Terahertz sensing in corneal tissues

Abstract

This work introduces the potential application of terahertz (THz) sensing to the field of ophthalmology, where it is uniquely suited due to its nonionizing photon energy and high sensitivity to water content. Reflective THz imaging and spectrometry data are reported on ex-vivo porcine corneas prepared with uniform water concentrations using polyethylene glycol (PEG) solutions. At 79% water concentration by mass, the measured reflectivity of the cornea was 20.4%, 14.7%, 11.7%, 9.6%, and 7.4% at 0.2, 0.4, 0.6, 0.8, and 1 THz, respectively. Comparison of nine corneas hydrated from 79.1% to 91.5% concentration by mass demonstrated an approximately linear relationship between THz reflectivity and water concentration, with a monotonically decreasing slope as the frequency increases. The THz-corneal tissue interaction is simulated with a Bruggeman model with excellent agreement. THz applications to corneal dystrophy, graft rejection, and refractive surgery are examined from the context of these measurements.

In vivo terahertz imaging of rat skin burns

“…9 Additionally, our previous work has shown that THz imaging is extremely sensitive to changes in the local water concentration in skin (and has been demonstrated in a number of phantom characterization targets). 3,5,7 Therefore, burn wounds are ideally suited for THz imaging applications as they cover a relatively large area of skin and are known to provoke an extreme postinjury response. This response is apparent in the image Fig.…”

“…The last decade has witnessed significant proliferation of THz devices, technologies, and applications with considerable attention given to medical imaging and diagnostics. 1 THz medical imaging has been applied to the detection and spatial mapping of skin cancer, 2 corneal hydration, 3 and breast cancer. 4 Recently, THz imaging has been successfully applied to the imaging of burn wounds on ex vivo pig.…”

“…A 35 × 35 mm 2 scan of the windowed abdomen skin was taken prior to injury. Following this, a burn was inflicted using a brass brand in the shape of a "+" (20 × 20 × 20 mm 3 ) within the control scan area where the "+" measures 20 × 20 mm 2 and each "arm" is ∼2.5 mm wide. The brand was heated to 220°C using a hot plate to induce a deep partial thickness burn as confirmed by visual inspection and histology.…”

Terahertz spectroscopy for the assessment of burn injuriesin vivo

“…15 Difference in the water content of the tissue has been recently proposed as the main basis for many biomedical and biological applications of terahertz radiation. [16][17][18] Pickwell et al furthermore showed that a double Debye dielectric relaxation model can be used to describe the terahertz response of healthy human skin, 19,20 which is very similar to the model often used for polar liquids. 21 Pulsed-terahertz emissions have also been used to image and delineate basal cell carcinoma [22][23][24] and human breast cancer tumor margins, 25,26 based on the differences in the water content of the cancerous tumor versus healthy tissue.…”

Assessment of corneal hydration sensing in the terahertz band:in vivoresults at 100 GHz

“…[1][2][3][4][5][6][7][8] THz images of thermal burns were first demonstrated on ex vivo chicken skin burned using an argon ion laser by Mittleman et al 9 It has been demonstrated again in ex vivo porcine skin burns induced using a thermal brand. 10 THz imaging of chemical burns was demonstrated on 33% sulfuric acid burns on ex vivo porcine skin by Bennett et al 6 This study achieved time-resolved imaging which showed the severity of the burn progressing over a 2-h time course. THz evaluation of water content was also used to distinguish cirrhosis in liver tissue extracted from Sprague-Dawley (SD) rats.…”