Object ID: 00000018WIA30F72870GYZ
Topic ID: id_40023682 Version: 1.13
Date: Jul 26, 2022 1:23:54 PM

Gradient output limits

Safety parameter levels approved for the Second Controlled Operating Mode are set by the Investigational Review Board (IRB) or other human studies boards.Gradient output levels are measured as a percentage of the mean peripheral nerve stimulation threshold (PNS).

CAUTION

Continuous patient observation and contact are required in all modes of operation. Medical Supervision is required in the First or Second Level controlled operating modes.

The MR system gradients are capable of operating under several modes:

Normal Operating Mode: mode of operation of the MR equipment in which none of the outputs have a value that can cause physiological stress to patients.
First Level Controlled Operating Mode: mode of operation of the MR equipment in which one or more outputs reach a value that can cause physiological stress to patients which needs to be controlled by medical supervision.
Second Level Controlled Operating Mode: mode of operation of the MR equipment in which one or more outputs reach a value that can produce significant risk for patients, for which explicit ethical approval is required (i.e. a human studies protocol approved to local requirements).

IEC 60601-2-33: 201.7.9.2.101 (i)

The table below lists system operating modes and associated threshold limits. It gives d|B|/dt for the maximum magnitude values of the vector sum of the field components generated by each of the three GRADIENT UNITS simultaneously at the published peak gradient strength and peak slew rate. The values are in terms of d|B|/dt at various diameters (in meters) from the gradient coil axis. The diameters include 0.2 m, 0.4 m, and the bore diameter minus 0.1 m. The values include no peripheral nerve stimulation limits.

Table 1. Maximum d|B|/dt on cylinders of various diameters at the MR system slew rate
max d\|B\|/dt [T/s]	D= 0.2 (m)	D = 0.4 (m)	D = 0.45 (m)	D = 0.5 (m)	D = 0.6 (m)
VRMW 70 cm bore	43.3	57.5	N/A	N/A	86.8

CAUTION

Gradient output may be controlled by Local Approval.

IEC gradient output limits


Operating mode	PNS Limit
Normal	80% mean nerve stimulation threshold
First Level (controlled mode)	100% of the mean nerve stimulation threshold. Requires you to click the [Accept] button to proceed when the Normal mode dB/dt or SAR limits are exceeded, but Second Level mode has not yet been reached.
Second Level (controlled mode)	Requires research key and IRB or Human Ethical Committee approval of the research to be conducted.