Jani J, Breysem L, Maes F, Boulvain M, Roubliova X, Lewi L, Vaast P, Biard J-M, Cannie M, Deprest J
Centre for Surgical Technologies, Faculty of Medicine, Katholieke Universiteit Leuven, Belgium.
Ultrasound Obstet Gynecol. 2005 Mar;25(3):270-6. doi: 10.1002/uog.1866.
Lung volume measurement by fetal magnetic resonance imaging (fetMRI) has been used to predict survival of fetuses with isolated congenital diaphragmatic hernia (CDH). So far, the accuracy and precision of fetMRI for volumetry of either the normal or hypoplastic developing lung has not been formally studied.
A total of nine sheep carrying 14 fetuses underwent fetMRI under general anesthesia at a mean of 118 days' gestational age (term = 145 days). A total of 61 organs were measured in nine normal fetal sheep and five that underwent surgical creation of diaphragmatic hernia (DH), so as to induce pulmonary hypoplasia. Lungs were measured on T2-WI (weighted images) in three different planes, while liver and kidneys were measured in the axial (T1-WI) and sagittal (T2-WI) planes, respectively. Necropsy was done within 24 h after fetMRI to determine the volume postmortem by the water displacement method. Values were linearly correlated and a Bland and Altman analysis was done for volume measurement comparison, calculating means +/- SD, bias (mean of the difference of volume measurements), precision (SD of the difference) and absolute and proportionate limits of agreement for both methods. The accuracy of fetMRI volume measurement was determined for different organ groups by calculating the median relative error and precision index, both being measures of error in proportion to the magnitude of the volume measured, as a clinically relevant proxy of potential errors.
The fetMRI volume measurements were on average larger than postmortem volumes, except for the kidneys. Kidney volume determination had a relative error of 29%, while measurements of larger organs had larger relative errors (42% for liver). Normal lungs were less accurately measured in the coronal or sagittal than in the axial plane (relative error 53%, 73% and 38%, respectively; P < 0.05 for sagittal vs. axial). Axially-measured lung volumes were more accurate for lungs of normal sheep compared to DH lungs (relative error 38% vs. 73%, respectively; P < 0.05).
FetMRI measured systematically higher volumes for organs such as fetal liver or lung. This may be related to fluid loss or lack of perfusion at the time of necropsy. Measurement of lung volume by fetMRI was most accurate in the axial plane. Measurements of lung and liver volumes by fetMRI in normal sheep were both in agreement with volumes measured at necropsy. Loss of accuracy for DH-lungs in comparison with the accuracy when measuring other similarly small organs, such as kidneys, suggests that fetMRI measurements can be less accurate for hypoplastic lungs related to CDH. With improving hardware, it might become easier to render the fetal lung and determine its volume reliably.
通过胎儿磁共振成像（fetMRI）测量肺容积已被用于预测单纯性先天性膈疝（CDH）胎儿的存活率。到目前为止，fetMRI对正常或发育不全的肺进行容积测量的准确性和精确性尚未得到正式研究。
共有9只怀有14只胎儿的绵羊在平均妊娠118天（足月为145天）时接受全身麻醉下的fetMRI检查。对9只正常胎儿绵羊和5只接受膈疝（DH）手术造模以诱导肺发育不全的绵羊的61个器官进行测量。在三个不同平面的T2加权图像（WI）上测量肺，而肝脏和肾脏分别在轴位（T1-WI）和矢状位（T2-WI）平面上测量。在fetMRI检查后24小时内进行尸检，通过水置换法确定死后体积。对数值进行线性相关分析，并进行Bland和Altman分析以比较体积测量结果，计算两种方法的均值±标准差、偏差（体积测量差值的均值）、精确性（差值的标准差）以及绝对和相对一致性界限。通过计算中位数相对误差和精确性指数来确定fetMRI体积测量对不同器官组的准确性，这两个指标均是与测量体积大小成比例的误差度量，作为潜在误差的临床相关指标。
除肾脏外，fetMRI测量的体积平均大于死后体积。肾脏体积测定的相对误差为29%，而较大器官的测量相对误差更大（肝脏为42%）。正常肺在冠状面或矢状面的测量准确性低于轴位平面（相对误差分别为53%、73%和38%；矢状面与轴位相比，P<0.05）。与DH肺相比，轴位测量的正常绵羊肺体积更准确（相对误差分别为38%和73%；P<0.05）。
FetMRI系统性地测量出胎儿肝脏或肺等器官的体积更高。这可能与尸检时的液体流失或灌注不足有关。FetMRI测量肺容积在轴位平面最准确。正常绵羊中通过fetMRI测量的肺和肝脏体积均与尸检时测量的体积一致。与测量其他类似小器官（如肾脏）的准确性相比，DH肺测量准确性的降低表明，对于与CDH相关的发育不全肺，fetMRI测量可能不太准确。随着硬件的改进，可靠地呈现胎儿肺并确定其体积可能会变得更容易。
