Bruker BioSpec 117 AVANCE III, Manual

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Laboratory infrastructure and interactions
5.3.2 Electromagnetic interactions
In the event of faulty installation or incorrect operation of an MR system, electromagnetic inter-
ference to other equipment in the vicinity of the MR system can occur.
Electromagnetic disturbances to the MR system have a negative impact on the disturbance-free
operation of an MR system.
Electromagnetic disturbances are either associated with conducted disturbances or transmitted
by electromagnetic fields. It can be split into the following categories:
▪ DC interference, e.g. due to transient DC consumers
▪ Low frequency interference, e.g. in a frequency range between 1Hz and 1kHz
▪ High frequency interference, e.g. in a range of clock frequencies or NMR resonance fre-
quencies
The disturbances may be of magnetic and/or electrical origin. Both types of disturbance are rel-
evant for MR systems. Different measures must be considered for the different categories and
different types of disturbance when the electromagnetic shielding is implemented.
5.3.2.1 DC and LF interference
DC interference
is produced e.g. by elevators or subways. Very strong electromagnetic distur-
bance fields can thereby generated in the immediate vicinity of the DC conductor. Long-range,
weak magnetic fields are generated in sections of the area spanned by the DC conductor that
are to some extent far away.
Low frequency (LF) disturbance
is often caused by transformers (50/60HZ), ventilation mo-
tors (approx. 30-100Hz), lighting facilities, or by railway lines (16 2/3 Hz).
Low frequency and DC interference are measured using a fluxgate magnetometer. Measure-
ments must have a minimum accuracy of 100nT and be carried out in the following places:
▪
Magnet room
: In the area of the magnet volume, the z components of the field disturbance
(parallel to the magnetic field axis) must be measured
▪
Technical room
In the area of the electronics cabinet, all components of field disturbance
must be measured
The course of the magnetic field disturbance must be logged and analyzed at different times of
the day and over several hours.
Disturbance in the magnet room
Disturbance in the magnet room
Table 5.3: Disturbance in the magnet room
Disturbance in the technical room
Disturbance in the technical room
Table 5.4: Disturbance in the technical room
Type of disturbance Limit value
Disturbance over hours and days with constant progression 5000 nT/h
Jumps and short-term disturbance 500 nT
50/60Hz disturbances as well as all higher harmonics 500 nT
Periodic disturbance up to 10kHz 500 nT
Field disturbance due to lighting systems, measured at intervals of
5cm 500 nT
Type of disturbance Limit value
50/60Hz disturbance as well as all higher harmonics 500 nT
Periodic disturbance up to 10kHz 500 nT