Fetal imaging

Presently, MRI is an adjunct to prenatal sonography. It provides information that can aid in the diagnosis of fetal anomalies, affect prenatal counseling and management of the pregnancy, and guide prenatal intervention and delivery planning. With further advances in technology, particularly shorter scan times and better image resolution, the applications for fetal imaging are likely to increase.     

Fetal MR imaging

Ultrasonography is the primary prenatal screening modality used in the evaluation of the fetus and the maternal pelvis. However, fetal MR imaging plays a complementary role to prenatal ultrasound in the evaluation of the fetus with suspected abnormalities. MR imaging's role includes confirming or excluding possible lesions, defining their full extent, aiding in their characterization, and demonstrating other associated abnormalities. As newer techniques such as diffusion imaging, MR spectroscopy, and functional studies are used more widely, it is hoped that additional information will be made available by this modality to physicians evaluating and taking care of fetuses.     

Fetal magnetic resonance imaging

Ultrafast magnetic resonance imaging (MRI) sequences have changed the use of MRI to evaluate fetal abnormalities. Currently, the best application is the evaluation of suspected brain abnormalities found on ultrasound. MRI differentiates the various types of fetal ventriculomegaly. Superior posterior fossa visualization allows differentiation of Dandy-Walker malformation from a large cisterna magna. Anomalies of the corpus callosum can be seen. MRI also is valuable in the evaluation of fetal giant neck masses for planning delivery of the baby and surgery for life-threatening airway obstruction. In the chest, MRI differentiates masses such as diaphragmatic hernia, cystic adenomatoid malformation, and sequestration, and it aids in planning fetal surgery because MRI directly visualizes the position of the lung, liver, and bowel.     

磁共振扩散加权与弥散张量成像原理分析及比较

磁共振扩散加权与弥散张量成像作为磁共振成像新技术已经应用于临床.迫切要求我们对这两种成像方法有较全面的认识和准确的把握.本文全面系统地介绍磁共振扩散加权与弥散张量成像的原理,阐明相关概念,分析重要成像参数的影响及二者的差别.     

Fetal brain MR imaging

In the past 10 years, improvements in MR imaging and faster imaging techniques have dramatically increased the use of in-utero fetal brain MR imaging. Challenging abnormalities now can be diagnosed prenatally through a careful analysis of morphology and signal changes. Using illustrations of normal brain development as a starting point, this article illustrates and discusses major brain malformations and specific morphologic changes, destructive lesions, and isolated ventriculomegalies, and the advantages and disadvantages of T1 and T2 sequences are provided.     

Basic concepts of MR imaging, diffusion MR imaging, and diffusion tensor imaging

MR image contrast is based on intrinsic tissue properties and specific pulse sequences and parameter adjustments. A growing number of MRI imaging applications are based on diffusion properties of water. To better understand MRI diffusion-weighted imaging, a brief overview of MR physics is presented in this article followed by physics of the evolving techniques of diffusion MR imaging and diffusion tensor imaging.     

胎儿磁共振——磁共振检查的新领域

随着磁共振成像技术的改进,MRI现在可应用于胎儿诊断。MRI提供的胎儿结构信息的深度,意味着它不仅仅是超声有用的辅助诊断手段,史能清晰地显示胎儿结构,避免超声的局限性。目前,MRI在胎儿中枢神经系统异常中的诊断最有价值,在中枢神经系统,在脑室扩大、胼胝体发育不全和后颅窝畸形的诊断中最有优势,此外,在胎儿胸部和其他系统畸形诊断中逐渐显示优势。MRI还能准确测量胎儿器官体积和重量,可以评估胎儿生长受限。一些MRI新技术如弥散加权成像、磁共振波谱和功能成像也逐渐应用于胎儿,可以提高我们对胎儿在子宫内代谢和发育信息的认识。本文将详细介绍胎儿MRI的安全性、技术及各系统临床应用。     

Hybrid diffusion imaging

Diffusion measurements in the human central nervous system are complex to characterize and a broad spectrum of methods have been proposed. In this study, a comprehensive diffusion encoding and analysis approach, hybrid diffusion imaging (HYDI), is described. The HYDI encoding scheme is composed of multiple concentric "shells" of constant diffusion weighting, which may be used to characterize the signal behavior with low, moderate and high diffusion weighting. HYDI facilitates the application of multiple data analyses strategies including diffusion tensor imaging (DTI), multi-exponential diffusion measurements, diffusion spectrum imaging (DSI) and q-ball imaging (QBI). These different analysis strategies may provide complementary information. DTI measures (mean diffusivity and fractional anisotropy) may be estimated from either data in the inner shells or the entire HYDI data. Fast and slow diffusivities were estimated using a nonlinear least squares bi-exponential fit on geometric means of the HYDI shells. DSI measurements from the entire HYDI data yield empirical model-independent diffusion information and are well-suited for characterizing tissue regions with complex diffusion behavior. DSI measurements were characterized using the zero displacement probability and the mean-squared displacement. The outermost HYDI shell was analyzed using QBI analysis to estimate the orientation distribution function (ODF), which is useful for characterizing the directions of multiple fiber groups within a voxel. In this study, an HYDI encoding scheme with 102 diffusion-weighted measurements was obtained over most of the human cerebrum in under 30 min.     

Fetal brain imaging: a comparison between magnetic resonance imaging and dedicated neurosonography.

OBJECTIVES: To evaluate whether fetal brain magnetic resonance imaging (MRI) adds useful clinical information to that obtained by dedicated fetal neurosonography using a combined transabdominal and transvaginal approach in fetuses with suspected brain anomalies. METHODS: In the 2-year period between January 2000 and January 2002, 42 fetuses underwent neurosonographic and MRI examinations of the brain. The referral indications were: asymmetric ventriculomegaly (13), ventriculomegaly (7), periventricular cysts (2), suspected midline findings (7), agenesis of the corpus callosum (3), infratentorial pathology (3), cytomegalovirus (CMV) infection (2) and miscellaneous indications (5). RESULTS: Neurosonography and MRI produced similar diagnoses in 29 fetuses: normal examination (10), isolated asymmetric ventriculomegaly (11), isolated ventriculomegaly (3), periventricular cysts (2), agenesis of the corpus callosum (1), pericallosal lipoma (1) and cerebellar hemorrhage (1). The neurosonographic diagnoses were more accurate in seven patients: hemimegalencephaly, pericallosal lipoma, signs of CMV infection, brain anomalies associated with agenesis of the corpus callosum and three fetuses with a normal ultrasound scan in which MRI suggested a parenchymal abnormality. MRI provided a more accurate diagnosis in three patients: a third ventricular dilatation was ruled out, normal ventricles in a fetus with an ultrasonographic finding of asymmetric ventricles, and diagnosis of progression of asymmetric ventriculomegaly. In three patients the identified pathologies were differently interpreted, each examination provided another aspect of the anomaly or a definitive diagnosis was not possible. CONCLUSIONS: Our study demonstrated that dedicated neurosonography is equal to MRI in the diagnosis of fetal brain anomalies. In most of the cases MRI confirmed the ultrasonographic diagnosis; in a minority of cases each modality provided additional/different information. The major role of MRI was in reassurance of the parents regarding the presence or absence of brain anomalies.     

扩散张量成像和扩散峰度成像在颈髓疾病中的应用进展

DTI和扩散峰度成像(DKI)能早期发现并定量分析颈髓内部微细结构的改变,对指导临床和判断颈椎疾病的预后有重要意义。本文就DTI、DKI成像原理及其在颈髓疾病中的应用进行综述。     

心血管磁共振弥散张量成像及弥散频谱成像研究进展

心血管磁共振(cardiovascular magnetic resonance,CMR)多种成像技术可以观察心脏结构功能、心肌组织特征乃至能量代谢.包括弥散加权成像(diffusion weighted imaging,DWI)、弥散张量成像(diffusion tensor imaging,DTI)及弥散频谱成像(diffusion spectrum magnetic resonance imaging,DSI)在内的弥散成像技术一直是CMR最具挑战性及目前尚未常规成熟开展的检查技术,尤以DTI及DSI为甚.本综述将重点阐述DTI及DSI的基本技术及近年来在心血管领域的应用进展.     

磁共振扩散峰度成像评价宫颈癌放疗后变化的小鼠实验研究

目的评价宫颈癌小鼠模型放疗前后的磁共振扩散峰度成像参数变化情况。材料与方法建立皮下种植成瘤的宫颈癌小鼠模型11只,在一侧腹股沟区及对侧腋下分别成瘤,对腹股沟区肿瘤行一次性大剂量放疗照射,腋下肿瘤作为未经放疗的对照组。对两部位肿瘤放疗前及放疗后1周左右行常规MR T2WI及磁共振扩散峰度成像(diffusion kurtosis imaging,DKI)成像,感兴趣区选取肿瘤全层面,计算表观扩散系数(apparent diffusion coefficient,ADC)值、平均扩散率(mean diffusivity,MD)、平均峰度值(mean kurtosis,MK)的平均值(av)及中位值(m)。对比放疗前各参数值的相关性(Pearson相关性检验),以及放疗前后在放疗组和对照组的变化差异(配对t检验)。结果放疗前的ADC值与MK之间存在强负相关性,ADC值与MD之间存在强正相关性(相关系数均大于0.7)。与放疗前相比,腹股沟组肿瘤放疗后的ADC值明显升高(ADCav分别为0.571±0.063×1 0~(-3) mm~2/s和0.6 1 1±0.0 5 5×1 0~(-3) mm~2/s,P=0.0 1 5;A D C m分别为0.543±0.052×10~(-3) mm~2/s和0.587±0.041×10~(-3) mm~2/s,P=0.013),MK值明显降低(MKav分别为1.14±0.12和1.02±0.10,P=0.003;MKm分别为1.13±0.10和1.14±0.10,P=0.003),而MD值的变化无统计学差异(MDav分别为0.856±0.105×10~(-3) mm~2/s和0.885±0.071×10~(-3) mm~2/s,P0.05;MDm分别为0.843±0.113×10~(-3) mm~2/s和0.878±0.081×10~(-3) mm~2/s,P0.05)。MK平均值变化幅度约9.4%,ADC平均值变化幅度约7.5%。对照组肿瘤前后两次ADC值、MD值和MK值均无统计学显著性差异(P0.05)。结论宫颈癌放疗后会引起ADC值的升高和MK的降低,其中MK的变化幅度相对稍高,提示扩散峰度成像用于放疗评价的可行性。