Keywords:terahertz, breast cancer, near-field imaging
Terahertz (THz) imaging has been expected as a non-invasive/non-stainging visualization technique for breast cancer margins during surgeries. Breast cancer is a generic name for a heterogeneous lesion comprising invasive adenocarcinoma, in situ adenocarcinoma, most frequently in the form of ductal carcinoma in situ (DCIS) and benign tissues. Therefore, it is essential to identify the margins of the invasive carcinoma and DCIS for intraoperative breast cancer margin assessment. Until now, numerous THz imaging studies of invasive carcinoma have been conducted; however, THz imaging analysis of DCIS has hardly been performed. Because the size of an individual DCIS lesion (50-500 µm) is much smaller than that of an invasive carcinoma, it is difficult to detect these lesions by conventional THz imaging, which has only a diffraction-limited spatial resolution of several millimeters. To address this drawback, we have recently developed a scanning point terahertz source (SPoTS) microscope with a resolution of 20 µm, in which a sample is in contact with a two-dimensionally-scannable point THz source generated at a pump-laser-focusing-spot in a GaAs crystal. In this study, using this microscope, we carried out THz near-field transmission imaging of a paraffin-embedded human breast cancer sample containing invasive carcinoma and DCIS, as a preliminary study. Consequently, we succeeded in discriminating the regions of DCIS, invasive ductal carcinoma (IDC), and fibroadipose (benign) tissue on a micrometer scale, in good agreement with the corresponding hematoxylin-and-eosin (H&E)-stained image. It was also observed that the THz extinction by DCIS was higher than that by IDC. This result can be caused by the near-field interaction between the THz waves and the cellular density, indicating that SPoTS microscopy may open the door to THz intraoperative diagnosis to accurately assess DCIS margins.