Over the past few decades, significant attention has been paid to the biomedical applications of terahertz (THz) technology. Nowadays, THz spectroscopy and imaging have allowed numerous demanding problems in the biological, medical, food, plant and pharmaceutical sciences to be solved. Among the biomedical applications, the label-free diagnosis of malignant and benign neoplasms represents one of the most attractive branches of THz technology. Despite this attractiveness, THz diagnosis methods are still far from being ready for use in medical practice. In this review, we consider modern research results in the THz diagnosis of malignant and benign neoplasms, along with the topical research and engineering problems which restrain the translation of THz technology to clinics. We start by analyzing the common models of THz-wave–tissue interactions and the effects of tissue exposure to THz waves. Then, we discuss the existing modalities of THz spectroscopic and imaging systems, which have either already been applied in medical imaging, or hold strong potential. We summarize the earlier-reported and original results of the THz measurements of neoplasms with different nosology and localization. We pay attention to the origin of contrast between healthy and pathological tissues in the THz spectra and images, and discuss the prospects of THz technology in non-invasive, minimally invasive and intraoperative diagnosis, as well as in aiding histology. Finally, we review the challenging problems of THz diagnosis, as well as attempts to solve them, which should bring THz technology much closer to medical practice. This review allows one to objectively uncover the benefits and weaknesses of THz technology in the diagnosis of malignant and benign neoplasms.

The skin is the layer of flexible outer tissue covering the body and functions as an interface with the environment.^1,2 The main function of the skin is the protection from external factors, for example, against various xenobiotics and pathogens. Water and temperature balances are also regulated based on the processes in the skin. The functions and dysfunctions of the skin, including many pathological conditions, have a significant impact on both the physical health and general wellness of a person.

Nowadays, composite materials are widely used in building and construction industry, in motor-vehicles, spacecrafts and aircrafts, and in biomedical science due to the ability of combining various consistent components for manufacturing composite materials with physical and chemical properties significantly different from the properties of each component. Polymer composite materials (PCMs) appear to be the most common type of composites. PCMs consist mainly of polymer binder reinforced with the glass-fiber-fabric. Although PCMs are widely applied, PCM manufacturing technology lacks the methods of non- destructive testing. In this paper we demonstrate that terahertz (THz) pulsed spectroscopy (TPS) appears to be a unique instrument for solving important problems of PCM manufacturing control. We experimentally demonstrate the efficiency of TPS for non-destructive control of PCM binder polymerization, since THz radiation is sensitive to changes of picosecond dynamics in media. Furthermore, we show the ability to detect the internal non-impregnated voids inside the PCM structure by means of THz time-of-flight tomography. These results highlight the potentials of TPS applications for non-destructive control of PCM manufacturing process.

An increasing interest in biomedical applications of terahertz (THz) radiation, featuring the frequencies of 0.1 to 3.0 THz, the free-space wavelengths of $\simeq 3\mathrm{mm}$ to $100\mu \mathrm{m}$, or the quantum energies of $\simeq 0.3$ to 10 meV (see Fig. 1), has been observed during the past few decades,^{1 – 5} driven by rapid progress in THz technology.^6,7 Numerous research papers demonstrate the potential of THz technology in label-free early noninvasive, least-invasive, and intraoperative diagnosis of malignant and benign neoplasms with different nosologies and localizations,^{3,4,8 – 18} sensing of glycated tissues and blood in the context of diabetes diagnosis,^{1,19 – 21} determining the degree of traumatic injuries,^{22 – 25} hydration levels,^{26 – 29} and viability³⁰ of tissues. Along with the diagnostic applications, THz technology holds strong potential in therapeutics,^31,32 for example, in nonthermal regulation in expression of genes associated with cancer and inflammatory diseases.³³ Nevertheless, THz therapy is still at the initial stage of its development.

We have developed a method of terahertz (THz) solid immersion (SI) microscopy for continuous-wave reflection-mode imaging of soft biological tissues with a sub-wavelength spatial resolution. In order to achieve strong reduction in the dimensions of the THz beam caustic, an electromagnetic wave is focused into the evanescent field volume behind a medium with a high refractive index. We have experimentally demonstrated a 0.15λ-resolution of the proposed imaging modality at λ = 500 μm, which is beyond the Abbe diffraction limit and represents a considerable improvement over the previously-reported arrangements of SI imaging setups. The proposed technique does not involve any sub-wavelength near-field probes and diaphragms, thus, avoiding the THz beam attenuation due to such elements. We have applied the developed method for THz imaging of various soft tissues: a plant leaf blade, cell spheroids, and tissues of the breast ex vivo. Our THz images clearly reveal sub-wavelength features in tissues, therefore, promising applications of THz SI microscopy in biology and medicine.