Friday, October 2, 2009

Are Static Magnetic Fields Dangerous?

Are static magnetic fields dangerous? This question has recently taken on added importance because a European directive is limiting a worker’s exposure to the strong static magnetic field in a magnetic resonance imager, thereby impeding research with MRI. A recent article by Denis Le Bihan on medicalphysicsweb.org asserts that
“those limits could end up preventing the technique from being used - just when European scientists are starting to lead the world in ultra-high-field (UHF) MRI magnet research. The initially proposed limits will immediately put the brakes on progress and, moreover, be a big blow to companies that make MRI scanners and magnets, such as Siemens, Philips, Bruker and Magnex. These firms could end up being unable to meet the growing global demand for clinical UHF MRI scanners, the high fields from which could boost the potential of MRI for healthcare and biomedical sciences, particularly for neurological applications.”
Physicist Bob Park, the author of Voodoo Science and the weekly newsletter What’s New, writes
MAGNETIC FIELDS: THE PRECAUTIONARY PRINCIPLE IN ACTION. According to Denis Le Bihan at the CEA-Saclay Centre, a European directive to prevent workers from being exposed to high magnetic fields could severely impact research into Ultrahigh-Field MRI which shows great promise particularly in neurological applications. It is particularly frustrating that limits on static magnetic fields resulted from the paranoia surrounding EMF, which was associated with everything from power lines to cell phones, Wi-Fi, Bluetooth, and other wireless devices. As I pointed out in an editorial in the Journal of the National Cancer Institute eight years ago, ‘there will always be some who will argue that the issue has not been completely settled. In science, few things ever are.’ "
Are these limits justified? Based on my knowledge of biomagnetism, I think not. There are few known mechanisms by which a static magnetic field can have a significant biological impact, except in unusual cases such as a person with a ferromagnetic medical implant, or in some animals (such as magnetotactic bacteria) that are believed to sense magnetic fields, presumably by the presence of ferromagnetic or superparamagnetic nanoparticles (magnetosomes). Russ Hobbie and I discuss the possible effects of weak magnetic fields in Chapter 9 of the 4th edition of Intermediate Physics for Medicine and Biology.

Denis Le Bihan is a leader in the field of MRI, known for his development of diffusion weighted imaging. He is director of NeuroSpin, a French institute aimed at developing and using ultra high field Magnetic Resonance to understand the brain. I knew Denis when we were both working at the National Institutes of Health in the 1990s. He was a close collaborator with my friend Peter Basser, and together they developed diffusion tensor imaging. (Incidentally, one of their early papers on this topic just received its 1000th citation in the citation index!) Let us hope that Le Bihan's important research is not interrupted unnecessarily by misguided government regulations.

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