An ex vivo comparative study of occlusal and proximal caries using terahertz and X-ray imaging.

OBJECTIVES:: To examine the effectiveness of terahertz (THz) pulsed imaging (TPI) in comparison to intraoral photostimulable phosphor late (PSP) and cone beam CT (CBCT) for the detection of dental caries ex vivo. METHODS:: Newly extracted 32 human permanent teeth surfaces (16 with caries and 16 without caries) were serially sectioned mesiodistally and imaged by using four image sets as follows: (1) CBCT; (2) PSP; (3) THz movie video; and (4) THz static images. All images were evaluated twice separately by two calibrated observers for the presence/absence of caries using a 5-grade rating/confidence scale. Weighted κ coefficients were calculated. Different image sets were compared with the histological gold-standard using the receiver operating characteristic and area under curves for each image set were compared using χ2 tests, with a significance level of α = 0.05. RESULTS:: Intra- and interobserverκ-values for all image sets were almost excellent ranging between 0.777 and 0.988. Mean Az values of observers and readings were 0.898 for CBCT, 0.888 for PSP images, 0.853 for THz static images and 0.781 for THz video movie. No statistically significant differences (p > 0.05) were found between Az values for the different image sets. When observer scores were evaluated according to caries location again no statistically significant differences (p > 0.05) were found between Az values for the occlusal and proximal caries for the four image sets. CONCLUSIONS:: Terahertz pulsed imaging was found to be successful for the detection of dental caries ex vivo.

Graphene-enabled electrically controlled terahertz spatial light modulators.

In this Letter, we demonstrate a broadband terahertz (THz) spatial light modulator using 5×5 arrays of large area graphene supercapacitors. Our approach relies on controlling spatial charge distribution on a passive matrix array of patterned graphene electrodes. By changing the voltage bias applied to the rows and columns, we were able to pattern the THz transmittance through the device with high modulation depth and low operation voltage. We anticipate that the simplicity of the device architecture with high contrast THz modulation over a broad spectral range could provide new tools for THz imaging and communication systems.

Dielectric properties of ethanol and gasoline mixtures by terahertz spectroscopy and an effective method for determination of ethanol content of gasoline.

Investigation of frequency dependent permittivity of mixture solutions provides information on the role of intermolecular interactions on relaxation processes of solvent and solute molecules. In this study the dielectric properties of ethanol/gasoline mixtures in the terahertz spectral region are investigated. Frequency dependent absorption coefficients, refractive indices, and complex permittivities of pure ethanol and gasoline, and their mixtures at varying ethanol volume percentages (v/v %) are reported. As the mixing ratio changes, meaningful shifts are observed in the frequency dependent refractive index and absorption coefficients associated with the dominant component, ethanol. The relaxation dynamics of the pure gasoline and ethanol are successfully modeled with the Debye model using the ultrafast nature of the terahertz transients, and those of mixture solutions are investigated by an additive model with an assumption of minimum interaction due to the significant differences in their molecular natures; polar and nonpolar. Successful modeling of the mixtures confirms the weak interaction assumption and enables us to accurately determine the ethanol content. Among five ethanol/gasoline blends, except for one mixture, the estimated percent ethanol in gasoline is predicted with an accuracy of ca. 1% with respect to the actual ethanol percentage. In addition, the results show that free OH contribution to the macroscopic polarization is significantly higher at low concentrations (5-20%) and lower at 50% compared to the case of pure ethanol. The measurements and analysis presented here show that time domain terahertz studies can offer invaluable insight into development of new models for polar/nonpolar complex mixture solutions.

Concentration-based measurement studies of L-tryptophan using terahertz time-domain spectroscopy (THz-TDS).

L-Tryptophan is an extremely important amino acid for a variety of biological functions in living organisms. In this study we were able to measure changes in the concentration of L-tryptophan when incorporated into pellets with polyethylene as a host. The changes were measured both through the characteristic absorption bands of the C11 and C12 bonds in the low terahertz frequency range and using changes in the refractive index where pellets with higher concentrations of L-tryptophan showed higher refractive indices. The volumetric concentration of L-tryptophan in the polyethylene pellet was accurately determined with a simple model that explains the contribution to the complex refractive index for the resultant sample due to the two constituent materials. These measurements show that terahertz time-domain techniques can be applied to detect variation in concentration of certain amino acids rapidly by examining the relative phase delay and amplitude change of the terahertz transients.

The role of oxidative stress and antioxidant defenses in Buerger disease and atherosclerotic peripheral arterial occlusive disease.

The aim of this study was to determine the status and the role of oxidative stress and antioxidant defenses in patients with Buerger disease and atherosclerotic peripheral arterial occlusive disease (PAOD). Seventy-three subjects resembling each other in general characteristics were involved in the study: 21 with lower extremity PAOD (mean age 53.05 +/- 10.8 years, 17 men and four women), 22 with Buerger disease (mean age 38.59 +/- 6.4 years, 19 men and three women), and 30 healthy volunteers (mean age 38.59 +/- 6.4 years, 22 men and eight women). We measured the levels of plasma malondialdehyde (MDA), paraoxonase (PON1), protein carbonyls, arylesterase, nitric oxide (NO), serum oxidized low-density lipoprotein (ox-LDL) and MDA, glutathione (GSH), glutathione reductase (GSH-red), glutathione peroxidase (GSH-px), superoxide dismutase (SOD), and catalase (CAT) in erythrocytes. Plasma protein carbonyls, serum ox-LDL, and plasma and erythrocyte MDA were significantly high in the Buerger disease group compared to the PAOD and control groups (p < 0.001). Plasma PON1 levels and GSH and GSH-px levels in erythrocytes in the Buerger disease group were significantly low compared to the PAOD and control groups (p < 0.001). GSH-red, SOD, and CAT levels in erythrocytes in the Buerger disease group were significantly lowcompared to the PAOD group (p < 0.01, p < 0.001, and p < 0.001, respectively). NO levels were significantly lower in the PAOD group compared to the control group (p < 0.05). The balance between oxidative stress and antioxidant capacity is more seriously impaired in Buerger disease than PAOD.