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Siemens AG Healthcare Sector 11/12 MR compatibility data sheet
16
Gradient stray field distribution relevant for assessing exposure to
MR workers
The diagram shows the magnetic stray field distribution of the gradient system along the
patient axis of the MAGNETOM Skyra with the XQ gradient system according to the
requirements of the IEC 60601-2-33 standard.
The magnetic fields generated by each of the three orthogonal gradient axis are calculated
on a coordinate grid on a virtual cylinder surface. The cylinder encompasses the patient
axis and starts in the magnet isocenter.
The grid is defined by:
•
a point pattern on the surface of a virtual cylinder with a diameter of 70 cm (i.e. max.
bore liner);
•
points on circles on the cylinder surface perpendicular to the cylinder axis with an
azimutal step width of 10 degrees (i.e. 36 points at the circumference) and an axial step
width of 4 cm.
The field values are calculated at max. currents that can be handled by the gradient ampli-
fiers. At each space point the field vectors generated by each gradient are calculated,
superimposed and then their magnitudes are derived. The max. magnitude field value that
can be found on each circle is selected and plotted along the z-axis.
By dividing the maximum field values by the shortest rise time, the dB/dt values can be
derived.
Shortest rise time Max dB / dt
XQ gradient 225 µs 60 mT/225 µs = 267 T/s