Pulsed magnetohydrodynamic blood flow in a rigid vessel under physiological pressure gradient

Blood flow in a steady magnetic field has been of great interest over recent years. Many researchers have examined the effects of magnetic fields on velocity profiles and arterial pressure, and major studies have focused on steady or sinusoidal flows. In this paper, we present a solution for pulsed magnetohydrodynamic blood flow with a somewhat realistic physiological pressure wave obtained using a Windkessel lumped model. A pressure gradient is derived along a rigid vessel placed at the output of a compliant module which receives the ventricle outflow. Then, velocity profile and flow rate expressions are derived in the rigid vessel in the presence of a steady transverse magnetic field. As expected, results showed flow retardation and flattening. The adaptability of our solution approach allowed a comparison with previously addressed flow cases and calculations presented a good coherence with those well established solutions.     

Validation of radiocarpal joint contact models based on images from a clinical MRI scanner

This study was undertaken to assess magnetic resonance imaging (MRI)-based radiocarpal surface contact models of functional loading in a clinical MRI scanner for future in vivo studies, by comparison with experimental measures from three cadaver forearm specimens. Experimental data were acquired using a Tekscan sensor during simulated light grasp. Magnetic resonance (MR) images were used to obtain model geometry and kinematics (image registration). Peak contact pressures (PPs) and average contact pressures (APs), contact forces and contact areas were determined in the radiolunate and radioscaphoid joints. Contact area was also measured directly from MR images acquired with load and compared with model data. Based on the validation criteria (within 25% of experimental data), out of the six articulations (three specimens with two articulations each), two met the criterion for AP (0%, 14%); one for peak pressure (20%); one for contact force (5%); four for contact area with respect to experiment (8%, 13%, 19% and 23%), and three contact areas met the criterion with respect to direct measurements (14%, 21% and 21%). Absolute differences between model and experimental PPs were reasonably low (within 2.5 MPa). Overall, the results indicate that MRI-based models generated from 3T clinical MR scanner appear sufficient to obtain clinically relevant data.     

Alterations in the rat electrocardiogram induced by stationary magnetic fields

A field strength dependent increase in the amplitude of the T-wave signal in the rat electrocardiogram (ECG) was observed during exposure to homogeneous, stationary magnetic fields. For 24 adult Sprague-Dawley and Buffalo rats of both sexes, the T-wave amplitude was found to increase by an average of 408% in a 2.0 Tesla (1 Tesla = 10⁴ Gauss) field. No significant magnetically induced changes were observed in other components of the ECG record, including the P wave and the QRS complex. The minimum field level at which augmentation of the T wave could be detected was 0.3 Tesla. The magnetically induced increase in T-wave amplitude occurred instantaneously, and was immediately reversible after exposure to fields as high as 2.0 Tesla. No abnormalities in any component of the ECG record, including the T wave, were noted during a period of 3 weeks following cessation of a continuous 5-h exposure of rats to a 1.5-Tesla field. The heart rate and breathing rate of adult rats were not altered during, or subsequent to, application of fields up to 2.0 Tesla. The effect of animal orientation within the field was tested using juvenile rats 3–14 days old. The maximum increase in T-wave amplitude was observed when subjects were placed with the long axis of the body perpendicular to the lines of magnetic induction. These experimental observations, as well as theoretical considerations, suggest that augmentation of the signal amplitude in the T-wave segment of the ECG may result from a superimposed electrical potential generated by aortic blood flow in the presence of a stationary magnetic field.     

Comparison of cortical activation patterns by somatosensory stimulation on the palm and dorsum of the hand

Abstract

Objectives: Little is known about differences of cortical activation according to body location. We attempted to compare brain activation patterns by somatosensory stimulation on the palm and dorsum of the hand, using functional magnetic resonance imaging (fMRI).

Method: We recruited 15 healthy right-handed volunteers for this study. fMRI was performed during touch stimulation using a rubber brush on an area of the same size on the palm or dorsum of the hand. Regions of interest (ROIs) were drawn at the primary sensory–motor cortex (SM1), posterior parietal cortex, and secondary somatosensory cortex.

Results: Group analysis of fMRI data indicated that touch stimulation on the palm resulted in production of more activated voxels in the contralateral SM1 and posterior parietal cortex than on the dorsum of the hand. The most activated ROI was found to be the contralateral SM1 by stimulation of the palm or dorsum, and the number of activated voxels (5875) of SM1 by palm stimulation was more than 2 times that (2282) of dorsum stimulation. The peak activated value in the SM1 by palm stimulation (16.43) was also higher than that of the dorsum (5.52).

Conclusion: We found that stimulation of the palm resulted in more cortical activation in the contralateral SM1 than stimulation of the dorsum. Our results suggested that the palm of the hand might have larger somatotopy of somatosensory representation for touch in the cerebral cortex than the dorsum of the hand. Our results would be useful as a rehabilitation strategy when more or less somatosensory stimulation of the hand is necessary.     

不同治疗方案对H22肝癌荷瘤小鼠的疗效比较

目的比较不同治疗方案对H22肝癌荷瘤小鼠的疗效。方法采用H22腋下实体瘤KM小鼠及小鼠标准化、计量化辨证方法,观察复合化疗方案局部注射、索拉非尼口服,及两者联合应用等对小鼠抑瘤率和证候的影响。结果所选用3个治疗方案均具有一定的抑瘤作用,综合对气血阴阳证候的影响及胸腺和脾脏重量,以复合化疗方案局部注射联合索拉非尼口服最好。结论局部介入联合索拉非尼口服方案疗效较好。     

组织学与核磁共振检测大鼠癫痫源性早期脑损伤的跨半球扩布特征

侵性强直电刺激(60Hz,2s)大鼠右侧背海马(hippocampus,DHPC)CAl基树突区,1次/d,连续刺激10d。分别在施加强直电刺激的第2、4、6、8或10d时进行核磁共振成像检测(T2 weighted magnetic resonamce image T2-WI),并对鼠脑进行组织学切片鉴定。结果表明,早期慢性癫痫源性脑损伤的病理性形态特征主要包括：(1)T2-WI检测侧脑室(lateral ventricle,LV)区域信号增强、组织学检测LV扩大和双侧对称性脉络膜丛病理性增生,后两者并非完全平行呈现。(2)组织学切片显示双侧LV扩大面积与T2-WI信号增强区域面积的脑区分布近似。与空白对照组大鼠相比,电刺激2、4、6、8和10d后,T2-WI信号增强区域面积显著增大(P=0．0259;P＝0．0184;P=0．0184;P＝0．0404;P＝0．0259)以及组织学鉴定LV面积增大(P＝0．0210;P＝0．01;P＝0．0100;P=0．0152).(3)定侧分析显示,T2-WI信号增强以及T2-WI信号增强区域面积和组织学鉴定LV面积扩大,在慢性刺激6d时均以植入电极的对侧为主;第10d时均以同侧为主。三项观察结果的一致性证实了癫痫源性早期脑损伤的跨半球动态扩布特征。     

磁性纳米材料的生物医学应用进展

以四氧化三铁为代表的医用磁性纳米材料具有独特的磁学性能、表面易功能化、良好的生物学相容性等特点,在纳米医学相关领域展现出巨大的应用前景,特别是近年来它作为可介导外场的智能材料,在材料设计和生物医学应用方面均取得了突破性的进展.鉴于此,本文围绕磁性氧化铁纳米材料的生物医学应用,着重介绍近年来其在磁共振影像探针、磁热和磁力效应的生物医学应用、诊疗一体化以及纳米酶催化等领域的研究进展,并对磁性纳米材料在生物医学领域未来的发展方向进行了展望.     

Which factors influence the ability of a computational model to predict the in vivo deformation behaviour of skeletal muscle?

Deep tissue injury (DTI) is a severe form of pressure ulcer where tissue damage starts in deep tissues underneath intact skin. Tissue deformation may play an important role in the aetiology, which can be investigated using an experimental–numerical approach. Recently, an animal-specific finite element model has been developed to simulate experiments in which muscle tissue was compressed with an indenter. In this study, the material behaviour and boundary conditions were adapted to improve the agreement between model and experiment and to investigate the influence of these adaptations on the predicted strain distribution. The use of a highly nonlinear material law and including friction between the indenter and the muscle both improved the quality of the model and considerably influenced the estimated strain distribution. With the improved model, the required sample size to detect significant differences between loading conditions can be diminished, which is clearly relevant in experiments involving animals.     

磁共振胰胆管成像联合增强扫描在壶腹周围病变中的价值

目的探讨磁共振胰胆管成像（MRCP）在壶腹周围病变中的应用价值。方法采用重T2加权MR水成像技术对63例患者行MRCP检查,图像经三维最大信号强度投影（3DMIP）后处理。结果63例患者中,3例为正常,60例发现不同程度病变,其中肿瘤患者36例（9例肝门区原发性胆管细胞癌、2例肝门转移癌、5例原发性肝癌、4例肝外胆管癌、5例壶腹癌、8例胰头癌、3例十二指肠癌）,灵敏度为93．2％;结石患者16例（6例胆总管结石、6例胆囊结石、4例肝总管结石）,灵敏度为89．5％;炎症患者8例（3例胆管炎、3例胰腺炎、2例十二指肠憩室合并感染）,灵敏度为83．2％。均与病理或临床诊断无统计学差异（P〉0．05）。结论MRCP可准确显示胆管梗阻部位,明确病变性质,对非梗阻性胆胰疾病,MRCP可显示病变与周围脏器的毗邻关系,但不能脱离MRI平扫和增强,是后者的一种有效补充。     

Prediction of Visceral Adipose Tissue Using Air Displacement Plethysmography in Children

Objective: To determine the ability of air displacement plethysmography (ADP) to predict visceral adipose tissue (VAT) volume in children. Research Methods and Procedures: Fifty‐five (33 boys/22 girls) white children 13 to 14 years old were studied. Anthropometric measures were collected for body mass, stature, BMI, and waist‐to‐hip ratio (WHR), and body fat percentage was estimated from triceps and subscapular skinfolds, bioelectrical impedance analysis, and ADP. VAT volume was determined using magnetic resonance imaging, using a multiple slice protocol at levels L1 to L5. Results: Boys had significantly (p ≤ 0.05) less VAT volume than girls [645.1 (360.5) cm³ vs. 1035.8 (717.3) cm³]. ADP explained the greatest proportion of the variance in VAT volume compared with the other anthropometric measures. Multiple regression analysis indicated that VAT volume was best predicted by ADP body fat percentage in boys [r² = 0.81, SE of the estimate (SEE) = 160.1, SEE coefficient of variation = 25%] and by WHR and BMI in girls (r² = 0.80, SEE = 337.71, SEE coefficient of variation = 33%). Discussion: Compared with the other anthropometric measures, ADP explains the greatest proportion of the variance in VAT volume in children 13 to 14 years old. For boys, ADP is the tool of choice to predict VAT volume, yet using the more simply collected measures of BMI and WHR is recommended for girls. However, large SE of the estimates remained, suggesting that if precision is needed, there is no surrogate for direct imaging of VAT.     

医学领域的磁共振成像革命——2003年诺贝尔生理及医学奖主要工作介绍

在磁场中 ,自旋的原子核会吸收频率与其自旋频率相同的电磁波 ,使自身能量增加 ,发生能级跃迁 ,当原子核迁移回原能级时 ,就会把多余的能量以电磁波的形式释放出来 ,称为核磁共振 (NMR) .磁共振成像(MRI)利用这一原理 ,依据所释放的能量在物质内部不同结构环境中不同的衰减 ,通过外加梯度磁场检测所发射出的电磁波 ,即可得知构成这一物体原子核的位置和种类 ,据此可以绘制成物体内部的结构图像 .将这种技术用于人体内部结构的成像 ,就产生出一种革命性的医学诊断工具 .快速变化的梯度磁场的应用 ,大大加快了磁共振成像的速度 ,使该技术在临床诊断、科学研究的应用成为现实 ,极大地推动了医学、神经生理学和认知神经科学的迅速发展     

Acute effects of cocaine on the neurobiology of cognitive control

Compromised ability to exert control over drug urges and drug-seeking behaviour is a characteristic of addiction. One specific cognitive control function, impulse control, has been shown to be a risk factor for the development of substance problems and has been linked in animal models to increased drug administration and relapse. We present evidence of a direct effect of cocaine on the neurobiology underlying impulse control. In a laboratory test of motor response inhibition, an intravenous cocaine administration improved task performance in 13 cocaine users. This improvement was accompanied by increased activation in right dorsolateral and inferior frontal cortex, regions considered critical for this cognitive function. Similarly, for both inhibitory control and action monitoring processes, cocaine normalized activation levels in lateral and medial prefrontal regions previously reported to be hypoactive in users relative to drug-naive controls. The acute amelioration of neurocognitive dysfunction may reflect a chronic dysregulation of those brain regions and the cognitive processes they subserve. Furthermore, the effects of cocaine on midline function suggest a dopaminergically mediated intersection between cocaine's acute reinforcing effects and its effects on cognitive control.     

Application of F magnetic resonance to study the efficacy of fluorine labeled drugs in the three-dimensional cultured breast cancer cells

The cellular monitoring of tumor response to treatments is important for drug discovery and drug development in cancer therapy. We studied efficacy of Herceptin, a common breast cancer drug conjugated with a fluorine organic compound, perfluoro-15-crown-5-ether (PFCE) which easily forms biocompatible emulsions. Three new pharmaceutical forms of Herceptin, Herceptin/PFCE, Herceptin/PFCE/Lipoplex and Herceptin/PFCE/HydraLink were synthesized for the ex vivo study of their efficacy in breast cancer treatment. The emulsions were administered to 10⁹ cells mL⁻¹ of HER-2 positive human adenocarcinoma (MCF-7) cells and the same amount of human mammary epithelial cells (HMEC) cultured in three-dimensional (3D) geometry using hollow fiber bioreactor (HFB) device. Following drugs administration ex vivo, fluorine-19 magnetic resonance imaging (¹⁹F MRI) was applied for cells imaging to measure their viability and to study drug efficacy over 72 h. To ensure optimum drug tracking, HydraLink was used to provide stable binding affinity of emulsified Herceptin to receptor while cationic lipid (Lipofectamine) was used to enhance lipophilicity of the emulsions.After 72 h of treatment with Herceptin, Herceptin/PFCE, Herceptin/PFCE/Lipoplex and Herceptin/PFCE/HydraLink the viability of cells was 54 ± 2%, 49 ± 3%, 43 ± 5% and 42 ± 1%, respectively, as compared with control 93 ± 2%. The efficacy (EC₅₀) of Herceptin conjugated with emulsions was found to be 970 ± 13 μg mL⁻¹ for Herceptin/PFCE, 645 ± 11 μg mL⁻¹ for Herceptin/PFCE/Lipoplex, 678 ± 7 μg mL⁻¹ for Herceptin/PFCE/HydraLink and 1000 ± 3 μg mL⁻¹ for Herceptin. The results show that fluorine emulsions improved the efficacy of Herceptin and ¹⁹F signal intensity changes validated drug efficiency. The significant correlations between duration of treatments and MCF-7 cells viability were observed. While we studied breast cancer cells, the fluorine emulsions could be applied for treatment of other cancer cells overexpressing HER-2.     

From cognitive to neural models of working memory

Working memory refers to the temporary retention of information that was just experienced or just retrieved from long-term memory but no longer exists in the external environment. These internal representations are short-lived, but can be stored for longer periods of time through active maintenance or rehearsal strategies, and can be subjected to various operations that manipulate the information in such a way that makes it useful for goal-directed behaviour. Empirical studies of working memory using neuroscientific techniques, such as neuronal recordings in monkeys or functional neuroimaging in humans, have advanced our knowledge of the underlying neural mechanisms of working memory. This rich dataset can be reconciled with behavioural findings derived from investigating the cognitive mechanisms underlying working memory. In this paper, I review the progress that has been made towards this effort by illustrating how investigations of the neural mechanisms underlying working memory can be influenced by cognitive models and, in turn, how cognitive models can be shaped and modified by neuroscientific data. One conclusion that arises from this research is that working memory can be viewed as neither a unitary nor a dedicated system. A network of brain regions, including the prefrontal cortex (PFC), is critical for the active maintenance of internal representations that are necessary for goal-directed behaviour. Thus, working memory is not localized to a single brain region but probably is an emergent property of the functional interactions between the PFC and the rest of the brain.     

磁共振波谱分析在颅脑胶质瘤分级中的应用研究

目的 分析脑胶质瘤的氢质子磁共振波谱（proton magnetic resonance spectroscopy,1H-MRS）表现及其临床意义;探讨脑胶质瘤的1H-MRS特点与其病理级别相关性.方法 搜集经临床手术、病理证实的脑胶质瘤病例49例,按照WHO诊断标准分成两组：低级别脑胶质瘤组、高级别脑胶质瘤组.所有患者在术前行1H-MRs检查,均在MR非增强成像的基础上获得.使用Philips Achieva 1.5T超导磁共振扫描仪,单体素或多体素扫描,点分辨法,检测不同区域代谢物变化.结果 脑胶质瘤的1H-MRS表现：肌酸（Cr）轻度下降,N-乙酰天门冬氨酸（NAA）显著下降,胆碱（Cho）显著增高.低、高级别脑胶质瘤的肿瘤组织与对侧止常脑组织的NAA、Cho、NAA/Cr、NAA/Cho值存在显著性差异（P〈0.05）;低级别和高级别脑胶质瘤的肿瘤组织的NAA/Cr、NAA/Cho值存在显著性差异（P〈0.05）.脑胶质瘤的NAA/Cho、Cho/Cr、NAA/Cr值与病理级别相关,其中NAA/Cho和NAA/Cr值反映肿瘤级别较稳定;NAA/Cr、NAA/Cho值呈负相关关系,Cho/Cr值呈正相关关系.结论 ：1H-MRS结合MKI能提高脑胶质瘤术前诊断的准确性.1H-MRS能对胶质瘤进行分级,反映胶质瘤代谢特性以及肿瘤生长潜能.     

不同海拔高度对健康成年男性心脏血流动力学和心电图的影响

目的:监测中国南极冰盖考察预选队员心血管系统随海拔增高的变化,探讨筛查低氧易感队员和急性高原病的防治。方法:用无创血流动力学监护仪和十二导联心电图机,在北京(40 m)、拉萨(3 650 m)、羊八井(4 300 m)对第25次和26次南极冰盖考察预选队员心血管功能进行连续动态性监测。结果:随着海拔的增高,心率、收缩压、舒张压、平均动脉压、外周血管阻力、外周血管阻力指数显著升高(P0.05),心输出量、心指数、搏出量、搏出指数、加速度指数、速度指数、左心射血时间显著降低(P0.05),预射血期呈降低趋势(P0.05)。结论:随着海拔的增高,预选队员的外周血管阻力显著升高,左心泵血和收缩功能减弱且与Q-TC间期呈负相关。     

三种森林生物量估测模型的比较分析

森林生物量的定量估算为全球碳储量、碳循环研究提供了重要的参考依据。该研究采用黑龙江长白山地区的TM影像和133块森林资源一类清查样地的数据, 选取地学参数、遥感反演参数等71个自变量分别构建多元逐步回归模型、传统BP (back propagation)神经网络模型和基于高斯误差函数的BP神经网络改进模型(Gaussian error function, Erf-BP), 进而估算该地区的森林生物量, 并进行比较分析。结果表明, 多元逐步回归模型估测的森林生物量预测精度为75%, 均方根误差为26.87 t·m^-2; 传统BP神经网络模型估测森林生物量的预测精度为80.92%, 均方根误差为21.44 t·m^-2; Erf-BP估测森林生物量的预测精度为82.22%, 均方根误差为20.83 t·m^-2。可见, 改进后的Erf-BP能更好地模拟生物量与各个因子之间的关系, 估算精度更高。