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Heating of metallic implants and instruments induced by gradient switching in a 1.5‐Tesla whole‐body unit
Author(s) -
Graf Hansjörg,
Steidle Günter,
Schick Fritz
Publication year - 2007
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.21157
Subject(s) - materials science , titanium , temperature gradient , copper , perpendicular , aluminium , optics , composite material , metallurgy , physics , geometry , mathematics , quantum mechanics
Purpose To examine gradient switching–induced heating of metallic parts. Materials and Methods Copper and titanium frames and sheets (≈50 × 50 mm 2 , 1.5 mm thick, frame width = 3 mm) surrounded by air were positioned in the scanner perpendicular to the static field horizontally 20 cm off‐center. During the execution of a sequence (three‐dimensional [3D] true fast imaging with steady precession [True‐FISP], TR = 6.4 msec) exploiting the gradient capabilities (maximum gradient = 40 mT/m, maximum slew rate = 200 T/m/second), heating was measured with an infrared camera. Radio frequency (RF) amplitude was set to zero volts. Heating of a copper frame with a narrowing to 1 mm over 20 mm at one side was examined in air and in addition surrounded by several liters of gelled saline using fiber‐optic thermography. Further heating studies were performed using an artificial hip made of titanium, and an aluminum replica of the hip prosthesis with the same geometry. Results For the copper specimens, considerable heating (>10°C) in air and in gelled saline (>1.2°C) could be observed. Heating of the titanium specimens was markedly less (≈1°C in air). For the titanium artificial hip no heating could be detected, while the rise in temperature for the aluminum replica was approximately 2.2°C. Conclusion Heating of more than 10°C solely due to gradient switching without any RF irradiation was demonstrated in isolated copper wire frames. Under specific conditions (high gradient duty cycle, metallic loop of sufficient inductance and low resistance, power matching) gradient switching–induced heating of conductive specimens must be considered. J. Magn. Reson. Imaging 2007;26:1328–1333. © 2007 Wiley‐Liss, Inc.