Joines W T, Shrivastav S, Jirtle R L
Department of Electrical Engineering, Duke University, Durham, North Carolina 27706.
Med Phys. 1989 Nov-Dec;16(6):840-4. doi: 10.1118/1.596308.
This paper compares two methods for determining the radio frequency absorbed power in tissue: from the measured electrical properties of the tissue, and from the induced temperature rise per unit time. In previous research, we measured the ratio frequency electrical properties of muscle, mammary gland, and malignant mammary tissue (SMT-2A mammary adenocarcinoma) in female W/Fu isogeneic rats. From those measurements we calculated for each tissue the power absorption versus frequency, and formed the ratio of malignant-to-normal power absorption. This ratio exhibited a peak within the 150 to 400 MHz range, indicating a selective absorption of power in this type of malignant tissue over that of the normal host tissue. In the present study, by an entirely different method, we have directly tested the results of our earlier research. We filled a 20-cm-long section of rigid coaxial line (ordinarily air filled) with either normal (beef muscle or fat) or malignant (SMT-2A) tissue, and measured the temperature increase versus time at the irradiated tissue surface for the same absorbed power in each tissue type. We made the measurements from 50 to 915 MHz, and found that the initial temperature increase per second per watt absorbed (dT/dt/Pa) was greater in malignant tissue than in muscle or fat at each frequency tested, with the greatest differences occurring below 450 MHz. Power absorption based on the measured values of dT/dt/Pa was again greatest for the malignant tissue (SMT-2A mammary adenocarcinoma) within the 150 to 400 MHz range.
一种是根据测得的组织电学特性来确定，另一种是根据单位时间内的温度升高来确定。在先前的研究中，我们测量了雌性W/Fu同基因大鼠的肌肉、乳腺和恶性乳腺组织（SMT-2A乳腺腺癌）的射频电学特性。根据这些测量结果，我们计算了每种组织的功率吸收与频率的关系，并形成了恶性组织与正常组织功率吸收的比值。该比值在150至400MHz范围内出现一个峰值，表明这种类型的恶性组织比正常宿主组织对功率有选择性吸收。在本研究中，我们采用了一种完全不同的方法，直接对我们早期研究的结果进行了测试。我们用正常组织（牛肉肌肉或脂肪）或恶性组织（SMT-2A）填充一段20厘米长的刚性同轴线（通常为空气填充），并在每种组织类型中相同吸收功率的情况下，测量辐照组织表面的温度随时间的升高情况。我们在50至915MHz范围内进行了测量，发现在每个测试频率下，每吸收一瓦功率时恶性组织的初始每秒温度升高（dT/dt/Pa）都大于肌肉或脂肪，最大差异出现在450MHz以下。基于dT/dt/Pa测量值的功率吸收在150至400MHz范围内再次以恶性组织（SMT-2A乳腺腺癌）为最大。
