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在确实需要的前提下,孕期满3个月的孕妇可行MRI检查,相关研究已经证实1.5 T胎儿磁共振成像(MRI)检查相对安全,但3 T胎儿MRI检查的安全性相关研究还很不够,随着3 T MRI设备在临床应用数量快速增加,加强相关研究非常有必要。为了分析3 T胎儿MRI检查的安全问题和成像质量,根据医学图像和国际标准建立了孕妇盆腔电磁模型,参照临床常规,分别在1.5 T和3 T鸟笼发射线圈激励下,采用时域有限差分法对用于衡量MRI安全问题的特定能量吸收率(SAR)和影响图像质量的射频B1场进行数值计算和分析。数值结果表明,3 T下孕妇盆腔各组织SAR的平均值和局部最大值分别比1.5T最多提高了2.79倍和3.96倍。特别地,3 T下皮肤、羊水SAR的局部最大值超出了安全阈值;3 T下过子宫颈、子宫体和子宫底的3个横断面上子宫区域内B1场的均匀性比1.5T分别降低了19%,25%和21%,而且3 T下子宫内B1场均匀性低于67%。结果表明,过高的局部SAR值和B1场的不均匀性将成为3 T磁共振应用于胎儿成像的主要限制因素。
In the real need of premise, pregnancy 3 months pregnant women feasible MRI examination, the relevant research has confirmed that 1.5 T fetal MRI examination is relatively safe, but 3 T fetal MRI safety studies are not enough, With the rapidly increasing number of 3 T MRI devices in clinical practice, it is necessary to strengthen the relevant research. In order to analyze the safety and imaging quality of 3 T fetus MRI examination, the pelvic electromagnetism model of pregnant women was established according to medical images and international standards. With reference to the clinical routine, respectively, under the excitation of 1.5T and 3T cage coil, the finite difference time domain The method was used to numerically calculate and analyze the specific energy absorption rate (SAR) used to measure MRI safety and the RF field B1 that affects image quality. The numerical results show that the mean and local maximum SAR of pelvic tissues in 3-T pregnant women are 2.79 times and 3.96 times higher than that of 1.5T respectively. In particular, the sub-3 T skin, amniotic fluid SAR local maximum exceeded the safety threshold; 3 T over the cervix, uterus and uterine end of the three cross-sectional uterine area B1 field uniformity than 1.5T decreased 19%, 25% and 21%, respectively, and the intrauterine B1 field uniformity at 3 T was less than 67%. The results show that excessive local SAR and nonuniformity of B1 field will be the main limiting factor in the application of 3T MRI in fetal imaging.