Lauer Ulrike A, Graf Hansjorg, Berger Alexander, Claussen Claus D, Schick Fritz
Section on Experimental Radiology, University Hospital Tubingen, Tubingen, Germany.
Magn Reson Imaging. 2005 May;23(4):563-9. doi: 10.1016/j.mri.2005.02.012.
Metallic implants cause enlarged artifacts in magnetic resonance (MR) images at higher magnetic fields, B0, due to their magnetic susceptibility. Interactions of conductive material with radio frequency (RF) pulses also change for higher field strengths, B0, due to the frequency dependence of resonance conditions. Systematic measurements on commercial aneurysm clips and simplified copper models were performed in order to investigate both phenomena at 1.5 and 3 T.
Six different commercial aneurysm clips made of titanium, straight copper wires and bent copper models were examined in Gd-DTPA-doped water. RF-related effects were measured by adapted 2D and 3D spin-echo sequences. For reliable differentiation from susceptibility-related effects, variable transmitter voltages were applied. In addition, RF-induced heating was controlled by an infrared (IR) camera.
At 3 T, a significant RF-induced electric response could be demonstrated for the copper samples and more moderate for one of the commercial clips, dependent on the geometrical structure determining possible resonant RF coupling. Related RF effects could be distinguished from susceptibility artifacts: a signal enhancement at reduced transmitter voltages indicated locally amplified B1-field amplitudes. No significant heating effect could be measured by IR measurements.
MR imaging was used to analyze possible RF-induced effects. At 3 T, resonant RF coupling even of small metallic implants has to be considered carefully. Despite a local enhancement of the RF amplitude, no significant RF-induced heating inside the surrounding fluid was found. A direct thermal endangering of patients seems to be unlikely, but extremely high B1-field amplitudes might occur adjacent to the metallic surface with potential nonthermal affection of tissue.
由于金属植入物的磁敏感性，在较高的静磁场（B0）下，金属植入物会在磁共振（MR）图像中导致伪影增大。由于共振条件的频率依赖性，导电材料与射频（RF）脉冲的相互作用在较高场强（B0）下也会发生变化。为了研究在1.5 T和3 T时的这两种现象，对商用动脉瘤夹和简化铜模型进行了系统测量。
在掺钆喷替酸葡甲胺（Gd-DTPA）的水中检查了六种由钛制成的不同商用动脉瘤夹、直铜丝和弯曲铜模型。通过调整的二维和三维自旋回波序列测量与射频相关的效应。为了与磁敏感性相关效应可靠区分，施加了可变的发射机电压。此外，通过红外（IR）相机控制射频感应加热。
在3 T时，对于铜样品可证明有显著的射频感应电响应，对于其中一个商用夹子则较为适中，这取决于决定可能的共振射频耦合的几何结构。相关的射频效应可与磁敏感性伪影区分开：发射机电压降低时信号增强表明局部B1场振幅放大。通过红外测量未测得显著的加热效应。
利用磁共振成像分析可能的射频感应效应。在3 T时，即使是小的金属植入物的共振射频耦合也必须仔细考虑。尽管射频振幅局部增强，但在周围流体内部未发现显著的射频感应加热。患者受到直接热危害的可能性似乎不大，但在金属表面附近可能会出现极高的B1场振幅，对组织有潜在的非热影响。
