常规MRI正常的新生儿缺氧缺血性脑病弥散张量成像初探

目的研究弥散张量MRI(diffusion-tensor MR imaging,DTI)对于临床诊断为新生儿缺氧缺血性脑病(hypoxic-ischemic encephalopathy,HIE)而常规MRI所见为正常病例的评估能力。方法选择20例常规MRI所见为正常的足月HIE患儿,以10例正常新生儿为对照,分组进行常规MRI、DTI扫描,测定两组新生儿相同感兴趣区(region of interest,ROI)的平均弥散度(mean diffusivity,Da)、分数各向异性(fractional anisotropy,FA)和相对各向异性值(relative anisotropy,RA)。用Student t—test法检验两组患儿各项指标,并观察比较两组新生儿的彩色FA图和彩色编码张量图。结果两组新生儿的Da在侧脑室前角前外侧白质、内囊后肢,放射冠各个感兴趣区均无显著性差异,而FA和RA值各感兴趣区则有明显差异,表现为HIE患儿FA值和RA值的下降,并且Da的高低与孕龄的长短有一定相关性。结论FA和RA是HIE患儿白质损伤或功能障碍的敏感指标,结合彩色FA图和彩色编码张量图可对患儿白质髓鞘的损伤作出较为准确、客观的评价,并可能在今后评估患儿的预后转归方面起重要作用。     

小脑上脚交叉的各向异性分数和表观弥散系数值与年龄、性别的相关性研究

目的量化比较不同年龄段小脑上脚交叉的各向异性分数(FA)值和与表观弥散系数(ADC)值,并探讨小脑上脚交叉的FA值、ADC值与年龄、性别的相关性。方法回顾性分析100例正常人群横轴位弥散张量成像(DTI)图像,其中男女各50例,年龄30⁷9岁,平均54.7岁。由一名专家运用感兴趣区(ROI)功能在FA图和ADC图上分别测量小脑上脚交叉的FA值和ADC值。配对或独立样本t检验比较性别间的差异,单因素方差分析用于各年龄组之间的差异,双变量相关用于分析年龄对小脑上脚交叉信号的影响或相关性。结果 100例健康成年人中,小脑上脚交叉的FA值(0.52±0.04)明显低于小脑上脚的FA值(0.71±0.05),差异具有统计学意义(t=-36.718,P=0.000)。其中小脑上脚交叉的男性和女性FA值分别为0.52±0.04和0.51±0.04,无统计学差异(t=1.404,P=0.164)。经双变量相关分析,小脑上脚交叉的FA值与年龄呈低度正相关(r=0.300,P=0.002)。小脑上脚交叉和小脑上脚的ADC值分别为(722.23±38.75)×10-6 mm2/s和(759.16±31.23)×10-6 mm2/s,有统计学差异(t=-8.047,P=0.000)。小脑上脚交叉的女性ADC值为(725.98±35.04)×10-6 mm2/s,虽然高于男性ADC值[(718.48±42.16)×10-6 mm2/s],但无统计学差异(t=-0.967,P=0.336)。经双变量相关分析,小脑上脚交叉的ADC值与年龄无相关性(r=-0.076,P=0.451)。结论在DTI图像中,小脑上脚交叉的FA值和ADC值均低于小脑上脚,并且均与性别没有相关性。随着年龄增大,FA值呈现增高趋势,ADC值则与年龄无相关性。本研究的结果可为今后的相关研究提供参考。     

急性大脑中动脉供血区脑梗死后大脑脚各向异性分数与运动诱发电位变化的关系

目的 探讨急性脑梗死后大脑脚各向异性分数(fractional anisotropy,FA)的变化特点及其与运动诱发电位(motor evoked potential,MEP)的关系,明确大脑脚FA下限值的临床意义.方法 根据对照组(n=105)的FA均数-1.64标准差确定正常大脑脚FA下限值.根据能否引出MEP将急...     

Measurement of thermal conductivity of bovine cortical bone

The thermal conductivity of cortical bone was characterized experimentally. Specimens were taken from the mid-diaphysis of bovine femora, and the rate of heat transfer was measured in three orthogonal directions. The conductivity was found to be 0.58±0.018 W/mK in the longitudinal direction, 0.53±0.030 W/mK in the circumferential direction, and 0.54±0.020 W/mK in the radial direction. Because the directional differences are small, it is concluded that bovine cortical bone can be treated as thermally isotropic.     

Alteration in surface muscle electrical anisotropy in the rat SOD1 model of amyotrophic lateral sclerosis

Objective

To evaluate the effects of progressive neurogenic change on surface-measured anisotropy via study in the rat superoxide dismutase 1 (SOD1) G93A amyotrophic lateral sclerosis (ALS) model.

Methods

Eight male ALS rats were studied over a period of 10 weeks. In each, the 20 kHz to 1 MHz electrical impedance of the gastrocnemius-soleus complex was measured with electrodes placed at 0° and at 90° relative to the major muscle fiber direction. The major outcome measure, the anisotropy difference (AD) for each of the resistance, reactance, and phase, was calculated as 90-0° values.

Results

All three parameters showed substantial alterations with disease progression. However, the phase AD demonstrated the most substantial change, increasing from 1.8 ± 1.58° to 10.2 ± 2.13° (mean ± standard error) comparing the first and last set of measurements (p = 0.028).

Conclusions

Anisotropy increases substantially with disease progression in the ALS rat.

Significance

Measurement of surface electrical anisotropy offers a non-invasive means for quantifying neurogenic change in muscle.     

Multiple white matter tract abnormalities underlie cognitive impairment in RRMS

Diffusion tensor imaging (DTI) is a sensitive tool for detecting microstructural tissue damage in vivo. In this study, we investigated DTI abnormalities in individuals with relapsing remitting multiple sclerosis (RRMS) and examined the relations between imaging-based measures of white matter injury and cognitive impairment. DTI-derived metrics using tract-based spatial statistics (TBSS) were compared between 37 individuals with RRMS and 20 healthy controls. Cognitive impairment was assessed with three standard tests: the Symbol Digit Modalities Test (SDMT), which measures cognitive processing speed and visual working memory, the Rey Auditory Verbal Learning Test (RAVLT), which examines verbal memory, and the Paced Auditory Serial Addition Test (PASAT), which assesses sustained attention and working memory. Correlations between DTI-metrics and cognition were explored in regions demonstrating significant differences between the RRMS patients and the control group. Lower fractional anisotropy (FA) was found in RRMS participants compared to controls across the tract skeleton (0.40 ± 0.03 vs. 0.43 ± 0.01, p < 0.01). In areas of reduced FA, mean diffusivity was increased and was dominated by increased radial diffusivity with no significant change in axial diffusivity, an indication of the role of damage to CNS myelin in MS pathology. In the RRMS group, voxelwise correlations were found between FA reduction and cognitive impairment in cognitively-relevant tracts, predominantly in the posterior thalamic radiation, the sagittal stratum, and the corpus callosum; the strongest correlations were with SDMT measures, with contributions to these associations from both lesion and normal-appearing white matter. Moreover, results using threshold-free cluster enhancement (TFCE) showed more widespread white matter involvement compared to cluster-based thresholding. These findings indicate the important role for DTI in delineating mechanisms underlying MS-associated cognitive impairment and suggest that DTI could play a critical role in monitoring the clinical and cognitive effects of the disease.     

The interaction of standard oxime reactivators with hemicholinium-3 sensitive choline carriers

Organophosphorus poisoning manifests as a cholinergic syndrome due to an inhibition of acetylcholinesterase. It is treated symptomatically by anticholinergics and oxime reactivators are used as causal antidotes. Reactivators possess a complex mechanism of action and interact at various levels of the cholinergic transmission. The aim of this study was to investigate the effect of standard oxime reactivators (HI-6, obidoxime, trimedoxime, methoxime and pralidoxime) on the hemicholinium-3 sensitive carriers, which are involved in the high-affinity choline uptake (HACU) transport, a key regulatory step in the synthesis of acetylcholine. The activity of the carriers was estimated in vitro on hippocampal synaptosomes using the substrate (3H)-choline and the competitive inhibitor (3H)-hemicholinium-3. Furthermore, the effect of the reactivators on the fluidity of hippocampal membranes was assessed. All tested compounds, except methoxime, showed an acute inhibitory effect on the carriers, however, only at μM concentrations. Trimedoxime showed the highest potency to inhibit HACU among all tested compounds (I(max) 62%, IC(50)=3 μM). All compounds, except HI-6, influenced also a membrane fluidity in the region of the hydrophilic heads of phospholipid bilayer, nevertheless, only methoxime was able to penetrate more deeply into the hydrocarbon core. We suggest that the direct interaction of oxime reactivators with the carrier protein (HI-6 and trimedoxime) and/or the changes in carrier conformation mediated by alterations in membrane fluidity (trimedoxime, obidoxime and pralidoxime) could occur here. The influence of reactivators on the carriers could be unfavorable in the case of their prolonged administration in vivo. From this point of view, the application of methoxime appears to be the best.     

Age-related decline in white matter tract integrity and cognitive performance: A DTI tractography and structural equation modeling study

Age-related decline in microstructural integrity of certain white matter tracts may explain cognitive decline associated with normal aging. Whole brain tractography and a clustering segmentation in 48 healthy individuals across the adult lifespan were used to examine: interhemispheric (corpus callosum), intrahemispheric association (cingulum, uncinate, arcuate, inferior longitudinal, inferior occipitofrontal), and projection (corticospinal) fibers. Principal components analysis reduced cognitive tests into 6 meaningful factors: (1) memory and executive function; (2) visuomotor dexterity; (3) motor speed; (4) attention and working memory; (5) set-shifting/flexibility; and (6) visuospatial construction. Using theory-based structural equation modeling, relationships among age, white matter tract integrity, and cognitive performance were investigated. Parsimonious model fit demonstrated relationships where decline in white matter integrity may explain age-related decline in cognitive performance: inferior longitudinal fasciculus (ILF) with visuomotor dexterity; the inferior occipitofrontal fasciculus with visuospatial construction; and posterior fibers (i.e., splenium) of the corpus callosum with memory and executive function. Our findings suggest that decline in the microstructural integrity of white matter fibers can account for cognitive decline in normal aging.     

Supersonic shear wave elastography of in vivo pig kidney: influence of blood pressure, urinary pressure and tissue anisotropy

The in vivo influence of renal anisotropy and of urinary and vascular pressure on elasticity values using ultrasonic supersonic shear wave elastography was studied in pigs. Experiments were conducted in agreement with the European Commission guidelines and directives of the French Research Ministry. Six kidneys in three pigs were studied in vivo. Elasticity of renal cortex and medulla was quantified through the shear modulus (μ) by using the supersonic shear imaging technique with an 8 MHz linear ultrasound probe. All measurements were done peroperatively both in the axis and perpendicular to the main axis of pyramids, in normal condition, after progressive increase of urinary pressure, and after renal artery and renal vein ligation. In normal conditions, cortical (C) and medullary (M) elasticity values were always higher when acquisitions were realized with the ultrasound main axis perpendicular to main pyramid axis (C_//: 7.7 ± 2.3 kPa; M_//: 8.7 ± 2.5 kPa) than parallel (C_⊥: 6.9 ± 1.4 kPa; M_⊥: 6.6 ± 2.3 kPa), demonstrating an effect of renal anisotropy. In renal cortex, two bands were separated, inner cortex showing higher elasticity values (IC_⊥: 8.1 ± 1.9 kPa) than outer cortex (OC_⊥: 6.9 ± 1.4 kPa). Renal artery and renal vein ligation induced a decrease and an increase of elasticity respectively. Parenchymal elasticity increased linearly with elevation of urinary pressure. Intrarenal elasticity values vary with tissue anisotropy and, with vascular and urinary pressure levels. These parameters have to be taken into account for interpretation of tissue changes. Separation of outer and inner cortex could be attributable to perfusion differences.     

Anisotropic crystal deformation measurements determined using powder X-ray diffraction and a new in situ compression stage

This report addresses the development of experimental and computational estimations of the anisotropic elastic moduli (EM) of single crystals to aid in the a priori (i.e., starting with the crystal structure) prediction of the trend as a function of the direction of applied stress. Experimentally EM values in the normal direction to the X-, Y- and Z-planes of block shaped aspirin and acetaminophen crystals were determined using data generated by the newly designed compression stage housed in our powder X-ray diffractometer. Computational estimations of EM were made using the applicable modules in Material Studio^® 5.5. The measured EM values normal to the (1 0 0), (0 2 0) and (0 0 2) planes of aspirin, and (2 0 −1), (0 2 0) and (0 0 1) planes of acetaminophen crystals by both methods succeeded in detected the anisotropic behavior. However, disparity in the relative values between measured EM values by different techniques was observed. This may be attributed to deformation sources other than lattice compression including inelastic processes such as local failure and plasticity as well as deformation at the crystal-probe interfaces due to crystal surface roughness (asperities). The trend of the ratio of the values from the respective methods showed reasonable agreement and promise for the technique. The present approach demonstrated the suitability of the compression stage to determine and predict anisotropic EM of subjected small molecular organic crystals.