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800581-2.11 NeurOne System User Manual.doc
MRI related RF heating
For safe use in doing the combined EEG/MR measurements it is essential to understand
how to avoid the risks on the test subject that is caused by the total amount of RF energy
exerted onto
watery-gel filled electrode cavities over time
.
Based on published study of fMRI safety issue it has been shown that normal EPI BOLD
measurement there is practically no temperature increase over time at all. With SPGR
sequence the temperature increase over the same time is a bit larger than for the EPI, but
without physiological significance. In the same study Fast Spin Echo (FSE) recording with
multiple echoes (up to 16) largely inflated total RF over time, causing the temperature rapid
increase immediately after the onset of the measurement and that temperature increase
shall be considered dangerous from the physiological point of view.
As conclusion of those results
only
the total amount of RF energy on the watery-gel over
time that governs whether there is or there is not any heating. If there is a constant influx of
RF energy, it does not take much for this to be a positive heating>cooling ratio which in
process of the time
causes the hazardous heating on the brain tissue of test subject.
It is essential to understand that safe legal SAR threshold according to SAR calculation do
not assume the presence of water on the outside of the skin i.e. the gel on the electrode.
Even though
sequence including the TSE/FSE class
which is safe and legal according to
the SAR calculation
might cause fatal temperature increase and is therefore absolutely
forbidden to use.
For safe use
MR Conditional labeled system parts are scientific equipment for
INVESTIGATIONAL USE ONLY!
NeurOne System MR conditional parts are to be used in MR systems up to 3T field
strength and that the only sequences it is intended for use with are stock EPI BOLD
sequences.
The flip angle shall be reduced to less than 90° and thus reduce the total RF over
time (e.g. Gradient Echo, FLASH and SPGR sequences).
Only use sequences which have a low number of RF pulses are allowed.
Never use acceleration factor greater than 2 with Siemens MPRAGE T1.
Never use sequences that have more than one additional inversion pulse.
Never use anything with "Fast" or "Turbo" in its name, since these sequences
typically are VERY high in total RF over time.
