Applications of terahertz (THz) technology to medical imaging

Abstract

An imaging system has been developed based on pulses of Terahertz (THz) radiation generated and detected using all-optical effects accessed by irradiating semiconductors with ultrafast (fs-ps) pulses of visible laser light. This technique, commonly referred to as T-Ray Imaging or THz Pulse Imaging (TPI), holds enormous promise for certain aspects of medical imaging. We have conducted an initial survey of possible medical applications of TPI and demonstrated that TPI images show good contrast between different animal tissue types (muscle, fat, kidney, skin, cartilage). Moreover, the diagnostic power of TPI has been elucidated by the spectra available at each pixel in the image, which are markedly different for the different tissue types. This suggests that the spectral information inherent in TPI might be used to identify the type of soft and hard tissue at each pixel in an image and provide other diagnostic information not afforded by conventional imaging techniques.Preliminary TPI studies ofpork skin show that 3D tomographic imaging ofthe skin surface and thickness is possible, and data from experiments on models of the human dermis are presented which demonstrate that different constituents of skin have different refractive indices. Lastly, we present the first THz image of human tissue, namely an extracted tooth. The time of flight of THz pulses through the tooth allows the thickness of the enamel to be determined, and is used to create an image showing the enamel and dentine regions. Absorption of THz pulses in the tooth allows the pulp cavity region to be identified. Initial evidence strongly suggests that TPI may be used to provide valuable diagnostic information pertaining to the enamel, dentine, and the pulp cavity.

Accuracy and resolution of THz reflection spectroscopy for medical imaging

“…The first demonstration of biomedical THz imaging (Hu and Nuss 1995) concluded that a distinction could be made between porcine muscle and fat with the hypothesis that the difference in water content of the two materials was responsible for the contrast. Water is one of the main constituents of biological tissue: penetration depths range from typically a few hundred microns in high water content tissues to approximately a centimetre in tissues with a high fat content (Arnone et al 1999, Fitzgerald et al 2005. Since this first demonstration, the number of reported biomedical studies using THz imaging has increased greatly to include teeth and artificial skin models (Arnone et al 1999), healthy skin and basal cell carcinoma both in vitro and in vivo (Woodward et al 2002, excised breast tumours , cortical bone (Stringer et al 2005) and burns (Taylor et al 2008).…”

“…Water is one of the main constituents of biological tissue: penetration depths range from typically a few hundred microns in high water content tissues to approximately a centimetre in tissues with a high fat content (Arnone et al 1999, Fitzgerald et al 2005. Since this first demonstration, the number of reported biomedical studies using THz imaging has increased greatly to include teeth and artificial skin models (Arnone et al 1999), healthy skin and basal cell carcinoma both in vitro and in vivo (Woodward et al 2002, excised breast tumours , cortical bone (Stringer et al 2005) and burns (Taylor et al 2008). Spectroscopic studies in the THz frequency range of excised tissues have shown statistically significant differences between tumours, normal and adipose tissues .…”

Terahertz-Wave Spectroscopy for Precise Histopathological Imaging of Tumor and Non-tumor Lesions in Paraffin Sections

“…Use in imaging for histopathological diagnosis has been reported since the latter half of the 1990s. Contrast images associated with different degrees of absorption or reflection of THz waves have been obtained for normal tissues, such as muscles, fatty tissue and cartilage, as well as for cancer tissue (Arnone et al 1999;Knobloch et al 2002;Woodward et al 2002aWoodward et al , 2002bWoodward et al , 2003Wallace et al 2004a;Nishizawa et al 2005;Fitzgerald et al 2006;Nakajima et al 2007).…”

“…© 2011 Tohoku University Medical Press Terahertz (THz; 10 12 Hz) waves are located roughly between the visible light and microwave domains and have a frequency of around 10 12 Hz. THz wavelength ranges from 3 mm to 30 μm (Arnone et al 1999;Ferguson and Zhang 2002;Nishizawa 2005) (Fig. 1).…”

Time-Frequency Analysis in Terahertz-Pulsed Imaging

“…The perceived advantages of using the terahertz band for biomedical applications include its sensitivity to the presence of water which may be of use for detecting or characterizing disease state, the lack of a hazard from ionization, relatively less Rayleigh scattering than for infrared and visible radiation, and the possibility of characteristic "signatures" from different tissues in health and in disease [Arnone et al 1999, Mittleman et al 1999, Smye et al 2001. These characteristic signals may result from water content (section 1.2.1.1) or other chemical features related to the composition or functional properties of the tissues.…”