Arseniy A. Gavdush

Accuracy of sample material parameters reconstruction using terahertz pulsed spectroscopy

New experimental and theoretical results for the material parameter reconstruction using terahertz (THz) pulsed spectroscopy (TPS) are presented. The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. In order to both verify the algorithm and to estimate the reconstruction accuracy, test sample material parameters obtained with the TPS were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated for the spectral range, corresponding to the BWO sensitivity and located between 0.2 and 1.2 THz. The numerical simulations were applied for determining the material parameter reconstruction stability in the presence of white Gaussian noise in TPS waveforms as well as fluctuations in the femtosecond (FS) optical pulse duration. We report a strong dependence of the inverse problem solution stability on these factors. We found that the instabi...

Highly Accurate in Vivo Terahertz Spectroscopy of Healthy Skin: Variation of Refractive Index and Absorption Coefficient Along the Human Body

A method to reconstruct the terahertz (THz) refractive index and absorption coefficient of in vivo tissue using THz pulsed spectroscopy (TPS) has been proposed. The method utilizes a reference THz window to fix the sample of interest during the TPS reflection mode measurements. Satellite pulses caused by multiple THz-wave reflections in the reference window are taken into account to accurately solve the inverse problem. The stability of the proposed method in the presence of various factors, including digital noise in the TPS waveforms and fluctuations of the reference THz window position, has been accurately analyzed. The method has been implemented to study in vivo the THz refractive index and absorption coefficient of the human skin. The skin from three persons has been measured, and the results agree with the well-known data on healthy skin spectroscopy in general, except for several regions of the skin. Thus, for the elbow, the hand, the knee, and the heel the THz refractive index and absorption coefficient considerably differ from the average values. The observed results are of principle importance for further development of novel approaches to skin diagnosis based on THz technologies.

A Method of Studying Spectral Optical Characteristics of a Homogeneous Medium by Means of Terahertz Time-Domain Spectroscopy

We have developed an algorithm for solving an inverse problem related to the reconstruction of spectral dependences of terahertz (THz) optical characteristics of a homogeneous medium in the form of a plane-parallel plate, which is based on processing signals obtained by a THz time-domain spectrometer. In contrast to existing methods, the developed algorithm allows studying the optical properties of dielectric samples that have a small thickness (down to 0.1 mm) and low index of refraction. Optical characteristics in the THz spectral range are determined by minimization of the error functional constructed based on experimental and theoretical complex transfer functions of the sample, wherein the theoretical transfer function is obtained by using a model of a Fabry-Perot quasi-resonator. The proposed method is experimentally verified by studying optical properties of test samples. The reconstructed THz optical characteristics are compared with the characteristics of the same test media obtained by means of the THz backward-wave oscillator spectroscopy, which allowed estimating the accuracy of the proposed method.

Novel Algorithm for Sample Material Parameter Determination using THz Time-Domain Spectrometer Signal Processing

In our research we have developed a novel sample material parameter determination algorithm which could be used for characterization of very thin flats. Utilizing this algorithm one could find optical properties of the media which are thin enough to cause appearance of the satellite pulses in TDS system signal, transmitted through the flat sample. The algorithm is based on the minimization of the Error function (minimization between the theoretical model of sample transfer function and the experimental data collected with THz pulsed spectrometer). The algorithm was implemented experimentally and tested by means of the test samples characterization. The results of the algorithm implementation were compared with the results of the same test sample studying using terahertz backward-wave oscillator spectroscopy.

In vivo spectroscopy of healthy skin and pathology in terahertz frequency range

Biomedical applications of terahertz (THz) technology and, in particular, THz pulsed spectroscopy have attracted considerable interest in the scientific community. A lot of papers have been dedicated to studying the ability for human disease diagnosis, including the diagnosis of human skin cancers. In this paper we have studied the THz material parameters and THz dielectric properties of human skin and pathology in vivo, and THz pulsed spectroscopy has been utilized for this purpose. We have found a contrast between material parameters of basal cell carcinoma and healthy skin, and we have also compared the THz material parameters of dysplastic and non-dysplastic pigmentary nevi in order to study the ability for early melanoma diagnosis. Significant differences between the THz material parameters of healthy skin and pathology have been detected, thus, THz pulsed spectroscopy promises to be become an effective tool for non-invasive diagnosis of skin neoplasms.

A Comparison of Terahertz Pulsed Spectroscopy and Backward-Wave Oscillator Spectroscopy

This paper presents new experimental and theoretical results for the material parameter reconstruction utilizing the terahertz (THz) pulsed spectroscopy (TPS). The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. The algorithm takes into account multiple reflections of THz pulse within the flat sample during the transmission mode measurements. Therefore the samples with small thickness or low refractive index could be studied utilizing the proposed method. In order to estimate the reconstruction accuracy, test sample material parameters, obtained with the TPS, were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated.

In vitro terahertz spectroscopy of gelatin-embedded human brain tumors: a pilot study

We have performed the in vitro terahertz (THz) spectroscopy of human brain tumors. In order to fix tissues for the THz measurements, we have applied the gelatin embedding. It allows for preserving tissues from hydration/dehydration and sustaining their THz response similar to that of the freshly-excised tissues for a long time after resection. We have assembled an experimental setup for the reflection-mode measurements of human brain tissues based on the THz pulsed spectrometer. We have used this setup to study in vitro the refractive index and the amplitude absorption coefficient of 2 samples of malignant glioma (grade IV), 1 sample of meningioma (grade I), and samples of intact tissues. We have observed significant differences between the THz responses of normal and pathological tissues of the brain. The results of this paper highlight the potential of the THz technology in the intraoperative neurodiagnosis of tumors relying on the endogenous labels of tumorous tissues.

Terahertz spectroscopy of immersion optical clearing agents: DMSO, PG, EG, PEG

Application of terahertz (THz) spectroscopy for biological tissues is strongly limited by the extremely low penetration depth due to THz absorption by tissue water. One of the possible solution of such problem is the usage of THz wave penetration-enhancing agents (PEA) for optical clearing of tissues. In the present paper, the transmission-mode THz spectroscopy of a set of PEAs (polyethylene glycol with different molecular weight, propylene glycol, ethylene glycol, and dimethyl sulfoxide) was performed in order to reconstruct their dielectric properties and compare them with that of water. The obtained results emphasize the feasibility of using PEG to enhance the depth of THz wave penetration into tissues.

Terahertz dielectric spectroscopy of malignancies (Conference Presentation)

Terahertz (THz) pulsed spectroscopy is a convenient instrument for studying the THz dielectric response of healthy and abnormal tissue in a wide spectral range. One of the most promising applications of THz pulsed spectroscopy is associated with non-invasive, least-invasive and intraoperative medical diagnostics of malignancies in various localizations, including the skin, the breast, the colon, and the brain [1]. In our research, we developed a method for reconstructing the THz dielectric response of biotissues in vitro and in vivo using the THz pulsed spectroscopy [2–5]. We applied this method for studying healthy and pathological tissues of the skin and the brain. (i) We observed statistical differences between THz dielectric properties of ordinary and dysplastic nevi of the skin in vivo. This highlights an ability for non-invasive early diagnosis of dysplastic nevi and melanomas of the skin using the THz spectroscopy and imaging [3–5]. (ii) By studying the THz dielectric permittivity of non-melanoma skin cancers in vitro (i.e. basal cell carcinoma and squamous cell carcinoma), we justify an ability for discriminating malignant tissues from surrounding normal skin using preoperative and intraoperative THz imaging [6,7]. (iii) Finally, the results of measuring the THz dielectric response of gelatin-fixed malignancies of the brain in vitro allow us to analyze an ability for discriminating brain gliomas from surrounding normal tissues during the neurosurgery using the THz technologies. The observed results of THz measurements agrees well with the data of biotissues studying using other modern modalities of optical imaging, such as intraoperative exogenous fluorescence imaging and optical coherence tomography, as well as with the data of biotissue histology. These results highlight the prospective of THz spectroscopy, imaging and endoscopy use for non-invasive, least-invasive and intraoperative medical diagnosis of malignancies. [1] O.A. Smolyanskaya,·M.M. Nazarov,·O.P. Cherkasova,·J.-P. Guillet,·J.-L. Coutaz, A.A. Konovko, Y.V.Kistenev,·P. Mounaix, I.A. Ozheredov, V.L. Vaks, A. Yaroslavsky,·N.V. Chernomyrdin, K.I. Zaytsev, S.A. Kozlov,·J.-H. Son, V. Wallace,·A.P. Shkurinov, ·V.V. Tuchin, “Terahertz biophotonics as a tool for studies of dielectricand spectral properties of tissues and bioliquids relatedto water content,” Progress in Quantum Electronics (2017, Submitted). [2] IEEE Transactions on Terahertz Science and Technology 5(5), 817 (2015). [3] Applied Physics Letters 106(5), 053702 (2015) [4] European Journal of Cancer 51, S167 (2015). [5] Optics and Spectroscopy 119(3), 404 (2015). [6] Journal of Physics: Conference Series 486(1), 012014 (2014). [7] Journal of Physics: Conference Series 584(1), 012023 (2015).

In vivo terahertz pulsed spectroscopy of dysplastic and non-dysplastic skin nevi

The results of the in vivo terahertz (THz) pulsed spectroscopy (TPS) of pigmentary skin nevi are reported. Observed THz dielectric permittivity of healthy skin and dysplastic and non-dysplastic skin nevi exhibits significant contrast in THz frequency range. Dysplastic skin nevus is a precursor of melanoma, which is reportedly the most dangerous cancer of the skin. Therefore, the THz dielectric spectroscopy is potentially an effective tool for non-invasive early diagnosis of melanomas of the skin.