Nakamura T, Fukuda K, Hayakawa K, Aoki I, Matsumoto K, Sekine T, Ueda H, Shimizu Y
Institute for Frontier Medical Sciences, Kyoto University, Japan.
Front Med Biol Eng. 2001;11(2):117-29. doi: 10.1163/156855701316922298.
To determine the mechanism of burn injury associated with magnetic resonance imaging (MRI), the induced current in the loops of a conductive lead was measured. Seven types of loops with effective areas within the range from 100 to 12 000 cm2 were made and then each loop was placed in the bore of a whole-body MR system at 0.5 T and MRI was carried out. During radio frequency (RF) irradiation, an induced voltage was observed in loops that were placed with their axes parallel to the linearly polarized transmitting RF field. The voltage had a sincfunction characteristic and was within the range 55-235 V at the RF pulse sequence for usual MR imaging. When the axis was vertical, negligible current was observed. A resistor inserted into the circuit of a 30 x 40 cm loop sparked and burned out. Simple loops of conductive material may result in the induction of a large and potentially hazardous voltage in the imaging system. Self-resonance of such a loop may add greatly to hazards by increasing the effective coupling to the RF transmitter. Also, impedance matching of the inserted resistor with the impedance of the loop increases the dissipated power at the resistor.
为了确定与磁共振成像（MRI）相关的烧伤机制，测量了导电导线环中的感应电流。制作了七种有效面积在100至12000平方厘米范围内的环，然后将每个环置于0.5T的全身MR系统的孔中并进行MRI检查。在射频（RF）照射期间，在其轴与线性极化发射RF场平行放置的环中观察到感应电压。该电压具有 sinc 函数特性，在用于常规MR成像的RF脉冲序列下，电压范围为55 - 235V。当轴垂直时，观察到的电流可忽略不计。插入到一个30×40厘米环的电路中的电阻器产生火花并烧坏。导电材料的简单环可能会在成像系统中感应出大的且潜在危险的电压。这种环的自谐振可能会通过增加与RF发射器的有效耦合而极大地增加危险。此外，插入电阻器与环的阻抗的阻抗匹配会增加电阻器处的耗散功率。
