组织介电特性离体测量和MR EPT技术理论研究初探

发布时间：2018-03-11 21:13

本文选题：介电特性　切入点：开端同轴线法　出处：《南方医科大学》2017年硕士论文　论文类型：学位论文

【摘要】：生物组织介电特性(electricalproperties,EPs)主要包括电导率(σ)和相对介电常数(εr),是生物组织在电磁场作用下表现出的电特性。相关研究已表明人体肿瘤组织与正常组织介电特性存在较大差异,因此人体组织介电特性信息可用于肿瘤的诊断,而且可能为癌症的早期诊断提供帮助。目前,常用组织介电特性测量方法有开端同轴线法和磁共振介电特性断层成像技术(magnetic resonance electrical property tomography,MR EPT)等,本文首先运用开端同轴线法对结直肠正常与癌变组织介电特性进行了离体测量;然后对MR EPT技术进行了初步的理论研究,量化分析了 MR EPT核心算法的重建误差,并对该技术的固有分辨能力进行了理论分析。结直肠正常与癌变组织介电特性离体测量研究中,首先用开端同轴线法测量85位结直肠肿瘤患者的结直肠切除组织的介电特性;其次用Cole-Cole模型对测量结果进行拟合;最后比较正常组织与肿瘤组织介电特性拟合结果。结果显示,正常组织与肿瘤组织介电特性存在较大差异,当频率为128MHz时,肿瘤组织ε和σ分别比正常组织高14.6%和17%。MR EPT核心算法重建误差研究中,首先量化分析MR EPT核心算法在不同组织交界处的重建误差,其次对64MHz、128MHz和298MHz下MR EPT核心算法在非均匀负载中应用时的重建误差进行比较。结果显示,MR EPT核心算法在不同组织交界的重建误差均不一样,各组织交界上σ和εr的平均相对重建误差分别大于0.3986和0.2218。该算法在非均匀负载中应用时的重建误差随共振频率的增大而减小,当共振频率为64MHz时,ε和σ的平均相对重建误差分别为 28.71%和 9.11%。MREPT固有分辨能力的理论分析中,首先建立一系列具有不同介电特性对比度的电磁模型,仿真得到模型发射场B1+,进而通过MR EPT核心算法重建电磁模型介电特性;然后对MR EPT固有分辨能力进行定义和评估;最后对可能影响MR EPT固有分辨能力的因素进行分析。结果显示,MR EPT固有分辨能力与ROI大小正相关,MR EPT最大固有电导率分辨能力和相对介电常数分辨能力均为1/1.02。本文对结直肠正常与癌变组织介电特性进行了离体测量,并对MR EPT技术进行了初步的理论研究。结直肠组织离体测量研究表明结直肠肿瘤组织与正常组织介电特性存在较大差异,所测结果可作为介电特性相关研究的基础数据;MR EPT技术的初步理论研究对降低MR EPT核心算法在非均匀组织中的重建误差,实现高精度的MR EPT技术有一定的参考价值,为早日将MR EPT技术应用到肿瘤早期诊断中做出了贡献。
[Abstract]:The dielectric properties of biological tissues mainly include electrical conductivity (蟽) and relative dielectric constant (蔚 r), which are the electrical properties of biological tissues under the action of electromagnetic field. Relevant studies have shown that there are great differences between the dielectric properties of human tumor tissues and normal tissues. Therefore, the information of dielectric properties of human tissues can be used in the diagnosis of cancer, and may be helpful for the early diagnosis of cancer. The common methods for measuring the dielectric properties of colorectal cancer tissues are starting coaxial method and resonance electrical property tomographic imaging technique. In this paper, the dielectric properties of colorectal normal and cancerous tissues are measured in vitro by the method of starting coaxial line. Then, the theory of Mr EPT technology is studied, and the reconstruction error of Mr EPT core algorithm is analyzed quantitatively. In the in vitro measurement of the dielectric characteristics of colorectal normal and cancerous tissues, the dielectric properties of 85 colorectal cancer patients were measured by starting coaxial method. Secondly, the measured results were fitted with Cole-Cole model, and the dielectric characteristics of normal tissue and tumor tissue were compared. The results showed that the dielectric characteristics of normal tissue and tumor tissue were different, when the frequency was 128MHz, The reconstruction error of Mr EPT core algorithm is 14.6% and 17.5% higher than that of normal tissue, respectively. Firstly, the reconstruction error of Mr EPT core algorithm at the junction of different tissues is analyzed quantitatively. Secondly, the reconstruction error of Mr EPT core algorithm at 128MHz and 298MHz is compared. The results show that the reconstruction error of Mr EPT core algorithm is different at the junction of different tissues. The average relative reconstruction errors of 蟽 and 蔚 r at the junctions of tissues are greater than 0.3986 and 0.2218, respectively. The reconstruction error decreases with the increase of resonance frequency. When the resonance frequency is 64MHz, the average relative reconstruction errors of 蔚 and 蟽 are 28.71% and 9.11 respectively. In the theoretical analysis of intrinsic resolution of MREPT, a series of electromagnetic models with different contrast of dielectric properties are established, and the emulation results of the emitter B1 are obtained. Then the dielectric properties of the electromagnetic model are reconstructed by Mr EPT core algorithm, and the inherent resolution of Mr EPT is defined and evaluated. Finally, the factors that may affect the inherent resolution of Mr EPT are analyzed. The results show that the intrinsic resolution of Mr EPT is positively correlated with the magnitude of ROI. The resolution of the maximum intrinsic conductivity and the relative dielectric constant of Mr EPT are both 1 / 1.02. The dielectric properties of colorectal normal and cancerous tissues were measured in vitro. The in vitro measurement of colorectal tissue showed that the dielectric properties of colorectal tumor tissues were different from those of normal tissues. The measured results can be used as the basic data for the study of dielectric properties. The preliminary theoretical study of Mr EPT technique has some reference value for reducing the reconstruction error of Mr EPT core algorithm in non-uniform tissue and realizing high precision Mr EPT technology. It has contributed to the early application of Mr EPT technique in the early diagnosis of tumor.
【学位授予单位】：南方医科大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R730.4;R445.2

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