Hand J W, Li Y, Thomas E L, Rutherford M A, Hajnal J V
Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College, London, UK.
Magn Reson Med. 2006 Apr;55(4):883-93. doi: 10.1002/mrm.20824.
There is uncertainty regarding the risk posed by magnetic resonance imaging (MRI) examinations to pregnant patients. The most frequently used methods, such as single-shot fast spin echo (ssFSE), often require operation at the specific absorption rate (SAR) limits imposed by safety guidelines. With the introduction of higher-field systems, such limits will be even more significant for fetal imaging. An electromagnetic solver based on the time domain finite integration technique (FIT) was used to predict SAR in an anatomically realistic model of a pregnant patient (28 weeks' gestation) associated with the radiofrequency (RF) fields from birdcage body coils typical of 1.5 T and 3 T MRI systems (i.e., operating at approximately 64 and 127 MHz, respectively). The results suggest that 1) the highest local SAR is in the mother, with the fetus being exposed to a peak of approximately 40-60% of that value at 64 MHz, increasing to approximately 50-70% at 127 MHz; 2) compliance with U.S. Food and Drug Administration (FDA) and International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines requires control of SAR values averaged over 1 g or 10 g of tissue, respectively; and 3) compliance with Medical Device Agency (MDA) guidelines requires control of the maximum SAR(10g) within the fetus.
磁共振成像（MRI）检查对孕妇构成的风险存在不确定性。最常用的方法，如单次激发快速自旋回波（ssFSE），通常需要在安全指南规定的比吸收率（SAR）限制下操作。随着更高场强系统的引入，这种限制对胎儿成像将更加显著。基于时域有限积分技术（FIT）的电磁求解器被用于预测在一名怀孕28周患者的解剖学真实模型中与1.5T和3T MRI系统典型的鸟笼式体线圈的射频（RF）场相关的SAR（即分别在约64MHz和127MHz下运行）。结果表明：1）最高局部SAR在母亲体内体内，胎儿暴露于该值峰值的约40-60%（64MHz时），在127MHz时增至约50-70%；2）符合美国食品药品监督管理局（FDA）和国际非电离辐射防护委员会（ICNIRP）指南分别要求控制在1g或10g组织上平均的SAR值；3）符合医疗器械局（MDA）指南要求控制胎儿内的最大SAR(10g)。
