The terahertz (1 THz = 1012 Hz, 3 mm or 33 cm-1) region of the electromagnetic spectrum is typically defined in the frequency range 100 GHz to 10 THz, corresponding to a wavelength range of 3 mm to 30 microns. Following the development of coherent sources and detectors in the early eighties, there has been growing interest in the role of terahertz technology in global homeland security. The terahertz region offers a huge expanse of unused bandwidth. The ability of terahertz radiation to probe intermolecular interactions, large amplitude vibrations and rotational modes, in addition to showing polarization sensitivity makes terahertz radiation a unique and diverse region of the electromagnetic spectrum. Terahertz radiation is also able to 'see through' common materials, such as clothing, thick smoke and dust, which are often considered as opaque in other regions of the electromagnetic spectrum. This paper reviews the role of terahertz technology in homeland security and associated limitations of this field.
The terahertz region of the electromagnetic spectrum is typically defined in the frequency range 100 GHz to 10 THz, corresponding to a wavelength range of 3 mm to 30 microns. The millimetre wave region lies between 30 GHz and 300 GHz, corresponding to a wavelength range of 10 cm to 1 mm and overlaps a portion of the terahertz region. Following the development of coherent sources and detectors in the early eighties, there has been growing interest in the role of terahertz technology for security and defence. The terahertz region offers a huge expanse of unused bandwidth, which currently presents a significant advantage for both security and defense initiatives. The ability of terahertz radiation to probe intermolecular interactions, large amplitude vibrations and rotational modes, in addition to showing polarization sensitivity makes terahertz radiation a unique and diverse region of the electromagnetic spectrum. The additional ability of both terahertz and millimeter wave radiation to 'see through' common materials, such as thick smoke, fog and dust, which are often considered as opaque in other regions of the electromagnetic spectrum offers further advantages over other optical techniques. Due to the heavy attenuation of terahertz radiation by water vapour, millimeter wave technology is more suited for long range, all-weather imaging systems, whereas terahertz technology has more potential for high resolution short range imaging and spectroscopy. The potential of terahertz and millimetre wave technology and their associated potential for port and harbour security initiatives are discussed.
Terahertz pulsed imaging is a non-invasive, non-ionizing imaging technique, using electromagnetic radiation defined in the frequency range 0.1 THz to 10 THz. Using reflection imaging systems with a frequency range 0.1 THz to 4 THz a far field diffraction limited lateral resolution of 3 mm to 110 microns is attainable. A three layer analytical model has been developed to simulate the hydration properties of skin in reflection. Earlier in vivo hydration measurements of the volar forearm and palm of the hand (thenar) are compared to this model. The time-domain analysis technique “time post pulse” (TPP) used to differentiate between diseased and normal tissue in a study of basal cell carcinoma was applied to the data. An increase in the value of TPP is observed with occlusion in the viable epidermis. This is attributed to an increase in the flux of water across the epidermis or dermis with increased stratum corneum hydration. This is verified by the literature. The change is observed in less than six minutes occlusion, making terahertz technology one of the most sensitive techniques for monitoring skin hydration levels. The contrast observed at the stratum corneum-viable epidermis interface is similar to that seen between diseased and normal tissue. Although water provides a good marker for studying diseased tissue, comparing results from DNA and protein analysis, it is not yet possible to conclude whether the contrast observed in basal cell carcinoma is due to increased water within the diseased tissue, a change in the vibrational modes of water with other functional groups, or a change in the vibrational modes of the functional groups alone. Further studies are required to determine whether terahertz technology is capable of differentiating between different histological subtypes in a collective system such as skin at a macroscopic level. The three layer analytical model provides a useful adjunct for identifying the source of contrast observed in the top surface of skin.
The terahertz (1 THz = 1012 Hz, 3 mm or 33 cm-1) region of the electromagnetic spectrum is typically defined in the frequency range 100 GHz to 10 THz, corresponding to a wavelength range of 3 mm to 30 microns. Owing to a lack of suitable coherent sources and detectors, this region has only been investigated in earnest in the last ten years for terrestrial imaging and spectroscopy applications. Its role in the medical, pharmaceutical, non-destructive testing and more recently security industries is now being examined. The terahertz frequency range is of particular interest since it is able to probe several molecular interactions including the intermolecular vibrations, large amplitude vibrations and twisting and torsional modes. Molecules have also shown polarization sensitivity to the incident terahertz radiation. The ability of terahertz radiation to investigate conformational change makes it an important part of the electromagnetic spectrum. Terahertz radiation has the potential to provide additional information, which may complement other optically based sensing technologies. The use of terahertz technology in the security and defence industry is discussed, with a specific focus on biological and chemical sensing. The challenges faced in bringing terahertz technology into the market place will be discussed.
We demonstrate the application of terahertz pulsed imaging (TPI) in reflection geometry as a diagnostic aid for epithelial
cancer, specifically basal cell carcinoma. Epithelial cancer, which includes skin, breast and colon cancer, accounts for
about 85% of all cancers. The terahertz (THz) region is typically defined in the frequency range of 0.1-10 THz. The
sensitivity of terahertz radiation to water makes TPI an ideal technique for the study of skin, particularly as cancerous
tissue has been shown to contain more water than normal tissue. Twenty-one ex vivo skin samples from a previous
study, which successfully identified all 17 samples exhibiting basal cell carcinoma, were analysed in detail using
time-domain algorithms to determine the role of TPI as a diagnostic aid. Eight parameters were assessed, four of which
were identified as uncorrelated. The samples were classified into two groups: diseased tissue, and tissue without disease.
A sensitivity and specificity greater than 80 % for six of the parameters was attained. These results demonstrate the
potential of TPI as a diagnostic aid.
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.
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.
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.
Advanced Biomedical and Clinical Diagnostic Systems VI
20 January 2008 | San Jose, California, United States
Advanced Biomedical and Clinical Diagnostic Systems V
21 January 2007 | San Jose, California, United States
Optics and Photonics in Global Homeland Security II
19 April 2006 | Orlando (Kissimmee), Florida, United States
Advanced Biomedical and Clinical Diagnostic Systems IV
22 January 2006 | San Jose, California, United States
Advanced Biomedical and Clinical Diagnostic Systems III
23 January 2005 | San Jose, CA, United States
Course Instructor
SC718: Terahertz Technology in Homeland Security and Defense
This course will introduce the basic techniques in terahertz technology for imaging and spectroscopy in homeland security and defense. The course reviews the progress of the technology in the security and defense arena, including recent developments in sources and detectors. The focus will be specifically on the application of the technology for improvised explosive device (IED) detection and chemical and biological sensing. The methods required for the successful imaging and spectroscopy of target materials will be discussed, in addition to the appropriate implementation of standards for identifying the viability of terahertz technology in this arena. The student will receive an understanding of the challenges and potential of terahertz technology in homeland security and defense.
SC697: Terahertz Techniques in Medical Imaging and Spectroscopy
This course will introduce the basic techniques in terahertz technology for medical imaging and spectroscopy. The course reviews the progress of the technology in the medical and pharmaceutical industry, and discusses the current advantages and disadvantages of the technology compared to other optical imaging and spectroscopy techniques. The methods required for the successful imaging and spectroscopy of biological samples will be discussed, in addition to good working practices. The student will receive an understanding of the challenges and potential of terahertz technology for medical imaging and spectroscopy.
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