Moros E G, Pickard W F
Radiation Oncology Section, Mallinckrodt Institute of Radiology, Washington University, 4511 Forest Park Boulevard, Saint Louis, Missouri 63108, USA.
Radiat Res. 1999 Sep;152(3):312-20.
The problem of measuring a spatially varying specific absorption rate (SAR) by thermal techniques is treated both analytically and numerically. It is shown that, unless the measurement is attempted at an inflection point of the SAR distribution, it will be confounded by thermal diffusion within the medium. Rules of thumb are provided to enable the experimenter to gauge the thermal conduction contributions (i.e. error) to the thermally determined SAR near a spatial extremum. The simplest of these is that the width t(m) [s] of the time window, over which temperature variation associated with SAR is measured, should satisfy the inequality t(m) </approximately alpha(2)/pi(2)D, where alpha [m] is a characteristic length scale of the spatial variation of the SAR and D [m(2)/s] is the thermal diffusivity of the medium. The above considerations are valid, independent of the source of the deposited energy.
通过热技术测量空间变化的比吸收率（SAR）的问题，从解析和数值两方面进行了探讨。结果表明，除非在SAR分布的拐点处进行测量，否则测量结果会受到介质内热扩散的干扰。文中给出了一些经验法则，以便实验者能够评估在空间极值附近热传导对通过热测量确定的SAR的贡献（即误差）。其中最简单的一条是，测量与SAR相关的温度变化的时间窗口宽度t(m) [秒]应满足不等式t(m) </大约α(2)/π(2)D，其中α [米]是SAR空间变化的特征长度尺度，D [平方米/秒]是介质的热扩散率。上述考虑是有效的，与沉积能量的来源无关。
