【作者】 宋健；

【导师】 赵志钦；

【作者基本信息】 电子科技大学 ， 电磁场与微波技术， 2015， 博士

【摘要】 乳腺癌是女性癌症中发病率最高的一种,严重威胁着人类健康。乳腺癌的早期诊断对病患的治疗和康复起着至关重要的作用。因此,对可用于乳腺癌早期检测的新型成像技术的研究已引起国内外学者的广泛关注。微波致热超声成像(Microwave Induced Thermo-acoustic Tomography,MITAT)作为新兴成像技术,兼具了微波成像和超声成像的双重优势,在生物医学检测尤其是早期乳腺癌检测上有重大的应用前景。本文针对MITAT技术的机理和系统研制中的关键问题,采用数值仿真和实验验证相结合的技术路线,对MITAT技术展开了深入而广泛的研究,主要研究内容包括:MITAT系统涉及到微波工程、阵列信号处理、超声成像和生物医学等诸多学科,在系统设计中涉及到强电磁辐射对微弱热声信号检测形成干扰,微波辐射天线受声学器件干扰及天线近场功率密度分布不均匀等诸多问题,针对这些问题通过优化超声探头布局及微波辐射子系统等手段使之得到解决。通过采用仿体材料的热声成像实验,验证了所搭建MITAT系统的性能。根据MITAT的系统特性,提出了MITAT系统一体化仿真框架。在MITAT一体化仿真中,由于MITAT技术的多物理场特性,分别采用时域有限积分(Finite Integration Time Domain,FITD)和k-space伪谱(Pseudo-spectral,PS)方法对一体化仿真中的微波问题和声波问题进行仿真,确保了一体化仿真的效率。通过仿真与相对应实验的结果对比,一体化仿真的正确性得到验证。在MITAT一体化仿真的基础上,提出了基于一体化仿真的热声图像修正方法。该方法针对热声成像中微波辐射不均匀及天线近场测量比较困难的问题,利用一体化仿真得出系统中成像层析面的微波功率密度分布。在仿真得到的微波功率密度分布的基础上对热声图像进行修正,解决了因微波辐射不均匀造成的MITAT系统的“漏检”和“错检”的问题。针对乳癌肿瘤组织和正常腺体组织介电参数差异不大而导致的热声图像对比度不足的问题,研究了以碳纳米管作为热声成像对比剂的可行性。在研究过程中制作了不同CNTs含量的仿体材料并分别测量了这些仿体材料的等效电导率和声速,根据测量结果讨论CNTs对仿体材料介电特性和声参数的影响。同时,通过研究不同CNTs含量的仿体样品的热声响应强度,发现CNTs含量为1%(质量比)时,样品热声响应强度将增加一倍以上。结合碳纳米管在其他成像领域的应用及本文研究内容,碳纳米管作为MITAT的成像对比剂,可以有效解决乳腺肿瘤组织和正常腺体组织对比度不足的问题,为MITAT技术的进一步发展提供了保证。利用搭建的MITAT系统,进行了真实乳腺组织的热声成像实验。在实验中,采用了不同的乳腺组织,包括正常脂肪组织、良性纤维瘤组织和不同临床分期肿瘤组织进行了热声成像。通过实验得出了不同组织的热声响应强度和热声成像效果。同时,在实验中分别采用了单个样品、多个样品、混合组织样品及正常组织包裹肿瘤样品等多种实验形式验证了所搭建MITAT系统的成像能力,为MITAT技术的临床应用打下了基础。此外,为了进一步提高系统所重构热声图像的分辨率,研究了高功率短微波脉冲为激励源的热声成像体制,对比了纳秒级短脉冲与目前所用微波脉冲(微秒级脉宽)所产生热声信号的特性。实验研究证明高功率短脉冲可以有效克服生物组织内能量积累和图像分辨率之间的矛盾,在保证热声信号信噪比的前体下,提高了热声信号的频域带宽,从而提高热声图像分辨率。本文研究了MITAT技术在成像系统研制改进、一体化仿真、图像对比度增强方法等方面的内容,提出了基于一体化仿真的图像修正方法,验证了以CNTs作为成像对比剂的可行性;同时,通过真实人体离体组织样品实验证明了MITAT在乳腺癌检测上潜力;最后,实验验证了以高功率短脉冲为激励源的热声成像体制在热声信号频谱宽度上具有优势,为MITAT系统的进一步发展提供了方向。更多还原

【Abstract】 Breast cancer is the most frequently diagnosed cancer in women and it is a serious threat to human health. Early diagnosis is very important to the treatment and recovery of the patient. Therefore, the new imaging detection techniques that can be applied in the early breast cancer detection attract wide interests of the researchers at home and abroad.Microwave induced thermo-acoustic tomography(MITAT) has the both advantages of microwave imaging and ultrasound imaging as an emerging imaging method. It has great potential in the biomediacl application especially in the early breast cancer detection.Aiming to the mechanism of MITAT and key techniques in the system development,the strategy of combining the numerical simulations and experiments is employed to promote the research. The main research contents of this thesis are as follows:There involves microwave engineering, array signal processing, ultrasound imaging and biomedical engineering in MITAT system. Thus, there are some issues such as the interfere to the weak TA signal due to the strong EM radiation,the interaction between EM and acoustic components and the non-uniform distribution of the microwave power density in the antenna near field.These issues can be solved through optimizing the layout of ultrasound transducers and the microwave radiation subsystem. The performances of the improved MITAT system are verified by the imaging experiments for tissue mimicking(TM) material samples.According to the characteristics of MITAT, an integrated simulation framework is proposed. In the integrated simulation, in order to improve the simulation efficiency and considering of the multiple physical characters, finite integration time domain(FITD)method and k-space pseudo-spectral(PS) method are employed to solve the electromagnetic(EM) and acoustic issues,respectively. The effectiveness of the integrated simulation is verified through the comparisons between the simulations and experimental results. Based on the integrated simulation of MITAT system, an image correction method is proposed. For eliminating the influence caused by the non-uniform distribution of the microwave power density in the near filed of the antenna,the microwave power density distribution in the tomography plane can be obtained by the simulation instead of the complex actual measurements. The TA image can be corrected by utilizing the simulated distribution of microwave power density and the “missing detection”and “false detection”of the system due to the non-uniform power density distribution are eliminated.For solving the insufficient TA contrast between the tumor tissue and the normal glandular tissue caused by the similarity of the dielectric properties, the feasibility of carbon nanotubes(CNTs) being used as imaging agents is evaluated. The influences of CNTs to the dielectric and acoustic properties are investigated through the measurements for the TM samples with different CNTs contents. Meanwhile, it is founded that the 1%weight concentration of CNTs can increase the TA response more than one times through evaluating the contrast enhancement of different CNTs concentrations. Considering of the other imaging applications of CNTs and the research contents in this thesis, CNTs has the potential to be developed as the TA imaging agents to overcome the limitation due to the low TA contrast between the tumor and gland and provide basis for the further development of MITAT.Different breast samples including normal adipose tissue,benign fibroma and tumor samples in different clinical stages are employed to perform the TA imaging experiments in the established MITAT system and the TA responses and images of these samples are obtained. In these experiments, multiple sample forms including single sample, multiple samples, hybrid sample and tumor sample embedded in the normal tissue are utilized to verify the imaging ability of the established MITAT system and these experiments provide early verification for the clinical application. Meanwhile, in order to improve the image resolution of the MITAT system, TA imaging with high-power short microwave pulse which is utilized as the radiation source is researched. The characteristics of the TA signals excited by the current microwave source and the nanosecond level microwave source are compared. The results show that the high-power short pulse can effectively overcome the contradiction between the energy accumulation and the image resolution.Under the premise of the signal to noise ratio(SNR) of TA signal is satisfactory, high-power short pulse can extend the frequency spectrum of TA signals and increase the resolution.In this thesis, system development,integrated simulation and image contrast enhancements are investigated. An image correction method is proposed and the feasibility of CNTs being used as the imaging agents is verified. Meanwhile, the potential of MITAT to the breast cancer detection is proved through the imaging experiments for the real ex-vivo samples. The contrast enhancement of CNTs is evaluated and the feasibility of the CNTs is used as imaging agents is proved. Finally, the experimental results show that TA imaging with high-power short pulse has advantages in the spectral bandwidth and predict the further developing direction of MITAT.更多还原