创伤性脑水肿的在体研究

目的 探讨在体研究创作性脑水肿的方法。方法 选择１５个频率点,测量大鼠中度颅脑的创伤后伤区组织的电阻抗,分析脑水肿的变化。结果 伤后早期细胞外液电阻（Ｒｅ）明显下降,细胞内液电阻（Ｒｉ）无明显变化,Ｒｅ／Ｒｉ也明显下降;６ｈ后Ｒｅ略有升高,Ｒｉ明显下降,Ｒｅ／Ｒｉ明显增加;伤后２４～７２ｈ脑水肿达高峰,伤后７基本恢复。结论 伤后早期电阻抗的变化提示发生了血管源性脑水肿,伤后６ｈ电阻抗变化表明细胞内     

尾吊大鼠血液细胞电阻抗谱的Cole-Cole模型分析

目的利用Cole-Cole数学模型研究尾吊大鼠血液细胞电阻抗频谱的变化。方法通过非线性数值计算,对血液细胞的Bode图,Nyquist图和Nichols图进行Cole-Cole方程的曲线拟合,比较对照组(Con)与尾吊组(SUS)Cole-Cole模型参数。结果尾吊60 d大鼠血液细胞电阻抗频谱Cole-Cole模型参数变化显示:阻抗高频极限值(R∞)和阻抗增量(ΔR1,ΔR2)减小;特征频率(fC1,fC2)和β驰豫散射角(α1,α2)增加。结论可以通过Cole-Cole数学方程参数表达尾吊大鼠血液细胞电阻抗频谱特性变化。     

同时工作于四种频率的多频电阻抗断层成像系统

目的 建立一个可减小组织阻抗动态变化影响的多频电阻抗断层成像数据采集系统。方法 采用数字合成技术产生含有4种频率分量的激励信号,将其注入成像目标,然后采用正交序列数字解调法提取各频率分量下的阻抗信息。结果 所实现的成像系统可工作于1．6～380kHz。在100kHz时,该系统仍具有65dB的共模抑制比。工作频率范围内,100Ω电阻上的测量精度优于-80dB。基于物理模型的成像结果可清楚的反映出模型内阻抗实、虚部等参数的变化情况。结论 所建立的多频成像系统具有较高的测量精度,能够满足多频成像研究需要。     

生物电阻抗特征参数提取方法及测量系统的研究

目的：研究生物组织的电阻抗特性，提取电学阻抗模型的特征参数。方法：研制一种四电极法阻抗测量系统以提取不同组织阻抗的幅度和相位特性。对兔子的部分离体组织进行实验，并对实验结果进行分析，利用迭代式的最小二乘曲线拟合方法提取不同组织的特征参数。结果：用迭代式的最小二乘法拟合出的曲线与实测组织的阻抗轨迹相吻合，验证了Cole-Cole理论，并分别计算出了兔子的部分离体组织－－肾、肌肉、肝和肺组织的特征参数τ、R0、R∞和α。结论：Cole-Cole阻抗方程与等效模型能较好地反映出组织阻抗的实部和虚部在不同频率下的相对变化，因而可用于定量地分析复阻抗频率特性的变化，所计算出的复阻抗特征参数可以作为区分不同组织的一项指标。     

乳腺癌浸润部位对其电阻抗频谱特性影响的研究

目的 研究人体乳腺癌浸润部位对其电阻抗频谱特性的影响,为乳腺电阻抗扫描成像仪器检查结果中出现"暗区"现象提供实验依据和基础数据. 方法依据乳腺癌浸润部位不同分为2组:浸润到脂肪组和浸润到腺体组,采用英国Solartron公司1255B型频响分析仪,四电极法离体测量组织电阻抗频谱特性,测量频率1 Hz～1 MHz.采用非线性曲线拟合的方法得到cole-cole模型参数.结果 从电阻抗特性实部看,浸润到脂肪组中乳腺癌的电阻率大大低于周围脂肪组织;而浸润到腺体组的乳腺癌组织的电阻率高于周围腺体组织;从电阻抗特性虚部看,各种测量组织的特征频率有所不同:脂肪组织的特征频率在1 kHz左右,乳腺癌组织在200 k～300 kHz;腺体组织为2 k～3 kHz.结论 无论是测量数据还是模型参数,乳腺癌及其周围组织的电阻抗特性存在显著性差异,同时发现癌组织浸润的部位不同,其差异有所不同.     

1H-MR波谱评价骨骼肌细胞内脂肪含量的在体和模型研究

目的 解释骨骼肌1H-MRS中的脂峰形态及其影响因素,建立利用骨骼肌1H-MRS评价肌细胞内脂肪的方法 .方法 取5名健康志愿者的小腿胫骨前肌和比目鱼肌区域行1H-MRS检查,改变小腿纵轴与主磁场(B0)之间的角度,观察0.80～1.80 ppm(×10-6)处脂峰形态的变化.体外模型研究采用毛细玻璃管束中灌注大豆油和脂肪乳液,分别模拟肌纤维细胞外、细胞内脂肪,比较脂峰随模璎与B0角度变化的特征.结果小腿骨骼肌在0.80～1.80 ppm处可以观察到3～4个峰,各峰相差约0.20～0.30 ppm;当小腿纵轴与B0所成角度增大时,胫骨前肌肌纤维间隙内的脂肪(EMCL)的亚甲基峰逐渐向右侧移位.体外模型很好地模拟了在体骨骼肌1H-MRS脂峰形态,在0.80～1.80 ppm处出现2组甘油三酸酯亚甲基峰和甲基峰,其中心频率相差0.20～0.30 ppm,分别代表肌细胞内、外脂肪.由于骨骼肌组织肌纤维走行的高度有序性及肌细胞内、外脂肪的分子分布状态不同,两者感应的化学位移不同而表现出波峰的分离.这种肌细胞内外脂肪峰的分离在肌束与B0一致时最大,在两者夹角接近魔角(54.7°)时无法分离.结论骨骼肌1H-MRS中肌细胞内、外脂肪发生分离,是一种无创性评价肌细胞内脂肪含量的有效方法 ;胫骨前肌是进行1H-MRS检查的理想部位.     

心肌窦房结细胞数学模型比较研究

目的为了增强对哺乳动物心肌窦房结细胞的深入认识,比较了近年来对兔窦房结细胞电生理特性的研究所建立的各类数学模型。方法利用C++源代码编写各类窦房结电生理参数模型。集中研究了各模型的动作电位波形、电生理参数(最大心舒张电位MDP,动作电位幅值APA,周期长度CL,上升沿速度UV)、离子电流、局部差异性和细胞内钙离子动力学。结果 Demir模型中MDP、APA、UV值显示出此模型可以很好地描述中心窦房结区域到周围窦房结区域过渡处的细胞,但其相对较小的CL表现出来的却是周围窦房结细胞的特性。Dokos模型有着明显的相对较长的自发性心舒张去极化期,其MDP、CL、UV值同样反映了过渡处细胞的电生理特性,而其较小的APA值却是典型的窦房结中心细胞的电生理特性值。Zhang模型能够分别反映窦房结中心细胞和周围细胞的电生理特性,与实验最为相符。Maltsev模型中除了MDP值比中心细胞实验值稍小外,其他参数均与实验值相符。结论各心肌窦房结模型均有其缺点,但Zhang等人建立的模型对窦房结细胞局部差异性得出了与实验最为相符的结论 ,而Maltsev等人建立的模型是迄今为止对细胞内钙离子瞬变过程描述最为详尽的模型。     

大鼠骨骼肌细胞的频域电生理特性研究

目的:在100Hz～100MHz频率范围研究大鼠骨骼肌细胞的电生理特性,为进一步探讨骨骼肌疲劳或力竭的频域电特性研究奠定基础。方法:使用Agilent4294A阻抗分析仪测量大鼠腓肠肌组织的交流阻抗,通过细胞介电谱、Cole-Cole图、介电损失因子△ε″和介电损耗角正切△tgδ的频谱分析,建立了正常大鼠腓肠肌细胞的频域电生理特性参数(介电参数)。结果:(1)大鼠腓肠肌细胞介电响应具有频率依存性关系:介电常数ε随电场频率的增加而降低,电导率κ随频率的增加而上升;(2)大鼠腓肠肌细胞的频域介电参数(κL、κh、εL、εh、△ε″max、△tgδmax、fC1、fC2)在平行方向与垂直方向上存在差异;(3)交流电场对大鼠腓肠肌细胞的作用具有介电弛豫现象,表现为两个中心特征频率:第一特征频率fC1(∥)=fC1(⊥)=1.02kHz和第二特征频率fC2(∥)=59.31kHz,fC2(⊥)=380.04kHz。结论:利用本实验方法可获得骨骼肌细胞频域电生理指标,其中第一特征频率fC1和第二特征频率fC2是频域电特性的特色参数。     

电阻抗监护小猪腹膜后注血模型的研究

目的 使用小猪腹膜后注血模型来研究电阻抗成像监测创伤导致的腹膜后出血的可行性,为电阻抗成像的临床应用提供必要的理论和现实依据.方法 5头小猪行腹膜后穿刺置管,经导管持续注入血液,模拟创伤性腹膜后出血,应用电阻抗成像临测小猪注血部位的阻抗和图像变化情况.结果 5头腹膜后注血小猪电阻抗监护图像成像清晰,稳定.注血部位的阻抗值随注血量的增加而持续降低,图像灰度变化明显.经CT及解剖验证,后腹膜完整,血液局限于腹膜后间隙内.结论 在小猪腹膜后注血模型的基础上,使用电阻抗监护腹膜后出血成像清晰,对比明显.     

基于径向基函数神经网络的两步核磁共振头部组织电阻抗成像算法

目的 基于径向基函数(radial basic function,RBF)神经网络的两步核磁共振电阻抗成像(magnetic resonance electrical impedance tomography,MREIT) 算法,对人体头部进行MREIT.方法 首先利用高分辨率的核磁共振成像(magnetic resonance imaging,MRI)系统对成像物体进行三维构建和不同组织的边界区分;然后利用RBF MREIT方法对物体内不同组织的均匀电阻抗分布进行估计,并采用基于径向基函数-遗传算法的MREIT技术对每种组织有限元模型中每个单元的电阻抗值进行估计.结果 在三层球头模型(scalp skull brain,SSB)上进行的仿真实验证明了利用两步 MREIT算法进行头部组织三维电阻抗图像重构的合理性与可行性.结论 该两步MREIT算法可以用于头部组织三维电阻抗图像重构,具有潜在的应用价值.     

Determination of extracellular/intracellular fluid ratios from magnetic resonance images: accuracy, feasibility, and implementation

This study determines the accuracy and feasibility of using localized spin-lattice (T1) relaxation time measurements from magnetic resonance (MR) images to follow changes in extracellular/intracellular fluid ratios in defined subvolumes of living tissue. A red blood cell suspension was used as a test system and a simple two-compartment model incorporating fast exchange was found to suffice for the conversion of T1 values to volume ratios. The technique requires the addition of gadolinium-DTPA to the model system to selectively enhance relaxation in the extracellular fluid space. No detectable amount of gadolinium-DTPA was found to enter the intracellular fluid space, and all magnetization decay plots obtained from both intracellular constituents and complete RBC suspensions consisted of a single exponential. Both of these results are compatible with assumptions underlying our physical model. The NMR-determined fluid ratio values were compared to those measured via the microhematocrit technique. Partial saturation image-mode determinations are strongly correlated to microhematocrit data (R2 = 0.945) and indicate that localized cell volume changes may be followed with a sensitivity of +/- 2.2%. These values compare favorably with those produced when nonimaging inversion-recovery techniques are used to determine the MR hematocrit (R2 = 0.962, sensitivity = +/- 1.1%). This technique, with modification, should be applicable to the comparison of ratios of extracellular/intracellular fluid volumes in structurally complex tissues where small subvolumes of homogeneous cell structure could be examined.     

Prediction of electrical impedance parameters for the simulated leg segment of an aircraft pilot under G-stress

BACKGROUND: Blood accumulation in the lower extremities of fighter pilots has been known to induce loss of peripheral vision and consciousness. G suits and anti-G straining maneuvers applied to lower limbs do not work according to the actual status of blood accumulation. Therefore, the problem of blood accumulation in the legs requires further investigation. METHOD: The leg segment of an aircraft pilot has been modeled as a cylinder containing its anatomical structure of skin-fat layer, muscles, bones, and blood volume in the form of inner cylinders. Finite element analysis (FEA) was applied to the leg model with suitable boundary conditions. Predicted leg-segment electrical impedance (LEI) without blood accumulation has been compared with the measured experimental value using electrical impedance plethysmography (EIP). The effects of 7% blood pooling were analyzed by electrical impedance of the leg segment and its constituents by increasing the diameter of blood volume cylinder. RESULTS: The LEI has been predicted to be 46.7 omega, which corresponds well with experimental value of 46.0 omega and predicted value, being 1.58% higher. Predicted LEI was reduced to 44.2 omega during simulation of blood accumulation in FE model. The relative contributions of admittance for leg constituents fat, muscle, bones and blood volume are also found to be 2.96, 75.58, 0.33, and 11.13%, respectively. CONCLUSION: A computer simulation technique has been developed to predict electrical impedance parameters of the leg segment and its constituents with and without blood pooling. These results will be useful in further research and clinical applications for aircraft pilots under acceleration (G) stress.     

多频电阻抗扫描的Cole-Cole模型分析

目的研究适合于多频电阻抗扫描测量数据的分析方法,为深入研究电阻抗扫描技术打下基础。方法根据传统的阻抗形式Cole—Cole模型经验公式,推导出与电阻抗扫描测量结果匹配的导纳形式Cole-Cole公式。依据最小二乘原理,估计导纳形式Cole—Cole模型的各个参数。结果人体实测数据的导纳形式Cole-Cole轨迹图与最小二乘估计圆弧吻合良好。同一电极阵列上的测量数据可以按照电极位置生成导纳形式Cole—Cole模型4个参数的三维分布图。结论导纳形式Cole—Cole轨迹图能清晰地反映不同电极处的传输导纳随激励频率改变而引起的差异。导纳形式Cole—Cole模型的参数分布图,可从不同的物理含义上解释多频电阻抗扫描测量的结果。两者都有助于准确诊断疾病。     

Theoretical Model for Water Diffusion in Tissues

Water diffusion in a tissue model is studied both analytically and numerically. Tissue is regarded as a periodic array of boxes surrounded by partially permeable membranes (cells), embedded in an extracellular medium, intracellular and extracellular diffusion coefficients may differ. Expressions for the apparent diffusion coefficients (ADC) in isotropic and noniso-tropic tissues are derived and compared with Monte Carlo simulations. Calculated ADCs disagree with values obtained from the widely used “fast exchange” formula. Effects of differences between intracellular and extracellular T₂ relaxation times on measured values of ADC and T₂ are discussed. The general analysis is specifically applied to the changes occurring in ADC following ischemic insults to brain tissue. It is found that although membranes affect ADC significantly, the observed changes in diffusion cannot be due to reduced membrane permeabilities. They may result from the combined effect of changes in cellular volume fraction, extracellular and intracellular diffusion.     

Diffusion properties of NAA in human corpus callosum as studied with diffusion tensor spectroscopy.

In diffusion tensor imaging (DTI) the anisotropic movement of water is exploited to characterize microstructure. One confounding issue of DTI is the presence of intra- and extracellular components contributing to the measured diffusivity. This causes an ambiguity in determining the underlying cause of diffusion properties, particularly the fractional anisotropy (FA). In this study an intracellular constituent, N-acetyl aspartate (NAA), was used to probe intracellular diffusion, while water molecules were used to probe the combined intra- and extracellular diffusion. NAA and water diffusion measurements were made in anterior and medial corpus callosum (CC) regions, which are referred to as R1 and R2, respectively. FA(NAA) was found to be greater than FA(Water) in both CC regions, thus indicating a higher degree of anisotropy within the intracellular space in comparison to the combined intra- and extracellular spaces. A decreasing trend in the FA of NAA and water was observed between R1 and R2, while the radial diffusivity (RD) for both molecules increased. The increase in RD(NAA) is particularly significant, thus explaining the more significant decrease in FA(NAA) between the two regions. It is suggested that diffusion tensor spectroscopy of NAA can potentially be used to further characterize microscopic anatomic organization in white matter.