Re: RADSAFE digest 926

[Dick King <king@ukulele.reasoning.com>]

>> 
>> Date: 10 May 1996 09:02:06 -0700
>> From: "GORDON MILLER" <GORDON.MILLER@quickmail.llnl.gov>
>> Subject: Re: Static Magnetic Field G
>> 
>>                       RE>>Static Magnetic Field Gu                 5/10/96
>> 
>> These are static fields.  The numbers are in gauss units.
>> 
>> The counterpart limit for 60 Hz, from the TLVs, is 10 gauss.  Time varying
>> fields can induce current flows, the basis of the TLV, while 0 Hz fields do
>> not.  For 0 Hz fields, induced voltages occur during the ejection of the
>> blood, an fluid with ions, into the aorta (and other large vessels) at high
>> speed.  This induces a "magnetohydrodynamic" voltage that coincides with the t
>> wave of an EKG.  Magnetic interactions require change, either by changing the
>> field or by movement of charges as in blood flow.

Interesting point...

The 1.5 Tesla magnetic field of an MRI machine is parallel to the aorta for
other reasons, but that coincidence minimizes the induced MHD voltage within a
patient undergoing MRI.

BUT there's a hairpin turn at the top of the aorta, just under the collarbone,
with about 5cm radius.  What kind of voltage would be induced from vessel wall
to wall in a patient being MRIed in, say, the thorassic vertibrae?

-dk