Development of a compact terahertz time-domain spectrometer for the measurement of the optical properties of biological tissues

Abstract

Terahertz spectrometers and imaging systems are currently being evaluated as biomedical tools for skin burn assessment. These systems show promise, but due to their size and weight, they have restricted portability, and are impractical for military and battlefield settings where space is limited. In this study, we developed and tested the performance of a compact, light, and portable THz time-domain spectroscopy (THz-TDS) device. Optical properties were collected with this system from 0.1 to 1.6 THz for water, ethanol, and several ex vivo porcine tissues (muscle, adipose, skin). For all samples tested, we found that the index of refraction (n) decreases with frequency, while the absorption coefficient (μ(a)) increases with frequency. Muscle, adipose, and frozen/thawed skin samples exhibited comparable n values ranging between 2.5 and 2.0, whereas the n values for freshly harvested skin were roughly 40% lower. Additionally, we found that the freshly harvested samples exhibited higher μ(a) values than the frozen/thawed skin samples. Overall, for all liquids and tissues tested, we found that our system measured optical property values that were consistent with those reported in the literature. These results suggest that our compact THz spectrometer performed comparable to its larger counterparts, and therefore may be a useful and practical tool for skin health assessment.

Using a portable terahertz spectrometer to measure the optical properties ofin vivohuman skin

“…These values are comparable to those reported in previous reports. 7,8,[11][12][13] Our statistical analyses indicate that the magnitude of the absorption coefficient is comparable for all tissue regions that we measured [ Fig. 3(b)].…”

“…[1][2][3] Several medical and biological applications are also under development to improve detection and diagnosis of skin cancers, burns, and other pathologies. [4][5][6][7][8][9][10][11][12] Despite the elevated interest to develop THz-based applications, few basic science research investigations have been conducted to better understand the fundamental mechanisms governing THz-tissue interactions. In fact, only a few studies have been conducted to characterize the optical properties of in vivo human tissues at THz frequencies.…”

Surfing the spectrum – what is on the horizon?

“…Production of these waves is possible by exposure of Zinc-telluride Crystals to pulses of visible or infra-red light and detection is now feasible with advancements in photoconductive detectors 4 . Terahertz pulses are strongly absorbed by water, and tissue penetration appears to be limited to the micron level 5 . Image production is from the reflected wave (figure 3 6 ) and in mineralised tissue it is proving difficult to focus the reflected beam 7 .…”

Label-free protein detection using terahertz time-domain spectroscopy

“…The vibrational and rotational energy levels of large molecules, especially biological macromolecules mostly lie in the THz wave band [15,16]. Biological molecular vibrations and rotations involve intra/inter molecular weak hydrogen bonds, van der Waals forces, conformational changes, non-bonded hydrophobic and hydrophilic interactions [17,18]. Moreover, THz radiation excites the aforementioned vibrations and rotations that can be revealed by refractive index spectrum and absorption (or transmission) spectrum of biological molecules by their individual symmetries and structures in the THz frequency range [19,20].…”