In this work, the safety aspects of the Magnetic Resonance Imaging and Spectroscopy (MRI/MRS) systems are reviewed. Focus is placed on the interaction between the electric and magnetic fields generated by such instruments and the human body. An understanding of these interactions has become ever more important with the push to higher field strengths. Knowledge of MRI safety can not only guide RF coil and pulse sequence design but can also affect sequence selections, thereby ensuring safe and efficient system operation. Due to the signal to noise advantages of high field MRI systems, increases in the static magnetic field are inevitable. However, in addition to the static magnetic field, power intense sequences, fast gradient switching, and localized imaging/spectroscopy all have the potential of subjecting the human body to intense magnetic and electric field fluctuations. This further accentuates the need for a detailed understanding of the effects of exposure to these fields. In this work, some of the issues addressed are new, while others are well established. In either case, it is hoped that this compilation will enable all of us to pay greater attention to these matters and increase the current state of understanding through novel experimental studies. The discussion broadens the range of radio frequency effects to the microwave limit. This was accomplished in view of the latest efforts for realization of ultra high field (UHF) human MRI. In this regard, recently constructed ultra high field whole body systems will provide a new testing ground for safety issues. The proliferation of high field (1.0–3.0 tesla), very high field (3.0–7.0 tesla), and ultra high field (≥7 tesla) whole body MRI's calls for a review of the safety literature that can guide future studies of critical health related issues. An effort has been made to present an up to date analysis of the biological effects within MR, covering a wide range of properties from cellular and physiological to clinical. © 2000 John Wiley & Sons, Inc. Concepts Magn Reson 12: 321–359, 2000

Biological effects and health implications in magnetic resonance imaging

In this study, we investigated the effects of strong magnetic fields of up to 14 T on the near-infrared spectrum of water molecules. We used a near-infrared spectrophotometer, which has an external optical cell box in a 14 T superconducting magnet. We measured the near-infrared spectrum of water in the range of 900–2000 nm by changing the optical path lengths from 0.1 to 100 mm. The peak wavelengths in the near-infrared spectrum in the range of 900–2000 nm of water, increased in length by 1–3 nm under a 14 T magnetic field. Also, we measured a near-infrared spectrum of glucose solutions under a magnetic field at 14 T to investigate the hydration of sugar. In contrast to the case of water, the peak wavelength of glucose solutions showed blueshift under a 14 T magnetic field. When the magnetic fields were changed from 0 to 14 T, the differential optical absorbance of the glucose solution at 958 nm increased compared to the controls. There is a possibility that the 14 T magnetic field affects the formation of hydrogen bonds of water molecules and the hydration of glucose molecules.

Structure of water molecules under 14 T magnetic field

Strong static magnetic field effects on yeast proliferation and distribution.

The effects of magnetic fields on biological and chemical processes are investigated. Time-varying magnetic fields produce eddy currents which stimulate excitable tissues at low frequencies and give rise to thermal effects at high frequencies. Biological and chemical effects of static magnetic fields are poorly understood. The effects of magnetic fields on combustion of alcohol and hydrocarbons are studied to simulate in part the oxidation of organic matter in the living body. The combustion temperature of alcohol with platinum catalysis decreases rapidly within a range 100-200°C when the place of combustion reaction is exposed to gradient magnetic fields (0.5-1.4T, 20- 200 T/m). To explain this phenomenon, an experiment is demonstrated where candle flames are exposed to gradient magnetic fields. The flames bend so as to escape from magnetic fields of higher intensities. The study is focused on the role of oxygen as a paramagnetic molecule and on the behavior of charged particles in magnetic fields. In contrast with the combustion experiments, no clear positive effects are observed in experiments of biochemical reactions and embryogenesis under magnetic fields of the same intensities.

Experimental difficulties in observing the effects of magnetic fields on biological and chemical processes

This study determines the effect of the configuration of the magnetic field on the movement of gas bubbles that evolve from platinum electrodes. Oxygen and hydrogen bubbles respectively evolve from the surface of the anode and cathode and behave differently in the presence of a magnetic field due to their paramagnetic and diamagnetic characteristics. A magnetic field perpendicular to the surface of the horizontal electrode causes the bubbles to revolve. Oxygen and hydrogen bubbles revolve in opposite directions to create a swirling flow and spread the bubbles between the electrodes, which increases conductivity and the effectiveness of electrolysis. For vertical electrodes under the influence of a parallel magnetic field, a horizontal Lorentz force effectively detaches the bubbles and increases the conductivity and the effectiveness of electrolysis. However, if the layout of the electrodes and magnetic field results in upward or downward Lorentz forces that counter the buoyancy force, a sluggish flow in the duct inhibits the movement of the bubbles and decreases the conductivity and the charging performance. The results in this study determine the optimal layout for an electrode and a magnetic field to increase the conductivity and the effectiveness of water electrolysis, which is applicable to various fields including energy conversion, biotechnology, and magnetohydrodynamic thruster used in seawater.

/pdf/the-effect-of-magnetic-field-on-the-dynamics-of-gas-bubbles-3t3p3uamvs.pdf

The effect of magnetic field on the dynamics of gas bubbles in water electrolysis.

Possible influence of d.c. magnetic fields on the behavior of oxygen dissolved in aqueous solutions is studied in order to widen the basic understanding of biological effects of magnetic fields. Oxygen concentration in the solution is controlled either by introduction of oxygen gas into the solution until the solution is saturated with oxygen gas at 1 atm pure oxygen, or by introduction of argon gas into the solution until the solution is saturated with argon gas it 1 atm pure argon. Then, the solution is contacted with air at 1 atm pressure. During the recovery process of the dissolved oxygen concentration from the nonequilibrium state to the equilibrium state, a part of the solution is exposed to 1.0 T magnetic field with a gradient of 10 T/m for 30 - 60 min. The spatial distribution of oxygen concentration in the solution was redistributed by the magnetic field. The relative change in oxygen concentration with position was around ±1 - ±7 %. In contrast, in the experiment under the equilibrium state of oxygen pressure, no redistribution of the dissolved oxygen was observed.

Redistribution of dissolved oxygen concentration under strong DC magnetic fields

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Redistribution of dissolved oxygen concentration under strong DC magnetic fields