Department of Engineering Design, Indian Institute of Technology Madras, Chennai, India.
Phys Med Biol. 2010 Sep 21;55(18):5417-35. doi: 10.1088/0031-9155/55/18/010. Epub 2010 Aug 25.
We present the modeling efforts on antenna design, frequency selection and receiver sensitivity estimation to detect vesicoureteral reflux (VUR) using microwave (MW) radiometry as warm urine from the bladder maintained at fever range temperature using a MW hyperthermia device reflows into the kidneys. The radiometer center frequency (f(c)), frequency band (Deltaf) and aperture radius (r(a)) of the physical antenna for kidney temperature monitoring are determined using a simplified universal antenna model with a circular aperture. Anatomical information extracted from the computed tomography (CT) images of children aged 4-6 years is used to construct a layered 3D tissue model. Radiometric antenna efficiency is evaluated in terms of the ratio of the power collected from the target at depth to the total power received by the antenna (eta). The power ratio of the theoretical antenna is used to design a microstrip log spiral antenna with directional radiation pattern over f(c) +/- Deltaf/2. Power received by the log spiral from the deep target is enhanced using a thin low-loss dielectric matching layer. A cylindrical metal cup is proposed to shield the antenna from electromagnetic interference (EMI). Transient thermal simulations are carried out to determine the minimum detectable change in the antenna brightness temperature (deltaT(B)) for 15-25 mL urine refluxes at 40-42 degrees C located 35 mm from the skin surface. Theoretical antenna simulations indicate maximum eta over 1.1-1.6 GHz for r(a) = 30-40 mm. Simulations of the 35 mm radius tapered log spiral yielded a higher power ratio over f(c) +/- Deltaf/2 for the 35-40 mm deep targets in the presence of an optimal matching layer. Radiometric temperature calculations indicate deltaT(B) 0.1 K for the 15 mL urine at 40 degrees C and 35 mm depth. Higher eta and deltaT(B) were observed for the antenna and matching layer inside the metal cup. Reflection measurements of the log spiral in a saline phantom are in agreement with the simulation data. The numerical study suggests that a radiometer with f(c) = 1.35 GHz, Deltaf = 500 MHz and detector sensitivity better than 0.1 K would be the appropriate tool to noninvasively detect VUR using the log spiral antenna.
我们介绍了天线设计、频率选择和接收机灵敏度估计的建模工作，以使用微波（MW）辐射测量法检测膀胱输尿管反流（VUR），当使用 MW 热疗装置将膀胱中的温暖尿液保持在发热温度范围内时，尿液会回流到肾脏。用于监测肾脏温度的物理天线的辐射计中心频率（f(c)）、频带（Deltaf）和孔径半径（r(a)）是使用具有圆形孔径的简化通用天线模型确定的。从 4-6 岁儿童的计算机断层扫描（CT）图像中提取的解剖学信息用于构建分层 3D 组织模型。辐射计天线效率是通过从目标深处收集的功率与天线接收的总功率之比（eta）来评估的。理论天线的功率比用于设计具有在 f(c) +/- Deltaf/2 上具有定向辐射模式的微带对数螺旋天线。使用薄的低损耗介电匹配层来增强对数螺旋从深目标接收的功率。提出了一个圆柱形金属杯，以防止天线受到电磁干扰（EMI）的影响。进行瞬态热模拟以确定位于皮肤表面 35 毫米处的 40-42 摄氏度的 15-25 毫升尿液反流的天线亮度温度（deltaT(B)）的最小可检测变化。理论天线模拟表明，对于 r(a) = 30-40 毫米，eta 超过 1.1-1.6 GHz。对于具有最佳匹配层的 35-40 毫米深目标，35 毫米半径渐缩对数螺旋的模拟产生了在 f(c) +/- Deltaf/2 上更高的功率比。辐射计温度计算表明，在 40 摄氏度和 35 毫米深度下，15 毫升尿液的 deltaT(B)为 0.1 K。在金属杯内的天线和匹配层观察到更高的 eta 和 deltaT(B)。对数螺旋在盐溶液中的反射测量与模拟数据一致。数值研究表明，中心频率为 1.35 GHz、频带为 500 MHz、探测器灵敏度优于 0.1 K 的辐射计将是使用对数螺旋天线无创检测 VUR 的合适工具。
