Doin vivoterahertz imaging systems comply with safety guidelines?
- 1 August 2003
- journal article
- Published by Laser Institute of America in Journal of Laser Applications
- Vol. 15 (3), 192-198
- https://doi.org/10.2351/1.1585079
Abstract
Techniques for the coherent generation and detection of electromagnetic radiation in the far infrared, or terahertz, region of the electromagneticspectrum have recently developed rapidly and may soon be applied for in vivomedical 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 safetyanalysis has been performed, based on current guidelines for skin exposure to radiation of wavelengths 2.6 μm–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.Keywords
This publication has 25 references indexed in Scilit:
- Terahertz imaging and spectroscopy of human skin in vivoPublished by SPIE-Intl Soc Optical Eng ,2001
- Diagnosis of Dental Cavity and Osteoporosis Using Terahertz Transmission ImagesPublished by Springer Science and Business Media LLC ,2001
- Biomedical applications of terahertz pulse imagingPublished by SPIE-Intl Soc Optical Eng ,2000
- Recent advances in terahertz imagingApplied Physics B Laser and Optics, 1999
- T-ray imagingIEEE Journal of Selected Topics in Quantum Electronics, 1996
- Chemistry is right for T-ray imagingIEEE Circuits and Devices Magazine, 1996
- Imaging with terahertz wavesOptics Letters, 1995
- High-brightness terahertz beams characterized with an ultrafast detectorApplied Physics Letters, 1989
- Electrooptical generation and detection of femtosecond electrical transientsIEEE Journal of Quantum Electronics, 1988
- Subpicosecond photoconducting dipole antennasIEEE Journal of Quantum Electronics, 1988