微波热疗辐射器聚束方法的研究进展

肿瘤的热疗法是当前肿瘤放疗、化疗的有效辅助疗法.影响肿瘤的微波热疗效果的决定性因素是微波能量在肿瘤组织中的合理分布,如何提高微波辐射器的辐射效率,将辐射的微波能聚焦在肿瘤体是当前辐射器研究的重点.文中针对国内外已研制的微波热疗辐射器,从单辐射器和辐射器阵列两个方面综述辐射器聚束的方法及研究工作进展.     

微波热疗天线在生物组织中温度分布的模拟

模拟微波肿瘤热疗条件下生物组织中的温度分布,对临床治疗中微波热疗天线的设计、选择及治疗方案的确定具有重要意义.本文结合电磁场的时域有限差分(FDTD)和温度场的有限差分方法模拟了微波热疗天线在生物组织中产生的温度分布.通过单极子天线对等效组织模型的加热温度模拟结果与实验测量结果比较,对微波热疗天线在生物组织中产生的温度场模拟程序进行了验证.     

热疗用微波辐射器长度对其性能影响的理论分析

本文分析了一种带冷却水的用于人体体腔内部热疗的绝缘偶极子微波辐射器的特性。利用辐射器上的电流分布导出辐射阻抗和驻波经与辐射器长度的关系式，探讨了体腔周围被加热生物组织中分布的比吸收率，进而根据热平衡方程得到辐射器长度对温度场分布的影响，为体腔内部热疗用微波辐射器的设计提供了理论依据。     

一款高效微波聚焦热疗系统的设计

为了有效提高微波热疗系统的能量利用效率,改善肿瘤治疗效果,设计一款高效率微波聚焦热疗系统。该系统的辐射器采用36单元环形阵列天线,人体等效模型采用三层匹配介质加载,并利用天线聚焦算法实现辐射器能量在人体模型深部的靶向聚焦。仿真和实验结果表明,相比于单层人体匹配介质层加载的系统,该系统能量利用效率达到之前的3倍,既实现了体外微波能量的有效穿透,又保证了穿透到人体内部的电磁能量靶向聚焦,克服了一般微波热疗系统中由于散射和折射引起的电磁能量损耗问题。     

一种小型化体外挽袖微带圆贴片微波热疗天线北大核心CSCD

小体积生物组织进行微波热疗过程中,热疗天线辐射的微波能量聚焦体积过大、治疗范围超出热疗目标区域烧伤其余健康组织,针对这一问题,文中提出了一种小型化体外挽袖式微带热疗天线。它由SMA连接器法兰盘两侧焊接的挽袖圆铜壳及两个圆形微带贴片组成。微带贴片的介质基底是相对介电常数为4.4的FR-4材料,基底厚1.6 mm。实测天线在915 MHz的反射系数为-18.5 dB,试验中由该天线加热40 mm×40 mm×40 mm的小体积猪肉组织,并采取红外热成像仪和热电偶两种测温方式测试天线加热情况,研究结果表明该天线有效治疗区域为20 mm×20 mm×10 mm的半椭球型,温度分布较为均匀,适用于小体积体外微波热疗系统。     

微波热疗机模糊控制器设计

微波热疗是一种治疗肿瘤的新方法 ,主要利用微波能沉积于病灶区时所产生的高温杀灭肿瘤细胞。但其温度控制问题属于不确定性问题 ,采用经典控制论设计控制系统遇到障碍。模糊技术是解决不确定性问题的一种有效手段 ,将模糊控制技术应用于微波医疗设备是一种的新的尝试 ,并且收到较为理想的效果     

一种新型的内腔式微波医用辐射器

本文提出了一种新型的内脏式微波医用辐射器。该辐射器用来对宫颈、肠道等肿瘤进行插入式热疗。它与传统型技状辐射器不同的是，用双圆锥代替了柱状结构，并使辐射器的纵向电流分布趋于均匀、热疗更为安全和有效。文中利用等效传输线模型对其编程计算，证实了新型辐射器沿线电流分布具有均衡的优点，从而使热分布产生类似的变化。理论计算结果与实测温度分布相比，一致性很好。因而提高了辐射器的临床应用价值。     

脉冲调制微波辐照生物组织的热效应及红外热成像研究

针对微波连续加热造成生物组织温升过高而损伤正常组织,提出计算机编码的脉冲调制微波辐照生物组织,有效控制加热区域内的温度分布.采用红外热成像的方式观察分层仿生体模中各层的温度分布,分析讨论脉冲调制微波占空比、频率和功率对生物组织加热区域内温度分布的影响.结果表明,采用提高脉冲调制微波占空比和功率或在一定范围内改变调制脉冲频率的方式来提高生物组织加热区域内的热效应.该方法将为肿瘤微波热疗提供新的有效加热方式和途径.     

微波前列腺治疗仪的研制

本文阐述了微波前列腺治疗仪的原理和设计,采用频率为915MHz的微波对前列腺进行热疗。特殊设计的固态微波源和表面冷却技术,使加热区仅局限在前列腺上。特制的治疗导管和辐射器,可以实现经尿道或经直肠进行治疗。所用的热敏传感器的测温精度可达0.1℃,运用微型计算机对治疗的全过程进行自动测温、控温,并实时记录、显示、打印治疗参数和病例资料管理。     

2450MHz医用微波辐射天线的设计

设计了一种工作在2450MHz频率的新型的医用微波热疗天线。采用有限元数值分析方法针对人体肌肉组织微波热疗模型,对单极辐射天线和改进的挽袖圆顶辐射天线在肌肉组织中产生的电磁场分布及单位质量电磁能量吸收率(SAR)进行了模拟计算,并且比较了挽袖圆顶天线和挽袖天线在2-3GHz频率之间的S11值。结果显示:挽袖圆顶天线通过优化的挽袖结构,减少了天线的能量反射,能量的分布不会随天线插入组织深度的不同而引起变化,优化的顶部结构可得到更好的反射特性。     

Microwave cancer imaging exploiting magnetic nanoparticles as contrast agent

In this paper, a microwave technique for breast cancer imaging is presented. The approach is based on the use of magnetic nanoparticles as contrast agent to induce a nonnull magnetic contrast selectively localized within the tumor. This allows us to face cancer imaging as the reconstruction of a magnetic contrast from the corresponding scattered field. To extract, from the measured data the contribution due to the magnetic contrast, i.e., the signal meaningful for cancer imaging, the approach exploits the possibility of modulating the magnetic response of magnetic nanoparticles by means of a polarizing magnetic field. The achievable reconstruction capabilities and the robustness against uncertainties on the electric features of the surrounding electric scenario are assessed by means of numerical examples.     

Square Monopole Antenna Application in Localization of Tumors in Three Dimensions by Confocal Microwave Imaging for Breast Cancer Detection: Experimental Measurement

In this paper, application of a designed antenna for microwave imaging is evaluated. In previous research, application of an UWB antenna for microwave imaging was investigated. To the best of the author’s knowledge, the designed antenna was the smallest UWB antenna designed at the time of publication, for breast cancer detection. The smaller size antennas can cause more clutter in the image while, on the other hand, make it possible to use more antennas in the array at the same surface. Therefore, the smaller size of the antenna makes microwave imaging more challenging. Simulation results showed successful detection of 10 mm and 5 mm tumors by 16 UWB antennas with the hemispherical arrangement. For signal processing, the Delay-Multiply-and-Sum Algorithm is used for image reconstruction. In this paper results of two experimental microwave imaging is presented. Two tumors at different locations are placed and microwave imaging is performed. The experimental proves that the designed antenna in an array of 16 antennas is capable of detecting the 5 mm tumor in different location.

     

Microwave imaging via space-time beamforming for early detection of breast cancer

A method of microwave imaging via space-time (MIST) beamforming is proposed for detecting early-stage breast cancer. An array of antennas is located near the surface of the breast and an ultrawideband (UWB) signal is transmitted sequentially from each antenna. The received backscattered signals are passed through a space-time beamformer that is designed to image backscattered signal energy as a function of location. The beamformer spatially focuses the backscattered signals to discriminate against clutter and noise while compensating for frequency-dependent propagation effects. As a consequence of the significant dielectric-properties contrast between normal and malignant tissue, localized regions of large backscatter energy levels in the image correspond to malignant tumors. A data-adaptive algorithm for removing artifacts in the received signals due to backscatter from the skin-breast interface is also presented. The effectiveness of these algorithms is demonstrated using a variety of numerical breast phantoms based on anatomically realistic MRI-derived FDTD models of the breast. Very small (2 mm) malignant tumors embedded within the complex fibroglandular structure of the breast are easily detected above the background clutter. The MIST approach is shown to offer significant improvement in performance over previous UWB microwave breast cancer detection techniques based on simpler focusing schemes.     

早期乳腺肿瘤的超宽带微波成像

通过采用时域有限差分方法探讨了一种收发天线分离的早期乳腺癌超宽带微波成像检测方案.在收发共用的超宽带天线设计中要求天线的终端反射不超过-120dB,而采用收发天线分离方案则避免了这一苛刻要求.采用共焦成像算法给出的成像结果表明,该方案亦可探测直径10mm以下的早期乳腺肿瘤.     

Dielectric characterization of PCL-based thermoplastic materials for microwave diagnostic and therapeutic applications

We propose the use of a polycaprolactone (PCL)-based thermoplastic mesh as a tissue-immobilization interface for microwave imaging and microwave hyperthermia treatment. An investigation of the dielectric properties of two PCL-based thermoplastic materials in the frequency range of 0.5-3.5 GHz is presented. The frequency-dependent dielectric constant and effective conductivity of the PCL-based thermoplastics are characterized using measurements of microstrip transmission lines fabricated on substrates comprised of the thermoplastic meshes. We also examine the impact of the presence of a PCL-based thermoplastic mesh on microwave breast imaging. We use a numerical test bed comprised of a previously reported 3-D anatomically realistic breast phantom and a multi-frequency microwave inverse scattering algorithm. We demonstrate that the PCL-based thermoplastic material and the assumed biocompatible medium of vegetable oil are sufficiently well matched such that the PCL layer may be neglected by the imaging solution without sacrificing imaging quality. Our results suggest that PCL-based thermoplastics are promising materials as tissue immobilization structures for microwave diagnostic and therapeutic applications.     

Microwave radiometry: its importance to the detection of cancer

The author discusses developments in the medical uses of microwave radiometry, particularly in relation to the early detection of cancer, as well as the significance of and progress in related antenna technology. In the treatment of cancer, microwave hyperthermia is accepted as an adjunct to radiation therapy in the treatment of superficial lesions. Although not as widely reported, the use of microwave radiometry as a noninvasive, passive technique for the early detection of cancer appears promising. Wider acceptance of these methods, however, awaits fundamental improvements in the ability to focus energy at depth in human tissue, an important and nontrivial antenna problem. Antenna development is described, and the improvements required if microwave technology is to provide a practical solution to the detection and treatment of cancer are indicated     

Preclinical Prototype Development of a Microwave Tomography System for Breast Cancer Detection

As a supplement to X‐ray mammography, microwave imaging is a new and promising technique for breast cancer detection. Through solving the nonlinear inverse scattering problem, microwave tomography (MT) creates images from measured signals using antennas. In this paper, we describe a developed MT system and an iterative Gauss‐Newton algorithm. At each iteration, this algorithm determines the updated values by solving the set of normal equations using Tikhonov regularization. Some examples of successful image reconstruction are presented.     

Microwave thermography: principles, methods and clinical applications.

We review the physical principles, method of operation, measurement limitations, and potential medical applications of microwave thermography. We present detailed results of a study of breast cancer detection at 1.3 and 3.3 GHz, including the dependence of detection rates on microwave frequency, time, tumor depth, and tumor size. At 1.3 GHz, microwave thermography detects breast cancer as well as infrared thermography (true-positive rate = 0.76 when true-negative rate = 0.63). When the two methods are combined, the true-positive rate increases by about 0.1 over that of either method alone.     

Zwitterionic Polysulfamide Drug Nanogels with Microwave Augmented Tumor Accumulation and On‐Demand Drug Release for Enhanced Cancer Therapy

Zwitterionic polymers demonstrate as a class of antifouling materials with long blood circulation in living subjects. Despite extensive research on their antifouling abilities, the responsive zwitterionic polymers that can change their properties by mild outside signals are poorly explored. Herein, a sulfamide‐based zwitterionic monomer is developed and used to synthesize a series of polysulfamide‐based (poly (2‐((2‐(methacryloyloxy)ethyl) dimethylammonio)acetyl) (phenylsulfonyl) amide (PMEDAPA)) nanogels as drug carriers for effective cancer therapy. PMEDAPA nanogels are proved to exhibit prolonged blood circulation without inducing the accelerated blood clearance phenomenon. Intriguingly, PMEDAPA nanogels can sensitively respond to hyperthermia by adjusting the crosslinker degree. After modified with transferrin (Tf), the nanogels (PMEDAPA‐Tf) achieve shielded tumor targeting at normothermia, while exhibiting recovered tumor targeting at hyperthermia, leading to enhanced tumor accumulation. Meanwhile, PMEDAPA‐Tf nanogels show superior penetration ability in 3D tumor spheroids and faster drug release at hyperthermia compared with that at normothermia. In combination with mild microwave heating (≈41 °C), the drug‐loaded PMEDAPA‐Tf nanogels show a pronounced tumor inhibition effect in a humanized orthotropic liver cancer model. Therefore, the study provides a novel hyperthermia‐responsive zwitterionic nanogel that can achieve augmented tumor accumulation and on‐demand drug release assisted with clinically used microwave heating for cancer therapy.