Experimental and Model-based Terahertz Imaging and Spectroscopy for Mice, Human, and Phantom Breast Cancer Tissue

The goal of this work is to investigate terahertz technology for assessing the surgical margins of breast tumors through electromagnetic modeling and terahertz experiments. The measurements were conducted using a pulsed terahertz system that provides time and frequency domain signals. Three types of breast tissues were investigated in this work. The first was formalin-fixed, paraffin-embedded tissues from human infiltrating ductal and lobular carcinomas. The second was human tumors excised within 24-hours of lumpectomy or mastectomy surgeries. The third was xenograft and transgenic mice breast cancer tumors grown in a controlled laboratory environment to achieve more data for statistical analysis.;Experimental pulsed terahertz imaging first used thin sections (10-30 mum thick) of fixed breast cancer tissue on slides. Electromagnetic inverse scattering models, in transmission and reflection modes, were developed to retrieve the tissue refractive index and absorption coefficient. Terahertz spectroscopy was utilized to experimentally collect data from breast tissues for these models. The results demonstrated that transmission mode is suitable for lossless materials while the reflection model is more suitable for biological materials where the skin depth of terahertz waves does not exceed 100 microm. The reflection model was implemented to estimate the polarization of the incident terahertz signal of the system, which was shown to be a hybridization of TE and TM modes.;Terahertz imaging of three-dimensional human breast cancer blocks of tissue embedded in paraffin was achieved through the reflection model. The terahertz beam can be focused at depths inside the block to produce images in the x-y planes (z-scan). The time-of-flight analysis was applied to terahertz signals reflected at each depth demonstrating the margins of cancerous regions inside the block as validated with pathology images at each depth. In addition, phantom tissues that mimic freshly excised infiltrating ductal carcinoma human tumors were developed with and without embedded carbon nanometer-scale onion-like carbon particles. These particles exhibited a strong terahertz signal interaction with tissue demonstrating a potential to greatly improve the image contrast.;The results presented in this work showed, in most cases, a significant differentiation in terahertz images between cancer and healthy tissue as validated with histopathology images.