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Choi DH, Shin JH, Lee IM, Park KH. Investigations on Practical Issues in Solid Immersion Lens Based Sub-Wavelength Terahertz Imaging Technique: System Stability Verification and Interference Pattern Removal. SENSORS (BASEL, SWITZERLAND) 2021; 21:6990. [PMID: 34770295 PMCID: PMC8588359 DOI: 10.3390/s21216990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 10/19/2021] [Accepted: 10/19/2021] [Indexed: 11/22/2022]
Abstract
Terahertz (THz) imaging techniques are attractive for a wide range of applications, such as non-destructive testing, biological sensing, and security imaging. We investigate practical issues in THz imaging systems based on a solid immersion lens (SIL). The system stability in terms of longitudinal misalignment of the SIL is experimentally verified by showing that the diffraction-limited sub-wavelength beam size (0.7 λ) is maintained as long as the SIL is axially located within the depth-of-focus (~13 λ) of the objective lens. The origin of the fringe patterns, which are undesirable but inevitable in THz imaging systems that use continuous waves, is analytically studied, and a method for minimizing the interference patterns is proposed. By combining two THz images obtained at different axial positions of the object and separated by λ/4, the interference patterns are significantly reduced, and the information hidden under the interference patterns is unveiled. The broad applicability of the proposed method is demonstrated by imaging objects with different surface profiles. Our work proves that the resolution of conventional THz imaging systems can easily be enhanced by simply inserting a SIL in front of the object with high tolerance in the longitudinal misalignment and provides a method enabling THz imaging for objects with different surface profiles.
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Affiliation(s)
- Da-Hye Choi
- Terahertz Research Section, Electronics and Telecommunications Research Institute, Daejeon 34129, Korea; (J.-H.S.); (I.-M.L.); (K.H.P.)
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Wang XB, Cheng L, Wu Y, Zhu DP, Wang L, Zhu JX, Yang H, Chia EEM. Topological-insulator-based terahertz modulator. Sci Rep 2017; 7:13486. [PMID: 29044164 PMCID: PMC5647436 DOI: 10.1038/s41598-017-13701-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 09/27/2017] [Indexed: 11/30/2022] Open
Abstract
Three dimensional topological insulators, as a new phase of quantum matters, are characterized by an insulating gap in the bulk and a metallic state on the surface. Particularly, most of the topological insulators have narrow band gaps, and hence have promising applications in the area of terahertz optoelectronics. In this work, we experimentally demonstrate an electronically-tunable terahertz intensity modulator based on Bi1:5Sb0:5Te1:8Se1:2 single crystal, one of the most insulating topological insulators. A relative frequency-independent modulation depth of ~62% over a wide frequency range from 0.3 to 1.4 THz has been achieved at room temperature, by applying a bias current of 100 mA. The modulation in the low current regime can be further enhanced at low temperature. We propose that the extraordinarily large modulation is a consequence of thermally-activated carrier absorption in the semiconducting bulk states. Our work provides a new application of topological insulators for terahertz technology.
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Affiliation(s)
- X B Wang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore
| | - L Cheng
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore
| | - Y Wu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - D P Zhu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - L Wang
- School of Applied Sciences, RMIT University, Melbourne, Victoria, 3001, Australia
| | - Jian-Xin Zhu
- Theoretical Division and Center for Integrated Nanotechnologies, Los Alamos National Laboratory, New Mexico, 87545, USA
| | - Hyunsoo Yang
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore.
| | - Elbert E M Chia
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore.
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Dolganova IN, Zaytsev KI, Metelkina AA, Karasik VE, Yurchenko SO. A hybrid continuous-wave terahertz imaging system. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:113704. [PMID: 26628141 DOI: 10.1063/1.4935495] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A hybrid (active-passive mode) terahertz (THz) imaging system and an algorithm for imaging synthesis are proposed to enhance the THz image quality. The concept of image contrast is used to compare active and passive THz imaging. Combining the measurement of the self-emitted radiation of the object with the back-scattered source radiation measurement, it becomes possible to use the THz image to retrieve maximum information about the object. The experimental results confirm the advantages of hybrid THz imaging systems, which can be generalized for a wide range of applications in the material sciences, chemical physics, bio-systems, etc.
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Affiliation(s)
- Irina N Dolganova
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
| | - Kirill I Zaytsev
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
| | - Anna A Metelkina
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
| | - Valeriy E Karasik
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
| | - Stanislav O Yurchenko
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
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Pogson EM, McNamara J, Metcalfe P, Lewis RA. Comparing and evaluating the efficacy of the TOR18FG Leeds test X-ray phantom for T-rays. Quant Imaging Med Surg 2013; 3:18-27. [PMID: 23483115 PMCID: PMC3591503 DOI: 10.3978/j.issn.2223-4292.2013.02.05] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2013] [Accepted: 02/27/2013] [Indexed: 11/14/2022]
Abstract
The commercially available X-ray fluoroscopy quality assurance phantom, the Leeds test object TOR18FG, was found to be suitable to assess T-ray image quality in the range (0.1-0.4) THz at a depth of 0.5 cm. Previous to this only custom made phantoms, made especially for the T-ray region, assessed T-ray spatial resolution. However, if sub-wavelength techniques are used, the Leeds test phantom may be implemented to measure the T-ray systems spatial resolution, allowing us to directly compare X-ray and T-ray spatial resolution. The systems compared include a Gulmay Orthovoltage machine (X-ray), the On Board Imager (OBI) of a Varian linear accelerator (X-ray), a two-colour system (T-ray) and Terahertz Time Domain Spectroscopy (THz-TDS) system. X-rays were found to have a spatial resolution of 1.25 lp/mm using the On Board Imager of a Varian Linear Accelerator whilst T-rays imaged using a broadband source imaged through a spatial pinhole had a spatial resolution of 0.56 lp/mm. The TOR18FG background material was found to block, 90% and 99% of the broadband T-rays emitted from a THz-TDS photo-conductive emitter, at 0.4 THz and 0.53 THz respectively. Contrast sensitivity was found to be 3% for 25 cm × 25 cm X-ray field at 65 kV, whilst this value could not be established for T-rays using the TOR18FG. All contrast circles were found to be the same for T-rays i.e. all 40% at 0.1 THz. Images of the same leaf were taken with diagnostic X-rays and both broadband and continuous wave (CW) T-ray systems. T-rays proved superior in providing image contrast, for a hydrated leaf, over X-rays.
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Affiliation(s)
- Elise Maree Pogson
- Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Joanne McNamara
- Department of Medical Physics, Illawarra Cancer Care Centre, Locked Bag 8808, South Coast Mail Centre, Wollongong, NSW 2521, Australia
| | - Peter Metcalfe
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Roger A Lewis
- Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia
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Fitzgerald AJ, Pinder S, Purushotham AD, O'Kelly P, Ashworth PC, Wallace VP. Classification of terahertz-pulsed imaging data from excised breast tissue. JOURNAL OF BIOMEDICAL OPTICS 2012; 17:016005. [PMID: 22352655 DOI: 10.1117/1.jbo.17.1.016005] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
We investigate the efficacy of using data reduction techniques to aid classification of terahertz (THz) pulse data obtained from tumor and normal breast tissue. Fifty-one samples were studied from patients undergoing breast surgery at Addenbrooke's Hospital in Cambridge and Guy's Hospital in London. Three methods of data reduction were used: ten heuristic parameters, principal components of the pulses, and principal components of the ten parameter space. Classification was performed using the support vector machine approach with a radial basis function. The best classification accuracy, when using all ten components, came from using the principal components on the pulses and principal components on the parameter, with an accuracy of 92%. When less than ten components were used, the principal components on the parameter space outperformed the other methods. As a visual demonstration of the classification technique, we apply the data reduction/classification to several example images and demonstrate that, aside from some interpatient variability and edge effects, the algorithm gives good classification on terahertz data from breast tissue. The results indicate that under controlled conditions data reduction and SVM classification can be used with good accuracy to classify tumor and normal breast tissue.
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Huang SY, Wang YXJ, Yeung DKW, Ahuja AT, Zhang YT, Pickwell-MacPherson E. Tissue characterization using terahertz pulsed imaging in reflection geometry. Phys Med Biol 2008; 54:149-60. [DOI: 10.1088/0031-9155/54/1/010] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Abstract
Phantoms are commonly used in medical imaging for quality assurance, calibration, research and teaching. They may include test patterns or simulations of organs, but in either case a tissue substitute medium is an important component of the phantom. The aim of this work was to identify materials suitable for use as tissue substitutes for the relatively new medical imaging modality terahertz pulsed imaging. Samples of different concentrations of the candidate materials TX151 and napthol green dye were prepared, and measurements made of the frequency-dependent absorption coefficient (0.5 to 1.5 THz) and refractive index (0.5 to 1.0 THz). These results were compared qualitatively with measurements made in a similar way on samples of excised human tissue (skin, adipose tissue and striated muscle). Both materials would be suitable for phantoms where the dominant mechanism to be simulated is absorption (approximately 100 cm(-1) at 1 THz) and where simulation of the strength of reflections from boundaries is not important; for example, test patterns for spatial resolution measurements. Only TX151 had a frequency-dependent refractive index close to that of tissue, and could therefore be used to simulate the layered structure of skin, the complexity of microvasculature or to investigate frequency-dependent interference effects that have been noted in terahertz images.
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Affiliation(s)
- Gillian C Walker
- University of Leeds, Wellcome Wing, Leeds General Infirmary, Leeds, LS1 3EX, UK
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Berry E, Handley JW, Fitzgerald AJ, Merchant WJ, Boyle RD, Zinov'ev NN, Miles RE, Chamberlain JM, Smith MA. Multispectral classification techniques for terahertz pulsed imaging: an example in histopathology. Med Eng Phys 2004; 26:423-30. [PMID: 15147750 DOI: 10.1016/j.medengphy.2004.02.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2003] [Revised: 02/02/2004] [Accepted: 02/19/2004] [Indexed: 11/27/2022]
Abstract
Terahertz pulsed imaging is a spectroscopic imaging modality using pulses of electromagnetic radiation (100 GHz-10 THz), and there has been recent interest in studying biomedical specimens. It is usual to display parametric images derived from the measured pulses. In this work, classification was achieved by applying multispectral clustering techniques to sets of parametric images. It was hypothesised that adequate information for clustering was carried in a small number of parametric images, providing these were weighted by complementary physical properties. Materials prepared for histopathological examination were chosen because their condition remained stable during long imaging periods and because their dehydrated state led to greater penetration of the radiation. Two specimens were examined in this pilot study, one of basal cell carcinoma and one of melanoma. Unsupervised ISODATA classification using three selected parametric terahertz pulsed images was compared qualitatively with k-means classification using the shape of the whole time series, and with conventional stained microscope slides. There was good qualitative agreement between the classifications. Classifications were consistent with the morphological appearances expected, but further work is required to determine if tumour discrimination is possible. The results have implications for the future development of the technique as the need for only a small number of features could lead to considerably reduced acquisition times.
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Affiliation(s)
- Elizabeth Berry
- Academic Unit of Medical Physics, University of Leeds, Wellcome Wing, Leeds General Infirmary, Great George Street, Leeds LS1 3EX, UK.
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