Graf Hansjörg, Steidle Günter, Schick Fritz
Section on Experimental Radiology, Department of Diagnostic Radiology, University Hospital Tübingen, Tübingen, Germany.
J Magn Reson Imaging. 2007 Nov;26(5):1328-33. doi: 10.1002/jmri.21157.
To examine gradient switching-induced heating of metallic parts.
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.
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.
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.
研究梯度切换引起的金属部件发热情况。
将空气包围的铜质和钛质框架及薄片（约50×50mm²，厚1.5mm，框架宽度 = 3mm）水平偏离中心20cm放置在扫描仪中，使其垂直于静磁场。在执行利用梯度能力的序列（三维[3D]稳态进动真快速成像[True - FISP]，TR = 6.4毫秒）期间（最大梯度 = 40mT/m，最大 slew 率 = 200T/m/秒），用红外热像仪测量发热情况。射频（RF）幅度设置为零伏。使用光纤热成像技术，在空气中以及另外用几升凝胶状生理盐水包围的情况下，研究一侧在20mm范围内变窄至1mm的铜框架的发热情况。使用由钛制成的人工髋关节以及具有相同几何形状的髋关节假体铝制复制品进行了进一步的发热研究。
对于铜质样本，在空气中可观察到显著发热（>10℃），在凝胶状生理盐水中发热（>1.2℃）。钛质样本的发热明显较少（在空气中约1℃）。对于钛制人工髋关节未检测到发热，而铝制复制品的温度升高约为2.2℃。
在孤立的铜丝框架中，仅因梯度切换而无任何射频辐射时发热超过10℃得到了证实。在特定条件下（高梯度占空比、具有足够电感和低电阻的金属回路、功率匹配），必须考虑梯度切换引起的导电样本发热。
