B-FFE、DWI及SWI序列在胎儿磁共振成像股骨长度测量中的对比研究

Comparative study of B-FFE,DWI and SWI sequences in the measurement of femoral length in fetal magnetic resonance imaging

目的:研究平衡式快速场回波(B-FFE)、磁共振扩散加权成像(DWI)及磁敏感加权成像(SWI)序列在胎儿磁共振成像股骨长度测量方面的诊断价值,为临床提供准确股骨长度测量值。方法:随机选取本院磁共振胎儿股骨检查的43例孕妇,扫描序列包括B-FFE、DWI及SWI序列,分析各序列股骨解剖结构及影像表现,对三组序列图像质量评分、图像信噪比(SNR)、对比噪声比(CNR)、特异吸收率(SAR)值及采集时间比较分析,对显示股骨解剖结构、形态及测量进行统计学分析。结果:43例孕妇中,图像质量评分方面:B-FFE、DWI、SWI序列评分分别为1.767±0.571、1.395±0.791、1.279±0.826。三组序列Wilcoxon符号秩检验,B-FFE序列与DWI序列,P=0.002,两者存在差异,B-FFE序列与SWI序列,P<0.001,两者存在显著差异,DWI序列与SWI序列,P=0.461,两者无显著差异。SNR、CNR方面:B-FFE序列组股骨干SNR明显高于及DWI、SWI序列组(F=52.240、104.458,P均<0.001),差异具有统计学意义,SWI序列组股骨上端骨骺端SNR高于DWI序列组(F=7.948,P<0.05),差异具有统计学意义,SWI序列组股骨上端骨骺端SNR与B-FFE序列组(F=0.299,P>0.05),差异无统计学意义;SWI序列组CNR高于B-FFE及DWI序列组(F=7.526、12.759,P<0.05),差异具有统计学意义。SAR值方面:B-FFE、DWI、SWI分别为2.0±0.08 W/kg、1.2±0.05 W/kg、0.1±0.05 W/kg。单次采集时间:SWI采集时间最短,B-FFE、DWI序列次之。结论:B-FFE、DWI、SWI序列在显示胎儿股骨解剖结构及影像表现方面各有优缺点,B-FFE序列能简单、快捷获取股骨图像、不易受呼吸运动及胎动伪影影响,容易完成检查,主观评分最高;DWI序列显示骨骺特征性高信号,方便测量股骨长度,但扫描时间长,容易受胎动伪影影响;SWI序列能清晰显示骨干影像表现,扫描时间短,需要多次屏气,容易受运动伪影影响。因此需根据现场胎儿胎动及孕妇及胎儿配合情况选择相应序列进行胎儿股骨扫描,本院常采用扫描B-FFE序列为主,DWI及SWI序列为辅进行胎儿股骨扫描。

Objective:To study the diagnostic value of balanced fast field echo(B-FFE),MRI diffusion weighted imaging(DWI)and susceptibility weighted imaging(SWI)sequences in the measurement of fetal femur length on MRI,and to provide the accurate femoral length measurement for the clinic value.Methods:43 pregnant women were randomly selected from our hospital for fetal femoral magnetic resonance examination.The scanning sequences were B-FFE,DWI and SWI.The femoral anatomical structure and image of each sequence were analyzed.The image quality and signal-to-noise ratio(SNR)of the three sets of sequences were scored.Comparative noise ratio(CNR),specific absorption rate(SAR)value and acquisition time were comparatively analyzed.The anatomical structure,morphology and measurement of the femur were statistically analyzed.Results:Among the 43 pregnant women,the image quality scores of B-FFE,DWI,and SWI sequence were 1.767±0.571,1.395±0.791,1.279±0.826,respectively.The results of the Wilcoxon signed rank test of three sets of sequences were:significant differences between B-FFE and DWI sequence(P=0.002)and between B-FFE and SWI sequence(P<0.001);but not between DWI and SWI sequence(P=0.461).As for SNR and CNR:the SNR of the femoral shaft in the B-FFE group was higher than that in the DWI and SWI groups(F=52.240,104.458,P<0.001).The SNR of the upper femoral epiphysis of the SWI group was significantly higher than that of the DWI group(F=7.948,P<0.05).The SNR of the upper femoral epiphysis of the SWI group was not statistically significant different compared with the B-FFE group(F=0.299,P>0.05).The CNR of the SWI group was statistically higher than that of the B-FFE and DWI groups(F=7.526,12.759,P<0.05).The SAR value of B-FFE,DWI,and SWI were(2.0±0.08)W/kg,(1.2±0.05)W/kg,(0.1±0.05)W/kg,respectively.The acquisition time of SWI was the shortest,followed by B-FFE and DWI sequences.Conclusion:B-FFE,DWI and SWI sequences have their own advantages and disadvantages in displaying fetal femoral anatomical structure.B-FFE sequence can easily and quickly obtain femur images,is not susceptible to respiratory motion and fetal motion artifacts,and is easy to complete the scan,with the highest subjective score.The DWI sequence shows the characteristic high signal of the epiphysis,which is convenient for measuring the length of the femur,but the scanning time is long and is easily affected by fetal movement artifacts.The SWI sequence can clearly display the femoral diaphysis,the scanning time is short,it requires multiple breath holdings,and is easily affected by movement artifacts.Therefore,it is necessary to select the corresponding sequence for fetal femoral scan according to the on-site fetal movement and the cooperation of pregnant women and fetuses.The B-FFE sequence is often used as the main scan sequence in our hospital,and the DWI and SWI as the supplementary sequences for fetal femur scan.