Summary: RF Heating Due to Conductive Wires During MRI
Depends on the Phase Distribution of the Transmit Field
Christopher J. Yeung, Robert C. Susil, and Ergin Atalar*
In many studies concerning wire heating during MR imaging, a
"resonant wire length" that maximizes RF heating is deter-
mined. This may lead to the nonintuitive conclusion that adding
more wire, so as to avoid this resonant length, will actually
improve heating safety. Through a theoretical analysis using the
method of moments, we show that this behavior depends on
the phase distribution of the RF transmit field. If the RF transmit
field has linear phase, with slope equal to the real part of the
wavenumber in the tissue, long wires always heat more than
short wires. In order to characterize the intrinsic safety of a
device without reference to a specific body coil design, this
maximum-tip heating phase distribution must be considered.
Finally, adjusting the phase distribution of the electric field
generated by an RF transmit coil may lead to an "implant-
friendly" coil design. Magn Reson Med 48:10961098, 2002.
© 2002 Wiley-Liss, Inc.
Key words: safety; RF heating; interventional MRI; method of