基于生物阻抗谱的细胞悬浮液浓度识别方法研究

基于生物阻抗谱技术提出一种细胞悬浮液浓度自动识别方法,该方法结合了多元线性回归算法和生物阻抗谱技术,能够快速准确地识别细胞悬浮液的浓度.首先,提出一种细胞位置随机分布策略,模拟细胞的真实存在状态;其次,采用数值仿真的方法生成2400组不同浓度的正常、癌变以及混合的细胞模型并计算生物阻抗谱数据;然后,利用多元线性回归、支持向量机和梯度提升三种回归算法分别对癌变细胞浓度进行鉴别,仿真结果表明,多元线性回归算法为最佳回归模型,其平均拟合优度和均方误差分别是0.9997和0.0008;最后,将多元线性回归算法应用于不同浓度的红细胞悬浮液的识别中,实验结果显示其平均拟合优度和均方误差分别是0.9998和0.0079,说明该方法具有较高的细胞悬浮液浓度识别能力.     

基于生物阻抗谱的细胞电学特性研究

生物阻抗谱是一种非侵入式、免标记、能够定量分析的检测技术,将其应用于生物细胞及组织的生理、病理分析中具有很大优势.本文采用数值仿真的方法研究了单细胞电学特性与其结构之间的关系,并通过实验进行了验证.根据细胞的生理特征,依据细胞的双壳模型与单壳模型理论分别建立了不同种类细胞的电学模型,研究了细胞种类、细胞膜、细胞核对细胞电学特性的影响.数值分析结果表明:1)细胞结构尺寸的变化引起细胞电学特性的改变,因此,依据细胞电学特性能够准确实现细胞分类; 2)柯尔-柯尔(Cole-Cole)图上高频与低频的两个半圆弧分别是由细胞质或细胞外液的离子极化、细胞膜与细胞外液之间的界面极化引起的;3)细胞核大小对测量阻抗的影响主要在低频段,是由细胞核与细胞内液的界面极化引起的,当存在细胞膜且当细胞核的核质比小于0.25时可忽略其影响.为验证仿真结果,对20%不同活性的酵母菌进行了实验.实验结果表明,运用本文建立的细胞电学模型,可以准确检测细胞的不同活性.该方法对实现细胞的精准电阻抗检测提供了理论依据,具有重要的应用价值.     

基于δ声波场的生物组织光学断层成像研究

利用δ声波场和近红外光漫射理论实现生物组织的断层成像是一种新颖医学 成像方法. 通过构建一个δ声波场并作用到生物组织中，仅改变组织内作用点上的光学特性参数，并影响近红外光在组织中的传播特性而改变组织表面的光强分布. 利用组织表面光强改变量与作用点上组织光学参数改变量之间的内在关系，可以通过对δ声波场作用点上断层的扫描实现组织内部的断层成像. 该方法具有广泛的临床医学应用前景，为乳腺癌的早期检测提供一种有效方法. 关键词： 光学断层成像 δ声波场 漫射方程 生物组织     

超宽带微波检测早期乳腺肿瘤三维仿真

超宽带微波成像技术可作为有效的方法用于乳房早期乳腺肿瘤的检测. 该方法基于乳房组织和肿瘤之间较大的电学特性差异的特点进行成像, 能提供足够的分辨率以及足够的穿透深度. 本文采用时域有限差分方法建立超宽带微波信号在三维乳房组织中传播的模型, 并采用单极德拜模型完成了生物组织色散特性的模拟. 利用8发9收的天线阵列实现微波肿瘤探测, 利用共焦成像算法对乳房组织进行图像重构并进行肿瘤定位. 仿真结果显示共焦成像算法能够实现最小直径3 mm的肿瘤的检测, 同时证实了超宽带微波成像技术应用于早期乳腺肿瘤检测的有效性. 关键词： 微波成像 肿瘤检测 时域有限差分 共焦成像算法     

基于multisine激励与整周期采样的多频电阻抗成像系统设计

本文从周期信号的整周期采样无频谱泄露这一原理出发,提出基于multisine信号的整周期采样理论,从理论上推导出满足multisine整周期采样的采样率设置条件,构建了基于FPGA+数模转换器+模数转换器的整周期采样实现方法,研制了一种基于multisine激励和整周期采样的新型多频电阻抗成像(mfEIT)系统;设计了胡萝卜棒+黄瓜棒的双目标成像模型,并进行了多频时差成像和频差成像实验.实验表明,本mfEIT系统能够在一个基波周期(1 ms)内实现20个频率点(2—997 kHz)多目标组织边界的全频阻抗测量,成像结果可区分具有不同电特性生物组织的结构与位置.本文提出的基于multisine信号的整周期采样理论及其实现方法,只需一个multisine基波周期即可完成一次全频阻抗测量,为研制高速mfEIT系统奠定了理论和技术基础.     

三维磁共振电阻抗成像的改进分层灵敏度算法

针对人体组织电导率的三维成像问题,提出一种改进的分层灵敏度磁共振电阻抗重建算法.利用单方向磁感应强度信息,对三维电导率图像实行分层重建,每层重建仅利用该层磁通密度分量测量数据,然后对单层重建结果进行修正以获得三维电导率重建图像.三介质长方体模型上的仿真实验证明,改进的分层重建算法改善了层间串扰现象,可以获得比一般分层算法甚至整体算法更高的图像分辨率,而且重建时间较整体算法显著减少;基于人体腿模型的仿真实验表明该算法对复杂模型三维重构的可行性;最后通过仿体实验验证算法的重建效果.改进的分层灵敏度重建算法降低了灵敏度矩阵法的计算机硬件需求,减少了重建时间,对MREIT的三维重建具有较高的成像精度和求解效率.     

高光谱成像技术鉴别菠菜叶片农药残留种类

利用高光谱成像技术无损鉴别菠菜叶片农药残留种类。采用高光谱成像仪采集900~1 700 nm波段内的光谱数据,采用多元散射校正对光谱数据进行预处理。利用主成分分析对不同种类菠菜样品的光谱数据进行分析,结果表明主成分分析能在可视化层面对不同种类的农药残留菠菜样品进行有效判别。另外,将卡方检验特征选择算法分别与支持向量机、朴素贝叶斯、决策树和线性判别分析算法结合,并采用10-fold交叉验证评价方法,筛选出最佳波段和最优判别模型（线性判别模型）。筛选出的8个特征波长为1 439.3,1 442.5,1 445.8,1 449,1 452.3,1 455.5,1 458.7,1 462 nm,模型的预测准确率达到0.993且10次交叉验证的标准差为0.009。结果表明,基于高光谱成像技术能准确地识别菠菜叶片上的农药残留种类。     

低场永磁体磁共振射频场映像

射频场映像是通过一定算法对磁共振射频线圈的发射场进行重建的方法.高场下的射频场经过生物组织时会发生明显变化,在其基础上可以反演生物组织体内电特性,进而对癌症等疾病进行早期诊断,是对生物组织的磁共振结构成像的有力补充.目前为止,射频场映像和电特性研究都以高场鸟笼线圈为主,对低场下的相控阵研究较少.本文主要研究了低场永磁体磁共振射频场的均匀度.有限元仿真和实验验证了在17.8 MHz激励下,射频场在空载和负载下均匀度均发生较大变化.射频场均匀度在负载下的改变在一定程度上可以反映负载生物组织的电特性,对磁共振电特性实用化研究提供了一定的参考价值.     

头部电阻抗成像正问题的解析解研究

建立头颅的球型仿真模型.用头皮、颅骨、脑脊髓和脑组织四层同心球结构模拟头颅.对各层组织采用复数电导率,用分离变量法分析头颅球模型在最外层(头皮层)表面施加点电流激励的情况下,内层的电位分布.根据电位分布的表达式,绘制出颅内的电位等位线图.分析电流注入角度对电位分布的影响.仿真结果表明,当颅内脑组织电导率变化时,头皮表面电位的实部变化明显大于虚部,激励电流频率变化对头皮表面电位虚部的影响较为明显.研究结果可用于分析头部电阻抗成像问题.     

PLS-DA法判别分析木材生物腐朽的研究

利用近红外光谱结合PLS-DA判别分析方法可用于食品、药品和农产品等的快速识别或检测,因此,研究利用近红外光谱结合PLS-DA方法来检测木材的生物腐朽。研究结果表明：应用近红外光谱结合PLS-DA方法对培训集样本建立的判别模型,其校正及验证结果与实际分类变量的相关系数均超过0.94,SEC和SEP都低于0.17; 利用模型对未参与建模的样本进行检测,发现该模型对未腐朽、白腐和褐腐三种类型样本的判别准确率均为100%(偏差均小于0.5); 与SIMCA法相比,PLS-DA法对木材生物腐朽样本的判别准确率更高,说明应用近红外光谱结合PLS-DA方法能快速地检测到木材的生物腐朽,并能准确地判别出木材的生物腐朽类型。     

S波段微波热致超声成像系统研究

微波热致超声成像技术通过向物体发射微波脉冲, 导致物体吸收电磁波温度迅速升高, 产生瞬时压力波, 从而激发产生超声波信号, 通过传感器对产生的超声波信号进行采集并成像, 最终还原了反映物体吸收电磁波能量特性的图像, 由于此方法兼具了微波成像的高对比性和超声成像的高分辨率特点, 理论上验证了热声成像技术对早期乳腺肿瘤检测的可行性. 本实验兼顾系统成像深度和分辨率, 采用S波段的微波脉冲信号源对物体进行辐射, 利用圆形扫描方式对待测物体进行检测, 同时为了更好的验证成像性能, 本实验同时使用了肿瘤仿体及实际生物组织进行成像实验. 通过实验分析, 验证了该系统对肿瘤仿体和生物组织检测的有效性, 以及系统的高分辨率和高对比度特性, 为早期乳房肿瘤检测提供了进一步的理论支撑.     

Lorentz force electrical impedance tomography using pulse compression technique

Lorentz force electrical impedance tomography(LFEIT) combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high contrast and high resolution hybrid imaging modality. In this study, pulse compression working together with a linearly frequency modulated ultrasound pulse was investigated in LFEIT. Experiments were done on agar phantoms having the same level of electrical conductivity as soft biological tissues. The results showed that:(i) LFEIT using pulse compression could detect the location of the electrical conductivity variations precisely;(ii)LFEIT using pulse compression could get the same performance of detecting electrical conductivity variations as the traditional LFEIT using high voltage narrow pulse but reduce the peak stimulating power to the transducer by 25.5 dB;(iii)axial resolution of 1 mm could be obtained using modulation frequency bandwidth 2 MHz.     

基于电阻抗层析成像的高强度聚焦超声温度监测技术

作为一种对正常组织无损伤且不易引起癌细胞转移的非入侵肿瘤治疗手段,高强度聚焦超声(HIFU)治疗过程中焦域的温度监测是实现剂量精准控制的关键.本文基于生物组织的温度-电阻抗的关系,将电阻抗层析成像(EIT)和HIFU治疗相结合,提出了一种利用组织焦平面的表面电压实现电阻抗重构的检测技术.建立了HIFU治疗和EIT综合系统模型,在考虑组织的声吸收条件下,对三维Helmholtz方程在柱坐标下的声场计算进行了二维简化,并引入Pennes生物热传导方程来计算HIFU焦域的声压和温升分布特性;引入生物组织的温度-电阻抗关系,基于麦克斯韦电磁场理论,建立了具有温度分布HIFU焦域的电流和电压计算模型,利用恒流注入的边界条件实现电场计算,获得焦平面的表面电压分布.在数值计算中,利用实验聚焦换能器参数,模拟了在固定声功率下组织焦域的声场和温度场分布,以及中心和偏心聚焦条件下不同治疗时刻的电导率分布;然后通过对称电极的循环电流注入,计算了组织模型焦平面内的电流密度和电势分布,获得了焦平面圆周分布的表面电极电压;进一步采用修正的牛顿-拉夫逊算法,利用32×32的表面电极电压实现了焦平面内电导率分布的重建.结果表明,基于温度-电阻抗关系的EIT电导率重建技术不但能准确定位HIFU焦域中心,还能恢复HIFU治疗中焦域的温度分布,证明了EIT用于HIFU治疗中温度监测的可行性,为其疗效评估和剂量控制提供了一种无创电阻抗测量和成像新方法.     

Raman spectroscopic analysis of breast cancer tissues: identifying differences between normal,invasive ductal carcinoma and ductal carcinoma in situ of the breast tissue

A relatively non‐destructive method employing Raman spectroscopy for the analysis of histopathological specimens is described. Raman spectroscopy has allowed qualitative analysis of the same specimen used for histopathological evaluation. Breast cancer tissues have been analysed to demonstrate the feasibility of the chemical changes taking place in the biological tissue, which can be identified precisely, and the results are reproducible. Raman analysis of tissue sections provides distinct spectra that can be used to distinguish between the nuclear grades of ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) of the breast. Sixty cases of breast carcinoma including DCIS and IDC and seven cases of normal breast tissues were studied employing the Raman spectroscopic technique. This study reports for the first time spectral differences between DCIS grades. It is concluded that Raman spectroscopy can objectively distinguish between DCIS and IDC grades and is non‐destructive and reproducible. It should become possible in future to use Raman spectroscopy as an informative and quantitative method suitable for classification of grades and diagnosis of breast carcinoma. Copyright © 2007 John Wiley & Sons, Ltd.     

Acoustic impedance microscopy for biological tissue characterization

A new method for two-dimensional acoustic impedance imaging for biological tissue characterization with micro-scale resolution was proposed. A biological tissue was placed on a plastic substrate with a thickness of 0.5 mm. A focused acoustic pulse with a wide frequency band was irradiated from the “rear side” of the substrate. In order to generate the acoustic wave, an electric pulse with two nanoseconds in width was applied to a PVDF-TrFE type transducer. The component of echo intensity at an appropriate frequency was extracted from the signal received at the same transducer, by performing a time–frequency domain analysis. The spectrum intensity was interpreted into local acoustic impedance of the target tissue. The acoustic impedance of the substrate was carefully assessed prior to the measurement, since it strongly affects the echo intensity. In addition, a calibration was performed using a reference material of which acoustic impedance was known. The reference material was attached on the same substrate at different position in the field of view. An acoustic impedance microscopy with 200 × 200 pixels, its typical field of view being 2 × 2 mm, was obtained by scanning the transducer. The development of parallel fiber in cerebella cultures was clearly observed as the contrast in acoustic impedance, without staining the specimen. The technique is believed to be a powerful tool for biological tissue characterization, as no staining nor slicing is required.     

斜位电流注入磁共振电阻抗成像（MREIT）与硬件设计

现有的磁共振电阻抗成像(MREIT)方法只适用于主磁场平行水平面的磁共振系统,本文中提出了一种新的MREIT方法即斜位电流注入磁共振电阻抗成像,同时适用于主磁场垂直于水平面的磁共振系统. 硬件系统以磁共振主控计算机为控制中心,将MRI与EIT有机结合于一体：(1)能够测量注入电流在成像体内部感应磁场的磁感应强度B(x,y,z);(2)向成像体注入电流;(3)满足时序匹配要求;(4)测量边界电压. 文章还展示了利用此装置所得的初步实验结果.     

Boundary normal pressure-based electrical conductivity reconstruction for magneto–acoustic tomography with magnetic induction

As a kind of multi-physics imaging approach integrating the advantages of electrical impedance tomography and ultrasound imaging with the improved spatial resolution and image contrast, magneto–acoustic tomography with magnetic induction(MAT-MI) is demonstrated to have the capability of electrical impedance contrast imaging for biological tissues with conductivity differences. By being detected with a strong directional transducer, abrupt pressure change is proved to be generated by the gradient of the induced Lorentz force along the force direction at conductivity boundary. A simplified boundary normal pressure(BNP)-based conductivity reconstruction algorithm is proposed and the formula for conductivity distribution inside the object with the clear physical meaning of pressure derivative, is derived. Numerical simulations of acoustic pressure and conductivity reconstruction are conducted based on a 2-layer eccentric cylindrical phantom model using Hilbert transform. The reconstructed two-dimensional conductivity images accord well with the model, thus successfully making up the deficiency of only imaging conductivity boundary in traditional MAT-MI. The proposed method is also demonstrated to have a spatial resolution of one wavelength. This study provides a new method of reconstructing accurate electrical conductivity and suggests the potential applications of MAT-MI in imaging biological tissues with conductivity difference.     

Verification and application of a finite-difference model for quasi-electrostatic scanning impedance imaging

We have previously introduced liquid-contact scanning impedance imaging (SII) as a high resolution, high contrast method for imaging electrical impedance. This technique has shown its potential to measure the impedance distribution of biological tissues. In this paper, a numerical model is developed to describe the SII system based on the finite difference method. Good correspondence can be observed when comparing data simulated using the model with experimental data. The relationships between measurable resolution and system parameters such as height are shown in both simulation results and measurements. It is shown that the numerical model provides a good explanation for experimental results and can also assist in the design of the dual-conductor impedance probe used in this imaging method. Model predictions on both the conductor spacing and the resistor R used in the system have been made indicating their relationships to an empirical notion of resolution. The simulation result of the conductor spacing also gives an insight to the function of the dual-conductor probe. Based on this model, an optimum probe design can be obtained by balancing ultimate resolution with the signal-to-noise ratio by adjusting spacing and resistor values.