Dry microwave imaging (MWI) systems are more practical, hygienic, and fast to operate since they do not require immersion liquid. However, the dielectric contrast between air and the part of the body under examination is larger, causing larger refraction effects. Including refraction in the image reconstruction algorithm significantly increases the computational effort, especially when imaging nonuniform shapes. Hence, our systematic study aims to evaluate the impact of neglecting refraction effects on MWI by using quantitative metrics and define objective guidelines that are lacking in the literature. We perform comparative studies with a spherical numerical phantom (which is typically used to represent simplified breast or head phantoms) by varying the phantom relative permittivity values between 4 and 40, metallic targets diameter between 5 and 15 mm, and the number of probing antennas. Additionally, the refraction effects are evaluated with anthropomorphic body phantoms representing a breast and the axillary region. We numerically and experimentally show that refraction tends to have a greater impact on imaging results when phantom relative permittivity values exceed 8, while it has a minor effect in the remaining tested cases. This favors potential fast real-time image reconstruction. This letter provides useful criteria to decide whether refraction should be considered or not for imaging reconstruction when developing new dry medical MWI setups.

中文翻译：

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在干式医用微波成像装置中评估折射效应

干式微波成像（MWI）系统不需要浸没液体，因此更加实用，卫生且可快速操作。但是，空气与被检查的身体部位之间的介电对比度较大，从而导致较大的折射效果。在图像重建算法中包括折射会大大增加计算量，尤其是在对不均匀形状进行成像时。因此，我们的系统研究旨在通过使用定量指标来评估忽略折射效应对MWI的影响，并定义文献中缺乏的客观指南。我们通过在4到40之间改变模型的相对介电常数值，对球形数字模型（通常用于表示简化的乳房或头部模型）进行比较研究，直径在5到15毫米之间的金属靶以及探测天线的数量。另外，用代表乳房和腋窝区域的拟人化体模来评估折射效果。我们通过数值和实验表明，当幻象相对介电常数值超过8时，折射往往会对成像结果产生更大的影响，而在其余测试案例中，折射的影响较小。这有利于潜在的快速实时图像重建。这封信提供了有用的标准，以决定在开发新的干式医疗MWI装置时是否应考虑折射以进行成像重建。我们通过数值和实验表明，当幻象相对介电常数值超过8时，折射往往会对成像结果产生更大的影响，而在其余测试案例中，折射的影响较小。这有利于潜在的快速实时图像重建。这封信提供了有用的标准，可用于在开发新的干式医疗MWI装置时决定是否应考虑屈光以进行成像重建。我们通过数值和实验表明，当幻象相对介电常数值超过8时，折射往往会对成像结果产生更大的影响，而在其余测试案例中，折射的影响较小。这有利于潜在的快速实时图像重建。这封信提供了有用的标准，可用于在开发新的干式医疗MWI装置时决定是否应考虑屈光以进行成像重建。