Limitations and significance of thermal washout data obtained during microwave and ultrasound hyperthermia.
Limitations and significance of thermal washout data obtained during microwave and ultrasound hyperthermia.
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DOI：
10.3109/02656739009140824
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
W. Newman;P. P. Lele-P.;H. F. Bowman
中科院分区：
文献类型：
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作者：
W. Newman;P. P. Lele-P.;H. F. Bowman
在临床热疗中，通过忽略组织热传导和将热冲洗数据拟合到简单的、以灌注为主的指数模型来计算“有效血流量”是很常见的。我们已经应用这种方法来表征在哈佛-麻省理工学院热疗中心治疗的患者的散热机制，通过分析在治疗过程中通过暂时中断加热获得的热冲洗曲线。不幸的是，这些对病人治疗过程中“有效血流量”的测量结果并不一致。这些不一致源于临床情况固有的不确定性：实际热边界条件和加热场的时空特征。为了量化这些观察结果，导出了组织生物热方程的格林函数解，使各种加热几何形状产生的温度场易于计算。该方法已应用于超声和微波热疗装置局部能量沉积后的温度衰减曲线分析。这些结果表明，热冲洗数据既依赖于组织特性和灌注，也依赖于患者和会话特定参数。对于超声加热后有效血流量的测量，误差取决于在被加热体积内的测量位置，加热几何形状和在衰变之前加热的持续时间；对于微波加热，结果取决于测量点在加热场内的位置、加热频率和表面边界条件，是加热、冷却还是绝缘。因此，如果没有正确模拟加热几何形状、边界条件和初始条件，任何有效组织特性的计算都将是定性的，而不是定量的，并且可能导致有关组织和肿瘤反应的错误和误导性结论。
It is common in clinical hyperthermia to calculate an 'effective blood flow' by neglecting tissue thermal conduction and fitting thermal washout data to a simple, perfusion-dominated exponential model. We have applied this approach to characterize thermal dissipative mechanisms in patients treated at the Harvard-MIT Hyperthermia Center, by analysing thermal washout curves which were obtained during treatment sessions by momentarily interrupting the applied heating. Unfortunately, these measurements of 'effective blood flow' in patient sessions have given inconsistent results. These inconsistencies arise from uncertainties inherent in the clinical situation: the actual thermal boundary conditions and the spatiotemporal characteristics of the heating field. To quantify these observations a Green's function solution to the tissue bioheat equation has been derived, to enable temperature fields produced by various heating geometries to be easily calculated. This has been applied to the analysis of temperature decay curves following local energy deposition representative of ultrasound and microwave hyperthermia therapy devices. These results show that thermal washout data are as dependent on patient- and session-specific parameters as on tissue properties and perfusion. For measurements of effective blood flow following ultrasonic heating, errors are dependent on the measurement position within the heated volume, heating geometry, and duration of heating prior to the decay; for microwave heating, results are dependent on the position of the measurement point within the heated field, the heating frequency, and the surface boundary conditions, whether heated, cooled, or insulated. Thus, any effective tissue property calculated without correctly modelling the heating geometry, boundary conditions and initial conditions will be of a qualitative rather than quantitative nature, and may lead to erroneous and misleading conclusions concerning tissue and tumour response.