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Terahertz Imaging and Remote Sensing Design for Applications in Medical Imaging


THz region (1 mm - 0.1 mm, or 300 GHz and 3 THz) of the electromagnetic spectrum attracts applications in medical imaging, with its high dielectric constant of water, low non-ionizing photon energy (0.4-40 meV), and robustness against scattering from rough surface interface. This study investigates THz optical imaging system design and engineering, and explores implementation of THz imaging method for application in remote sensing of physiological tissue. Specifically, the focus of this manuscript is to explore two important topics in remote sensing design, with analysis of quasi-optical systems design and effect of rough surface scattering in THz wavelength.

An overview of THz imaging field and application to medical imaging are presented. A survey of current methods THz imaging and remote sensing scheme is made to provide context for system design consideration. As an example, the direct-detection THz imaging system is characterized, and used in experiments for the following sections.

In the second section, a detailed analysis of commonly used quasi-optical component (off-axis parabolic mirrors) is performed to investigate its focusing properties at THz wavelength. Additional attention is directed to polarization aberration effect in the propagation of coherent, linearly polarized THz beam through series of mirrors.

The third section applies Kirchhoff random rough surface scattering theory at THz region, and provides analysis of signal strength and variance in the signal-to-noise ratio (SNR) in imaging.

Lastly, a beam-scanning imaging system is constructed and demonstrated as an effort toward practical clinical application. The system employs a spinning polygon mirror and Michelson interferometer based design to allow source, detector, and target to remain fixed and perform imaging at a dramatically faster speed. The system achieves a focused THz beam diameter of 1.66mm and a large depth of field of >25 mm, and acquisition speed of minimum 100 pixels/s. Images of characterization targets and ex vivo tissue samples are presented.

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