Abstract
This work presents experimental and analytical comparison of terahertz transmission and reflection imaging modes for assessing breast carcinoma in excised paraffin-embedded human breast tissue. Modeling for both transmission and reflection imaging is developed. The refractive index and absorption coefficient of the tissue samples are obtained. The reflection measurements taken at the system's fixed oblique angle of 30° are shown to be a hybridization of TE and TM modes. The models are validated with transmission spectroscopy at fixed points on fresh bovine muscle and fat tissues. Images based on the calculated absorption coefficient and index of refraction of bovine tissue are successfully compared with the terahertz magnitude and phase measured in the reflection mode. The validated techniques are extended to 20 and 30 μm slices of fixed human lobular carcinoma and infiltrating ductal carcinoma mounted on polystyrene microscope slides in order to investigate the terahertz differentiation of the carcinoma with non-cancerous tissue. Both transmission and reflection imaging show clear differentiation in carcinoma versus healthy tissue. However, when using the reflection mode, in the calculation of the thin tissue properties, the absorption is shown to be sensitive to small phase variations that arise due to deviations in slide and tissue thickness and non-ideal tissue adhesion. On the other hand, the results show that the transmission mode is much less sensitive to these phase variations. The results also demonstrate that reflection imaging provides higher resolution and more clear margins between cancerous and fibroglandular regions, cancerous and fatty regions, and fibroglandular and fatty tissue regions. In addition, more features consistent with high power pathology images are exhibited in the reflection mode images.
Highlights
Terahertz (THz) has been a greatly expanding field of research in recent years
The incident terahertz pulse is directed by parabolic mirrors to the sample space for either transmission imaging (Fig. 1(a)) or reflection imaging (Fig. 1(b))
The results demonstrated that THz imaging is capable of clearly differentiating the margins of both lobular carcinoma and infiltrating ductal carcinoma from surrounding fibroglandular and fatty tissue for the dehydrated tissues used in this work
Summary
Terahertz (THz) has been a greatly expanding field of research in recent years. While historically THz frequencies (0.1 to 4 THz) were difficult to access due to the gap between electronic and optical generation techniques, the advent of more reliable THz sources has opened up this range for a wide variety of potential applications [1]. Investigations using a THz transmission setup have shown the potential of applying spectroscopy across an imaging scan in order to perform regional solutions of the properties of the sample under test. This concept has been applied for assessment of crystal formations in pharmaceuticals [22] and in biomedical imaging for observing the degradation of bone tissue [23]. The outline of the paper is as follows: Section 2 will address the methodology including the THz system and sample preparation; Section 3 will detail the propagation modeling; Section 4 will validate the modeling with property measurements of fresh bovine tissue; Section 5 will extend the imaging and characterization to excised human breast carcinomas; and Section 6 will address challenges and future work
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