Patient safety concept for multichannel transmit coils.
OBJECTIVE
To propose and illustrate a safety concept for multichannel transmit coils in MRI based on finite-differences time-domain (FDTD) simulations and validated by measurements.


METHODS
FDTD simulations of specific absorption rate (SAR) distributions in a cylindrical agarose phantom were carried out for various radio frequency (RF) driving conditions of a four-element coil array. Additionally, maps of transmit amplitude, signal phase, and temperature rise following RF heating were measured by MRI.


RESULTS
Quantitative agreement was achieved between simulated and measured field distributions, thus validating the numerical modeling. When applying the same RF power to each element of the coil array but systematically varying the RF phase between its elements, the maximum of the SAR distribution was found to vary by a factor of about 15.


CONCLUSIONS
Our results demonstrate that current RF safety approaches are inadequate to deal with the new challenge of multichannel transmit coils. We propose a new concept based on a systematic investigation of the parameter space for RF phases and amplitudes. In this way the driving conditions generating the highest local SAR values per unit power can be identified and appropriately considered in the RF safety concept of a given MRI system.
Seifert
Frank
F
Physikalisch Technische Bundesanstalt, Braunschweig und Berlin, Germany.
Wübbeler
Gerd
G
Junge
Sven
S
Ittermann
Bernd
B
Rinneberg
Herbert
H
D001822:Body Burden; D003198:Computer Simulation; D004574:Electromagnetic Fields; D004869:Equipment Safety / Q000379:methods*; D005858:Germany; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008954:Models, Biological; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000379:methods; D011835:Radiation Protection / Q000379:methods*; D012062:Relative Biological Effectiveness; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D014159:Transducers; D014915:Whole-Body Counting / Q000379:methods*