INTERNATIONAL COMMISSION ON NON‐IONIZING RADIATION PROTECTION
ICNIRP PUBLICATION – 2009 ICNIRP STATEMENT
AMENDMENT TO THE ICNIRP "STATEMENT ON
MEDICAL MAGNETIC RESONANCE (MR)
PROCEDURES: PROTECTION OF PATIENTS" PUBLISHED IN: HEALTH PHYSICS 97(3):259‐261; 2009
ICNIRP Statement
AMENDMENT TO THE ICNIRP "STATEMENT ON MEDICAL
MAGNETIC RESONANCE (MR) PROCEDURES: PROTECTION
OF PATIENTS"
The International Commission on Non-Ionizing Radiation Protection*
INTRODUCTION
ICNIRP PUBLISHED in 2004 a statement on the protection of
patients undergoing medical magnetic resonance (MR)
procedures (ICNIRP 2004). This statement was intended for
use by international and national medical device regulatory
authorities, MR users and health professionals, and those
involved in the design and manufacture of MR equipment
for clinical applications. Contraindications, precautions, and
safety considerations for the patients were given. Recom-
mendations on research with volunteers were also given.
Since publication of that statement, there have been
further studies of the possible health effects of exposure to
the high static magnetic field levels used in the new
generation of MR systems (summarized by Noble et al.
2005 and AGNIR 2008) and in 2006 the World Health
Organization (WHO) published a health risk assessment of
static magnetic field exposure (WHO 2006). A revision
concerning patient exposure to MR clinical procedures has
been made by the UK Health Protection Agency (HPA
2008). In addition, ICNIRP has recently published revised
guidance on occupational and general public exposure to
static magnetic fields (ICNIRP 2009). These revised guide-
lines recommend that occupational exposure of the head
and trunk should not exceed a spatial peak magnetic flux
density of 2 tesla (T) except for the following circumstance.
For work applications for which exposures above 2 T are
deemed necessary, exposure up to 8 T can be permitted if
the environment is controlled and appropriate work prac-
tices are implemented to control movement-induced effects.
Further guidance was issued regarding exposure of the
general public.
In the light of this updated static magnetic field
guidance and of the continuing development of MR
technology and its important and wide-ranging applica-
tions in clinical diagnosis (Gowland 2005), ICNIRP has
decided to issue an amendment of the statement concern-
ing patient exposure to static magnetic fields during these
procedures. The advice concerning patient exposure to
the switched gradient fields and radiofrequency (RF)
fields recommended by ICNIRP (2004) remains current.
RATIONALE
The following is a brief summary of the conclusions
regarding studies of the possible health effects resulting
from exposure to static magnetic fields published since
the ICNIRP (2004) statement. Most of the new studies
have concerned laboratory investigations of effects in-
duced during movement in and around MR systems of up
to 7 T and the associated dosimetry regarding movement-
induced electric fields and currents.
Dosimetry: movement-induced electric fields
and currents
Time-varying magnetic fields induce electric fields
and currents in living tissues in accordance with Fara-
day’s law of induction. Such fields and currents may also
be induced by movement in a static magnetic field. In
particular, motion along a field gradient or rotational
motion, either in a uniform field or in a field gradient,
produces a change in flux linkage which induces an
electric current, in contrast to linear motion of the body
within a uniform static field. With regard to linear
movement in a gradient field, the magnitude of the
induced currents and associated electric fields increases
with velocity of the movement and amplitude of the
gradient. Calculations suggest that such induced electric
fields will be substantial during normal movement
around or within fields Ͼ2–3 T (Crozier and Liu 2005),
and may account for the numerous reports of vertigo,
nausea and flickering light sensations (termed magnetic
or magneto-phosphenes) experienced by patients, volun-
teers and workers moving in the field (Schenck et al.
1992; Chakeres and de Vocht 2005; de Vocht et al.
* ICNIRP, c/o BfS—G. Ziegelberger, Ingolstaedter Landstr. 1,
85764 Oberschleissheim, Germany.
For correspondence contact G. Ziegelberger at the above address,
or email at info@icnirp.org.
(Manuscript accepted 26 May 2009)
0017-9078090
Copyright © 2009 Health Physics Society2592006b). For a body moving at a constant speed of 0.5 msϪ1into a 4 T magnet, Crozier and Liu (2005) estimate
the maximum induced electric field strength in the body
to be approximately 2 V mϪ1
(WHO 2007). It should be
noted that frequencies associated with body movement
are likely to be less than 10 Hz, the frequency below
which accommodation decreases the electrical excitabil-
ity of nerve tissue due to the slow inactivation of the
voltage-gated sodium ion channels (Bezanilla 2000).
Laboratory studies
The conclusion of ICNIRP in 2004 regarding a lack
of effects whilst stationary in a static field of 8 T has been
confirmed in an MR study in which the static field
component was 9.4 T (Atkinson et al. 2007) where no
change was seen in heart rate or systolic blood pressure
or in other measures of vital functions.
Several studies have reported that individuals ex-
posed to static magnetic fields above 2–3 T experience
transient sensory effects associated with motion in a
static field gradient such as vertigo, nausea, a metallic
taste, and magnetic phosphenes when moving the eyes or
head (Schenck et al. 1992; de Vocht et al. 2006a and b;
Atkinson et al. 2007). However, the occurrence and
severity of these symptoms can be decreased by slowing
the rate of motion of an individual through the magnetic
field gradient (Chakeres and de Vocht 2005).
The theoretical and experimental basis for magnetic-
field-induced vertigo experienced by people working in and
around strong static magnetic fields has been investigated in
some detail by Glover et al. (2007). Movement of volun-
teers into the bore of a 7 T whole-body magnet at a speed
of 0.1 m sϪ1
resulted in a sensation of rotation (pitch
forwards or backwards) in some but not all of the subjects.
The direction of apparent rotation was reversed when the
orientation of the subject was reversed in relation to the
field, e.g., by moving from a supine to a prone position,
suggesting an effect of induced current on the neural output
of the vestibular system. Head movement within the homo-
geneous (zero gradient) field at the center of the magnet
resulted in mild to severe vertigo-like effects, and in some
cases nausea, for up to 30 minutes.
In contrast to movement-induced effects, postural
sway was increased in some (less than 50%) of the
subjects standing stationary adjacent to the MR scanner
in a field of ϳ0.8 T. The effect is thought to be consistent
with differences in magnetic susceptibility between the
calcite crystals that comprise the otoconia of the vestib-
ular organ and the surrounding fluid.
Sensitivity to these effects varies considerably between
individuals. Thresholds for motion-induced vertigo in sen-
sitive people were estimated to be of the order of 1 T sϪ1forgreater than 1 s, and of a field-gradient product of 1 T2mϪ1for postural sway. The long integration times required for
these effects to become apparent are indicative of the
relatively low frequency response (0.4–4 Hz) of the ves-
tibular system (Grossman et al. 1988; Pozzo et al. 1990;
MacDougall and Moore 2005).
In conclusion, current information does not indicate
any serious health effects resulting from acute exposure
to static magnetic fields up to 8 T. It should be noted,
however, that such exposures can lead to potentially
unpleasant sensory effects such as vertigo during head or
body movement.
Epidemiological studies
ICNIRP (2004) noted that there have been no
epidemiological studies performed to assess possible
long-term health effects in patients (or volunteers) and
recommended that such research be carried out, particu-
larly on individuals such as volunteers with high levels of
exposure. It remains the case that there is no specific
information regarding possible long-term health effects.
Mechanistic considerations however, suggest that any
effects are likely to be acute.
RECOMMENDATIONS
ICNIRP notes that it is the responsibility of medical
doctors to balance the risk and benefit to a patient
undergoing an MR examination. It remains the case that,
as noted by ICNIRP (2004), very little is known about
the effects of static magnetic fields in excess of 4 T
on the growth and development of fetuses and infants,
and therefore some caution may be warranted regarding
their imaging above 4 T.
The three-tier approach used previously by ICNIRP
(2004) is still considered to afford adequate levels of
protection to patients as well as provide no hindrance to
routine clinical imaging. Additionally, it provides flexi-
bility for research and for further development of diag-
nostic procedures. These tiers were, in summary:
●くろまる Routine MR examinations for all patients (normal
operating mode);
●くろまる Specific MR examinations outside the normal operat-
ing range, where discomfort and/or adverse effects for
some patients may occur. A clinical decision must be
taken to balance such effects against foreseen benefits;
exposure must be carried out under medical supervi-
sion (controlled operating mode); and
●くろまる Experimental MR procedures, at levels outside the
controlled operating range, for which special ethical
approval may be required in view of the potential risks
(experimental operating mode).
260 Health Physics September 2009, Volume 97, Number 3
It is recommended that until further information
becomes available, the limits on static magnetic field
exposure recommended by ICNIRP (2004) should be as
follows for each operating mode:
●くろまる For the normal operating mode there should be an
upper limit for whole-body exposure of 4 T, in view of
uncertainties regarding the effects of higher fields,
including effects on fetuses and infants;
●くろまる For the controlled operating mode, there should be an
upper limit for whole-body exposure of 8 T. ICNIRP
considers that the exposures permitted under the con-
trolled operating mode should be based on levels for
which there is appreciable human evidence, and should
not go higher than this; and
●くろまる For the experimental operating mode above 8 T, a
progressively cautious approach is suggested for in-
creasingly high magnetic flux densities due to uncer-
tainties regarding possible effects of flow potentials on
heart function. In the light of these possible effects, it
is concluded that patients should be exposed to such
fields only with appropriate clinical monitoring.
There is a need to ensure that patients are moved
slowly into the magnet bore, to avoid the possibility of
vertigo and nausea. Thresholds for motion-induced ver-
tigo have been estimated to be around 1 T sϪ1
for greater
than 1 s; avoiding these sensations is likely to afford
protection against other effects of induced electric fields
and currents that arise as a consequence of motion in a
static magnetic field.
During the preparation of the statement, the com-
position of the International Commission on Non-
Ionizing Radiation Protection was as follows:
P. Vecchia, Chairman, Italy
R. Matthes, Vice-Chairman, Germany
M. Feychting, Sweden
A. Green, Australia
K. Jokela, Finland
J. Lin, U.S.
A. Peralta, Philippines
R. Saunders, United Kingdom
K. Schulmeister, Austria
P. So
̈derberg, Sweden
B. Stuck, U.S.
A. Swerdlow, United Kingdom
B. Veyret, France
Chairman Emeritus, M. Repacholi, Australia
Scientific Secretary, G. Ziegelberger, Austria
Acknowledgments—The support received by ICNIRP from the European
Commission, and the German Federal Ministry for the Environment is
gratefully acknowledged.
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ICNIRP Statement ●くろまる ICNIRP