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101.
In diffusion tensor magnetic resonance imaging (DT-MRI), limitations concerning complex fiber architecture (when an image voxel contains fiber populations with more than one dominant orientation) are well-known. Fractional anisotropy (FA) values are lower in such areas because of a lower directionality of diffusion on the voxel-scale, which makes the interpretation of FA less straightforward. Moreover, the interpretation of the axial and radial diffusivities is far from trivial when there is more than one dominant fiber orientation within a voxel. In this work, using (i) theoretical considerations, (ii) simulations, and (iii) experimental data, it is demonstrated that the mean diffusivity (or the trace of the diffusion tensor) is lower in complex white matter configurations, compared with tissue where there is a single dominant fiber orientation within the voxel. We show that the magnitude of this reduction depends on various factors, including configurational and microstructural properties (e.g., the relative contributions of different fiber populations) and acquisition settings (e.g., the b-value). These results increase our understanding of the quantitative metrics obtained from DT-MRI and, in particular, the effect of the microstructural architecture on the mean diffusivity. More importantly, they reinforce the growing awareness that differences in DT-MRI metrics need to be interpreted cautiously. 相似文献
102.
超低出生体重儿红细胞输注的临床分析 总被引:1,自引:0,他引:1
探讨超低出生体重(ELBW)儿减少红细胞输注的可能性。方法对1989~1997年9年间256
例超低出生体重儿的红细胞输注进行临床分析。在此期间红细胞输注指征进行了3次制订,对检验样本的采
血量进行了严格的控制,部分病例应用了重组人促红细胞生成素治疗。结果1994年以后有1/4的ELBW儿
不需要输注红细胞,1989~1997年平均输血次数由7次降至2.7次(P<0.01)。按出生体重累计红细胞输注
量由163.5mL/kg降至69.2mL/kg(P<0.01),接受供血者人数由6.3人降至1.5人(P<0.01)。红细胞输注
前的平均红细胞压积比,机械通气者由0.43降至0.34、自主呼吸者由0.41降至0.31。ELBW儿更加不成熟,平
均胎龄由27.4周减至26.0周,平均出生体重由833g降至741g。存活率仍达78%,住院时间没有延长,严重并
发症如视网膜病、动脉导管未闭、脑室出血的发生率没有增加。结论制订严格的红细胞输注指征有助于减少
输血次数和接受供血者人数,且患儿临床耐受良好。 相似文献
103.
104.
脑康泰胶囊对阿尔茨海默氏病大鼠学习记忆作用的影响 总被引:1,自引:0,他引:1
目的:观察脑康泰胶囊对阿尔茨海默氏病模型大鼠学习记忆作用的影响。方法:采用脑立体定向颅内注射啉酸所致阿尔第默氏病(Alzheimers disease.AD)大鼠模型的方法。结果:脑康泰胶囊可显著增加强AD大鼠被动学习和主动学习的能力。调节脑组织中单胺类递质含量及血清中相关激素水平,并显著改善AD模型大鼠的脑电图。结论:脑康泰胶囊显著改善AD大鼠学习记忆能力的作用,其机制与其调节中枢递质及激素水平等相关。 相似文献
105.
Obstruction of the small intestine: accuracy and role of CT in diagnosis 总被引:17,自引:0,他引:17
Maglinte DD; Gage SN; Harmon BH; Kelvin FM; Hage JP; Chua GT; Ng AC; Graffis RF; Chernish SM 《Radiology》1993,188(1):61
106.
我们成功地建立了一个新的层析等电点聚焦的三步程序.细菌培养液首先以CG-50吸附,洗脱出的粗毒素溶液在PBE_(94)柱上进行层析等电点聚焦.分别用5mMTris-Base pH9.4和Buffalyte_(8-4) pH5.4缓冲液洗脱,出现多个洗脱峰,即刻测定pH值.收集pH6.8~7.1的洗脱液,混合、浓缩,最后通过Sephacryl s-200过滤,以0.05M PBS pH6.8洗脱,出现3个峰,毒素在第1峰.毒素纯度为98%,回收率89%,p17.6,MW28500,SDS-PAGE上1条带.以~(125)I标记SED作探针的电泳转移和放射自显影均证明了提纯SED的免疫学特异性.免疫扩散试验,即使200μg/ml SED与不产毒素的FRI-184抗血清,也未有可见沉淀线. 相似文献
107.
We investigated whether cigarette smoking, measured by follicular fluid
concentrations of cotinine (a major metabolite of nicotine), affects the
maturity of oocytes from women undergoing in-vitro fertilization (IVF) and
embryo transfer. In 234 women, follicular fluid samples were assessed for
cotinine and their 2020 oocytes were assessed for maturity stage. Data on
individual proportions of oocytes which were mature (OM) and were
fertilized (OF) were analysed by regression in relation to age and
follicular fluid cotinine. OF gave an independent assessment of oocyte
maturity. Both age and follicular fluid cotinine entered the OM and OF
regressions and were significant. The age-adjusted regression coefficients
for log cotinine were positive; greater cotinine concentrations usually
accompanied greater OM and OF. The cotinine effect on OM was positive in
younger women, but it became negative (decreased OM with increasing
cotinine concentrations) in older women (> or = 40 years). We further
found in older women an average reduction of approximately 50% in the
number of mature oocytes; this reduced number was lower than the number of
embryos usually transferred. Smoking can reduce the number of mature
oocytes even further, therefore risking a negative IVF-embryo transfer
outcome. This may be the reason why the negative effects of smoking become
clinically detectable in older women.
相似文献
108.
109.
Recently, a discrimination measure for feature extraction for two-class data, called the maximum discriminating (MDF) measure (Talukder and Casasent [Neural Networks 14 (2001) 1201-1218]), was introduced. In the present paper, it is shown that the MDF discrimination measure produces exactly the same results as the classical Fisher criterion, on the condition that the two prior probabilities are chosen to be equal. The effect of unequal priors on the efficiency of the measures is also discussed. 相似文献
110.