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3 RF Shielding Effectiveness and Ground Isolation Testing
3.1 Ambient Radio Frequency Interference (RFI)
The MR System operates with a highly sensitive RF receiving front end to be able to capture the
signal of an object scanned. A Limited level of RF interference (RFI) at the installation site is
needed for the proper operation for the MR System. The RFI level will depend on the
electromagnetic environment and the equipment installed at the vicinity of the installation site,
some examples are radio stations, land mobile radio transmitter stations. RF sources which can
adversely affect image quality may be generated by discrete frequency or broadband noise (RF)
sources.
3.2 Introduction
3.2.1 Discrete RF Interference
Discrete RF interferences are narrowband and fixed frequency. The Magnet Room must be RF
shielded from RFI sources so external RF energy does not degrade the MR system RF
receivers at the system imaging frequencies. Some potential sources for discrete frequency
signals are radio station transmitters, mobile or hand-held RF transmitting devices, in general
any intended RF transmitter or non-intended transmitters but with clocked digital electronic
circuits.
3.2.2 Broadband RF Interference
Broadband RF noise is a single transient or continuous series of transient disturbances caused
by an electrical discharge. Low humidity environmental conditions will have higher probability of
electrical discharge. The electrical discharge can occur due to electrical arcing (micro arcing) or
merely a static discharge. Some potential sources capable of producing electrical discharge
include:
1. Loose hardware/fasteners vibration or movement (electrical continuity must always be
maintained)
2. Flooring material including raised access flooring (panels & support hardware) and carpeting
3. Electrical fixtures, including:
a. Lighting fixtures
b. Track lighting
c. Emergency lighting
d. Battery chargers
e. Outlets
4. Ducting for HVAC and cable routing
5. RF Shield seals (walls, doors, windows, etc.)
3.2.3 Ambient Radio Frequency Interference (RFI) Site Survey
When a RFI site survey is considered, it is recommended to be completed before the purchase
and installation of the RF shielded room.
Chapter 7 Appendix
SIGNA Voyager Pre-Installation
Direction 5680008–1EN, Revision 2
157
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