Siemens MAGNETOM Skyra fit Operator's Manual page 113

Noticeable effects on the
SAR limits
SAR monitoring
MAGNETOM Skyra fit | syngo MR E11
Print No. M6-04401.621.02.02.02
During the MR measurement, patients may experience heat
patient sensations on the skin and, as a consequence of the RF energy
absorption, patients may begin to perspire during the course of the
MR examination. Their pulse rate may increase as well. The individual
effects vary from patient to patient. The intensity of these effects
depends on the measurement program selected. As compared to the
Normal Operating Mode, measurement programs with considerably
higher intensities may be used in the First Level Controlled Operating
Mode. Following the examination, the body will cool off. The pulse
rate will return to normal.
Temperature control inside the examination
sensor, located near the air intake for the tunnel ventilation, monitors
the room temperature. If the room temperature exceeds 25°C, the
SAR limits are regulated and lowered by 0.25 W/kg per °C exceeding
25°C. As a result, the parameters of certain MR measurement
sequences may need to be adjusted.

Considering all possible tolerances, the SAR values (quantities)
are always calculated based on the worst-case assumption. This
ensures that the specific SAR limit is maintained.
Depending on the medical question, different coils are used for the
RF transmission (for example, head, extremity or body coil). The
different coils lead to different RF exposure situations for the patient.
Therefore, different SAR quantities and corresponding limits have
been established (for example, head SAR, whole body SAR, local SAR,
and SAR of the exposed part of the body). According to the guideline
for monitoring SAR, the software automatically determines the SAR
quantities and the corresponding limits to be monitored and to be
applied respectively. For the actual RF exposure situation, one of the
above-mentioned SAR quantities will show the highest "value to limit
ratio". For example, in the case of a head examination with a typical
head coil, this will be the global head SAR. If however, a transmitting
coil with an inhomogeneous RF field is applied, this will be the local
SAR.
SAR limits are observed by a software monitoring function.
MR system operation
room: A temperature
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