MRI在诊断胎儿肾发育异常中的价值

目的 探讨MRI在诊断胎儿肾发育异常(FRDA)中的价值.方法 采用MR扩散加权成像(DWI)和快速成像序列对11例超声(US)提示FRDA的胎儿进行盆腹部横断面、矢状面及冠状面扫描,将MRI表现与产前和产后超声结果对照.结果 MRI诊断结果与产后US一致,MRI和产后US诊断一侧异位肾4例(左侧2例、右侧2例,其中1例产前US诊断为右肾缺如),一侧肾缺如5例(左侧2例、右侧3例,其中1例产前US诊断为左肾发育不全),1例左肾发育不全,1例双肾发育不全(产前US诊断为右肾缺如伴左肾发育不全).结论 MRI可以清晰显示胎儿肾的形态和位置,是产前US诊断FRDA的重要补充.     

Investigation of normal organ development with fetal MRI

The understanding of the presentation of normal organ development on fetal MRI forms the basis for recognition of pathological states. During the second and third trimesters, maturational processes include changes in size, shape and signal intensities of organs. Visualization of these developmental processes requires tailored MR protocols. Further prerequisites for recognition of normal maturational states are unequivocal intrauterine orientation with respect to left and right body halves, fetal proportions, and knowledge about the MR presentation of extrafetal/intrauterine organs. Emphasis is laid on the demonstration of normal MR appearance of organs that are frequently involved in malformation syndromes. In addition, examples of time-dependent contrast enhancement of intrauterine structures are given.     

MRI of normal fetal brain development

Normal fetal brain maturation can be studied by in vivo magnetic resonance imaging (MRI) from the 18th gestational week (GW) to term, and relies primarily on T2-weighted and diffusion-weighted (DW) sequences. These maturational changes must be interpreted with a knowledge of the histological background and the temporal course of the respective developmental steps. In addition, MR presentation of developing and transient structures must be considered. Signal changes associated with maturational processes can mainly be ascribed to the following changes in tissue composition and organization, which occur at the histological level: (1) a decrease in water content and increasing cell-density can be recognized as a shortening of T1- and T2-relaxation times, leading to increased T1-weighted and decreased T2-weighted intensity, respectively; (2) the arrangement of microanatomical structures to create a symmetrical or asymmetrical environment, leading to structural differences that may be demonstrated by DW-anisotropy; (3) changes in non-structural qualities, such as the onset of a membrane potential in premyelinating axons. The latter process also influences the appearance of a structure on DW sequences. Thus, we will review the in vivo MR appearance of different maturational states of the fetal brain and relate these maturational states to anatomical, histological, and in vitro MRI data. Then, the development of the cerebral cortex, white matter, temporal lobe, and cerebellum will be reviewed, and the MR appearance of transient structures of the fetal brain will be shown. Emphasis will be placed on the appearance of the different structures with the various sequences. In addition, the possible utility of dynamic fetal sequences in assessing spontaneous fetal movements is discussed.     

胎儿小脑蚓部发育的MRI研究

目的:描述正常胎儿标本小脑蚓部在不同孕周的正常发育生长曲线,并探讨胎儿丹迪-沃克综合征(DWS)的MRI表现。方法:对63例胎龄15～40周的胎儿标本行3.0T MRI扫描,从中选出52例符合要求的进行测量,扫描序列为T1WI、T2WI;扫描方位:矢状位扫描为主,辅以冠状位及横轴位;观察及测量内容:测量小脑蚓部的前后径(正中矢状面第四脑室顶点至水平裂处蚓部后缘最大距离)、上蚓高度及下蚓高度(上蚓的最高点及下蚓的最低点分别到前后径线的垂直距离)。对上述测量结果与孕龄间作回归分析。然后对6例经MRI诊断为DWS的病例进行回顾性分析。结果:小脑蚓部前后径、上蚓高度及下蚓高度分别与孕龄呈线性正相关,而上蚓高度总是略大于下蚓高度(P<0.05),多数标本正中矢状面T1WI、T2WI可清晰显示原裂及下后裂。DWS主要表现为小脑蚓部缺如或发育不良,测量数据小于正常胎儿,第四脑室与后颅窝囊肿相通或小脑延髓池增宽。结论:MRI可明确显示正常胎儿小脑蚓部在17孕周以后的正常发育表现及变化规律,而DWS的MRI表现具有特征性,MRI是诊断DWS最理想的影像学方法。     

MRI of normal and pathological fetal lung development

Normal fetal lung development is a complex process influenced by mechanical and many biochemical factors. In addition to ultrasound, fetal magnetic resonance imaging (MRI) constitutes a new method to investigate this process in vivo during the second and third trimester. The techniques of MRI volumetry, assessment of signal intensities, and MRI spectroscopy of the fetal lung have been used to analyze this process and have already been applied clinically to identify abnormal fetal lung growth. Particularly in conditions such as oligohydramnios and congenital diaphragmatic hernia (CDH), pulmonary hypoplasia may be the cause of neonatal death. A precise diagnosis and quantification of compromised fetal lung development may improve post- and perinatal management. The main events in fetal lung development are reviewed and MR volumetric data from 106 normal fetuses, as well as different examples of pathological lung growth, are provided.     

MRI对胎儿脑发育的结构和功能定量评估

采用多模态常规和功能MRI新技术定量计算不同孕期胎儿脑结构、体积以及脑功能连接,可以获得不同孕期胎儿脑发育结构和功能图谱,进而为胎儿脑发育产前定量评估提供指南性参照标准。综述多模态MRI计算胎儿脑体积的方法和量化指标、三维重建中晚孕期胎儿脑体积和区域分割测量以及皮质脑回分割,阐述MRI新技术对明确微观脑白质纤维束及构建胎儿脑网络图谱的临床意义,及其对胎儿脑发育异常临床诊断可提供的参考价值。     

Normal fetal brain development: MR imaging with a half-Fourier rapid acquisition with relaxation enhancement sequence

PURPOSE: To analyze normal maturation of the fetal brain with half-Fourier rapid acquisition with relaxation enhancement (RARE) magnetic resonance (MR) imaging. MATERIALS AND METHODS: The normal brains of 25 fetuses of 12-38 weeks gestational age were examined in utero with half-Fourier RARE imaging. Gyrus maturation, gray and white matter differentiation, ventricle-to-brain diameter ratio, and subarachnoid space size were evaluated with respect to gestational age. RESULTS: At 12-23 weeks, the brain had a smooth surface, and two or three layers were differentiated in the cerebral cortex. At 24-26 weeks, only a few shallow grooves were seen in the central sulcus, and three layers, including the immature cortex, intermediate zone, and germinal matrix, were differentiated in all fetuses. At 27-29 weeks, sulcus formation was observed in various regions of the brain parenchyma, and the germinal matrix became invisible. Sulcation was seen in the whole cerebral cortex from 30 weeks on. However, the cortex did not undergo infolding, and opercular formation was not seen before 33 weeks. At 23 weeks and earlier, the cerebral ventricles were large; thereafter, they gradually became smaller. The subarachnoid space overlying the cortical convexities was slightly dilated at all gestational ages, most markedly at 21-26 weeks. CONCLUSION: Changes in brain maturation proceed through stages in an orderly and predictable fashion and can be evaluated reliably with half-Fourier RARE MR imaging.     

MRI in fetal necropsy

The fetal autopsy involves a series of investigations of the corpse, most of which are noninvasive and acceptable to the majority of parents and their physicians. The value of the perinatal autopsy is manyfold and well established, and the results can provide a basis for parental and family counseling, inform future obstetric management, and provide audit for prenatal care. Many techniques originally developed for diagnosis, such as histology, biochemical tests, photography, x-rays, and cytogenetic karyotyping, have become standard tools in perinatal autopsies. However, there has been an inexorable decline in the autopsy consent rate over the last 30 years due to social and cultural factors, and perhaps ignorance of the benefits to be derived from the examination. Growing evidence suggests that postmortem fetal MRI can assist the pathologist at autopsy, and in many cases can obviate the need for dissection or at least minimize and focus it. For the majority of cases in which no consent for surgical autopsy is given, MRI together with other noninvasive postmortem tests can provide a great deal of the information that was previously available only from autopsy.     

儿童脊柱正常MRI与胎儿脊柱骨发育

目的 :探讨胎儿椎体和椎间盘的组织学结构以及儿童脊柱的正常X线和MRI表现。方法 :44周胎儿X线平片 1例 ;儿童脊柱正常椎体MRI 13例 ;胎儿脊柱标本 2 6例 ,全部标本经固定、水冲洗、分批脱水、火棉胶包埋后制成脊柱标本整体切片 ,HE染色。结果 :44周胎儿脊柱每个椎体前面X线表现均有“V”字形凹陷。 13例儿童脊柱正常椎体MRI ,共分析了110个椎体的信号变化 ,其T1WI和T2 WI表现 :44 %的椎体前面“V”形凹陷呈高信号 ,63 %的椎体后面“V”形凹陷 ;16.4%的椎体前后面均凹陷 ;47%的椎体中心有雪花样高信号 ;13例中有 9例各椎体内均有双层低信号生长线。 2 6例胎儿脊柱椎体的组织学结构 :① 12周和 15周胎儿 ,椎体软骨内血管数量较多 ;②胎儿椎体前、后面中部凹陷 ,以膜内成骨形成“V”字形骨皮 ,不同病例椎体前面或后面均可见凹陷 ,出现率 9.6%～ 2 7.1% ,有 2例在椎体前面“V”字骨皮内形成松质骨小梁 ,并有骨髓形成 ;③椎体骨化中心有红髓和血管 :椎体后面“V”字骨皮内的大静脉窦与骨化中心静脉窦相通 ;④椎间盘 :只见于 12周的胎儿椎间盘内有血管 ,2例紧贴椎间盘的软骨椎体内见无细胞区 ,且部分髓核物突入椎体软骨内。结论 :4～ 11岁儿童脊柱正常椎体MRI表现仍然相应的保持着胎儿脊柱骨发育的组织学特点     

Normal renal growth in children with myelodysplasia

Optimum urologic management of children with myelodysplasia includes periodic assessment of upper tract anatomy and renal growth. To investigate the perception that many children with spina bifida but without a history of intrinsic renal disease have small kidneys when compared with age-matched standard renal growth charts, 212 children with spina bifida were studied retrospectively, measuring renal length on excretory urograms. Patients with known vesicoureteric reflux of grade 2 or greater, congenital renal anomalies, hydronephrosis, renal scarring, or urinary diversion were excluded. For 95 patients aged 2 days to 19 days, 249 urograms were available for evaluation. Renal lengths were measured on the supine 5-min urogram. Mean values and standard deviations were calculated for each age group. Mean renal length for each age group fell below the mean of the standard curves devised by Hodson and Currarino, with increasing deviation from the mean with age.     

磁共振扩散加权成像评价胎儿肾脏功能的初步研究

目的：探讨表观扩散系数(ADC)值在正常胎儿肾脏上是否具有规律及特点,为应用磁共振扩散加权成像(DWI)评价胎儿肾脏功能提供正常数据参考。方法对71例经超声和常规 MR 检查均诊断肾脏正常的胎儿进行产前 DWI 扫描,b 值取100、200、500、700 s/mm2,分别统计分析左右肾感兴趣区(ROI)同 b 值、ADC 值差异,单侧肾不同 b 值、ADC 值差异以及双肾平均 ADC值与孕周的相关性。结果除 b=100 s/mm2,左右肾间 ADC 值存在统计学差异,其余各组间比较均无统计学差异。同侧肾不同 b值比较中,除右肾 b=100 s/mm2与 b=700 s/mm2组间比较无统计学意义,其余各组间比较均有统计学意义。同时随孕周增大,双肾 ADC 值均呈下降趋势。结论DWI 评价胎儿肾脏发育是可行的,不同 b 值得到的 ADC 值可作为定量参数评估正常胎儿肾脏发育情况。     

Normal brain maturation in MRI

Normal brain maturation was evaluated with MR imaging of 36 neonate to 2-year-old patients. The myelination process in centrum semiovale was quantitatively assessed in 50 6-months- to 15-year-old children, and 40 adults aged 16-60 years. Imaging was performed with a 0.35 T superconducting MR unit using spin echo pulse sequences. On T1-weighted images, three stages of maturation could be observed: (1) neonates within 1 month; (2) 1-6 months of age; and (3) adult configuration after 6-7 months of age. Also on T2-weighted images three maturation stages could be defined: (1) neonatal pattern in the first 6 months of life; (2) signal inversion between 6-18 months; and (3) adult appearance after 18 months. Thus, the combination of T1- and T2-weighted images could lead us to the assessment of brain maturation in infants younger than 2 years. The myelination process in centrum semiovale was fast during the first 3 years followed by slow progression until 20-30 years of age.     

Effects of ozone exposure in rat lungs investigated with hyperpolarized 3 He MRI

PURPOSE: To investigate the effects of subchronic ozone exposure on rat lung ventilation using hyperpolarized (HP) (3)He MRI. MATERIALS AND METHODS: A total of 24 Sprague-Dawley rats, distributed in one control group and four groups exposed to 0.5 ppm ozone concentration for two days or six days, either continuously (22 hours/day) or alternatingly (12 hours/day). A three-step MRI protocol was designed and applied to each animal, including: 1) (3)He gas distribution images acquired at inspiratory capacity, 2) measurements of intrapulmonary (3)He diffusion coefficients, and 3) dynamic ventilation acquisitions performed during lung filling with (3)He. RESULTS: No differentiation between animals exposed to ozone and control animals was observed from the ventilation images obtained at inspiratory capacity. The (3)He diffusion coefficients were not statistically different from one group to another. Ventilation defects, appearing as delayed lung filling regions and heterogeneous lung filling, were observed in the dynamic lung ventilation image series. The percentage of animals with ventilation defects in the control, two-day, and six-day exposed groups were equal to 20%, 43% and 75%, respectively. In the subgroup of the animals exposed six days for 12 hours per day, the percentage of animals exhibiting ventilation defects was equal to 85%. CONCLUSION: Heterogeneous obstructive patterns in an experimental animal model of subchronic ozone exposure were observed using HP (3)He MRI.     

MRI of fetal genitourinary anomalies

OBJECTIVE: The objective of our study was to show examples of fetal MRI evaluations of congenital genitourinary anomalies and to review the embryology in relation to the MRI findings. CONCLUSION: MRI was performed on 35 pregnant women with sonographic findings that suggested that their fetuses had genitourinary anomalies. Oligohydramnios or anhydramnios was identified in 22 of 35 women and did not hinder visualization of anomalies. MRI allowed the amniotic fluid and the presence, location, and morphology of kidneys and bladder to be assessed in all fetuses at any stage of gestation and depicted sufficient anatomic detail for us to evaluate the perineum in 27 of 35 pregnancies. Therefore, we found MRI to be an excellent technique for revealing the anatomy of genitourinary anomalies in the fetus.     

Measurement of renal volumes with contrast-enhanced MRI

PURPOSE: To determine the accuracy of in vivo magnetic resonance imaging (MRI) measurement of total renal parenchymal volume and medullary fraction. MATERIALS and METHODS: Sixteen kidneys in eight pigs were imaged with a multiphasic contrast-enhanced fast three-dimensional sequence on a 1.5-T imager. Kidney segmentation, followed by a process of signal intensity thresholding for cortical and nephrographic phase datasets, allowed for MRI measurements of parenchymal volume and medullary fraction. Autopsy provided reference standards of renal volume, weight, and medullary fraction. RESULTS: An excellent correlation was found between MRI measurement of total renal parenchymal volume and autopsy volume (R2 = 0.86) and weight (R2 = 0.90). Medullary fraction (mean +/- SD) measured with MRI was 0.120 +/- 0.067, and with autopsy was 0.116 +/- 0.025 (t-test P = 0.84, F-test P = 0.001). CONCLUSION: MRI measurements of total renal volume are accurate. MRI measurements of medullary fraction show promise, but precision is limited when using a simple signal intensity thresholding algorithm.     

正常小脑蚓部的MRI测量

目的　在MRI上测量健康国人小脑蚓部的大小 ,探讨年龄和性别与其大小的关系。方法　 36 0例健康成人 ,男 180例 ,女180例 ,年龄 2 0～ 87岁。测量MRI上小脑蚓部径线 ,总面积及各叶面积。结果　小脑蚓部前后径及上下径在 6 0岁后呈下降趋势 ,前后径 5 0岁后开始呈下降趋势 ,6 0岁后更为明显。同年龄组小脑蚓部前叶面积及小脑蚓部总面积男性大于女性 ,而蚓部中叶及后叶面积在不同性别同年龄组间无明显差异。结论　正常人小脑蚓部径线及面积在 6 0岁后随年龄增长而下降 ,蚓部前叶男性大于女性。     

正常垂体腺的MRI研究

本文应用MRI观察了103例正常成人(男53例、女50例)垂体腺的形态、大小和信号强度特征。发现11例(10.6％)垂体腺形态呈凸隆型,其余为平坦或凹陷型。96例(93.2％)垂体后叶呈高信号强度,余为等信号强度。测量了垂体腺前后径、宽径、矢状高径和冠状高径,垂体后叶高径和前后径,垂体柄长径和前后径,为诊断垂体腺疾病提供了正常数据。报告了垂体柄和垂体腺的连接位置,讨论了垂体腺形态和信号强度特征等临床诊断意义。