MRI Safety: Question on Potential Burns

[vabamyyr]

Hi,

MRI safety manual says that whenever you are scanning a patient with a certain surface coil you should remove all unplugged coils from the bore during the scan. For example, if you have a head/neck + spine coil matrix with two coil ports and you are scanning only the spine part then you should either connect the head part also or remove head/neck coil from the bore.
I was wondering what is the physical mechanism that can cause patient burns?
For example, if you scan patient's spine and leave the head coil unplugged. I was thinking in the lines that somehow when the patient is in contact with the unplugged coil it could create a conducting loop between the unplugged coil, patient, patient table maybe and when this loop is in a RF field it causes current to flow in that loop that could cause burns to the patient.

 

[xts]

Thats not burns, but high voltage shock, what is dangerous.

MRI involves very strong magnetic field, so high voltage could get induced on open connectors of the coil as it changes its position with even small patient's moves or when the magnetic field is switched on/off. That voltage could possibly be dangerous if someone touches the connector. The same coil could also catch RF magnetic fields of other coils and thus got inducted voltage.

 

[Dale]

I think the concern would be two-fold, burns and bad images. A MRI coil is a structure which is, by design, resonant at the system's frequency. So, when you are running a pulse sequence that deposits a lot of RF then the coil will be absorbing a lot of energy, perhaps a few kilowatts, and could get hot. Plugging the coil into the table allows the system to "detune" the coil so that it is no longer resonant when the system is transmitting RF. Since it is not resonant, it absorbs little energy, perhaps a few milliwatts, and does not get hot.

With the interference of a resonant structure, even if it doesn't get hot, it should degrade your image quality, i.e. change local flip angles, add noise by inductive coupling to a bigger volume, etc.

 

[vabamyyr]

Thank you DaleSpam for your reply.

 

[Studiot]

The administrator at this forum (Bertus) is an MRI specialist who might answer your question authoritatively.

www.allaboutcircuits.com

go well