List: I thought the idea explained below would be a practical, no-cost way of testing the efficacy of magnetic therapy. Roger
At 02:39 PM 20/09/2001 -0400, Dr. Frank Stagg wrote: >To the list: When you think about it, if the magnetic theory is correct we >ought to see some improovement in all or most our patients we send for MRI >(something I wouldn't mind at all but haven't noted yet). After all, the >magnetic field of MRIs must be on the order of a million or more times >powerful the the so-called therapeutic magnets the quacks use. Actually, it's not; a cheap surplus hard drive magnet (they're used in the voice coil head actuators; all even slightly recent consumer hard drives have at least one) has about 1 Tesla field strength at its surface, and 1.5 Tesla is a common field strength for MRI machines. Stick a hard drive magnet without any convenient metalwork attached to it to your fridge, and you will _not_ be able to just pull it straight off again by hand. You have to slide it to a corner :-). A 1.5 Tesla MRI machine is filling a large volume with that field, mind you, while the hard drive magnet will only pick up nails at a range of about one inch (but they'll hit it _really_ hard :-). If field penetration of the body is important, you'd need a really gigantic permanent magnet, which would probably be impossible to make (it'd crush itself), to get the same field volume as a superconducting MRI-machine coil. But the difference in fields is one of quantity rather than quality. Since people using magnets therapeutically are often doing something like strapping a hard drive magnet (or vastly overpriced multi-level-marketed equivalent - see http://www.nikken.com/ ...) to their achy arthritis-ridden wrist, it's not out of the question that whatever an MRI machine could do for that wrist, the permanent magnet could too. Especially if they use a few magnets arranged around the wrist. Really small things like finger joints would be even easier, of course. You could easily get a large fraction of one Tesla through the whole flesh volume this way, I think. People who strap flexible fridge magnets to themselves, on the other hand, really _are_ dealing with minute fields, primarily thanks to the north-south pole alternation that these magnets use, which reduces the field to near-zero at any significant distance at all. Daniel Rutter
