10 MRIdian® system L-0009 Release 4.5 ViewRay, Inc.
Chapter 1: MRIdian® System Overview
1.9 Imaging System
The MRIdian Magnetic Resonance Imaging System (MRIS) is a 0.35T horizontal field MRI. The
superconducting magnet, RF coils, and gradient coil have been engineered by design to allow
operation with the radiotherapy gantry of the MRIdian system.
Three soft-tissue imaging planes can be captured continuously during treatment without
e
xposing the patient to unnecessary ionizing radiation. If the tumor or a critical structure
moves beyond a physician-defined boundary, the treatment beam is automatically paused;
when the structure moves back into the target zone, treatment automatically resumes.
Physicians can set both spatial and time thresholds for pausing treatment delivery, controlling
for the motion of a patient's organs based on real-time 4D MRI data.
During patient scanning, if there is an imaging error the following popup will be displayed on
the MRIdian
system console
Click > OK and then go to the MRI host console and dismiss the error message. After
dismissing the error message you can return to the MRIdian console and resume imaging. For
further instructions on imaging your patient see “Acquiring Images” on page 310 and “Using
Daily Images to Position the Patient” on page 338.
1.10 Cooling System
Because the magnet is a super-conducting magnet, it is filled with liquid helium as a coolant
to maintain the magnetic field. Following installation, the magnet is adjusted to the desired
operating field strength.
The ramped-up magnet does not require additional ele
ctric power to maintain the magnetic
field. However, a refrigeration system must be constantly operating to keep the liquid helium
from boiling off.
1.10.1 Magnetic Shielding
To minimize the effects of the magnetic fringe field on the environment, the magnet is
equipped with active super-conducting shielding.
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