and MEGE showed high sensitivity and specificity for determining FF. The FFs by DIXON and MEGE showed sequence dependency because DIXON had proportional and additional errors, and MEGE had a proportional error.

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We performed magnetic resonance angiography (MRA) and susceptibility-weighted imaging (SWI) to observe cerebral changes during a migraine attack in a 28-year-old man. MRA revealed regional arterial spasm, and findings of SWI were consistent with decreased blood flow and/or venous dilatation. Because these noninvasive techniques can be performed repeatedly at short intervals, they can be useful for evaluating hemodynamic changes during and after migraine attacks.

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We report 2 cases of primary breast cancer with swelling of the parasternal lymph nodes detected on diffusion-weighted imaging (DWI) as small parasternal nodules. After neoadjuvant chemotherapy, DWI showed disappearance of one node but a focus of subtle signal hyperintensity in the other. DWI findings correlated with the results of conventional breast contrast-enhanced magnetic resonance imaging before and after neoadjuvant chemotherapy.

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Conventional single-tensor tractography cannot depict the entire motor tract of the corticospinal tract because of fiber-crossing and other factors. Using a 3-tesla magnetic resonance (MR) unit, we compared single- and multi-tensor methods for the tract ratio of the 5 major components of the motor pathway, the lower extremity, trunk, hand, face, and tongue, in 5 healthy volunteers. Multi-tensor tractography is better than single-tensor tractography at 3T in depicting more fibers of non-trunk areas from the primary motor cortex.

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We investigated whether a rice pad could be used to reduce the geometric distortion in echo-planar diffusion-weighted images of the cervical spinal cord. In 10 healthy volunteers, we obtained sagittal plane images using the same imaging parameters with and without a rice pad. Two reviewers classified geometric distortion and visually assessed images. Use of a rice pad significantly reduced geometric distortion in the cervical spinal cord.

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