INTERNATIONAL COMMISSION ON NON‐IONIZING RADIATION PROTECTIONICNIRP STATEMENTAMENDMENT TO THE ICNIRP “STATEMENT ON
MEDICAL MAGNETIC RESONANCE (MR)
PROCEDURES: PROTECTION OF PATIENTS”

PUBLISHED IN: HEALTH PHYSICS 97(3):259‐261; 2009

ICNIRP PUBLICATION – 2009

ICNIRP Statement

AMENDMENT TO THE ICNIRP “STATEMENT ON MEDICALMAGNETIC RESONANCE (MR) PROCEDURES: PROTECTION
OF PATIENTS”
The International Commission on Non-Ionizing Radiation Protection*INTRODUCTION

technology and its important and wide-ranging applications in clinical diagnosis (Gowland 2005), ICNIRP hasdecided to issue an amendment of the statement concerning patient exposure to static magnetic fields during theseprocedures. The advice concerning patient exposure tothe switched gradient fields and radiofrequency (RF)fields recommended by ICNIRP (2004) remains current.

ICNIRP PUBLISHED in 2004 a statement on the protection ofpatients undergoing medical magnetic resonance (MR)procedures (ICNIRP 2004). This statement was intended foruse 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, andsafety considerations for the patients were given. Recommendations on research with volunteers were also given.
Since publication of that statement, there have beenfurther studies of the possible health effects of exposure to
the high static magnetic field levels used in the newgeneration of MR systems (summarized by Noble et al.
2005 and AGNIR 2008) and in 2006 the World HealthOrganization (WHO) published a health risk assessment ofstatic magnetic field exposure (WHO 2006). A revision
concerning patient exposure to MR clinical procedures has
been made by the UK Health Protection Agency (HPA2008). In addition, ICNIRP has recently published revised
guidance on occupational and general public exposure tostatic magnetic fields (ICNIRP 2009). These revised guidelines recommend that occupational exposure of the headand 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 practices are implemented to control movement-induced effects.
Further guidance was issued regarding exposure of thegeneral public.
In the light of this updated static magnetic fieldguidance and of the continuing development of MR

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 induced during movement in and around MR systems of up
to 7 T and the associated dosimetry regarding movementinduced 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 Faraday’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 rotationalmotion, either in a uniform field or in a field gradient,produces a change in flux linkage which induces anelectric current, in contrast to linear motion of the bodywithin a uniform static field. With regard to linear
movement in a gradient field, the magnitude of theinduced currents and associated electric fields increases
with velocity of the movement and amplitude of thegradient. Calculations suggest that such induced electricfields will be substantial during normal movement
around or within fields ⬎2–3 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, volunteers 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)
0017-9078/09/0
Copyright © 2009 Health Physics Society259

260

Health Physics

2006b). For a body moving at a constant speed of 0.5 ms⫺1 into a 4 T magnet, Crozier and Liu (2005) estimate
the maximum induced electric field strength in the bodyto be approximately 2 V m⫺1 (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 excitability of nerve tissue due to the slow inactivation of thevoltage-gated sodium ion channels (Bezanilla 2000).
Laboratory studies
The conclusion of ICNIRP in 2004 regarding a lackof effects whilst stationary in a static field of 8 T has been
confirmed in an MR study in which the static fieldcomponent was 9.4 T (Atkinson et al. 2007) where nochange was seen in heart rate or systolic blood pressure
or in other measures of vital functions.
Several studies have reported that individuals exposed to static magnetic fields above 2–3 T experiencetransient sensory effects associated with motion in astatic field gradient such as vertigo, nausea, a metallic
taste, and magnetic phosphenes when moving the eyes orhead (Schenck et al. 1992; de Vocht et al. 2006a and b;
Atkinson et al. 2007). However, the occurrence andseverity 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 magneticfield-induced vertigo experienced by people working in andaround strong static magnetic fields has been investigated insome detail by Glover et al. (2007). Movement of volunteers into the bore of a 7 T whole-body magnet at a speedof 0.1 m s⫺1 resulted in a sensation of rotation (pitchforwards or backwards) in some but not all of the subjects.
The direction of apparent rotation was reversed when theorientation of the subject was reversed in relation to thefield, e.g., by moving from a supine to a prone position,suggesting an effect of induced current on the neural outputof the vestibular system. Head movement within the homogeneous (zero gradient) field at the center of the magnet
resulted in mild to severe vertigo-like effects, and in somecases nausea, for up to 30 minutes.
In contrast to movement-induced effects, postural
sway was increased in some (less than 50%) of thesubjects standing stationary adjacent to the MR scannerin a field of ⬃0.8 T. The effect is thought to be consistent
with differences in magnetic susceptibility between thecalcite crystals that comprise the otoconia of the vestibular organ and the surrounding fluid.
Sensitivity to these effects varies considerably betweenindividuals. Thresholds for motion-induced vertigo in sensitive people were estimated to be of the order of 1 T s⫺1 forgreater than 1 s, and of a field-gradient product of 1 T2 m⫺1

September 2009, Volume 97, Number 3for postural sway. The long integration times required forthese effects to become apparent are indicative of therelatively low frequency response (0.4 – 4 Hz) of the vestibular 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 potentiallyunpleasant 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) andrecommended that such research be carried out, particularly on individuals such as volunteers with high levels ofexposure. It remains the case that there is no specificinformation regarding possible long-term health effects.
Mechanistic considerations however, suggest that anyeffects are likely to be acute.
RECOMMENDATIONSICNIRP notes that it is the responsibility of medical
doctors to balance the risk and benefit to a patientundergoing 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 ofprotection to patients as well as provide no hindrance toroutine clinical imaging. Additionally, it provides flexibility for research and for further development of diagnostic procedures. These tiers were, in summary:● Routine

MR examinations for all patients (normaloperating mode);● Specific MR examinations outside the normal operating range, where discomfort and/or adverse effects forsome patients may occur. A clinical decision must be
taken to balance such effects against foreseen benefits;
exposure must be carried out under medical supervision (controlled operating mode); and● Experimental MR procedures, at levels outside thecontrolled operating range, for which special ethicalapproval may be required in view of the potential risks(experimental operating mode).

ICNIRP Statement ● ICNIRP

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:● 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;● 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 controlled operating mode should be based on levels forwhich there is appreciable human evidence, and should
not go higher than this; and● For the experimental operating mode above 8 T, aprogressively cautious approach is suggested for increasingly high magnetic flux densities due to uncertainties regarding possible effects of flow potentials onheart function. In the light of these possible effects, it
is concluded that patients should be exposed to suchfields only with appropriate clinical monitoring.
There is a need to ensure that patients are moved
slowly into the magnet bore, to avoid the possibility ofvertigo and nausea. Thresholds for motion-induced vertigo have been estimated to be around 1 T s⫺1 for greaterthan 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 astatic magnetic field.
During the preparation of the statement, the composition of the International Commission on NonIonizing 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. Söderberg, Sweden
B. Stuck, U.S.
A. Swerdlow, United Kingdom
B. Veyret, France
Chairman Emeritus, M. Repacholi, Australia
Scientific Secretary, G. Ziegelberger, Austria

261

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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