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Do in vivo terahertz imaging systems comply with safety guidelines?

Berry, E., Walker, G.C., Fitzgerald, A.J., Zinov'ev, N.N., Chamberlain, M., Smye, S.W., Miles, R.E. and Smith, M.A. (2003) Do in vivo terahertz imaging systems comply with safety guidelines? Journal of Laser Applications, 15 (3). pp. 192-198. ISSN 1042-346X

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Abstract

Techniques for the coherent generation and detection of electromagnetic radiation in the far infrared, or terahertz, region of the electromagnetic spectrum have recently developed rapidly and may soon be applied for in vivo medical imaging. Both continuous wave and pulsed imaging systems are under development, with terahertz pulsed imaging being the more common method. Typically a pump and probe technique is used, with picosecond pulses of terahertz radiation generated from femtosecond infrared laser pulses, using an antenna or nonlinear crystal. After interaction with the subject either by transmission or reflection, coherent detection is achieved when the terahertz beam is combined with the probe laser beam. Raster scanning of the subject leads to an image data set comprising a time series representing the pulse at each pixel. A set of parametric images may be calculated, mapping the values of various parameters calculated from the shape of the pulses. A safety analysis has been performed, based on current guidelines for skin exposure to radiation of wavelengths 2.6 mum-20 mm (15 GHz-115 THz), to determine the maximum permissible exposure (MPE) for such a terahertz imaging system. The international guidelines for this range of wavelengths are drawn from two U.S. standards documents. The method for this analysis was taken from the American National Standard for the Safe Use of Lasers (ANSI Z136.1), and to ensure a conservative analysis, parameters were drawn from both this standard and from the IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields (C95.1). The calculated maximum permissible average beam power was 3 mW, indicating that typical terahertz imaging systems are safe according to the current guidelines. Further developments may however result in systems that will exceed the calculated limit. Furthermore, the published MPEs for pulsed exposures are based on measurements at shorter wavelengths and with pulses of longer duration than those used in terahertz pulsed imaging systems, so the results should be treated with caution.

Item Type: Article
Copyright, Publisher and Additional Information: Copyright © 2003 Laser Institute of America. Reproduced with the permission of the copyright holder.
Keywords: terahertz pulsed imaging, hazard analysis, maximum permissible exposure (MPE), human, in vivo, skin, safety
Institution: The University of Leeds
Academic Units: The University of Leeds > Faculty of Medicine and Health (Leeds) > School of Medicine (Leeds) > Leeds Institute of Genetics, Health and Therapeutics (LIGHT) > Academic Unit of Medical Physics (Leeds)
The University of Leeds > Faculty of Engineering (Leeds) > School of Electronic & Electrical Engineering (Leeds) > Institute of Microwaves and Photonics (Leeds)
The University of Leeds > University of Leeds Research Centres and Institutes > Centre for Medical Imaging Research (Leeds)
Depositing User: Elizabeth Berry
Date Deposited: 13 Mar 2006
Last Modified: 10 Jun 2014 04:38
Published Version: http://scitation.aip.org/jla/
Status: Published
Refereed: Yes
URI: http://eprints.whiterose.ac.uk/id/eprint/819

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