Terahertz reflectometry imaging for low and high grade gliomas

A new horizon for neuroscience: terahertz biotechnology in brain research

Terahertz biotechnology has been increasingly applied in various biomedical fields and has especially shown great potential for application in brain sciences. In this article, we review the development of terahertz biotechnology and its applications in the field of neuropsychiatry. Available evidence indicates promising prospects for the use of terahertz spectroscopy and terahertz imaging techniques in the diagnosis of amyloid disease, cerebrovascular disease, glioma, psychiatric disease, traumatic brain injury, and myelin deficit. In vitro and animal experiments have also demonstrated the potential therapeutic value of terahertz technology in some neuropsychiatric diseases. Although the precise underlying mechanism of the interactions between terahertz electromagnetic waves and the biosystem is not yet fully understood, the research progress in this field shows great potential for biomedical noninvasive diagnostic and therapeutic applications. However, the biosafety of terahertz radiation requires further exploration regarding its two-sided efficacy in practical applications. This review demonstrates that terahertz biotechnology has the potential to be a promising method in the field of neuropsychiatry based on its unique advantages.

Exploring the impedance-matching effect in terahertz reflection imaging of skin tissue

Terahertz (THz) electromagnetic waves, known for their unique response to water, offer promising opportunities for next-generation biomedical diagnostics and novel cancer therapy technologies. This study investigated the impedance-matching effect, which enhances the efficiency of THz wave delivery into tissues and compensates for the signal distortion induced by the refractive index mismatch between the target and the sample substrate. Three candidate biocompatible materials, water, glycerol, and petroleum jelly were applied to a skin phantom and compared using THz two-dimensional imaging and time-of-flight imaging methods. Finally, we successfully demonstrated impedance-matching effect on mouse skin tissues.

Biomedical application of terahertz imaging technology: a narrative review

Background and Objective

Terahertz (THz) imaging has wide applications in biomedical research due to its properties, such as non-ionizing, non-invasive and distinctive spectral fingerprints. Over the past 6 years, the application of THz imaging in tumor tissue has made encouraging progress. However, due to the strong absorption of THz by water, the large size, high cost, and low sensitivity of THz devices, it is still difficult to be widely used in clinical practice. This paper provides ideas for researchers and promotes the development of THz imaging in clinical research.

Methods

The literature search was conducted in the Web of Science and PubMed databases using the keywords "Terahertz imaging", "Breast", "Brain", "Skin" and "Cancer". A total of 94 English language articles from 1 January, 2017 to 30 December, 2022 were reviewed.

Key Content and Findings

In this review, we briefly introduced the recent advances in THz near-field imaging, single-pixel imaging and real-time imaging, the applications of THz imaging for detecting breast, brain and skin tissues in the last 6 years were reviewed, and the advantages and existing challenges were identified. It is necessary to combine machine learning and metamaterials to develop real-time THz devices with small size, low cost and high sensitivity that can be widely used in clinical practice. More powerful THz detectors can be developed by combining graphene, designing structures and other methods to improve the sensitivity of the devices and obtain more accurate information. Establishing a THz database is one of the important methods to improve the repeatability and accuracy of imaging results.

Conclusions

THz technology is an effective method for tumor imaging. We believe that with the joint efforts of researchers and clinicians, accurate, real-time, and safe THz imaging will be widely applied in clinical practice in the future.

Terahertz technology and its applications in head and neck diseases

The terahertz (THz) radiation refers to electromagnetic waves between infrared and millimeter waves. THz technology has shown a significant potential for medical diagnosis and biomedical applications over the past three decades. Therefore, exploring the biological effects of THz waves has become an important new field in life sciences. Specifically, THz radiation has been proved to be able to diagnose and treat several head and neck diseases. In this review, we primarily discuss the biological characteristics of THz waves and clinical applications of THz technology, focusing on the research progress of THz technology in head and neck diseases (brain cancer, hypopharyngeal cancer, oral diseases, thyroid nodules, Alzheimer's disease, eyes diseases, and otitis). The future application perspectives of THz technologies in head and neck diseases are also highlighted and proposed.

Revolutionary approaches for cancer diagnosis by terahertz-based spectroscopy and imaging

Most tumors are easily missed and misdiagnosed due to the lack of specific clinical signs and symptoms in the early stage. Thus, an accurate, rapid and reliable early tumor detection method is highly desirable. The application of terahertz (THz) spectroscopy and imaging in biomedicine has made remarkable progress in the past two decades, which addresses the shortcomings of existing technologies and provides an alternative for early tumor diagnosis. Although issues such as size mismatch and strong absorption of THz waves by water have set hurdles for cancer diagnosis by THz technology, innovative materials and biosensors in recent years have led to possibilities for new THz biosensing and imaging methods. In this article, we reviewed the issues that need to be solved before THz technology is used for tumor-related biological sample detection and clinical auxiliary diagnosis. We focused on the recent research progress of THz technology, with an emphasis on biosensing and imaging. Finally, the application of THz spectroscopy and imaging for tumor diagnosis in clinical practice and the main challenges in this process were also mentioned. Collectively, THz-based spectroscopy and imaging reviewed here is envisioned as a cutting-edge approach for cancer diagnosis.

Triage of in vivo burn injuries and prediction of wound healing outcome using neural networks and modeling of the terahertz permittivity based on the double Debye dielectric parameters

The initial assessment of the depth of a burn injury during triage forms the basis for determination of the course of the clinical treatment plan. However, severe skin burns are highly dynamic and hard to predict. This results in a low accuracy rate of about 60 - 75% in the diagnosis of partial-thickness burns in the acute post-burn period. Terahertz time-domain spectroscopy (THz-TDS) has demonstrated a significant potential for non-invasive and timely estimation of the burn severity. Here, we describe a methodology for the measurement and numerical modeling of the dielectric permittivity of the in vivo porcine skin burns. We use the double Debye dielectric relaxation theory to model the permittivity of the burned tissue. We further investigate the origins of dielectric contrast between the burns of various severity, as determined histologically based on the percentage of the burned dermis, using the empirical Debye parameters. We demonstrate that the five parameters of the double Debye model can form an artificial neural network classification algorithm capable of automatic diagnosis of the severity of the burn injuries, and predicting its ultimate wound healing outcome by forecasting its re-epithelialization status in 28 days. Our results demonstrate that the Debye dielectric parameters provide a physics-based approach for the extraction of the biomedical diagnostic markers from the broadband THz pulses. This method can significantly boost dimensionality reduction of THz training data in artificial intelligence models and streamline machine learning algorithms.

Biomedical applications of terahertz spectra in clinical and molecular pathology of human glioma

Gliomas are the most common type of primary tumor originating in the central nervous system of adults. Tumor histological type, pathological grade, and molecular pathology are significant prognosis and predictive factors. In this study, we were aiming to predict histological type and molecular pathological features based on terahertz time-domain spectroscopy technology. Nine gliomas with different grades, one meningioma, and one lymphoma were enrolled. There were significant differences in terahertz absorption coefficient between normal brain tissue, tumoral-periphery, and tumoral-center tissue in specific frequency bands (0.2-1.4 THz). Histological type, pathological grade, and glioma-specific biomarkers were closely related to the terahertz absorption coefficient in both tumoral-periphery and tumoral-center tissues. Interestingly, tumoral-periphery showed more obvious differences than tumoral-center tissues in almost all aspects. All the results show that the terahertz technology has potential application value in the intraoperative real-time glioma recognition and diagnosis of glioma histological and molecular pathological features.

Measurement of tissue optical properties in a wide spectral range: a review [Invited]

A distinctive feature of this review is a critical analysis of methods and results of measurements of the optical properties of tissues in a wide spectral range from deep UV to terahertz waves. Much attention is paid to measurements of the refractive index of biological tissues and liquids, the knowledge of which is necessary for the effective application of many methods of optical imaging and diagnostics. The optical parameters of healthy and pathological tissues are presented, and the reasons for their differences are discussed, which is important for the discrimination of pathologies and the demarcation of their boundaries. When considering the interaction of terahertz radiation with tissues, the concept of an effective medium is discussed, and relaxation models of the effective optical properties of tissues are presented. Attention is drawn to the manifestation of the scattering properties of tissues in the THz range and the problems of measuring the optical properties of tissues in this range are discussed. In conclusion, a method for the dynamic analysis of the optical properties of tissues under optical clearing using an application of immersion agents is presented. The main mechanisms and technologies of optical clearing, as well as examples of the successful application for differentiation of healthy and pathological tissues, are analyzed.

Measurement and Modeling of the Optical Properties of Adipose Tissue in the Terahertz Range: Aspects of Disease Diagnosis

In this paper, the measurement and modeling of optical properties in the terahertz (THz) range of adipose tissue and its components with temperature changes were performed. Spectral measurements were made in the frequency range 0.25-1 THz. The structural models of main triglycerides of fatty acids are constructed using the B3LYP/6-31G(d) method and the Gaussian03, Revision B.03 program. The optical density (OD) of adipose tissue samples decreases as temperature increases, which can be associated mostly with the dehydration of the sample. Some inclusion of THz wave scattering suppression into the OD decrease can also be expected due to refractive index matching provided by free fatty acids released from adipocytes at thermally induced cell lipolysis. It was shown that the difference between the THz absorption spectra of water and fat makes it possible to estimate the water content in adipose tissue. The proposed model was verified on the basis of molecular modeling and a comparison with experimental data for terahertz spectra of adipose tissue during its heating. Knowing the exact percentage of free and bound water in adipose tissue can help diagnose and monitor diseases, such as diabetes, obesity, and cancer.

Terahertz Spectral Properties of PEO-Based Anti-Adhesion Films Cross-Linked by Electron Beam Irradiation

We investigated the spectral property changes in anti-adhesion films, which were cross-linked and surface-modified through electron beam irradiation, using terahertz time-domain spectroscopy (THz-TDS). Polyethylene oxide (PEO), which is a biocompatible and biodegradable polymer, was the main component of these anti-adhesion films being manufactured for testing. The terahertz characteristics of the films were affected by the porosity generated during the freeze-drying and compression processes of sample preparation, and this was confirmed using optical coherence tomography (OCT) imaging. An anti-adhesion polymer film made without porosity was measured by using the THz-TDS method, and it was confirmed that the refractive index and absorption coefficient were dependent on the crosslinking state. To our knowledge, this is the first experiment on the feasibility of monitoring cross-linking states using terahertz waves. The THz-TDS method has potential as a useful nondestructive technique for polymer inspection and analysis.

Supervised machine learning for automatic classification of in vivo scald and contact burn injuries using the terahertz Portable Handheld Spectral Reflection (PHASR) Scanner

We present an automatic classification strategy for early and accurate assessment of burn injuries using terahertz (THz) time-domain spectroscopic imaging. Burn injuries of different severity grades, representing superficial partial-thickness (SPT), deep partial-thickness (DPT), and full-thickness (FT) wounds, were created by a standardized porcine scald model. THz spectroscopic imaging was performed using our new fiber-coupled Portable HAndheld Spectral Reflection Scanner, incorporating a telecentric beam steering configuration and an f-[Formula: see text] scanning lens. ASynchronous Optical Sampling in a dual-fiber-laser THz spectrometer with 100 MHz repetition rate enabled high-speed spectroscopic measurements. Given twenty-four different samples composed of ten scald and ten contact burns and four healthy samples, supervised machine learning algorithms using THz-TDS spectra achieved areas under the receiver operating characteristic curves of 0.88, 0.93, and 0.93 when differentiating between SPT, DPT, and FT burns, respectively, as determined by independent histological assessments. These results show the potential utility of our new broadband THz PHASR Scanner for early and accurate triage of burn injuries.

Temperature dependent terahertz spectroscopy and imaging of orthotopic brain gliomas in mouse models

Terahertz (THz) spectroscopy and imaging were used to differentiate brain gliomas in a mouse model at different temperatures. The THz spectral difference between brain glioma and normal brain tissues at -10°C and 20°C was obtained in the 0.4-2.53 THz range. The absorption coefficient and refractive index values varied with both temperature and frequency. The fresh ex vivo brain glioma tissues were mapped by THz attenuated total reflection (ATR) imaging at 2.52 THz in the temperature range from -20°C to 35°C. Compared with histological examination, THz-ATR imaging could better display the tumor areas at a higher temperature. And the averaged reflectivity of normal tissue was increased with the increase of temperature, whereas the tumor region showed a decreasing trend. Thus, the larger THz imaging difference between glioma and normal tissues could be obtained. Moreover, in vivo brain gliomas in mouse models could also be differentiated clearly from normal brain tissues using THz-ATR imaging at 2.52 THz under room temperature. The THz-ATR images corresponded well with those of visual and hematoxylin and eosin (H&E) stained images. Therefore, this pilot study demonstrated that temperature dependence THz spectroscopy and imaging are helpful to the brain gliomas in mouse model detection.

A Review of Feasible Applications of THz Waves in Medical Diagnostics and Treatments

Introduction: Terahertz (THz) waves with frequencies in the range of 0.1 to 10 THz are electromagnetic radiation with growing applications in various fields of science and technology. Attractive features of this radiation have brought out many novel possibilities for medical diagnostics and treatments with considerable advantages compared to other conventional methods. Methods: In this paper, we present a review of more recent reports on practical applications of THz radiation for diagnostic, biosensing and clinical treatments. The review includes the diagnosis of breast, skin, mouth, cervical, lungs, small intestine, prostate, colon, and stomach cancers, the evaluation of biomolecules, the detection of genetic mutations, the determination of burn depth, the diagnosis of tooth decay, diabetes, and emotional-psychological states, the evaluation of corneal water to diagnose visual diseases, and wound healing monitoring. Further, it embraces the use of THz therapy in reducing the size of the tumor, treating skin cancer, and healing burn wounds, cardiovascular disease, corneal epithelium, angina, and THz heating. Results: This review has emphasized the capabilities of THz waves as a novel tool for future clinical diagnostics and treatments. Conclusion: The paper provides a comprehensive understanding of the feasible potential application of THz waves for clinical purposes and its advantages in comparison with other conventional tools.

Advances of terahertz technology in neuroscience: Current status and a future perspective

Terahertz (THz) waves are ranged between microwave and infrared region in the electromagnetic spectrum. THz technology has been demonstrated promising potential for biomedical applications. Exploration of biological effects of THz waves has emerged as a critical new area in life sciences. It is critical to uncover the effects of THz waves on complex biological systems in order to lay out the framework for THz technology development and future applications. Specifically, THz radiation has been shown to affect the nervous system, including the structure of nerve cell membranes, genes expressions, and cytokines level. In this review, we primarily discuss the biological impacts and mechanisms of THz waves on the nervous system at the organisms, cellular, and molecular levels. The future application perspectives of THz technologies in neuroscience are also highlighted and proposed.

Terahertz dielectric spectroscopy and solid immersion microscopy of ex vivo glioma model 101.8: brain tissue heterogeneity

Terahertz (THz) technology holds strong potential for the intraoperative label-free diagnosis of brain gliomas, aimed at ensuring their gross-total resection. Nevertheless, it is still far from clinical applications due to the limited knowledge about the THz-wave-brain tissue interactions. In this work, rat glioma model 101.8 was studied ex vivo using both the THz pulsed spectroscopy and the 0.15λ-resolution THz solid immersion microscopy (λ is a free-space wavelength). The considered homograft model mimics glioblastoma, possesses heterogeneous character, unclear margins, and microvascularity. Using the THz spectroscopy, effective THz optical properties of brain tissues were studied, as averaged within the diffraction-limited beam spot. Thus measured THz optical properties revealed a persistent difference between intact tissues and a tumor, along with fluctuations of the tissue response over the rat brain. The observed THz microscopic images showed heterogeneous character of brain tissues at the scale posed by the THz wavelengths, which is due to the distinct response of white and gray matters, the presence of different neurovascular structures, as well as due to the necrotic debris and hemorrhage in a tumor. Such heterogeneities might significantly complicate delineation of tumor margins during the intraoperative THz neurodiagnosis. The presented results for the first time pose the problem of studying the inhomogeneity of brain tissues that causes scattering of THz waves, as well as the urgent need to use the radiation transfer theory for describing the THz-wave - tissue interactions.

THz Sensing of Human Skin: A Review of Skin Modeling Approaches

The non-ionizing and non-invasive nature of THz radiation, combined with its high sensitivity to water, has made THz imaging and spectroscopy highly attractive for in vivo biomedical applications for many years. Among them, the skin is primarily investigated due to the short penetration depth of THz waves caused by the high attenuation by water in biological samples. However, a complete model of skin describing the THz-skin interaction is still needed. This is also fundamental to reveal the optical properties of the skin from the measured THz spectrum. It is crucial that the correct model is used, not just to ensure compatibility between different works, but more importantly to ensure the reliability of the data and conclusions. Therefore, in this review, we summarize the models applied to skin used in the THz regime, and we compare their adaptability, accuracy, and limitations. We show that most of the models attempt to extract the hydration profile inside the skin while there is also the anisotropic model that displays skin structural changes in the stratum corneum.

Label-Free Observation of Micrometric Inhomogeneity of Human Breast Cancer Cell Density Using Terahertz Near-Field Microscopy

Terahertz-light imaging is attracting great attention as a new approach in non-invasive/non-staining biopsy of cancerous tissues. Positively, terahertz light has been shown to be sensitive to the cell density, the hydration content, and the chemical composition of biological samples. However, the spatial resolution of terahertz imaging is typically limited to several millimeters, making it difficult to apply the technology to image biological tissues which have sub-terahertz-wavelength-scale inhomogeneity. For overcoming the resolution, we have recently developed a terahertz near-field microscope with a spatial resolution of 10 µm, named scanning point terahertz source (SPoTS) microscope. In contrast to conventional far-field terahertz techniques, this microscope features the near-field interactions between samples and point terahertz sources on a sub-terahertz-wavelength scale. Herein, to evaluate the usefulness of terahertz imaging in cancer tissue biopsy in greater detail, we performed terahertz near-field imaging of a paraffin-embedded human-breast-cancer section having sub-terahertz-wavelength-scale inhomogeneity of the cancer cell density using the SPoTS microscope. The observed terahertz images successfully visualized local (~250 µm) inhomogeneities of the cell density in breast invasive ductal carcinoma. These results may bypass the terahertz limitation in terms of spatial resolution and may further motivate the application of terahertz light to cancer tissue biopsy.

Genetic changes and growth promotion of glioblastoma by magnetic nanoparticles and a magnetic field

Aim: To confirm the biological effects of manganese ferrite magnetic nanoparticles (MFMNPs) and an external magnetic field on glioblastoma cells. Methods: U-87MG glioblastoma cells were prepared, into which the uptake of MFMNPs was high. The cells were then exposed to an external magnetic field using a neodymium magnet in vitro and in vivo. Results: LRP6 and TCF7 mRNA levels involved in the Wnt/β-catenin signaling pathway were elevated by the influence of MFMNPs and the external magnetic field. MFMNPs and the external magnetic field also accelerated tumor growth by approximately 7 days and decreased survival rates in animal experiments. Conclusion: When MFMNPs and an external magnetic field are applied for a long time on glioblastoma cells, mRNA expression related to Wnt/β-catenin signaling is increased and tumor growth is promoted.

Diagnosis of Glioma Molecular Markers by Terahertz Technologies

This review considers glioma molecular markers in brain tissues and body fluids, shows the pathways of their formation, and describes traditional methods of analysis. The most important optical properties of glioma markers in the terahertz (THz) frequency range are also presented. New metamaterial-based technologies for molecular marker detection at THz frequencies are discussed. A variety of machine learning methods, which allow the marker detection sensitivity and differentiation of healthy and tumor tissues to be improved with the aid of THz tools, are considered. The actual results on the application of THz techniques in the intraoperative diagnosis of brain gliomas are shown. THz technologies’ potential in molecular marker detection and defining the boundaries of the glioma’s tissue is discussed.

Terahertz dielectric spectroscopy of human brain gliomas and intact tissues ex vivo: double-Debye and double-overdamped-oscillator models of dielectric response

Terahertz (THz) technology offers novel opportunities in the intraoperative neurodiagnosis. Recently, the significant progress was achieved in the study of brain gliomas and intact tissues, highlighting a potential for THz technology in the intraoperative delineation of tumor margins. However, a lack of physical models describing the THz dielectric permittivity of healthy and pathological brain tissues restrains the further progress in this field. In the present work, the ex vivo THz dielectric response of human brain tissues was analyzed using relaxation models of complex dielectric permittivity. Dielectric response of tissues was parametrized by a pair of the Debye relaxators and a pair of the overdamped-oscillators - namely, the double-Debye (DD) and double-overdamped-oscillator (DO) models. Both models accurately reproduce the experimental curves for the intact tissues and the WHO Grades I-IV gliomas. While the DD model is more common for THz biophotonics, the DO model is more physically rigorous, since it satisfies the sum rule. In this way, the DO model and the sum rule were, then, applied to estimate the content of water in intact tissues and gliomas ex vivo. The observed results agreed well with the earlier-reported data, justifying water as a main endogenous label of brain tumors in the THz range. The developed models can be used to describe completely the THz-wave - human brain tissues interactions in the frameworks of classical electrodynamics, being quite important for further research and developments in THz neurodiagnosis of tumors.

Capability of physically reasonable OCT-based differentiation between intact brain tissues, human brain gliomas of different WHO grades, and glioma model 101.8 from rats

Optical coherence tomography (OCT) of the ex vivo rat and human brain tissue samples is performed. The set of samples comprises intact white and gray matter, as well as human brain gliomas of the World Health Organization (WHO) Grades I-IV and glioma model 101.8 from rats. Analysis of OCT signals is aimed at comparing the physically reasonable properties of tissues, and determining the attenuation coefficient, parameter related to effective refractive index, and their standard deviations. Data analysis is based on the linear discriminant analysis and estimation of their dispersion in a four-dimensional principal component space. The results demonstrate the distinct contrast between intact tissues and low-grade gliomas and moderate contrast between intact tissues and high-grade gliomas. Particularly, the mean values of attenuation coefficient are 7.56±0.91, 3.96±0.98, and 5.71±1.49 mm-1 for human white matter, glioma Grade I, and glioblastoma, respectively. The significant variability of optical properties of high Grades and essential differences between rat and human brain tissues are observed. The dispersion of properties enlarges with increase of the glioma WHO Grade, which can be attributed to the growing heterogeneity of pathological brain tissues. The results of this study reveal the advantages and drawbacks of OCT for the intraoperative diagnosis of brain gliomas and compare its abilities separately for different grades of malignancy. The perspective of OCT to differentiate low-grade gliomas is highlighted by the low performance of the existing intraoperational methods and instruments.

Label-free brain tissue imaging using large-area terahertz metamaterials

Terahertz (THz) imaging technology has shown significant potential for use in biomedical imaging owing to its non-ionizing characteristics by its low photon energy and its ultrabroadband spectral comparability with many molecular vibrational resonances. However, despite the significant advantage of being able to identify bio-materials in label-free configurations, most meaningful signals are buried by huge water absorption, thus it is very difficult to distinguish them using the small differences in optical constants at THz regime, limiting the practical application of this technology. Here, we demonstrate advanced THz imaging with enhanced color contrast by the use of THz field that is localized and enhanced by a nanometer-scale slot array. THz images of a biological specimen, such as mouse brain tissue and fingerprint, on a nano-slot array-based metamaterial sensing chip, which is elaborately fabricated in large-area, show a higher contrast and clearer boundary information in reflectance without any labeling. A reliable numerical solution to find accurate optical constants using THz nano-slot resonance for the quantitative analysis of target bio-specimens is also introduced. Finally, the precise optical properties of real bio-samples and atlas information are provided for specific areas where amyloid beta proteins, known to cause dementia, have accumulated in a mouse brain.

AVNP2 protects against cognitive impairments induced by C6 glioma by suppressing tumour associated inflammation in rats

Glioblastoma is a kind of malignant tumour and originates from the central nervous system. In the last century, some researchers and clinician have noticed that the psychosocial and neurocognitive functioning of patients with malignant gliomas can be impaired. Many clinical studies have demonstrated that part of patients, adults or children, diagnosed with glioblastoma will suffer from cognitive deficiency during their clinical course, especially in long-term survivors. Many nanoparticles (NPs) can inhibit the biological functions of tumours by modulating tumour-associated inflammation, which provokes angiogenesis and tumour growth. As one of the best antiviral nanoparticles (AVNPs), AVNP2 is the 2nd generation of AVNP2 that have been conjugated to graphite-graphene for improving physiochemical performance and reducing toxicity. AVNP2 inactivates viruses, such as the H1N1 and H5N1influenza viruses and even the SARS coronavirus, while it inhibits bacteria, such as MRSA and E. coli. As antimicrobials, nanoparticles are considered to be one of the vectors for the administration of therapeutic compounds. Yet, little is known about their potential functionalities and toxicities to the neurotoxic effects of cancer. Herein, we explored the functionality of AVNP2 on inhibiting C6 in glioma-bearing rats. The novel object-recognition test and open-field test showed that AVNP2 significantly improved the neuro-behaviour affected by C6 glioma. AVNP2 also alleviated the decline of long-term potentiation (LTP) and the decreased density of dendritic spines in the CA1 region induced by C6. Western blot assay and immunofluorescence staining showed that the expressions of synaptic-related proteins (PSD-95 and SYP) were increased, and these findings were in accordance with the results mentioned above. It revealed that the sizes of tumours in C6 glioma-bearing rats were smaller after treatment with AVNP2. The decreased expression of inflammatory factors (IL-1β, IL-6 and TNF-α) by Western blotting assay and ELISA, angiogenesis protein (VEGF) by Western blotting assay and other related proteins (BDNF, NF-ĸB, iNOS and COX-2) by Western blotting assay in peri-tumour tissue indicated that AVNP2 could control tumour-associated inflammation, thus efficiently ameliorating the local inflammatory condition and, to some extent, inhibiting angiogenesis in C6-bearing rats. In conclusion, our results suggested that AVNP2 could have an effect on the peri-tumor environment, obviously restraining the growth progress of gliomas, and eventually improving cognitive levels in C6-bearing rats.

[Determination of pathological margin of hypopharyngeal cancer by terahertz time-domain spectroscopy system]

Objective:To investigate the accuracy of the terahertz system in differentiating hypopharyngeal cancer from normal tissue and its role in determining the pathological incised margin of hypopharyngeal cancer. Method:The transplantation model of hypopharyngeal cancer in 5-week-old male BALB/c nude mice were established by subcutaneous injection. The obtained transplanted tumor specimens were pathologically diagnosed to determine the extent of tumor tissue. Tumor tissue, normal tissue and paracellular tissue of transplantation tumor were scanned by terahertz time-domain spectroscopy. The differential spectral data were obtained through the detection of frozen tissue sections and paraffin tissue sections, respectively. The results were compared by t-test. Result:The tarahertz absorption coefficient of tumor tissues was higher than that of normal tissues, and the difference was statistically significant when the detection frequency was greater than 0.48 THz in frozen sections（P<0.05）. In the paraffin sections, the difference was statistically significant within the effective spectrum range of 0.2-1.6 THz（P<0.01）. The difference of refractive index between tumor tissue and normal tissue was significant in specimens treated in two ways（P<0.01）. The absorption coefficient of adjacent tissue felt between that of normal tissue and tumor tissue. Conclusion:Terahertz technology can distinguish tumor tissues and normal tissues accurately, and can detect the spectral changes in adjacent tissues sensitively. Therefore, terahertz technology may become another tool for the judgment of pathologic margin.

Study of in vivo brain glioma in a mouse model using continuous-wave terahertz reflection imaging

We demonstrated that in vivo brain glioma in a mouse model using a continuous-wave terahertz reflection imaging system, as well as the ex vivo fresh brain tissues in mouse model. The tumor regions of in vivo and ex vivo brain tissues can be well distinguished by THz intensity imaging at the frequency of 2.52THz. The THz images with high sensitivity correlated well with magnetic resonance, visual and hematoxylin and eosin stained images. Furthermore, the THz spectral difference between brain gliomas and normal brain tissues were obtained in the 0.6THz to 2.8THz range, where brain gliomas have the higher refractive indices and absorption coefficients, and their differences increase particularly in the high frequency range. These results suggest that THz imaging has great potential as an alternative method for the intraoperative label-free diagnosis of brain glioma in vivo.

Multimodal Optical Diagnostics of Glycated Biological Tissues

Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia accompanied by the disruption of carbohydrate, lipid, and proteins metabolism and development of long-term microvascular, macrovascular, and neuropathic changes. This review presents the results of spectroscopic studies on the glycation of tissues and cell proteins in organisms with naturally developing and model diabetes and in vitro glycated samples in a wide range of electromagnetic waves, from visible light to terahertz radiation. Experiments on the refractometric measurements of glycated and oxygenated hemoglobin in broad wavelength and temperature ranges using digital holographic microscopy and diffraction tomography are discussed, as well as possible application of these methods in the diabetes diagnostics. It is shown that the development and implementation of multimodal approaches based on a combination of phase diagnostics with other methods is another promising direction in the diabetes diagnostics. The possibilities of using optical clearing agents for monitoring the diffusion of substances in the glycated tissues and blood flow dynamics in the pancreas of animals with induced diabetes have also been analyzed.

Terahertz spectroscopy of gelatin-embedded human brain gliomas of different grades: a road toward intraoperative THz diagnosis

We applied terahertz (THz)-pulsed spectroscopy to study ex vivo the refractive index and absorption coefficient of human brain gliomas featuring different grades, as well as perifocal regions containing both intact and edematous tissues. Glioma samples from 26 patients were considered and analyzed according to further histological examination. In order to fix tissues for the THz measurements, we applied gelatin embedding, which allows for sustaining their THz response unaltered, as compared to that of the freshly excised tissues. We observed a statistical difference between the THz optical constants of intact tissues and gliomas of grades I to IV, while the response of edema was similar to that of tumor. The results of this paper justify a potential of THz technology in the intraoperative label-free diagnosis of human brain gliomas for ensuring the gross-total resection.

Multicolor T-Ray Imaging Using Multispectral Metamaterials

Recent progress in ultrafast spectroscopy and semiconductor technology is enabling unique applications in screening, detection, and diagnostics in the Terahertz (T-ray) regime. The promise of efficaciously operation in this spectral region is tempered by the lack of devices that can spectrally analyze samples at sufficient temporal and spatial resolution. Real-time, multispectral T-ray (Mul-T) imaging is reported by designing and demonstrating hyperspectral metamaterial focal plane array (MM-FPA) interfaces allowing multiband (and individually tunable) responses without compromising on the pixel size. These MM-FPAs are fully compatible with existing microfabrication technologies and have low noise when operating in the ambient environment. When tested with a set of frequency switchable quantum cascade lasers (QCLs) for multicolor illumination, both MM-FPAs and QCLs can be tuned to operate at multiple discrete THz frequencies to match analyte "fingerprints." Versatile imaging capabilities are presented, including unambiguous identification of concealed substances with intrinsic and/or human-engineered THz characteristics as well as effective diagnosis of cancerous tissues without notable spectral signatures in the THz range, underscoring the utility of applying multispectral approaches in this compelling wavelength range for sensing/identification and medical imaging.

Strong polarization-dependent terahertz modulation of aligned Ag nanowires on Si substrate

Optically tunable, strong polarization-dependent transmission of terahertz pulses through aligned Ag nanowires on a Si substrate is demonstrated. Terahertz pulses primarily pass through the Ag nanowires and the transmittance is weakly dependent on the angle between the direction of polarization of the terahertz pulse and the direction of nanowire alignment. However, the transmission of a terahertz pulse through optically excited materials strongly depends on the polarization direction. The extinction ratio increases as the power of the pumping laser increases. The enhanced polarization dependency is explained by the redistribution of photocarriers, which accelerates the sintering effect along the direction of alignment of the Ag nanowires. The photocarrier redistribution effect is examined by the enhancement of terahertz emission from the sample. Oblique metal nanowires on Si could be utilized for designing optically tunable terahertz polarization modulators.

Measuring water contents in animal organ tissues using terahertz spectroscopic imaging

We investigated the water contents in several organ tissues such as the liver, spleen, kidney, and brain tissue of rats using the terahertz spectroscopic imaging technique. The water contents of the tissues were determined by using a simple equation containing the absorption coefficients of fresh and lyophilized tissues and water. We compared the measured water contents with the difference in mass of tissues before and after lyophilization. All results showed a good match except for the kidney, which has several Bowman's capsules.

High-sensitivity terahertz imaging of traumatic brain injury in a rat model

We demonstrated that different degrees of experimental traumatic brain injury (TBI) can be differentiated clearly in fresh slices of rat brain tissues using transmission-type terahertz (THz) imaging system. The high absorption region in THz images corresponded well with the injured area in visible images and magnetic resonance imaging results. The THz image and absorption characteristics of dehydrated paraffin-embedded brain slices and the hematoxylin and eosin (H&E)-stained microscopic images were investigated to account for the intrinsic differences in the THz images for the brain tissues suffered from different degrees of TBI and normal tissue aside from water. The THz absorption coefficients of rat brain tissues showed an increase in the aggravation of brain damage, particularly in the high-frequency range, whereas the cell density decreased as the order of mild, moderate, and severe TBI tissues compared with the normal tissue. Our results indicated that the different degrees of TBI were distinguishable owing to the different water contents and probable hematoma components distribution rather than intrinsic cell intensity. These promising results suggest that THz imaging has great potential as an alternative method for the fast diagnosis of TBI.

Glycerol dehydration of native and diabetic animal tissues studied by THz-TDS and NMR methods

The optical clearing method has been widely used for different spectral ranges where it provides tissue transparency. In this work, we observed the enhanced penetration of the terahertz waves inside biological samples (skin, kidney, and cornea) treated with glycerol solutions inducing changes of optical and dielectric properties. It was supported by the observed trend of free-to-bound water ratio measured by the nuclear magnetic resonance (NMR) method. The terahertz clearing efficiency was found to be less for diabetic samples than for normal ones. Results of the numerical simulation proved that pulse deformation is due to bigger penetration depth caused by the reduction of absorption and refraction at optical clearing.

Terahertz Spectroscopic Diagnosis of Myelin Deficit Brain in Mice and Rhesus Monkey with Chemometric Techniques

While myelin deficit of the central nervous system leads to several severe diseases, the definitive diagnostic means are lacking. We proposed and performed terahertz time-domain spectroscopy (THz-TDS) combined with chemometric techniques to discriminate and evaluate the severity of myelin deficit in mouse and rhesus monkey brains. The THz refractive index and absorption coefficient of paraffin-embedded brain tissues from both normal and mutant dysmyelinating mice are shown. Principal component analysis of time-domain THz signal (PCA-tdTHz) and absorption-refractive index relation of THz spectrum identified myelin deficit without exogenous labeling or any pretreatment. Further, with the established PCA-tdTHz, we evaluated the severity of myelin deficit lesions in rhesus monkey brain induced by experimental autoimmune encephalomyelitis, which is the most-studied animal model of multiple sclerosis. The results well matched the pathological analysis, indicating that PCA-tdTHz is a quick, powerful, evolving tool for identification and evaluation myelin deficit in preclinical animals and potentially in para-clinical human biopsy.

Wide-aperture aspherical lens for high-resolution terahertz imaging

In this paper, we introduce wide-aperture aspherical lens for high-resolution terahertz (THz) imaging. The lens has been designed and analyzed by numerical methods of geometrical optics and electrodynamics. It has been made of high-density polyethylene by shaping at computer-controlled lathe and characterized using a continuous-wave THz imaging setup based on a backward-wave oscillator and Golay detector. The concept of image contrast has been implemented to estimate image quality. According to the experimental data, the lens allows resolving two points spaced at 0.95λ distance with a contrast of 15%. To highlight high resolution in the THz images, the wide-aperture lens has been employed for studying printed electronic circuit board containing sub-wavelength-scale elements. The observed results justify the high efficiency of the proposed lens design.