Magnetic Resonance Imaging of the Normal Fetus and Placenta in Medium to Late Pregnancy

目的 了解正常胎儿主要器官及胎盘的MRI表现. 资料与方法 对36例孕20周以上正常胎儿行MRI检查,采用单次激发快速自旋回波序列(SSFSE),从胎儿头颅、躯干轴位、冠状位、矢状位等多体位观察胎儿各系统主要器官,包括脑、肺、心脏、肝、脾、胃肠道等和胎盘的解剖和MRI表现.结果 36例胎儿MRI检查结果表明:中枢神经系统:孕20周以后大脑三层结构在SSFSE上已经可以辨别,皮质与脑室周围的生发层呈稍低信号,中间白质为高信号.双侧侧脑室在25周前呈生理性扩大状态,枕角明显,25周后逐渐缩小;孕20周时,两侧大脑皮层光滑,无明显沟回形成;孕23周时,仅见双侧侧裂池初具形态;23～ 30周,两侧大脑皮质主要沟回逐渐形成;30～ 37周,两侧脑皮质脑沟、回形成明显增多.呼吸循环系统:两肺呈高信号,纵隔内心脏、大血管及两肺纹理呈低信号.消化系统:胃泡、胆囊呈高信号,肠管不扩张时呈等低信号,部分肠管内见低信号胎粪影.肝脏、脾脏呈等低信号位于上腹部两侧.泌尿系统:双侧肾脏呈卵圆形等低信号,膀胱呈囊性高信号位于盆腔内.骨骼、肌肉系统:脊柱、四肢呈低信号,肌肉呈等信号.胎盘信号从均匀、稍高信号向不均匀、稍低信号过渡,胎盘边缘也从平滑向分叶状过渡.结论 快速MRI能清楚显示胎儿各主要器官正常解剖和发育变化,同时可以对胎盘成熟度进行准确判断.     

单次激发快速自旋回波序列MR检查在胎儿先天性肠道闭锁中的应用

目的探讨单次激发快速自旋回波序列(SSFSE)在胎儿MR检查先天性肠道闭锁的应用价值。资料与方法对8例孕20周以上超声提示存在先天性肠道闭锁的胎儿行MR检查。采用SSFSE,选择胎儿头颅、躯干的常规体位,并重点行胎儿躯干横断位、冠状位、矢状位扫描,将产前MRI表现与引产后尸体解剖结果相对照。结果8例先天性肠闭锁,引产后尸检证实闭锁部位分别为空肠近段5例和回肠中段3例,后者同时合并胎儿腹腔积液,SSFSE上见扩张肠管以高信号为主;其中2例肠闭锁并发先天性肛门闭锁,SSFSE上扩张肠管内可见低信号胎粪;1例肠闭锁并发先天性食管闭锁,SSFSE上可见食管中段闭锁处高信号;1例肠闭锁并发膈疝,SSFSE冠状位上疝入物为部分肠管,可见左侧胸腔内少许散在高信号。结论 SSFSE MR检查能清楚显示胎儿先天性肠道闭锁,具有一定的临床诊断价值。     

Application of MR Single Fast Spin Echo Sequence in Fetal Congenital Intestinal Atresia

目的 探讨单次激发快速白旋回波序列(SSFSE)在胎儿MR检查先天性肠道闭锁的应用价值.资料与方法 对8例孕20周以上超声提示存在先天性肠道闭锁的胎儿行MR检查.采用SSFSE,选择胎儿头颅、躯干的常规体位,并重点行胎儿躯干横断位、冠状位、矢状位扫描,将产前MRI表现与引产后尸体解剖结果相对照.结果 8例先天性肠闭锁,引产后尸检证实闭锁部位分别为空肠近段5例和回肠中段3例,后者同时合并胎儿腹腔积液,SSFSE上见扩张肠管以高信号为主;其中2例肠闭锁并发先天性肛门闭锁,SSFSE上扩张肠管内可见低信号胎粪;1例肠闭锁并发先天性食管闭锁,SSFSE上可见食管中段闭锁处高信号;1例肠闭锁并发膈疝,SSFSE冠状位上疝人物为部分肠管,可见左侧胸腔内少许散在高信号.结论 SSFSE MR检查能清楚显示胎儿先天性肠道闭锁,具有一定的临床诊断价值.     

MRI在胎儿消化系统发育异常中的应用

目的探讨MRI在胎儿消化系统发育异常方面的应用价值。资料与方法对10例孕20周以上超声提示存在消化系统发育异常的胎儿行MR检查。采用单次激发快速自旋回波序列(SSFSE),选择胎儿头颅、躯干的常规体位,并重点行胎儿躯干横断位、冠状位、矢状位扫描,将产前MR表现与引产后尸体解剖结果相对照。结果 10例消化系统发育异常胎儿中,先天性小肠闭锁2例;引产后尸检证实闭锁部位分别为空肠近段和回肠中段,后者同时合并胎儿腹腔积液,SSFSE上见扩张肠管以高信号为主;先天性肛门闭锁5例,SSFSE上扩张肠管内可见低信号胎粪;膈疝2例,均位于左侧,疝入物1例为胃腔、1例为部分肠管,MR图像上表现为高信号胃腔、肠管上升至心脏水平;腹部包块1例,引产后证实为先天性肠系膜囊肿,表现为腹腔内高信号囊性包块。结论 MRI在胎儿消化系统发育异常方面具有一定的诊断价值。     

胎儿主要器官的正常解剖及MR表现

目的了解胎儿主要器官的正常解剖及MR表现。方法对47例胎儿行快速MR成像检查，使用序列为单次激发快速自旋回波序列，观察主要正常器官的解剖和MR表现，包括脑、肺、心脏、肝、脾、胃肠道、肾脏、膀胱、骨骼、脊柱和皮下脂肪，并按不同的胎龄分组观察。结果47例胎儿MR检查结果表明：孕20周时，胎儿各主要器官均已发育。20周左右，大脑皮层光滑，无脑回、脑沟，之后脑回、脑沟逐渐缓慢形成；肺、气管、支气管均呈高信号，心脏、大血管及肝脾呈低信号，胃肠道、肾孟肾盏、膀胱呈高信号，肾实质为等信号，骨骼、肌肉呈低信号；脊柱20周已形成，皮下脂肪20周可见，随胎龄增长逐渐增多。结论快速MR成像能清楚显示胎儿各主要器官的正常解剖和发育变化，胎儿主要器官的解剖和MR表现与新生儿有较大的差别。     

SSFSE和FIESTA序列在正常胎肺生物学测量中的对比研究

目的 基于SSFSE和FIESTA序列评价不同孕周正常胎肺体积及肺-肝信号强度比(LLSIR)值,建立22～38周正常胎儿肺体积的参考范围。方法 回顾性分析行胎儿磁共振SSFSE和FIESTA序列检查的330例单胎妊娠患者资料。使用ITK-SNAP软件描点勾勒,测出22～38周胎儿左、右肺及总肺体积的平均值、中位数、标准差、最小、最大值、上、下四分位数及95%置信区间。采用配对t检验对SSFSE和FIESTA序列所测左肺、右肺、总肺体积及LLSIR结果进行比较。结果 正常中晚期单胎妊娠,胎肺体积及LLSIR均与孕周呈显著正相关(均P<0.01)。SSFSE和FIESTA序列测得22～38周胎儿左肺、右肺及总肺体积差异无统计学意义(均P>0.05);而SSFSE和FIESTA序列测得LLSIR差异具有统计学意义(均P<0.01)。结论 胎儿肺体积与LLSIR随着胎儿孕周的增加而增加;FIESTA可替代SSFSE序列进行胎儿肺体积测量,但使用LLSIR来评估胎肺发育时应视具体情况而定。     

中晚孕期胎脑与胎盘表观扩散系数比值和孕周的相关性研究

目的 探讨中晚孕期胎儿不同脑区与胎盘的ADC比值和孕周的相关性。方法 回顾性分析本院MRI检查的单胎妊娠孕妇98例，MRI检查未见明显胎儿颅脑异常。孕妇年龄19～40岁，平均(28.74±4.46)岁。孕周21～38周，平均(29.73±3.87)周。测量胎盘、脑干、双侧小脑半球、基底核、丘脑及双侧各脑叶深部白质的ADC值，分析胎脑各区域ADC值与胎盘ADC值的相关性；并计算出胎脑各区域与胎盘ADC比值，分析该比值和孕周的相关性。结果 左右两侧大脑半球及小脑半球对称部位ADC值无统计学差异(P>0.05)。幕上深部白质的平均ADC值高于小脑半球、基底核、丘脑、脑干。胎脑各区域ADC值与胎盘ADC值无相关性(P>0.05)。额叶深部白质与胎盘ADC比值(F/P)和孕周呈显著正相关(r=0.272,P<0.01);丘脑与胎盘ADC比值(Th/P)、脑干与胎盘ADC比值(S/P)、小脑与胎盘ADC比值(C/P)和孕周呈显著负相关(r值分别为-0.301、-0.399、-0.445,P值均<0.01)。结论 中晚孕期正常胎儿脑组织与胎盘ADC比值随胎儿孕周的增加有一定变...     

产前MRI对胎儿卵巢囊肿的诊断价值

目的探讨产前MRI在胎儿卵巢囊肿中的诊断价值。方法回顾性分析产前诊断及手术确诊的40例胎儿卵巢囊肿的产前、产后MRI影像特征。结果产前MRI检查胎儿卵巢囊肿发生于单侧38例,双侧2例。病灶形态均为类圆形或椭圆形,边界光滑,囊壁较薄。32例病灶内部信号较均匀,T1WI呈均匀低或稍高信号,T2WI呈高信号,DWI扩散不受限,ADC图呈高信号;8例病灶内信号较混杂,T1WI呈稍低及稍高信号,T2WI呈不均匀的稍低信号并夹杂斑片状、点状高信号影,DWI部分扩散受限,ADC图呈低信号。病灶邻近的肠管均受压推移。产后随访发现20例肿块自行消退。有8例行腹腔镜探查手术,病理显示7例为卵巢单纯性囊肿伴出血,1例卵巢囊肿合并蒂扭转。结论产前MRI不仅能清晰显示胎儿卵巢囊肿的发生部位、形态、边界、范围、信号特点,还可评估肿块与邻近组织的结构以及其他合并症,能更好地为临床评估预后和产后治疗提供可靠的诊断依据。     

胎盘羊膜囊肿MRI诊断1例

正患者女,28岁。孕24周+5天,患者正常进行妊娠中期排畸超声检查,阳性发现"U"形脐带压迹,羊膜腔内见环形光带,范围约5.5cm×5.1cm,内见暗区,未探及明显血流信号。双侧脑室后角宽约0.9cm、1.0cm,后颅窝无明显增大。超声诊断:羊膜腔异常回声,一侧脑室轻度扩张。MRI检查影像显示:胎儿胎位为臀位,羊水量尚可,胎儿嘴前缘可见一个囊泡样结构,囊壁较薄,呈T2WI低信号,囊内呈T2WI稍低信号,大小约5.9cm×4.4cm。脐带     

胎儿中枢神经系统神经母细胞瘤1例

该文报道了1例中枢神经系统神经母细胞瘤胎儿的临床及影像资料。胎儿胎龄31+周, 胎儿颅脑MRI示左侧颞、枕叶不规则囊实性肿块, 边界不清, T1WI以稍高信号为主, 伴少量高信号及低信号, T2WI呈稍低及高信号, 扩散加权成像示部分病灶呈高信号。最终尸体解剖病理诊断为胎儿中枢神经系统神经母细胞瘤。     

Fetal lung-to-liver signal intensity ratio at MR imaging: development of a normal scale and possible role in predicting pulmonary hypoplasia in utero

PURPOSE: To define retrospectively a normal range for lung-to-liver signal intensity ratio (LLSIR) in fetuses of 16-40 weeks gestation by using half-Fourier single-shot turbo spin-echo magnetic resonance (MR) imaging. MATERIALS AND METHODS: Approval from the regional ethics review board for retrospective evaluation was obtained, and informed consent was waived. Retrospective analysis and follow-up of 157 pregnant women who underwent MR imaging over the past 4 years were performed. Seventy-four fetuses were subsequently identified as having clinically normal lung function or normal lung morphologic features at autopsy. A total of 141 normal lungs were analyzed, and the LLSIR was calculated from images on an MR workstation. A mixed-effects statistical model was applied, and 95% prediction intervals were calculated. Ten fetuses with hypoplastic lungs at autopsy were also evaluated. RESULTS: Plotting LLSIR against gestational age demonstrated that, according to the fitted mean curve, the signal intensity ratio was higher with more advanced gestational age. Statistical modeling suggests a quadratic relationship between gestational age and LLSIR. For fetuses in the normal population, the LLSIR ranged from 1.52 at 21 weeks gestation to 4.31 at 34 weeks gestation. For all hypoplastic lungs in fetuses at or beyond 25 weeks gestation, the LLSIR was outside the lower bound of the 95% prediction interval for the normal population. The distinction between hypoplastic lungs and normal lungs at less than 25 weeks gestation is less definitive. CONCLUSION: This study provides a normal scale with a 95% prediction interval for LLSIR.     

Normal fetal lumbar spine on postmortem MR imaging

BACKGROUND AND PURPOSE: There is an increasing interest in use of postmortem MR imaging as an adjunct or alternative to autopsy. Before evaluating spinal pathology on postmortem MR imaging, it is important to have knowledge of the normal appearance of the fetal spine at different gestational ages. The aim of this study is to describe the MR imaging appearances of normal development of the fetal spine at different gestational ages. METHODS: Postmortem MR imaging was performed on 30 fetuses ranging from 14 to 41 gestational weeks. There was no structural abnormality of the spine in these fetuses on MR imaging or at autopsy. Fast spin-echo T2-weighted MR imaging of the lumbar spine was performed in the coronal plane in all cases and supplemented by sagittal and/or axial imaging. The following parameters were measured: height of the L1/2 disk and L2 vertebral body and area of ossification center in L2 vertebral body as well as area of vertebral body. The signal intensity of the disk space and the vertebral level of conus termination were also assessed. RESULTS: The height and area of the vertebral body increased linearly with gestational age (P <.01). The increase in disk space was proportionally greater than the increase in vertebral body height as gestational age increased (P <.01). The disk space appeared as a linear low-signal-intensity area in fetuses < or = 21 weeks gestation but increasingly developed high signal intensity in the disk after 21 weeks. The size of the ossification center increased with gestational age (P <.01), and the ratio of ossification center to the overall size of the vertebral body also increased with gestational age (P <.01). In fetuses less than 35 weeks of age, the conus lay between L2 and L5 level, whereas in fetuses more than 35 weeks of age, the conus lay between L1/2 and L2/3 level. CONCLUSION: Understanding the normal growth and signal-intensity characteristics of the fetal spine on postmortem MR imaging is essential before studying abnormal fetal spine.     

Obstetrical magnetic resonance imaging: fetal anatomy

Nine patients who were 34-36 weeks pregnant underwent magnetic resonance (MR) imaging. Sagittal images using spin echo technique (TR 2.0 sec, TE 28 msec) were optimal for delineating fetal anatomy. The fetal cardiovascular, pulmonary, and central nervous systems were depicted in all cases. The heart and major vessels were readily seen due to the natural contrast of flowing blood. The intensity of the fluid-filled lungs greatly increased with a longer TR or TE, delimiting thorax from liver. The brain was relatively featureless due to the lack of gray-white matter differentiation. The umbilical cord within the amniotic fluid and its insertion into the placenta and fetus was identified in all cases. MR is a new modality for fetal imaging that offers tissue-characterization information that complements the superior anatomic detail of ultrasound scanning.     

Postmortem MR imaging of the fetal and stillborn central nervous system

BACKGROUND AND PURPOSE: Changes in the public perception of postmortem procedures in the United Kingdom have led to reduced numbers of autopsies being performed in the fetus and neonate. When autopsy is performed in this group, the brain is now usually studied without being formalin-fixed, which limits the available information. We evaluated the diagnostic accuracy of postmortem MR imaging of the fetal brain and spine when compared with the reference standard, autopsy. METHODS: We obtained high-spatial-resolution T2-weighted images (in-plane resolution approximately 0.4 mm) of the brain and spine in 40 fetuses and stillborn neonates (14-42 weeks gestational age) who were referred for autopsy. The MR findings were compared with those of autopsy, the reference standard, which had been performed independently. RESULTS: In eight cases, the autopsy did not provide structural information of the brain or spine, because assessment of the unfixed tissue was impossible. There was agreement between MR and autopsy findings in 31 (97%) of 32 cases in which comparison could be made. Eleven cases showed normal brain, and 20 cases showed a wide range of developmental and acquired abnormalities. The sensitivity of MR was 100%, specificity 92%, positive predictive value 95%, and negative predictive value 100%. CONCLUSION: MR imaging has a useful role in providing structural information of the central nervous system in fetuses and stillborn neonates.     

Diffusion-weighted MR imaging offers no advantage over routine noncontrast MR imaging in the detection of vertebral metastases

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging of the spine has been used to differentiate benign from pathologic vertebral body compression fractures. We sought to determine the utility of diffusion-weighted MR imaging in the detection of vertebral metastases and to compare it with conventional noncontrast T1- and T2-weighted MR imaging. METHODS: Fifteen patients with metastases to the spine were studied using conventional MR imaging and diffusion-weighted imaging. Blinded review of all images was undertaken, and patients were categorized according to whether they had focal or multiple lesions. The signal intensity of the lesions was compared on T1-, T2- (fast spin-echo), and diffusion-weighted images. RESULTS: In five patients with focal disease, metastases were hypointense on T1-weighted images; hypointense (n = 2), isointense (n = 1), or hyperintense (n = 2) on T2-weighted images; and hypointense (n = 3) or hyperintense (n = 2) on diffusion-weighted images with respect to presumed normal bone marrow. In 10 patients with disease in multiple sites, all lesions were hypointense on T1-weighted images; hypointense (n = 2), isointense (n = 4), hyperintense (n = 2), or mixed (n = 2) on T2-weighted images; and hypointense (n = 5), hyperintense (n = 3), or mixed (n = 2) on diffusion-weighted images with respect to presumed normal bone marrow. CONCLUSION: As used in this study, diffusion-weighted MR imaging of the spine showed no advantage in the detection and characterization of vertebral metastases as compared with noncontrast T1-weighted imaging, but was considered superior to T2-weighted imaging.     

肾上腺疾病的MR影像诊断

本文对５０例正常肾上腺，４２例共４９个肾上腺病灶的ＭＲ影像进行分析，结果表明：（１）正常肾上腺信号均匀，显示率与ＣＴ相似；（２）ＭＲ可清晰显示大于１．０ｃｍ的病灶及其与周围结构的关系；（３）ＭＲ对腺瘤与转移瘤的鉴别有较大的帮助，Ｔ＿２ＷＩ腺瘤类似于肝脏的信号强度，转移瘤与脂肪的信号强度相似；（４）嗜铬细胞瘤的ＭＲ影像有特异性，Ｔ＿２ＷＩ呈明显高信号，４５％见散在点状短Ｔ＿２低信号区。     

磁共振成像对胎儿异常及妊娠并发症的初步研究

目的：探讨MRI对胎儿发育异常、畸形及妊娠并发症的显示，研究MRI对该异常的诊断价值。资料与方法，对44例中，晚期孕妇行MRI检查，观察和分析胎儿各脏器及母体附属结构的形态、信号变化。结果：胎儿的大多数脏器及母体的附属结构（如胎脑、胎心、胎肝、胎盘、子宫等）显示良好。发现2例前置胎盘、12例脐带绕颈、1例胎儿宫内发育迟缓及1例葡萄胎等异常。结论：MRI能较好地显示胎儿的发育异常、畸形及妊娠并发症，较超声优越，对胎儿生长发育状况的研究有重要价值。     

Ultrafast MR imaging of the normal posterior fossa in fetuses

OBJECTIVE: The purpose of our study was to determine if a standard imaging protocol using ultrafast MR sequences could adequately reveal normal posterior fossa anatomy in fetuses and, if so, to document a template on MR imaging for normal posterior fossa development. MATERIALS AND METHODS: A retrospective review found 66 MR imaging studies of 63 fetuses, 16-39 weeks' gestation age (mean, 25 weeks' gestation), who were referred between June 1996 and May 1999 for evaluation of non-central nervous system anomalies revealed on prenatal sonography. All fetuses had normal brains and spines on prenatal sonography. The standard MR imaging protocol included axial, sagittal, and coronal half-Fourier acquisition single-shot turbo spin echo (HASTE); sagittal and coronal two-dimensional fast low-angle shot (FLASH); and axial turbo T1-weighted FLASH images through the fetal brain. Structures that we analyzed were the fourth ventricle, the cisterna magna, the vermis, the cerebellar hemispheres, and the brainstem. Using the HASTE sequences, we documented gestational age-specific signal intensity changes in the cerebellar hemispheres and the brainstem. RESULTS: The posterior fossa anatomy was sufficiently well defined to exclude abnormalities of the fourth ventricle and cerebellar vermis in all cases. Because of high T2-weighting, good contrast enhancement, and good signal-to-noise ratios, HASTE images provided the best anatomic definition of the posterior fossa. CONCLUSION: Normal posterior fossa anatomy can be adequately shown on ultrafast MR images, which can be helpful when prenatal sonography is equivocal.     

Supratentorial parenchyma in the developing fetal brain: in vitro MR study with histologic comparison.

PURPOSETo assess the in vitro MR signal of the developing brain through histologic comparisons.METHODSFive healthy fetal specimens aged 16, 19, 22, 27, and 34 gestational weeks were studied in vitro using T1- and T2-weighted sequences in frontal and axial planes. Neuropathologic studies included sections in the same frontal plane. Comparison of histologic sections with measurements of the relative widths of the layers of different signal intensities enabled us to assign cellular correspondence to each MR layer.RESULTSIn the cerebral mantle, a layered pattern was observed on both T1- and T2-weighted images. In the basal ganglia, signal from the pallidum and thalamus was isointense with white matter from 16 to 22 weeks'' gestation; then, from 27 and 34 weeks'' gestation, the signal was relatively high on T1-weighted images and low on T2-weighted images. The neostriatum had a relatively low signal on T1-weighted images and a high signal on T2-weighted images from 16 to 27 weeks'' gestation: then, at 34 weeks'' gestation, the signal was relatively high on T1-weighted images and low on T2-weighted images.CONCLUSIONMR imaging can clearly show specific patterns of growing fetal brain in vitro.