IEC 60601-2-33:2002/AMD2:2007

IEC 60601-2-33
Edition 2.0 2007-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
AMENDMENT 2
AMENDEMENT 2
Medical electrical equipment –
Part 2-33: Particular requirements for the safety of magnetic resonance
equipment for medical diagnosis

Appareils électromédicaux –
Partie 2-33: Règles particulières de sécurité relatives aux appareils à résonance
magnétique utilisés pour le diagnostic médical

IEC 60601-2-33 A2:2007
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IEC 60601-2-33
Edition 2.0 2007-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
AMENDMENT 2
AMENDEMENT 2
Medical electrical equipment –
Part 2-33: Particular requirements for the safety of magnetic resonance
equipment for medical diagnosis

Appareils électromédicaux –
Partie 2-33: Règles particulières de sécurité relatives aux appareils à résonance
magnétique utilisés pour le diagnostic médical

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
R
CODE PRIX
ICS 11.040.55 ISBN 2-8318-9358-5

– 2 – 60601-2-33 Amend.2 © IEC:2007

FOREWORD
This amendment has been prepared by subcommittee 62B: Medical imaging equipment, of

IEC Technical Committee 62: Electrical equipment in medical practice.

The text of this amendment is based on the following documents:

FDIS Report on voting
62B/663/FDIS 62B/675/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the maintenance result date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
_____________
INTRODUCTION to Amendment 2
This second amendment to IEC 60601-2-33 addresses technical aspects of the medical
diagnostic MR SYSTEM and the MR EQUIPMENT therein, related to the safety of PATIENTS
examined with this system, the safety of the MR WORKER involved with its operation and the
safety of the MR WORKER involved with the development, manufacturing, installation, and
servicing of the MR SYSTEM. The new aspect introduced in this second amendment addresses
the fact that in some countries electromagnetic field (EMF) exposure of workers is or will be
limited by law.
Page 11
INTRODUCTION
Replace the second paragraph by the following:
SYSTEM
This International Standard addresses technical aspects of the medical diagnostic MR
and the MR EQUIPMENT therein, related to the safety of PATIENTS examined with this system,
the safety of the MR WORKER involved with its operation and the safety of the MR WORKER
involved with the development, manufacturing, installation, and servicing of the MR SYSTEM.
Where limits of electromagnetic fields (EMF) exposure of PATIENTS and MR WORKER are
stated, these limits do not imply that such levels of exposure can be assumed to be
acceptable for workers in other professional settings and for the population at large. The limits
provide a sensible balance between risks for the PATIENTS and MR WORKERS and benefits for
the PATIENTS.
60601-2-33 Amend.2 © IEC:2007 – 3 –

Add, after the second paragraph, the following new text:

The introduced EMF exposure limits required in this standard for an MR WORKER are equal to

those allowed for PATIENTS. All exposure levels allowed for a PATIENT and for an MR WORKER

protect them against negative instantaneous and long-term health effects.

Subjective short-term physiological and sensory effects are expected for the exposure to

static magnetic fields only, these influence the well being of the MR WORKER marginally and

only during or shortly after exposure.

For the exposure to GRADIENT OUTPUT and RF transmit fields, normally no short-term

physiological and sensory effects are expected for MR WORKERS.

In addition no experimental or theoretical basis for cumulative biological effects in humans,
resulting from exposure at the allowed levels has been generally accepted.
Add, to the list of examples of organisational aspects in the fourth paragraph, the following
new item:
− rules to minimize and to limit the exposure of MR WORKERS.

Page 13
1 Scope and object
1.2 Object
Replace the first paragraph by the following:
This particular standard establishes requirements for the safety of MR EQUIPMENT to provide
protection for the PATIENT and the MR WORKER.
NOTE This standard presumes that the MR WORKERS are properly screened medically, and properly trained and
instructed in their duties.
Page 15
2 Terminology and definitions
2.12 Miscellaneous
Add, on page 21, the following new definition:
2.12.107
MR WORKER
person that because of his/her profession has to enter the CONTROLLED ACCESS AREA or
equivalent of the MAGNETIC RESONANCE SYSTEM
NOTE Other persons like MR volunteers and PATIENT carers are not covered by this definition, however
OPERATORS and staff are included in this definition (see rationale)

Page 27
6.8.2 INSTRUCTIONS FOR USE
aa) Pre-screening prior to an MR EXAMINATION
Replace the title of 6.8.2 aa) by:
aa) Pre-screening of the PATIENT and MR WORKER

– 4 – 60601-2-33 Amend.2 © IEC:2007

Replace the first paragraph of 6.8.2 aa) as follows:

INSTRUCTIONS FOR USE shall provide clear recommendations to the USER regarding pre-

screening of PATIENTS and MR WORKERS. This specifically applies to those PATIENTS and MR

WORKERS who could be placed at risk due to their professional activity, past medical history,

present medical state and/or the physical environment of the MR EQUIPMENT. These
instructions shall indicate the need for a pre-screening program to identify such PATIENTS and

MR WORKERS at risk, and shall provide recommendations to adequately safeguard these

PATIENTS and MR WORKERS from injury. For the MR WORKER especially the risk due to the past

professional activity, which may have caused accidental implantation of ferromagnetic

materials, shall be considered.

dd) Excessive acoustic noise
Replace the title of 6.8.2 dd) by:
dd) Exposure of the PATIENT and MR WORKER to excessive acoustic noise
Replace the existing last dashed item by the following:
– shall draw attention to the fact that in some countries legislation may exist covering the
exposure of MR WORKERS to noise.
Add a last dash to 6.8.2 dd):
– shall state that for tasks in the CONTROLLED ACCESS AREA during scanning, the MR
WORKER shall wear adequate hearing protection to reach compliance with the rules for
protection of workers to noise.
hh) Static magnetic field
Replace the title of item hh) by:
hh) Exposure of the PATIENT and MR WORKER to the static magnetic field
Replace the first bullet of 6.8.2 hh) by:
– explain the possible effects that PATIENTS and MR WORKERS may experience when the
static magnetic field is above the level of NORMAL OPERATION MODE, paying particular
attention to the effects that may be experienced if the PATIENT or MR WORKER’S head is
moved rapidly while inside or close to the MR EQUIPMENT, including dizziness, vertigo,
and a metallic taste in the mouth;
Add the following dashed items:
– explain that when the main static magnetic field is higher than 2 T and not exceeding
4 T, the MR SYSTEM is continuously operating in the FIRST LEVEL CONTROLLED

OPERATION MODE and therefore ensure that MEDICAL SUPERVISION is provided for all
PATIENTS
– explain that adequate training shall be given to MR WORKERS to minimise adverse
health effects arising from the high static magnetic field. Explain the health effects
related to the increased static magnetic fields and explain the possible changes in the
MR compatibility of the tools and accessories used by the MR WORKER, as a function of
the value of the static magnetic field.
– explain that when the main static magnetic field is higher than 4 T, the MR system is
continuously operating in the SECOND LEVEL CONTROLLED OPERATION MODE and
therefore ensure that MEDICAL SUPERVISION is provided for all PATIENTS. Explain that in
this situation MR WORKERS shall not be allowed to access the MR EQUIPMENT without
local approval as required.
60601-2-33 Amend.2 © IEC:2007 – 5 –

ii) Time varying magnetic fields

Replace the title of item ii) by the following:

ii) Exposure of the PATIENT to time varying magnetic fields

Replace the first paragraph by the following:

For MR EQUIPMENT that is capable of operation at levels of GRADIENT OUTPUT above the

NORMAL OPERATING MODE, the INSTRUCTIONS FOR USE shall draw attention to risk factors, which

may increase the potential for peripheral nerve stimulation for the PATIENT and they shall

describe ways for the USER to mitigate these risk factors. The INSTRUCTIONS FOR USE shall:

jj) Radio frequency magnetic fields
Replace title of the item jj) by:
jj) Exposure of the PATIENT to radio frequency magnetic fields
Replace the first paragraph by the following:
The INSTRUCTIONS FOR USE shall draw attention to risk factors, which may increase the
potential for local excessive RF heating of the PATIENT and they shall describe ways for the
USER to mitigate these risk factors. These factors include:
kk) Occupational exposure
Replace the existing text of this item by the following new text:
The INSTRUCTIONS FOR USE shall draw attention to the fact that MR WORKERS can be exposed
to the electromagnetic fields (EMF) emitted by the MR EQUIPMENT. They shall provide
sufficient information relating to the risks from these exposures to enable safe working
procedures for the MR WORKER. The relevant requirements of 6.8.2 ii) and jj) for the PATIENT
shall also apply for the MR WORKER. This information shall also include
– specification of areas to which access by the MR WORKER is restricted, if any;
– the actual levels of the exposure in all areas accessible to the MR WORKER, expressed in
proper units for the static magnetic field (see 6.8.2 hh) and 51.104), the GRADIENT OUTPUT
(see 6.8.2.ii) and 51.102) and the RF transmit field (see 6.8.2 jj) and 51.103) generated by
the MR EQUIPMENT;
– instructions that the MR WORKER shall be informed and trained sufficiently so that they can
perform all their tasks safely in a way that minimizes their exposure to EMF emitted by the
MR EQUIPMENT;
– a statement that there is a possibility that mild peripheral nerve stimulation (PNS) may be
induced in the PATIENT and MR WORKER when exposed to the gradients in the FIRST LEVEL
CONTROLLED OPERATION MODE;.
The risk factors associated with the expected exposure levels for the MR WORKER shall be
explained. A description of ways for the MR WORKER to mitigate these risk factors shall be
given.
Known factors to draw attention to are the following:
– The possible physiological effect of exposure to RF radiation is heating. Exposure to RF
radiation can be minimised by keeping sufficient distance away from the transmit RF coil
or by reducing time of exposure during scanning;
– The possible physiological effect of exposure to the GRADIENT OUTPUT is peripheral nerve
stimulation for the person exposed. Exposure to GRADIENT OUTPUT can be minimised by
keeping sufficient distance away from the gradient coils during scanning.
– The possible physiological effects of exposure to the static magnetic field are dizziness,
vertigo, and a metallic taste in the mouth of the person exposed. Exposure to the static
magnetic field can be minimised by staying away from the magnet (not just during

– 6 – 60601-2-33 Amend.2 © IEC:2007

scanning but all the time) and by avoiding rapid movements of the head while in the static

magnetic field.
The INSTRUCTIONS FOR USE may state that, it is generally accepted that no published evidence

supporting the occurrence of cumulative and/or long-term effects after exposure to EMF

emitted by the MR EQUIPMENT exists.

The INSTRUCTIONS FOR USE shall state that extra precaution is advisable for pregnant MR

WORKERS, although there is no currently available epidemiological evidence for any negative

health effects. Local regulations may apply.

The INSTRUCTIONS FOR USE shall state that the limits for MR WORKERS may not be applicable

when an MR WORKER is pregnant. It may be required in some countries that the ‘member of

the public’ limit be applied to the foetus.
The INSTRUCTIONS FOR USE shall state that in some countries legislation may exist covering
occupational limits for exposure to EMF, that are lower than the limits for MR WORKER given in
this standard.
Page 39
6.8.3 Technical description
bb) compatibility technical specification sheet
Add to the dashed item Magnet the following additional bullet:
• For MR equipment that is capable of operation in the FIRST LEVEL CONTROLLED OPERATION
MODE or the SECOND LEVEL CONTROLLED OPERATION MODE for the static magnetic field, a plot
representing the 0,5 T, 1 T, 1,5 T, 2 T, 3 T and the 4 T iso-magnetic contours at positions
WORKER shall be included if the static magnetic field
accessible to and relevant for the MR
in the iso-centre exceeds any of these values.
Replace two existing dashed items as follows:
– Gradient system: type, amplitude, rise time, slew rate, and spatial distribution of the
maximum magnitude values of the vector sum of all three GRADIENT OUTPUTS at the
positions accessible to and relevant for the MR WORKER during scanning.
– RF system: types of RF transmit coil, amplifier peak r.m.s. power, applied maximum
transmit RF magnetic field and bandwidth, spatial distribution of the maximum transmit RF
magnetic field at the positions accessible to and relevant for the MR WORKER during
scanning.
Page 51
51.101 Operating modes
51.101.1 All operating modes
Replace item: c) by:
c) The MR EQUIPMENT shall provide information upon request about the relevant SAR and
relevant GRADIENT OUTPUT.
Page 53
51.101.3 FIRST LEVEL CONTROLLED OPERATING MODE
Replace item a) by:
a) Before the start of each scan, an indication of the operating mode defined by the value of
the GRADIENT OUTPUT which will actually be applied during the scan and the value of the
SAR which will actually be applied during the scan, and a prediction of these values (upon

60601-2-33 Amend.2 © IEC:2007 – 7 –

request) shall be displayed at the CONTROL PANEL. The value for the GRADIENT OUTPUT shall

be expressed as the percentage of the upper level of the FIRST LEVEL CONTROLLED

OPERATION MODE (L12) for the scan applied.

51.101.4 SECOND LEVEL CONTROLLED OPERATING MODE

Replace item b) by:
b) Before the start of each scan, an indication of the operating mode defined by the value of

the GRADIENT OUTPUT which will actually be applied during the scan and the value of the

SAR which will actually be applied during the scan, and a prediction of these values (upon

request) shall be displayed at the CONTROL PANEL. The value for the GRADIENT OUTPUT shall
be expressed as the percentage of the upper level of the FIRST LEVEL CONTROLLED
OPERATION MODE (L12) for the scan applied.
51.102 Protection against excessive low frequency field variations produced by the
gradient system.
51.102.1 Objectives for limitation of GRADIENT OUTPUT
Replace, on page 55, the first two sentences of the existing text by the following
The MR EQUIPMENT shall be designed to automatically control the GRADIENT OUTPUT so that
cardiac stimulation in the PATIENT and in the MR WORKER at any operating mode is prevented.
The MR EQUIPMENT shall be designed to automatically control the GRADIENT OUTPUT so that the
occurrence of intolerable peripheral nerve stimulation (PNS) in the PATIENT and in the MR
WORKER in any operating mode is minimised.
51.102.2 Limits for GRADIENT OUTPUT
Replace the existing first sentence by:
In this subclause, limits for the PATIENT and the MR WORKER are expressed either as the
electric field E induced in the PATIENT or the MR WORKER by the changing magnetic field of the
gradients, or by dB/dt, the time rate of change of that field.
Add the following note at the end of the subclause:
NOTE MR WORKER exposure limits are the same as for the PATIENTS. Compliance with the GRADIENT
OUTPUT limits for PATIENTS therefore automatically implies compliance for the MR WORKERS.

Page 61
51.103 Protection against excessive radio frequency energy

51.103.1 Limits for temperature
Add to the existing first paragraph the following new text:
WORKER caused by the MR EQUIPMENT are
Allowed values for the temperature rise of the MR
equal to the values for the PATIENT as defined in Table 104 for the NORMAL OPERATING MODE
and the FIRST LEVEL CONTROLLED OPERATING MODE.
Add the following note to Table 105:
NOTE MR WORKER exposure limits are the same as for the PATIENTS. Compliance with the SAR limits for
PATIENTS therefore in practice implies compliance for the MR WORKERS.

– 8 – 60601-2-33 Amend.2 © IEC:2007

Page 67
51.105 Methods to demonstrate compliance with the requirements

51.105.2 Determination of maximum GRADIENT OUTPUT

Add the following new title at the beginning of the existing text:

51.105.2.1 General requirement for the determination of the maximum GRADIENT

OUTPUT
Add the following new title just before the start of the italic text:

51.105.2.2 Determination of the maximum GRADIENT OUTPUT for the PATIENT

Add, on page 73, a new subclause 51.105.2.3 before 51.105.3:
51.105.2.3 Determination of the GRADIENT OUTPUT stray field as required for reporting
in 6.8.3 bb.
To be able to estimate the exposure for MR WORKERS, for each GRADIENT UNIT the spatial
maximum of the GRADIENT OUTPUT shall be determined in an extended COMPLIANCE VOLUME,
see Figures 107a and 107b. The specific point pattern shall represent worst-case locations
where the MR WORKER has access to and can be maximally exposed by the GRADIENT UNIT.
NOTE For transverse field magnet types the cylinder axis (i.e. patient axis) is perpendicular to the magnet axis.
The term patient bore is to be replaced by magnet gap between pole shoes; the term magnet length is to be
replaced by pole shoe diameter.
- The specific point pattern shall be located on a virtual cylinder surrounding the PATIENT
axis with a diameter equal to the minimum accessible PATIENT bore.
- The cylinder starts at the magnet isocentre and exceeds the PATIENT bore opening (half
the magnet length) by at least 0,5 m.
- In the cylinder axis direction the points shall have a separation of not more than 0,1 m.
- For each cylinder axis position at least 16 points shall be equidistantly spaced on the
cylinder surface (i.e. on a circle). The points shall include those located half way between
the x and y gradient axes (i.e. n x 45°, n = 1,3,5,7).
- The magnetic field vector for each GRADIENT OUTPUT shall be calculated using the law of
Biot-Savart or measured for each point on the cylinder.
- For each point the three FIELD vectors shall be summed and then the field magnitude
shall be determined.
- This maximum magnitude values shall be plotted along the cylinder axis position. The
axial position of the PATIENT bore opening shall be marked.
NOTE The pattern is also considered to be relevant for estimating possible PNS for the MR WORKER and
illustrates the relative field distribution outside the space accessible for the PATIENT.

Report of results:
• distance of points along cylinder axis;
• number of points azimuthally;
• graph of maximum magnitude values along the cylinder axis.

60601-2-33 Amend.2 © IEC:2007 – 9 –

Add the following Figure 107:
e
n
a
d
c
b
f
i
z
i
IEC  2102/07
Figure 107a – CYLINDRICAL MAGNET

e
n
a
b d
c
z
i
f
i
IEC  2103/07
Figure 107b – TRANSVERSE FIELD MAGNET
a magnet
b magnet isocentre
c patient axis and axis of a virtual cylinder
d diameter of virtual cylinder representing the minimum accessible patient bore;
e points on the cylinder surface where the magnitude of all three magnetic field vectors shall
n
be determined. The maximum magnetic field magnitude found on the cylinder surface at
distance z from the isocentre in any of the points e represents the worst case field on the
i n
surface f .
i
Figure 107 – Determination of the spatial maximum of the gradient output

– 10 – 60601-2-33 Amend.2 © IEC:2007

Add, on page 89, new subclause 51.105.3.3:

51.105.3.3 Determination of the B stray field as required for reporting in 6.8.3 bb)
The maximum RF transmit magnetic field of the RF transmit coil shall be measured or

WORKER.
calculated and reported at the positions accessible to and relevant for the MR

The B (z) field shall be measured or calculated at points along a straight line along the patient
axis beginning at the magnet isocentre.

NOTE For cylindrical magnets the patient axis is equivalent to the magnet axis; for TRANSVERSE FIELD MAGNET

types the cylinder axis (i.e. patient axis) is perpendicular to the magnet axis. It is sufficient to measure / calculate

the B field along the patient axis only because the B field is assumed to be sufficiently homogenous in each
1 1
transversal plane of the RF transmit coil.

- The distance between each successive point shall not exceed 0,1 m.
- The magnitude of the B field shall be measured or calculated for each point.
- When measured, the measurement can be performed by using a suitable pick up coil and
a network analyzer or by using an RF signal generator and a spectrum analyzer. For
magnets with circular polarized RF transmit field it is sufficient to determine the radial
component only.
2 2
(z) and B (0) shall be calculated for each point.
- The ratio of B
1 1
- The calculated value for a single point at a distance z from the magnet isocentre shall
apply to all locations on a base area of a virtual cone to represent worst-case condition
on this base area, see Figures 108a and 108b. The base area of the cone is the area
perpendicular to the straight line at distance z from the isocentre. The cone is defined by
the opening angle given by the projection from the magnet isocentre to the magnet
aperture. The height of the cone is given by the distance z. For TRANSVERSE FIELD MAGNET
types the area is defined by the superposition of base areas by rotating the cone around
the magnet isocentre.
NOTE See rationale for detailed explanation.
Report of results:
- coordinates of the points where B (z) is measured or calculated
(z) in the measured points relative to the magnitude
- magnitude of the magnetic field B
B (0) in the isocentre
60601-2-33 Amend.2 © IEC:2007 – 11 –

Add the following new Figure 108:

e
i
a
c
b
f
i
z
i
IEC  2104/07
Figure 108 a) – CYLINDRICAL MAGNET
e
i
a
c
b
f
i
IEC  2105/07
Figure 108 b) – TRANSVERSE FIELD MAGNET
a magnet
b magnet isocentre
c patient axis
z distance of point e from isocentre.
i i
2 2
B (z ) shall be determined by measurement or calculation. The ratio B (z ) and B (0) shall be
1 i 1 i 1
calculated for each point e . The calculated value in point e shall apply for the corresponding
i i
grey area f . The value in point e always represents a worst case for any location within the
i i
area f .
i
Figure 108 – Determination of the B stray field
– 12 – 60601-2-33 Amend.2 © IEC:2007

Page 95
Annex AA – Examples of warning signs and prohibitive signs

Add the following new text at the end of the annex:

Extra examples for the marking introduced for medical devices and other items for safety in

1)
the MR environment are introduced in the ASTM standard F2503-05 . This relates

specifically to markings for MR Safe, MR Conditional and MR Unsafe devices.

Page 97
Annex BB – Guidance and rationale for particular subclauses
Add the following new texts to the guidance and rationale for particular subclauses:
Concerning Introduction:
The most important new aspect introduced in this second amendment is the fact that the
employer of the MR WORKER is now encouraged to define rules and formulate requirements
for MR WORKERS, because in some countries the EMF, produced by the MR SYSTEM, may
result in exposure of workers, which is or will be limited by law.
Concerning 2.12.107 MR WORKER
The concept of MR WORKERS is related to the level of exposure of this group of workers to the
EMFs emitted by the MR system. This level may be higher than what is allowed by legal
regulations in some countries for workers in general, creating for the MR WORKER the need of
special EMF exposure limits as defined in this standard. The EMF exposure limits stated in
this document permit the unrestricted presence of the MR WORKER in CONTROLLED ACCESS
AREA even during scanning. The level of these limits and the resulting risks to the MR WORKER
are discussed elsewhere in this annex.
The term MR WORKER includes all people working near the MR EQUIPMENT in the CONTROLLED
ACCESS AREA or equivalent either in the medical arena where the MR SYSTEM is installed and
being operated and serviced or at the manufacturer where the MR SYSTEM is being developed
and manufactured. As such the MR WORKER includes but is not limited to the personnel
SYSTEM, the OPERATOR and the medical staff, or the MR WORKER can be
maintaining the MR
the technical personnel at the MR manufacturer, development and manufacturing engineers,
installation and service personnel. Both groups of MR WORKERS are equally essential in
maintaining the medical benefits for the PATIENTS.

Apart form the MR WORKER, two further groups of individuals exposed to the EMFs emitted by
the MR system can be discerned. These are MR volunteers and MR PATIENT carers.
An MR volunteer is an individual who has freely consented to an investigational MR procedure
authorized by local regulations, and therefore is subject to the limits authorized by the ethics
committee. An MR volunteer is therefore not considered to be an MR WORKER according to the
definition in this standard.
An MR PATIENT carer is an individual, who supports the PATIENT during an examination and
therefore may be exposed to the same level as for PATIENTS. MR PATIENT carers therefore can
PATIENT. An MR PATIENT carer, who is not
be informed and screened in the same way as the
employed as an MR WORKER, is therefore not considered to be an MR WORKER according to
the definition in this standard.
___________
1)
ASTM F2503-05:2005, Standard Practice for Marking Medical Devices and Other Items for Safety in the
Magnetic Resonance Environment

60601-2-33 Amend.2 © IEC:2007 – 13 –

Replace, on page 99, the heading of the rationale for item 6.8.2 aa) as follows:

Concerning 6.8.2 aa) Pre-screening of the PATIENT and MR WORKER

Replace, on page 101, the heading of the rationale for item 6.8.2 dd) as follows:

Concerning 6.8.2 dd) Exposure of the PATIENT and MR WORKER to excessive acoustic

noise
Replace, on page 111, the heading of the rationale for items 6.8.2 hh) and 6.8.2 kk) as
follows:
Concerning 6.8.2 hh) Exposure of the PATIENT and MR WORKER to static magnetic field
Replace the fifth paragraph of the rationale concerning 6.8.2 hh) by the following:
It should be realized that the European Directive 2004/40/EC (as referred to in the rationale
for 6.8.2 kk)) does not currently include exposure limit values for workers for the static
magnetic field. Exposure limit values are given in Table 1 of the European Directive. The
lowest frequency range is ‘up to 1 Hz’ and thus does not include the 0 Hz of the static
magnetic field. Values for exposure to the static magnetic field may be introduced in the next
update of the European Directive in 2009. A guideline for these values may be introduced
much earlier and will probably be issued by ICNIRP (see rational for 6.8.2.kk)) in 2007.
Exposure to the static magnetic field for the MR WORKER is allowed up to 4 T in this standard.
This value is proposed because known physiological and sensory effects of the exposure to
static magnetic fields up to 4 T are limited to subjective observations like dizziness and
vertigo. These observations by the person involved can be dependent on the head movement
of the person during exposure and vary a lot between individuals and are not considered to be
a negative health effect for the MR WORKER apart from his/her general well being during
exposure.
Although for specific types of MR WORKER the frequency of exposure to static magnetic
fields > 2 T may be relative high, there is no generally accepted known HARM to these MR
WORKERS as a result of the sensory effects. In addition the probability of HARM to the PATIENT
as a result of these effects on the MR WORKER (resulting possibly in loss of concentration or
unstable hand control) is estimated to be very low. It is subject to separate work place and
function specific guidelines and regulations on working practice. Consequently, the risk
associated with both HAZARDS is estimated to be acceptable even at static magnetic fields up
to 4 T. For both the PATIENT and the MR WORKER, exposure to higher values than 4 T requires
approval following local regulations.
An important point for consideration is the fact that many published reports indicate that it is
not the exposure to the static magnetic field, but the movement in the static magnetic field
(including the stray field of the magnets of the MR EQUIPMENT), that results in the observed
physiological and sensory effects. It is claimed that just being exposed to the static magnetic
field (e.g. standing next to the magnet or laying still on the PATIENT support in the field) does
not create any sensory effect. This suggests exposure limits should be expressed in T/s
rather than T.
Movement in the inhomogeneous stray magnetic field of the magnet induces electric currents
in the human tissue, which may call for an exposure limit value. A recent publication [139] has
illustrated that the current densities induced can exceed the values set by the ICNIRP
guidelines [125] in the frequency range of a few Hz, which can be seen as the frequency
range relevant for the movement of an MR WORKER in the stray field of the magnet. Although
the static magnetic field exposure limit is not included in the European Directive 2004/40/EC,
the movement in the static magnetic field is not explicitly excluded and therefore exposure
limit values given in the directive currently must be interpreted as conflicting with current
practice with almost all high field MR SYSTEMS in the hospitals.

– 14 – 60601-2-33 Amend.2 © IEC:2007

In 2006 the World Health Organization published a report entitled: Environmental health

Criteria 232, Static fields [137]. This report is the result of an extensive review of all peer-

reviewed literature on the health effects of electric and magnetic static fields. More than 500

references to literature are given and discussed. It reports on the possible interaction

mechanisms with the human body, includes in vitro studies, animal studies, laboratory studies

on humans, epidemiological studies, health risk assessment and recommendations for further

studies. This report is the major source of input for the expected update of ICNIRP guidelines
for human exposure to static magnetic fields. It is however noted that the conclusion of this

extensive report specifically for the health effects related to static magnetic fields is still

formulated as: “Nonetheless, the severe lack of information has meant that it is not been

possible to properly characterise the risks from static field exposure.”

It may be added that at very high values of the static magnetic field (>10 T) effects are
reported on the third cleavage of the frog egg leading to developmental abnormalities as
reported by Denegre [136]. A theoretical investigation is published by Keltner [79], showing
that even at very high values of the static magnetic field (=10 T), magneto hydrodynamic
effects in the main blood vessels will still have an insignificant effect on vascular pressure.

Introduce a separate rational concerning 6.8.2 kk):
Concerning 6.8.2 kk) Occupational exposure
Limits for the protection of workers for exposure to electromagnetic fields are introduced in
the European Directive 2004/40/EC [124], which was accepted by the European Commission
in April 2004. The limits introduced, are based on the International Commission on Non-
Ionizing Radiation Protection (ICNIRP) guideline for workers in general [125].
The limits for electromagnetic exposure for the MR WORKER, introduced in this standard are in
excess of those permitted by the ICNIRP guideline [125] as the result of the following
rationale:
- The devices are expected to be designed and manufactured in such a way that, when
used under the conditions and for the purposes intended, they will not compromise the
clinical condition or the safety of PATIENTS, or the safety and health of USERS or, where
applicable, other persons, provided that any risks which may be associated with their use
constitute acceptable risks when weighed against the benefits to the PATIENT and are
compatible with a high level of protection of health and safety [138].
- It is the philosophy of ICNIRP to give exposure limits for the protection of workers in
general. ICNIRP does not consider the need to balance associated health risks with social
benefit (social and economical considerations are outside of the remit of ICNIRP) and
therefore ICNIRP cannot consider the possible relaxation of its guidelines for special
categories of workers based on social arguments. Thus, ICNIRP does not acknowledge
the specific and unique situation of MR WORKERS and more specifically the risk/benefit for

the PATIENT and balancing this benefit with the risk for the MR WORKER.
- ICNIRP guidelines for the safe exposure of MR PATIENTS are recently published [126].
Limits are identical to those in IEC 60601-2-33, 2nd edition (2002).
- This risk management approach is specifically applied for the exposure to static magnetic
fields for the MR WORKER, see the addition to the rational of 6.8.2 hh) in this 2nd
amendment
- The limits in the range of a few Hz to about 100 kHz for the MR WORKER are based on
thresholds for peripheral nerve and muscle stimulation and cardiac muscle stimulation and
are low enough to avoid all such physiological effects. There are no peer-reviewed
published reports of gradient-induced magneto-phosphenes.
- Since minimal peripheral nerve stimulation is accepted for the MR WORKER under some
circumstances, it may be required to give extra instructions to the MR WORKER to reduce
the exposure to the GRADIENT OUTPUT. For this reason a prediction of the expected
GRADIENT OUTPUT is now also displayed (on request) on the CONTROL PANEL and can be
used to either reduce exposure by creating sufficient distance from the scanner during

60601-2-33 Amend.2 © IEC:2007 – 15 –

scanning or by reducing the value of the GRADIENT OUTPUT to a lower value for the

requested scan.
For pregnant MR WORKERS extra precaution is advisable, but there is no epidemiological

evidence for any negative health effects. It is advisable for a pregnant MR WORKER not to stay

in the scan room during scanning to avoid unnecessary exposure to gradient and

radiofrequency electromagnetic fields and noise levels. Local regulations may apply.

Instructions for use state that the limits for workers may not be applicable when a MR WORKER

is pregnant. It may be required that the ‘member of the public’ limit may be applied to the

foetus in some countries.
The risk management approach is also applied for the exposure to the GRADIENT OUTPUT EMF

generated by MR SYSTEMS when balancing the probability of risk of ionizing radiation versus
MR [127]. The cumulative effect of exposure to ionizing radiation has been studied
extensively. Workers exposed to ionizing radiation with energy ≥ 12,4 electron volts (or 2 x
-18
10 Joules) are regulated by limits recommended by such groups as the National Council on
Radiation Protection and Measurements (NCRP) and the International Commission on
Radiation Protection (ICRP) [128]. The following illustrates the difference between that type of
radiation and the frequency range of the EMF in an MR SYSTEM (1 kHz – 1 GHz): An MR
scanner would need a magnetic field strength of 5,68 x 10 Tesla (the resonant frequency for
protons would be 2,4 x 10 Hz) to reach this threshold level (five orders of magnitude above
the field strengths of any current scanners). At 4 T the energy in any MR photons (assuming
the system is capable of radiating) would be a factor of 1,4 x 10 below the 12,4 electron volts
threshold. In fact, the energy of any 4 T photons would be a factor of 5,8 x 10 below the
threshold energy needed to break hydrogen-hydrogen bonding in water (the weakest of all
bonds) [129]. So, in MR biological interactions similar to radiation, damage by ionizing
radiation from single photons are not possible. This reasoning suggests that it can be
concluded that cumulative effects on the molecular level from EMF exposure from MRI will be
absent. To the working group’s knowledge, there are no peer-reviewed published studies up
to the present day that show any of these cumulative effects.
In the United States the annual occupational exposure limit [132, 133] for ionizing radiation
(10 CFR 20 subpart C) is 0,05 Sv (5 rem), while the general public may not be exposed to
more than 0,001 Sv (0.1 rem). The threshold for observable effects from ionizing radiation
[132] is about 0,05 Sv. A PATIENT receiving a head computed tomography (CT) scan is
estimated to receive up to 0,03 Sv [132]. The risk of dying from cancer from an exposure to
0,01 Sv (1 rem) has been estimated at 0,0005 [132]. In contrast, there is no known risk of
dying from MR exposures provided operating complies with IEC 60601-2-33 (2002) limits.
In conclusion, risks to MR WORKERS exposed to the possible EMF generated by MR SYSTEMS
appear to be very low. Workers exposed to ionizing radiation appear to be at higher, but still
acceptable risk levels.
nd
The probability of cardiac stimulation under the 2 edition of the IEC 60601-2-33 limits is

close to zero, as shown in the rationale of 51.102 4). Reilly [130] determined that cardiac
fibrillation thresholds follow a lognormal distribution with the threshold for the most sensitive
percentile about half the value for the median. In addition, Reilly estimated that for a given
animal the median cardiac stimulation threshold is about 40% of the cardiac fibrillation level.
Reilly estimated that the rate of change of the magnetic field, (dB/dt) , which may
1% cardiac
stimulate hearts in the most sensitive percentile of the population is related to the total
gradient ramp duration, d, and to a time constant, τ, and may be expressed by the following
equation:
⎛ dB⎞ 60
=
⎜ ⎟
dt
⎛ − d⎞
⎝ ⎠
1% cardiac
1− exp⎜ ⎟
τ
⎝ ⎠
Reilly used a value of 3 ms for τ. Bourland et al [90] found that thresholds for canine cardiac
...