激光诱导间质热疗中的治疗参数选择

目的：考察激光诱导间质热疗中各治疗参数对治疗效果的影响，对各治疗参数进行选择和优化。方法：基于光子传输理论，分别采用Monte Carlo模拟方法和Pennes生物传热方程求解生物组织中的能量分布和温度分布。结果：计算得到了一般加热系统、具有冷却设备的加热系统以及暂时阻断血液灌注条件下，激光波长、功率大小及激光加入头曝光时间对凝结区域大小的影响。结论：激光诱导间质热疗中，需要综合考虑生物组织特性和激光波长、功率及曝光时间等治疗参数来制定治疗方案。     

毫米波生物热效应的理论研究

从理论上研究了平面分层均匀组织人体模型在垂直入射毫米波照射下，体内电磁场、吸收功率、比吸收热、温度场及其分布，并对毫米波热疗机理进行了初步探讨。     

激光间质热疗的功能近红外疗效评估

探讨了利用功能近红外光谱(FNIRS)实时在体监测激光诱导肿瘤间质热疗(LITT)进行疗效评估的可行性。实验采用新鲜离体猪肝和肝癌小鼠皮下移植瘤模型,按不同激光功率和加热时间进行LITT毁损热疗,利用FNIRS监测系统同时监测热疗过程中约化散射系数μs′。结果表明,FNIRS监测系统获取的约化散射系数在LITT热疗过程中呈上升趋势,起始阶段上升较快,达到一定数值后趋于稳定。激光功率越大,μs′上升越快。组织成分不一样时,约化散射系数的变化趋势一致,曲线形态有所不同。因此,FNIRS可以用于LITT实时在体疗效评估,μs′可以作为一种新的LITT术中实时在体疗效评估因子,通过监测μs′的变化将有助于指导临床热疗。     

肝组织激光间质热疗温度与热损伤区域研究

基于光子传输理论,首先采用蒙特卡罗方法和Pennes生物传热方程模拟了肝组织激光间质热疗在不同功率不同加热时间下的温度分布,然后进行相应参数下的猪肝离体实验,获取相应的中心温度和热损伤区域大小,最后对理论模拟与离体实验的结果进行对比。对比结果表明:离体实验的中心最高温度低于对应的理论模拟值,理论模拟的53 ℃温度等高线椭圆长、短轴能较好的预测实际的热损伤区域大小。     

激光诱导间质热疗中生物组织吸收系数变化特性研究

利用近红外光谱技术进行生物组织激光诱导间质热疗（laser induced interstitial thermotherapy, LITT）实时监测,探讨LITT术中疗效评估基础。实验样本采用离体猪肝和小鼠皮下移植肝肿瘤,使用近红外光谱实时采集系统采集激光热疗过程中组织吸收系数。实验结果表明组织吸收系数在激光热疗过程中具有一定的变化规律,其中猪肝的变化规律非常明显,在低功率下呈现缓慢的上升,高功率下达到一定的温度（50℃左右）快速上升,并逐步达到稳定。肿瘤在热毁损时会根据瘤体的组织特性不同出现特异性变化,这些变化可以作为将来临床治疗的参考。实验结果表明在进行实体组织激光诱导间质热疗过程中,组织吸收系数作为实时监测因子具有一定的参考价值,而作为肿瘤的治疗评估因子还需要进一步探索。     

激光诱导间质热疗方法的离体模拟实验研究

本文建立了激光诱导间质热疗方法 (LITT)的离体模拟实验系统 ,在不同的输出功率、不同的加热时间下 ,实验测量了激光加热时的离体猪肝组织温度分布和热凝结区域的大小 ,与计算机模拟的结果进行了对比。实验发现 ,在相同的功率和加热时间下 ,会出现有无碳化两种不同现象。当临近激光加入头表面的生物组织产生碳化时 ,测量点处的温升和热凝结区域的体积将大于未发生碳化现象时的相应值     

基于MSP430的射频热疗系统设计

为了解决射频热疗中温度控制不精确的问题,设计了基于MSP430的射频热疗系统。采用红外温度传感器MLX90615测量靶区温度,利用PID算法对MSP430输出的脉冲宽度调制（Pulse Width Modulation,PWM）波的占空比进行调节,通过闭环系统实现了对射频热疗温度精确控制。使用键盘对温度进行设定,液晶屏实时显示测量温度值。经实验测试,本系统稳定可靠,温度控制误差在±0．5℃以内,具有良好的应用前景。     

基于MSP430的射频热疗系统设计

为了解决射频热疗中温度控制不精确的问题,设计了基于MSP430的射频热疗系统。采用红外温度传感器MLX90615测量靶区温度,利用PID算法对MSP430输出的脉冲宽度调制(Pulse Width Modulation,PWM)波的占空比进行调节,通过闭环系统实现了对射频热疗温度精确控制。使用键盘对温度进行设定,液晶屏实时显示测量温度值。经实验测试,本系统稳定可靠,温度控制误差在±0.5℃以内,具有良好的应用前景。     

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.     

近红外光谱技术在激光热疗监测中的应用研究

针对激光热疗中生物病变组织光学参数随温度变化的特点,将近红外光谱技术应用于激光诱导肿瘤间质热疗疗效监测,在线检测激光作用后生物病变组织的温度与光学参数的变化趋势,以此来对疗效进行评估。基于监测原理分析,设计实验系统,以肝癌小鼠皮下移植瘤为实验对象,研究不同激光功率和作用时间下,生物病变组织约化散射系数和温度的变化,并利用核磁共振成像技术对移植瘤术前、术后的影像进行对比。实验结果表明:病变组织的约化散射系数在激光热疗过程中呈上升趋势,起始阶段上升较快,达到一定数值后趋于稳定,整体变化趋势与温度变化趋势比较吻合,核磁影像对比也证实了治疗效果。因此,通过近红外光谱技术监测激光热疗中病变组织约化散射系数的变化可有助于指导临床激光热疗。     

Optimal microwave source distributions for heating off-centertumors in spheres of high water content tissue

A surface distribution of electric dipoles can be used to represent a multielement microwave hyperthermia applicator for noninvasive heating of off-center targets within a spherical high-water-content tissue volume, such as the head. A method for finding the optimal surface distributions for delivering maximum power for arbitrarily located deep tumors in such a uniform spherical volume is presented. The resulting focused power dissipation pattern for any tumor location has a global maximum at the tumor, and also is the largest spherical volume for which no healthy tissue is overheated. The optimization uses spherical field harmonics, centered at the tumor target, summed with suitable complex weights to iteratively minimize surface power. Once the best field distributions are derived, the current sources which generate these distributions are determined. The resulting excitations represent the theoretically ideal spherical microwave hyperthermia configuration that no physical applicator system can surpass     

Numerical simulation of annular-phased arrays of dipoles forhyperthermia of deep-seated tumors

We have used the finite-difference time domain (FDTD) method to calculate the SAR distributions from an annular-phased array of eight dipole antennas coupled through water "boluses" in anatomically based three-dimensional models of the human body. We evaluated the effect of tapered bolus chambers, frequency (100-120 MHz), dipole length (17-30 cm), and phase and amplitude of power to the various dipoles on the ability to focus energy in the region of deep-seated tumors in the prostate and the liver. Assuming tumor conductivity and permittivity to be similar or slightly higher than surrounding normal tissues, calculations indicate that adjustment of the noted parameters should result in considerable improvement in focusing of SAR distributions in tumor-bearing regions. If such calculations can be shown to correctly predict empirical measurements from complex inhomogeneous (although not necessarily anatomically correct) phantoms, they may be useful for hyperthermia treatment planning based on patient-specific anatomic models.     

Optimization of the deposited power distribution inside a layeredlossy medium irradiated by a coupled system of concentrically placedwaveguide applicators

A method is proposed for controlling the deposited power distribution in a layered cylindrical lossy model, irradiated by a phased-array hyperthermia system consisting of four waveguide applicators. A rigorous electromagnetic model of the heated tissue, which takes into account coupling phenomena between system elements, is used for predicting the electric field at any point inside tissue. The relative amplitudes and relative phases of the array elements are optimized in order to attain desired specific absorption rate (SAR) distributions inside and outside malignant tissues. A constrained nonlinear optimization problem is solved by using the penalty function method and the resulting unconstrained minimization of the penalty function is carried out by the downhill simplex method. Two practical phased-array hyperthermia systems have been studied and numerical results are presented     

Cancer therapy with localized hyperthermia using an invasive microwave system.

A system has been developed for producing local hyperthermia in small animal tumors by means of an invasive needle microwave antenna. Thermal distributions produced by this system using 1 GHz microwaves have been characterized in mammary adenocarcinomas (MTG-B) implanted in thighs of C3H mice. Therapeutic efficacy by hyperthermia was demonstrated by comparing MTG-B diameters in mice following control, sham or hyperthermia treatment. It is proposed that this system could be employed clinically to provide very local hyperthermia in deep-seated tumors.     

A Review of Magnetic Induction Methods for Hyperthermia Treatment of Cancer

Magnetic induction methods of producing power absorption in tissue are used for achieving tumor hyperthermia in experimental cancer therapy. Electromagnetic field distributions and associated tissue energy absorption rates (SAR) of concentric, pancake, and coaxially paired current coils are discussed. Application of the bioheat transfer equation using these SAR distributions yields predictions of normal tissue and intratumoral temperature elevations. The corroboration of these predictions by phantom, animal, and human studies confirms the importance of bioheat transfer modeling in evaluation of these hyperthermia methods. Tumor sizes, depths, and locations likely to be therapeutically heated by magnetic induction techniques are reviewed, based upon available evidence.     

Theoretical analysis of H-Horn annular phased array system for heating deep-seated tumors

This paper discusses a type of annular phased array system--H-Horn APA. The phase and amplitude control of power deposition patterns for this system are theoretically analyzed at a frequency of 200 MHz. The formulas for calculating E-field and SAR for this APA system are derived, and can be applied to other type APA systems. Models of computerized tomography (CT) scans from liver and lung regions have been used, respectively, for predicting optimization of E-field and SAR patterns in the case of the relative phase and amplitude changes. It is shown that the techniques of the phase and amplitude control of SAR patterns result in more selectively and effectively heating of tumors situated eccentrically and deeply within bodies of patients. The APA hyperthermia described in this paper shows great promise, and it looks very useful for developing clinical applications.     

Experimental investigation of an adaptive feedback algorithm forhot spot reduction in radio-frequency phased-array hyperthermia

A computer-controlled adaptive phased array radiofrequency hyperthermia system for improved therapeutic tumor heating is experimentally investigated. Adaptive array feedback techniques are used to modify the electric-field in hyperthermia experiments with a homogeneous saline phantom target. A hyperthermia phased-array antenna system has been modified to implement adaptive nulling and adaptive focusing algorithms. The hyperthermia system is a ring phased-array antenna applicator with four independently controlled RF transmitter channels operating at a CW frequency of 100 MHz. The hyperthermia phased array is made adaptive by software modifications which invoke a gradient-search feedback algorithm that controls the amplitude and phase of each transmitter channel. The gradient-search algorithm implements the method of steepest descent for adaptive nulling (power minimization) and the method of steepest ascent for adaptive focusing (power maximization). The feedback signals are measured by electric-field short-dipole probe antennas. The measured data indicate that with an adaptive hyperthermia array it may be possible to maximize the applied electric field at a tumor position in a complex scattering target body and simultaneously minimize or reduce the electric field at target positions where undesired high-temperature regions (hot spots) occur     

A Model for Impedance Determinations and Power Deposition Characterization in Three-Electrode Configurations for Capacitive Radio Frequency Hyperthermia?Part B: Current Flow and Power Deposition

The 2-D rectangular model for three-electrode radio frequency hyperthermia applicators established in Part A is applied to the determination of the current lines and the potential lines inside the system. Any electrode voltage distributions can be considered. Two figures illustrate the impact of the electric and the geometric parameters on these lines. They show that important changes in local current density, in electric field strength, and in electric field orientation are tied to the adjustments of the relevant parameters. Two successive sampling processes lead to the determination of the local power deposition. The figures which are displayed demonstrate the ability to move this deposition inside any useful area by means of proper trimming of the electrode voltage phases and magnitudes.     

An invasive microwave antenna for locally-induced hyperthermia for cancer therapy.

A microwave system has been developed and characterized for delivering heat directly into tumors. This system employs a microwave power source (3-10W) operating in the 500 MHz to 1.3 GHz frequency range, coaxial transmission line, and a monopole antenna. Absorbed power was measured in saline, in tissue equivalent phantoms, and in tumors in live and dead mice. Antennas were designed to operate at 500 MHz and 1 GHz, and the critical design parameters have been identified for this system. Analytical and experimental results obtained in our laboratory suggest that this system is capable of providing controlled temperature distributions appropriate for hyperthermia in animal tumors. Theoretical results predict that 3 GHz may be an optimum choice for this system in animal tumors of approximately 1 cm diameter; the microwave antenna system provides a heat distribution superior to that obtained using a resistance heater of similar dimensions. We propose that further development of this approach may overcome some of the problems associated with other systems which use external radiation sources, and implications for clinical application of this system are discussed.