Bioeffects of Static Magnetic Fields

Bioeffects of Static Magnetic Fields

The introduction of MR technology as a clinical imaging modality in the early 1980s is responsible for a substantial increase in human exposure to strong static magnetic fields. Most MR systems in use today operate at fields ranging from 0.2- to 3-Tesla. According to the latest guidelines from the U.S. Food and Drug Administration, clinical MR systems using static magnetic fields up to 8.0-Tesla are considered a “non-significant risk” for adult patients. The exposure of research subjects to fields above this level requires approval of the research protocol by an Institutional Review Board and the informed consent of the subjects. Currently, the most powerful MR system in the world used for human subjects operates at a static magnetic field strength of 9.4-Tesla. Investigations by Atkinson et al. and Vaughan et al. describe findings obtained in human subjects relative to the use of the 9.4-Tesla MR system.

With respect to short-term exposures, the available information that pertains to the effects of static magnetic fields on biological tissues is extensive. Investigations include studies on alterations in cell growth and morphology, cell reproduction and teratogenicity, DNA structure and gene expression, pre- and post-natal reproduction and development, blood brain barrier permeability, nerve activity, cognitive function and behavior, cardiovascular dynamics, hematological indices, temperature regulation, circadian rhythms, immune responsiveness, processing of visual and auditory information by the brain, and other biological processes.

The majority of these studies concluded that exposures to static magnetic fields produce no substantial harmful bioeffects. Although there have been reports of potentially injurious effects of static magnetic fields on isolated cells or organisms, no effect has been verified or firmly established as a scientific fact. The documented serious injuries and few fatalities that have occurred with MR system magnets were in associated with the inadvertent introduction or presence of ferromagnetic objects (e.g., oxygen tanks, wheelchairs, aneurysm clips, etc.) into the MR environment.

Regarding the effects of long-term exposures to static magnetic fields, there are several physical mechanisms of interaction between tissues and static magnetic fields that could theoretically lead to pathological changes in human subjects. However, quantitative analysis of these mechanisms indicates that they are below the threshold of significance with respect to long-term adverse bioeffects.

Presently, the peer-reviewed literature does not contain carefully controlled studies that support the absolute safety of chronic exposure to powerful magnetic fields. With the increased clinical use of interventional MR procedures, there is a critical need for such investigations. In addition, although there is no evidence for a cumulative effect of magnetic field exposure on health, further studies of the exposed populations (MR healthcare professionals, patients that undergo repeat studies, interventional MR users, etc.) will be helpful in establishing guidelines for occupational and patient exposures to powerful static magnetic fields.

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