Heating of metallic implants and instruments induced by gradient switching in a 1.5-Tesla whole-body unit.
OBJECTIVE
To examine gradient switching-induced heating of metallic parts.


METHODS
Copper and titanium frames and sheets ( approximately 50 x 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 degrees C) in air and in gelled saline (>1.2 degrees C) could be observed. Heating of the titanium specimens was markedly less ( approximately 1 degrees 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 degrees C.


CONCLUSIONS
Heating of more than 10 degrees 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.
Graf
Hansjörg
H
Section on Experimental Radiology, Department of Diagnostic Radiology, University Hospital Tübingen, Tübingen, Germany.
Steidle
Günter
G
Schick
Fritz
F
D004307:Dose-Response Relationship, Radiation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D004864:Equipment and Supplies; D006358:Hot Temperature; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008670:Metals / Q000528:radiation effects*; D019736:Prostheses and Implants; D011829:Radiation Dosage; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D051598:Whole Body Imaging / Q000295:instrumentation*
D008670:Metals