Re: MRI shielding

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

>Date:         Wed, 18 Mar 1998 07:34:30 -0500
>Reply-To: Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
>Sender: Medical Physics Listserver <medphys@lists.wayne.edu>
>From: "Joel E. Gray, Ph.D." <joelgray@M3.SPRYNET.COM>
>Subject:      Re: MRI shielding
>To: Multiple recipients of list MEDPHYS <MEDPHYS@LISTS.WAYNE.EDU>
>
>
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>John,
>
>Any device with an electron beam or electron flow (not in a wire) will be
>effected by fields of 1 gauss or less, e.g., image intensifiers, TVs, etc.
>Color TV are most dramatically effected since you have the additional issue
>of convergence of the three electron beams.
>
>Pacemakers are safe up to about 5 gauss.  Somewhere between 5 and 10 gauss
>they will switch from the synchronous to asynchronous mode.  The risk to
>the patient depends on the patient and the type of pacemaker.  These
>deviceses are switched to the asynchronous mode by the cardiologist as part
>of the pacemaker evaluation.  However, since you have to shield to 1 gauss
>to protect equipment, the pacemaker issue is not that important.
>
>Hope this helps!!
>
>     Joel
>
>Joel E. Gray, Ph.D., Consultant
>2804 Second Street Southwest, Suite 334
>Rochester, Minnesota 55902
>
>Ph  507-286-8910
>Cell Ph  507-269-4247
>Fax  507-286-8910
>e-mail  joelgray@m3.sprynet.com
>
>
>
>
>At 5:10 PM 3/18/98, John Simpson wrote:
>>         ** Mail from Medphys Listserver **
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>>Dear Joel
>>Thanks for the reply. It is my understanding that cardiac pacemakers and
>>items such as image intesifiers are even more sensitive to magnetic fields
>>than video monitors.
>>Would you see these as limiting factors even allowing for additional
shielding.
>>thanks in advance
>>
>>>
>>>         ** Mail from Medphys Listserver **
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>>>
>>>The first think to be affected will be color video type displays, even at
>>>fields of about 1 gauss.  Recommendation-- if you can add additional
>>>shielding to maintain the field strength at 1 gauss at the floor level of
>>>the floor above you will eliminate a lot of problems and other worries.
>>>
>>>Computers, tapes, floppy disks, etc-- no problem.
>>>
>>>If you would like to discuss this further please contact me directly.
>>>
>>>     Joel
>>>
>>>Joel E. Gray, Ph.D., Consultant
>>>2804 Second Street Southwest, Suite 334
>>>Rochester, Minnesota 55902
>>>
>>>Ph  507-286-8910
>>>Cell Ph  507-269-4247
>>>Fax  507-286-8910
>>>e-mail  joelgray@m3.sprynet.com
>>>
>>>
>>>
>>>
>>>At 12:26 PM 3/18/98, John Simpson wrote:
>>>>         ** Mail from Medphys Listserver **
>>>>If you reply to this message, it will be posted on Medphys for all the
>>>>subscribers to review ...
>>>>
>>>>
>>>>can anyone inform me what additional levels of protection would be required
>>>>if your mri unit is sited directly below the cardiac/intensive care units.
>>>>John Simpson
>>>>Director of Medical Physics
>>>>Townsville General Hospital
>>>>Queensland, Australia
>>>>simpsoj@citecuf.citec.qld.gov.au
>>>
>>>
>>John Simpson
>>Director of Medical Physics
>>Townsville General Hospital
>>Queensland, Australia
>>simpsoj@citecuf.citec.qld.gov.au
>