超声心动图对主动脉窦瘤破裂合并畸形的诊断价值

目的 评价超声心动图对主动脉窦瘤破裂合并畸形的诊断价值，探讨漏诊原因，以提高诊断阳性率。方法 回顾分析23例主动脉窦瘤破裂合并畸形的超声心动图特征，比较超声心动图与手术诊断结果。结果 超声心动图对主动脉窦瘤破裂合并畸形诊断符合率为86．95％（20／23），漏诊率为13．04％（3／23）。结论 超声心动图检查对诊断主动脉窦瘤破裂合并畸形有重要的临床价值，全面掌握超声知识，仔细认真地检查可避免漏诊。     

海藻糖对脂质膜保护作用的荧光分析

以蛋黄卵磷脂（EPC）为模型，通过反映磷脂头部基团运动情况的荧光各向异性的变化，研究海藻糖对蛋黄卵磷脂（EPC）脂质膜的保护作用，并对其机理进行探讨，试验表明：荧光各向异性A值曲线随温度变化呈抛物线形状。     

Correction of eddy-current distortions in diffusion tensor images using the known directions and strengths of diffusion gradients

Purpose

To correct eddy‐current artifacts in diffusion tensor (DT) images without the need to obtain auxiliary scans for the sole purpose of correction.

Materials and Methods

DT images are susceptible to distortions caused by eddy currents induced by large diffusion gradients. We propose a new postacquisition correction algorithm that does not require any auxiliary reference scans. It also avoids the problematic procedure of cross‐correlating images with significantly different contrasts. A linear model is used to describe the dependence of distortion parameters (translation, scaling, and shear) on the diffusion gradients. The model is solved numerically to provide an individual correction for every diffusion‐weighted (DW) image.

Results

The assumptions of the linear model were successfully verified in a series of experiments on a silicon oil phantom. The correction obtained for this phantom was compared with correction obtained by a previously published method. The algorithm was then shown to markedly reduce eddy‐current distortions in DT images from human subjects.

Conclusion

The proposed algorithm can accurately correct eddy‐current artifacts in DT images. Its principal advantages are that only images with comparable signals and contrasts are cross‐correlated, and no additional scans are required. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.

     

DIETARY CHOLESTEROL AND LIVER MICROSOMAL FATTY ACID DESATURASES

Dietary cholesterol increased the activity of rat liver microsomal fatty acid Δ⁹ desaturase, decreased that of Δ⁵ and Δ⁶ desaturases, and increased the fluorescence anisotrophy of 1,6-diphenyl-1,3,5-hexatriene.     

磁共振扩散张量成像评价幕上胶质瘤对锥体束的侵袭性

目的探讨MR DTI评价幕上胶质瘤对锥体束侵袭性的价值。方法对23例经手术病理证实的胶质瘤患者进行DTI分析。按照肿瘤恶性程度分为高(n=16)、低(n=7)级别胶质瘤;按照临床是否有肢体感觉和(或)运动异常分为有症状(n=11)和无症状(n=12)。分析测定患侧和对侧锥体束ADC值和FA值,并进行锥体束三维成像和统计学检验。结果高级别胶质瘤患侧内囊后肢层面锥体束FA值显著低于对侧(P<0.05)。高低级别胶质瘤各层面锥体束ADC值与对侧差异均无统计学意义。有肢体感觉和(或)运动异常者的患侧内囊后肢层面锥体束ADC值高于对侧(P<0.01),患侧锥体束内囊后肢层面及大脑脚层面锥体束FA值低于对侧(P<0.05),而脑桥层面FA值与对侧比较差异均无统计学意义(P>0.05)。有肢体感觉和(或)运动异常者的患侧锥体束重建可见锥体束浸润、破坏。结论应用DTI能够较准确地判定幕上胶质瘤对锥体束的侵袭情况。     

How does DWI correlate with white matter structures?

Diffusion-weighted MRI (DWI) is widely used to characterize brain white matter (WM), particularly through the use of diffusion tensor imaging (DTI). In this study the spatial characteristics of DWI in WM of cat visual cortex were investigated at 9.4T at very high resolution. It is shown that the spatial extent of the WM tract as measured from the DWI images depends highly on the b-value. In particular, when the diffusion gradient is applied perpendicular to the main direction of the fiber tract, the estimated thickness of the tract at the commonly used b-value of 1000 s/mm2 exceeds by 50% the thickness as it appears on a T2-weighted image. Only at b-values greater than 6000 s/mm2 does the thickness of the tract approach the thickness characterized by the T2-weighted image and that observed on histological slices of the same area. Further analysis of these results indicates that the choice of b-value of 1000 s/mm2 may not be optimal for the demarcation of anisotropic WM structures. DWI at high b-value may contain spatial information that is more specific to WM tracts.     

Assessing atrophy of the major white matter fiber bundles of the brain from diffusion tensor MRI data.

Brain atrophy is a typical feature of many neurological conditions. Therefore, quantitative evaluation and spatial characterization of atrophy are potentially useful for monitoring the evolution of central nervous system (CNS) disorders. In this study, a method for measuring atrophy of the major white matter (WM) fiber bundles in the brain using diffusion tensor (DT) MRI data is developed. To this end, an atlas was created from sets of diffusion anisotropy images from normal subjects, and the deformations necessary to match single subject anisotropy images to this atlas were then computed. Because diffusion anisotropy images were used, this approach should be sensitive to fiber bundle volume changes in the same way that using T1-weighted images allows gray matter volume changes to be measured. The Jacobian determinant of the deformation field for each subject was then used as a measure of contraction or expansion of the tissue at each image voxel. An overview of the nonlinear registration problem is given; then an optimization of the parameters for the chosen algorithm is performed and the method for producing the atlas is described. The effectiveness of the method was then tested on data from five patients with multiple sclerosis (MS) and two patients with amyotrophic lateral sclerosis (ALS).     

Diffusion tensor imaging (DTI) of rodent brains in vivo using a 1.5T clinical MR scanner

PURPOSE: To evaluate the feasibility of using a clinical 1.5T MR scanner to perform magnetic resonance (MR) diffusion tensor imaging (DTI) on in vivo rodent brains and to trace major rodent neuronal bundles with anatomical correlation. MATERIALS AND METHODS: Two normal adult Sprague Dawley (SD) rats were anesthetized and imaged in a 1.5T MR scanner with a microscopic coil. DTI was performed at a resolution of 0.94 mm x 0.94 mm x 0.5 mm (reconstructed to 0.47 mm x 0.47 mm x 0.5 mm, with b-factors of 600 seconds/mm2 and 1000 seconds/mm2) and a higher resolution of 0.63 mm x 0.63 mm x 0.5 mm (reconstructed to 0.235 mm x 0.235 mm x 0.5 mm, with a b-factor of 1500 seconds/mm2). The fiber-tracking results were correlated with corresponding anatomical sections stained to visualize neuronal fibers. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) of the neuronal fibers were measured and compared with results in published reports. RESULTS: Several major neuronal fiber tracts, including the corticospinal cord, corpus callosum, and anterior commissure, were identified in all DTI data sets. Stained anatomical sections obtained from the rats confirmed the location of these fibers. The ADC values (0.6-0.8 +/- 10(-3) mm2/second) of the fibers were similar to published figures. However, the FA values (0.3-0.35) were lower than those obtained in previous studies of white matter in rodent spinal cord. CONCLUSION: We have demonstrated the feasibility of using a 1.5T clinical MR scanner for neuronal fiber tracking in rodent brains. The technique will be useful in rodent neuroanatomy studies. Further investigation is encouraged to verify the FA values generated by DTI with such techniques.     

磁共振扩散张量成像评价轻度认知障碍患者的脑白质变化

目的 利用磁共振扩散张量成像评价轻度认知障碍患者与正常对照不同脑区的各向异性分数(FA)的差异.方法 分别对来自北京大学精神卫生研究所的23例轻度认知障碍患者及26名正常对照者行MR扫描,测定DTI图像上不同部位的FA值,并分析两组间各相同部位FA值的差异.结果 患者组双侧海马旁回及右侧颞叶白质的FA值低于对照组,差异有统计学意义.结论 MCI患者双侧海马旁回及右侧颞叶可能存在白质纤维束完整性的受损.