Meaney P M, Paulsen K D, Chang J T, Fanning M W, Hartov A
Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA.
IEEE Trans Med Imaging. 1999 Jun;18(6):508-18. doi: 10.1109/42.781016.
Model-based imaging techniques utilizing microwave signal illumination rely heavily on the ability to accurately represent the wave propagation with a suitable numerical model. To date, the highest quality images from our prototype system have been achieved utilizing a single transmitter/single receiver measurement system where both antennas are manually repositioned to facilitate multiple illuminations of the imaging region, thus requiring long data acquisition times. In an effort to develop a system that can acquire data in a real time manner, a 32-channel network has been fabricated with all ports capable of being electronically selected for either transmit or receive mode. The presence of a complete array of antenna elements at data collection time perturbs the field distributions being measured, which can subsequently degrade the image reconstruction due to increased data-model mismatch. Incorporating the nonactive antenna-compensation model from Part I of this paper into our hybrid element near field image reconstruction algorithm is shown to restore image quality when fixed antenna-array data acquisition is used. Improvements are most dramatic for inclusions located in near proximity to the antenna array itself, although cases of improvement in the recovery of centered heterogeneities are also illustrated. Increases in the frequency of illumination are found to warrant an increased need for nonactive antenna compensation. Quantitative measures of recovered inclusion shape and position reveal a systematic improvement in image reconstruction quality when the nonactive antenna-compensation model is employed. Improvements in electrical property value recovery of localized heterogeneities are also observed. Image reconstructions in freshly excised breast tissue illustrate the applicability of the approach when used with our two-dimensional microwave imaging system.
利用微波信号照射的基于模型的成像技术在很大程度上依赖于用合适的数值模型准确表示波传播的能力。迄今为止，我们原型系统获得的最高质量图像是利用单发射机/单接收机测量系统实现的，其中两个天线都需手动重新定位，以便对成像区域进行多次照射，因此需要较长的数据采集时间。为了开发一种能够实时采集数据的系统，已制作了一个32通道网络，其所有端口都能够通过电子方式选择用于发射或接收模式。在数据采集时存在完整的天线元件阵列会干扰所测量的场分布，这随后可能由于数据与模型的失配增加而使图像重建质量下降。当使用固定天线阵列数据采集时，将本文第一部分中的非有源天线补偿模型纳入我们的混合元件近场图像重建算法中，可恢复图像质量。对于位于靠近天线阵列本身的内含物，改进最为显著，不过也展示了在恢复中心不均匀性方面有所改进的情况。发现增加照射频率需要更多的非有源天线补偿。对恢复的内含物形状和位置的定量测量表明，采用非有源天线补偿模型时，图像重建质量有系统的提高。还观察到局部不均匀性的电特性值恢复有所改善。在新鲜切除的乳腺组织中的图像重建说明了该方法与我们的二维微波成像系统一起使用时的适用性。
