GE SIGNA Voyager, Предустановка

Страница: 158 / 178

1. The ambient RFI measured should be less than 100 millivolt per meter (100 dB microvolt per
meter)
2. The recommended centerband and bandwidth frequencies to be used when measuring RFI
are listed in the table below. (This table includes frequency bands important for both imaging
and spectroscopy):
Table 7-2: Radio Frequency Survey Specifications
Isotope Bandcenter MHz Bandwidth Hz
1
H
63.86 916,138
19 F
60.12 981,882
31 P
25.88 390,296
23
Na
16.90 242,773
13 C
16.06 233,925
3. RFI site surveys are to be performed by cycling through the preceding frequency bands and
a broad band range up to 100MHz ± 10 MHz (up to 145 MHz ± 10 MHz is recommended for
new sites to accommodate upgrades). Special emphasis, however, should be placed on the
1H band since this is used in proton imaging. The RFI site survey should be performed for a
length of time necessary to determine, within a reasonable degree of certainty, the
maximum field strength.
To ensure that RF noise peaks outside the bandwidths specified above do not actually
extend into these bandwidths and exceed the 100 millivolt per meter limit, adjust the
resolution of the test equipment (spectrum analyzer) according to the equation:
BW (resolution) = f
0
/50
where: BW = Bandwidth (resolution)
f
0
= Center frequency (for 1H: at 1.5 Tesla 63.86 MHz)
3.3 RF Shielding Effectiveness (SE) and Ground Isolation Test Methods
The shielding effectiveness test method defined within this appendix is in accordance with
methods and requirements from IEEE Std 299-2006 - IEEE STANDARD METHOD FOR
MEASURING THE EFFECTIVENESS OF ELECTROMAGNETIC SHIELDING ENCLOSURES.
3.3.1 Introduction
This appendix provides details on shielding Effectiveness (SE) the test method. MRI scanner is
highly sensitive to RF energy from sources outside of the RF shielded room. To ensure proper
operation of the MRI scanner, the RF shielded room is installed to reduce the interaction of
external RF electromagnetic fields with the MR scanner operation (it also prevents MR system
RF radiation from interfering with external RF systems, such as aircraft control).
NOTE:
Impinging Electromagnetic fields at the frequencies to test the RF shielded room may
not be planar.
SIGNA Voyager Pre-Installation
Direction 5680008–1EN, Revision 2
158 3 RF Shielding Effectiveness and Ground Isolation
Testing