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Brain awareness week at the European Parliament
The UE directive 2004/40/EC
and Magnetic Resonance Imaging
a debate
Thierry Metens Ph D
Université Libre de Bruxelles, Hôpital Erasme
Magnetic resonance Imaging MRI
Clinical MRI: strong C° evolution since early 1980's =>unique medical imaging progress
worldwide > 20000 scanners & > 60M exams/year
Brain MR:
unequalled tissue resolution (T1, T2, r, MTC, ...)
Emergency brain Imaging acute stroke, Diffusion MRI
Brain structural connectivity: Nerve Tractography
Brain activation: fMRI
Brain metabolism: MRS
WIP: Interventional procedures, brain peroperative MRI ,
MRI&FUS thermotherapy/drug delivery, ...
MRI
Both clinical and scientific unique data
MRI: the technical ingredients
Main Magnetic field (static) B0: 0.2 - 7.0T (earth ~ 50mT)
Clinical Brain: optimum @ 3.0T
Pulsed Magnetic field Gradients:1KHz switching rate
up to 60mT/m slew rate 200mT/m/ms
Gradient field shielding
B
z
Pulsed Radio 0frequency B1 field: B1 ~ 10-30mT @ 10-500MHz
Non ionizing radiation
Faraday Shielding
MRI: the technical ingredients
Main Magnetic field: B0 field shielding => Strong B0 gradient
Ferromagnetic objects attraction MAIN DANGER
Transient Vertigo
Pulsed Magnetic field Gradients:
dB/dt Nerve stimulation, Induced currents in patient and in the
close vicinity IEC Limits
Pulsed Radio frequency B1 field:
Patient tissue heating SAR IEC Limits
Includes any EM device: portable phone, Oven, MRI, ...
Exposure limit values & Action values
Conflict with MRI
exposure limit values: limits on exposure to electromagnetic fields which are
based directly on established health effects and biological considerations.
Compliance with these limits will ensure that workers exposed to electromagnetic
fields are protected against all known adverse health effects
action values: the magnitude of directly measurable parameters, provided in
terms of electric field strength (E), magnetic field strength (H), magnetic flux
density (B) and power density (S), at which one or more of the specified
measures in this Directive must be undertaken.
Compliance with these values will ensure compliance with the relevant exposure
limit values.
Includes any EM device: portable phone, Oven, MRI, ...
Exposure limit values & Action values
Conflict with MRI
Main Magnetic field: No ELV, AV 200mT clinical MRI 3 T
Limit reached < 50 cm from magnet edge, Patient installation impossible (3T)
Movement in B0: 1Hz, 40mA/m2 head & trunk
Exceeded <1m from magnet when v = 1m/s (Estimation < 500mA/m2 , factor 10)
Patient installation impossible
Pulsed Magnetic field Gradients: 1KHz
10mA/m2 head & Trunk During Scan Exceeded <1m from magnet edge
Patient critical monitoring (Anaesthesia, paediatric or IC patient) impossible
interventional procedure impossible ( factor x 50)
Pulsed Radio frequency B1 field: 10-100MHz
ELV Whole Body 0.4W/Kg, Head&Trunk 10W/Kg, Limbs 20W/Kg,
averaged over 6minutes Almost Never exceeded by Workers
The paradox
MRI would have to be replaced in some instances by X ray procedures
that have proven deleterious health effects on workers!
The development of MRI could slow down, especially: High field (
>7T), Brain studies, Interventional & therapeutic Targeted drug delivery
Alliance for MRI (UE MP, ESR, Scientific societies: statement &
petition)
The directive transposition has been postponed up to April 2012
( 2008/46/EC)
New ICNIRP recommendations for MRI (2009)
ICNIRP recommends also to take ferromagnetic object risk into account
(nb: yet in the directive obligations of employers)
The debate
The Directive is needed: Protection of Workers requires a legal frame
The limits must be based on safe values from demonstrated adverse health
effects, not on vague extrapolations or extreme precautionary values
Studies should be undertaken in order to develop effective measurement
devices to ensure limits are not exceeded in real life and to estimate
possible MRI long term effects
Propositions: Alliance = exemption/IEC limits? Modification of ELV/AV
for MRI?
Thank you for your attention
and for your essential work