Department of Biomedical Engineering, Faculty of Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel.
Med Phys. 2010 Jan;37(1):211-6. doi: 10.1118/1.3253992.
This article deals with the development of a minimal-invasive, infrared (IR) (8-12 microm spectral range) imaging technique that would improve upon current methods by using superparamagnetic nanostructured core/shell particles for imaging as well as for therapy. This technique may function as a diagnostic tool, thanks to the ability of specific bioconjugation of these nanoparticles to a tumor's outer surface. Hence, by applying an alternating magnetic field, the authors could cause a selective elevation of temperature of the nanoparticles for +1 - +5 degrees C, enabling tumor's imaging. Further elevation of the temperature over +10 degrees C will cause a necrotic effect, leading to localized irreversible damage to the cancerous site without harming the surrounding tissues. This technique may also serve as a targeted therapeutic tool under thermal feedback control.
Under alternative magnetic field, these biocompatible nanoparticles can generate heat, which propagates along the tissue (by thermal conduction), reaching the tissue's surface. Surface temperature distribution can be acquired by an IR camera and analyzed to retrieve nanoparticles' temperature and location within the tissue. An analytical-based steady-state solution for the thermal inverse problem was developed, considering an embedded point heat source. Based on this solution, the authors developed an algorithm that generates solutions for the corresponding forward problem, and based on discovered relations between the problem's characteristic, can derive the depth and temperature of the embedded heat source from the surface temperature profile, derived from the thermal image.
The algorithm was able to compute the heat source depth and power (proportional to its temperature) in two phases. Assuming that the surface temperature profile can be fitted to a Lorentzian curve, the first phase computing the source depth was based on a linear relation between the depth and the FWHM value of the surface temperature profile, which is independent of the source power. This relation varies between different tissues and surface conditions. The second phase computing the power (Q) was based on an exponential relation between the area (A) curve of the surface temperature profile and power (Q), dependent on the depth computed in the first phase. The simulation results show that given the tissue thermal properties, the surface conductance, and the ambient conditions, an inverse solution can be applied retrieving the depth and temperature of a point heat source from a 2D thermal image.
The predicted depth and heat source power were compared to the actual parameters (which were derived). Differences between the real and estimated values may occur primarily in computing the forward solution, which was used for the estimation itself. The fact that the computation is carried out discretely and the spatial resolution in the radial direction are influencing factors. To improve and eliminate these factors, the resolution may be increased or suitable interpolation and/or smoothing may be applied. Applying this algorithm on a spherical heat source volume may be feasible. A solution for the forward problem was established, yet incorporation of the source radius has to be further examined.
本文介绍了一种微创的红外（IR）（8-12 微米光谱范围）成像技术的发展，该技术将通过使用超顺磁纳米结构核/壳粒子进行成像和治疗来改进当前的方法。由于这些纳米粒子能够与肿瘤外表面进行特异性生物结合，因此该技术可以作为一种诊断工具。因此，通过施加交变磁场，作者可以使纳米粒子的温度选择性升高+1-+5°C，从而实现肿瘤成像。温度进一步升高到+10°C以上将导致坏死效应，导致癌灶的局部不可逆损伤，而不会伤害周围组织。该技术还可以作为热反馈控制下的靶向治疗工具。
在交变磁场下，这些生物相容性纳米粒子可以产生热量，这些热量沿组织传播（通过热传导），到达组织表面。可以通过红外摄像机获取表面温度分布，并进行分析以获取纳米粒子在组织内的温度和位置。针对嵌入式点热源，开发了一种用于热反问题的基于解析的稳态解。基于该解，作者开发了一种算法，该算法可以为相应的正问题生成解，并根据问题特征之间的关系，从热图像中推导出表面温度分布中嵌入热源的深度和温度。
该算法能够分两个阶段计算热源的深度和功率（与温度成正比）。假设表面温度分布可以拟合为洛伦兹曲线，则第一阶段计算源深度的算法基于深度与表面温度分布的半峰全宽值之间的线性关系，该关系与源功率无关。这种关系在不同的组织和表面条件之间变化。第二阶段计算功率（Q）的算法基于表面温度分布的面积（A）曲线与功率（Q）之间的指数关系，该关系取决于第一阶段计算的深度。模拟结果表明，给定组织的热特性、表面电导率和环境条件，逆解可以从二维热图像中提取点热源的深度和温度。
将预测的深度和热源功率与实际参数（推导得出的参数）进行比较。实际值和估计值之间的差异可能主要出现在正向解的计算中，而正向解又用于估计本身。离散计算和径向方向的空间分辨率是影响因素。为了改进和消除这些因素，可以提高分辨率或应用适当的插值和/或平滑。应用该算法于球形热源体积可能是可行的。已经建立了正向问题的解，但需要进一步研究源半径的纳入。
