Medical applications of terahertz imaging: a review of current technology and potential applications in biomedical engineering <s> Medical applications of <s> The rapidly developing field of terahertz (T-ray) imagin promises to provide a non-invasive method of identifying the composition of various objects. Biomedical diagnostics, semiconductor device diagnostics, trace gas analysis and moisture analysis for agriculture are among the growing number of important T-ray applications. We present results using an electro-optical sampling method and discuss how this can be simplified by sign a micro antenna array realized by MEMS technology. The challenges and advantages of both approaches are compared. <s> BIB001 </s> Medical applications of terahertz imaging: a review of current technology and potential applications in biomedical engineering <s> Medical applications of <s> In this paper, we describe and discuss three electrooptic-based terahertz imaging systems: the point scanning system, a two-dimensional charge-coupled device (CCD) system and a one-dimensional spatio-temporal chirped pulse imaging system. A complete comparison between the scanning system and CCD systems is given. We emphasize the CCD systems that provide high acquisition speed by taking unique advantage of parallel measurement. Possible improvements are also discussed. <s> BIB002
By comparison, photonic sources -lasers, photoconductive dipole antennas (PDA), and devices relying on optical mixing to generate THz radiation -are ubiquitous in medical applications. They are used to provide both narrowband continuous wave (CW) radiation and broadband THz pulses across a wide range of frequencies. Lasers, although viable, are still uncommon as a primary source of THz radiation in medical applications, owing to the cost, complexity and indeed size of the devices currently available. It is often easier to generate THz radiation by optically mixing light from two sources; typically two laser diodes, whose difference in frequency is in the THz range. Other methods can be used if pulsed operation is acceptable or, indeed, required. Photoconductive dipole antennas can be used to produce broadband THz pulses up to about 1 THz. Perhaps the most commonly used generation method, in medical applications, employs optical rectification, whereby the high frequency oscillations of a femtosecond laser pulse are rectified by an optical crystal, leaving only the envelope of the laser signal -which is a THz pulse BIB001 . It is worth noting that both PDA and optical rectification based sources require the use of a femtosecond pulsed laser, operating at a wavelength in the region of 800 nm. This adds considerably to the cost of these sources. As far as detection is concerned, one usually wants to employ a coherent detection scheme, so that both the amplitude and the phase of the THz field can be captured. Both PDA and optical rectification methods can be used to that end. Another notable detector type is based on an electrooptic effect, where the presence of a THz frequency electric field induces a birefringence in some optically transparent material. The magnitude of this effect, and thus the state of the THz field, can be ascertained by analyzing the change of the polarization states of fast optical pulses transmitted through the material BIB002 . In summary, the technology now exists to generate and detect coherent THz radiation at useful power levels, either as a continuous wave or as a series of pulses.