Chapter 2: Safety Information and Alerts
46 MRIdian® system L-0009 Release 4.5 ViewRay Inc.
2.10.2 Noticeable Effects on the Patient
During MR imaging, patients may experience heat sensations on the skin and may begin to
perspire. Their pulse rate may increase as well. The individual effects vary from patient to
patient. Following the MR imaging, the body will cool off and the pulse rate will return to
normal.
2.11 Peripheral Nerve Stimulation (dB/dt)
Magnetic Resonance Imaging is based, in part, on the use of time-varying magnetic fields
(dB/dt) which are produced by electric current field gradient coils.
These field gradients must be switched on and off rapidly (typically in less than a thousandth
of a second) to obtain images. And, by electromagnetic induction they generate electric fields
in the conducting tissues of the body.
These induced electric fields in the body can cause uncomfortable stimulation of the
peripheral nerves which is often perceived by the patient as a tingling or tapping sensation.
Although this peripheral nerve stimulation may cause some discomfort for the patient, it is
not harmful.
The MRIdian® MRIS uses a high-performance gradient system which has the potential to
induce peripheral nerve stimulation (PNS) in patients and MR workers during scans.
2.11.1 Operating Modes
The MRIdian MRI has two operating modes:
• Normal Mode
• First Level Controlled Operating Mode
Normal Mode is a lower gradient power mode.
First Level Controlled Mode has a higher gradient output. The higher the gradient output the
higher the probability and the intensity of peripheral nerve stimulation. Gradient output levels
are based on current literature related to safety, including IEC guidelines
Main Magnet (Bo): The MRIdian MRIS operates in the Normal Operating Mode for Bo at all
times. According to IEC 60601-2-33 (3rd Edition), a field strength of less than 3T is in the
Normal Operating Mode. The MRIdian® system operates at 0.35T.
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