The early identification of proximal carious lesions is still one of the most challenging issues in modern cariology and odontology, whereas several visual, optical, and radiographic techniques have been developed and improved in recent years.^1,2 Providing depth-resolved, high-resolution images of biological samples, optical coherence tomography (OCT) is a promising tool for detecting caries noninvasively, since first investigations of dental hard tissue in vitro and in vivo were performed by OCT,^3,4 and imaging in the near-infrared range proved convenient scattering and absorption properties.⁵ So far, OCT has shown the potential to provide effective and reproducible diagnoses for clinical applications,⁶ and algorithms that enable early caries segmentation from conventional OCT images have been presented.⁷ Additionally to the structural imaging based on backscattering intensities, miscellaneous modalities and extensions for OCT have been developed, which provide tissue-dependent contrast. This includes polarization sensitive imaging and the consequent measurement of depth-resolved birefringence, which until now has been applied in many biomedical as well as nonmedical fields.^8,9 In terms of hard dental tissue and caries detection, first polarization sensitive OCT (PS-OCT) measurements confirmed the birefringent properties of enamel and dentin,^4,10 and it was determined that demineralization, accompanying carious infections, results in depolarization of light.¹¹ Since then, several studies have shown the potential of PS-OCT to observe the internal structure and the remineralization of lesions, as well as an early detection of variously located caries.¹² 13. ^{– 14} Thereby, the occurring depolarization effect for linearly polarized incident light is usually evaluated by an intensity measurement of the perpendicular polarization state.¹⁵

The development of improved preservation techniques and the reliable assessment of donor grafts are main fields of research in transplantation medicine. Normothermic machine perfusion (NMP) is a promising alternative to static cold storage of organs, maintaining physiological conditions during preservation. In combination with NMP, we introduce hyperspectral imaging (HSI) as a novel approach for the monitoring of physiological kidney parameters. A line-scan HSI camera system was used to record images of porcine kidneys during NMP. Based on a dual-wavelength algorithm, the oxygen saturation levels were calculated from HSI recordings. Furthermore, we observed HSI images in the near-infrared (NIR) range in order to detect water characteristics of the kidney tissue. We found increasing levels of oxygenation during NMP and could discriminate between perfused and non-perfused areas. Cysts at the renal capsula were characterized by an absorption increase in the NIR band. Within this work, we showed that HSI is able to detect relevant chemical changes during NMP and allows the identification of pathologic variations.

The common way to diagnose hard and soft tissue irregularities in the oral cavity is initially the visual inspection by an experienced dentist followed by further medical examinations, such as radiological imaging and/or histopathological investigation. For the diagnosis of oral hard and soft tissues, the detection of early transformations is mostly hampered by poor visual access, low specificity of the diagnosis techniques, and/or limited feasibility of frequent screenings. Therefore, optical noninvasive diagnosis of oral tissue is promising to improve the accuracy of oral screening. Considering this demand, a rigid handheld endoscopic scanner was developed for optical coherence tomography (OCT). The novelty is the usage of a commercially near-infrared endoscope with fitting optics in combination with an established spectral-domain OCT system of our workgroup. By reaching a high spatial resolution, in vivo images of anterior and especially posterior dental and mucosal tissues were obtained from the oral cavity of two volunteers. The convincing image quality of the endoscopic OCT device is particularly obvious for the imaging of different regions of the human soft palate with highly scattering fibrous layer and capillary network within the lamina propria.

Various biological tissues change the polarization of light, for which reason tissue polarization properties can be important for the diagnosis of pathological alterations in tendons, bones, cartilages, teeth, and skin. Biological media are often birefringent caused by asymmetrically oriented structures, e.g., collagen fibers and dentinal microtubules, as well as molecular and mineralized compositions in biological tissue. Since polarization imaging is innovative and promising for medical diagnosis of pathologies, technical solutions for clinical in vivo applications are in demand. Because optical coherence tomography (OCT) is a prospective noninvasive imaging technique for three-dimensional high-resolution imaging of subsurface tissue morphology¹ 2. 3. ^{– 4} with the possibility of functional imaging by polarization-sensitive OCT (PS OCT), it is attractive for depth-resolved tissue-specific contrast imaging with high speed and sensitivity in vivo. Although conventional intensity-based OCT provides a high spatial resolution in the micrometer range, tissue micro- and nanostructures cannot be resolved optically. By detecting the polarization change of the reflected light with PS OCT, properties of polarization changing microstructures can provide information of early pathological alterations before morphological tissue remodeling occurs in larger scale detectable with intensity-based OCT.^5,6

The detection of the beginning demineralization process of dental hard tissue remains a challenging task in dentistry. As an alternative to bitewing radiographs, optical and spectroscopic technologies showed promising results for caries diagnosis. The aim of the present work is to give an overview of optical and spectroscopic properties of healthy and carious human teeth in vitro by means of Raman spectroscopy (RS), optical coherence tomography (OCT) and hyperspectral imaging (HSI). OCT was able to represent microstructural changes below the enamel surface and revealed increased scattering for white spot lesions and a white scattering trail for deeper lesions. HSI showed similar absorbance characteristics for healthy and demineralized enamel over the entire spectrum and a characteristic absorbance peak at 550 nm for discolored lesions. Already at early carious stages (white spot), we found a distinct loss of hydroxylapatite-related intensity at 959 cm⁻¹ in demineralized regions with RS. Healthy and demineralized tooth surfaces can be distinguished at different signal levels by means of RS, OCT and HSI. The presented modalities provide additional information to the current clinical diagnosis of caries such as microstructural changes, quantification of the demineralization and imaging of caries-related chemical changes.