Over the last decade advances in laser and semiconductor technology has allowed the investigation of terahertz region of the electromagnetic spectrum as a potential tool for medical imaging. The terahertz frequency range covers the far infrared wavelengths and is sensitive to librational and vibrational modes of molecules. Terahertz radiation is non-ionizing and is not highly scattered like visible and near infrared light. Terahertz Pulsed Imaging (TPI) has already been demonstrated as an effective tool for differentiating between tissue types in particular normal skin and basal cell carcinoma in vitro. TPI may prove advantageous in distinguishing type, lateral spread and depth of tumors. Here we present recent ex vivo results obtained with a portable TPI system in a clinical setting. It is hoped that this technique could be applied to other epithelial tissues, which give rise to more than 80% of all adult cancers and include common cancers of the skin, oral cavity, breast, colon and prostate.
There is strong interest in the development of sources that emit radiation in the far infrared (1-10 THz) frequency range for applications which include early detection of skin cancer, dental imaging, telecommunications, security scanning, gas sensing, astronomy, molecular spectroscopy, and the possible detection of biological weapons. While a number of THz sources are available, there are at present no compact, efficient, cheap and practical high-power solid-state sources such as light emitting diodes or lasers. Silicon is an excellent candidate for such a THz source since the lack of polar optical phonon scattering makes it an inherently low loss material at these frequencies. Furthermore, since over 97% of all microelectronics is presently silicon based, the realisation of a silicon based emitter/laser could potentially allow integration with conventional silicon-based microelectronics. In this paper THz electroluminescence from a Si/SiGe quantum cascade structure operating significantly above liquid helium temperatures is demonstrated. Fourier transform infrared spectroscopy was performed using step scan spectrometer with a liquid helium cooled Si-bolometer for detection. Spectra are presented demonstrating intersubband electroluminescence at a number of different frequencies. These spectral features agree very well with the theoretically calculated intersubband transitions predicted for the structure.
We demonstrate the application of Terahertz Pulse Imaging (TPI) in reflection geometry for the study of skin tissue and related cancers. The terahertz frequency regime of 0.1-100THz excites the vibrational modes of molecules, allowing for spectroscopic investigation. The sensitivity of terahertz to polar molecules, such as water, makes TPI suitable for studying the hydration levels in the stratum corneum and the determination of the lateral spread of skin cancer pre-operatively. By studying the terahertz pulse shape in the time domain we have been able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC). Measurements on scar tissue, which is known to contain less water than the surrounding skin, and on regions of inflammation, show a clear contrast in the THz image compared to normal skin. We discuss the time domain analysis techniques used to classify the different tissue types. Basal cell carcinoma shows a positive terahertz contrast, and inflammation and scar tissue shows a negative terahertz contrast compared to normal tissue. This demonstrates for the first time the potential of TPI both in the study of skin cancer and inflammatory related disorders.
TeraHertz Pulse Imaging (TPI) is a relatively new imaging modality for medical and dental imaging. The aim of the present study was to make a preliminary assessment of the potential uses of TPI in clinical dentistry, particularly in relation to caries detection and the detection and monitoring of erosion. Images were obtained in vitro using a new TPI system developed by TeraView Ltd. We present data showing that TPI in vitro images of approximal surfaces of whole teeth demonstrate a distinctive shadowing in the presence of natural carious lesions in enamel. The thickness of this enamel shadowing appears to be related to lesion depth. The use of non-ionizing radiation to image such lesions non-destructively in vitro represents a significant step towards such measurements in vivo. In addition, data is presented which indicates that TPI may have a potential role in the detection and monitoring of enamel erosion. In vitro experiments on whole incisor teeth show that TPI is capable of detecting relatively small artificially induced changes in the buccal or palatal surface of the enamel of these teeth. Imaging of enamel thickness at such a resolution without ionizing radiation would represent a significant breakthrough if applicable in vivo.
Generating images of layered tissue structures can give valuable information to clinicians. However, the provision of accurate imaging of certain tissue structures, like teeth, in 3-dimensions is still a difficult problem. We present a method that relies on the use of pulsed Terahertz radiation to gain 3-dimensional information from teeth samples. The method makes use of Terahertz Pulse Imaging (TPI) to provide depth information. Example images are shown where structures in teeth at depth are rendered. We discuss issues that arise using this imaging method and propose ways in which it could be used in clinical practice.
Terahertz (far-infrared) intersubband electroluminescence is reported in p-type Si/SiGe quantum wells and quantum cascade structures. Surface-normal emission (without the aid of a surface grating) from light hole - heavy hole intersubband transitions has been observed for the first time in a quantum cascade device. Edge-emission measurements have also been performed, which show emission from both heavy hole - heavy hole and light hole - heavy hole transitions, and have allowed demonstration of the polarisation dependence of the emitted power, according to the selection rules for the intersubband interactions. The electroluminescence is visible up to temperatures of ~150K, in the multiple quantum well structures, and >=77K in the quantum cascade structure.
We demonstrate the application of terahertz pulse imaging for the in-vivo study of human tissue, in this case the upper layers of human skin. The terahertz pulses comprise frequencies from below 100 GHz to over 2 THz and are generated using optical pulse excited semiconductor devices with a conversion efficiency of better than 10-3. The terahertz pulses are used to obtain tomographic information on the skin surface tissue. From the data the stratum corneum thickness and hydration may be mapped or cross-sectional images displayed.
We present Terahertz Pulse Imaging (TPI) results of different human tissue types. Our results are part of an initial study to explore the potential of TPI for biomedical applications. A survey of different tissue types has demonstrated the various contrast mechanisms that are available in TPI, allowing different tissue types to be readily identified. This encourages the pursuit of further studies of TPI for a variety of biomedical applications.
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 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. Moreover, the diagnostic power of TPI has been elicidated 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 imagin techniques. Preliminary TPI studies of pork skin show that 3D tomographic imaging of the 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 my be used to provide valuable diagnostic information pertaining to the enamel, dentine, and the pump cavity.