Entwicklung einer dermatoskopischen Kamera mit Müller-Matrix-Bildgebung

Moderne Methoden zur Diagnostik und Kontrolle von entzündlichen Hauterkrankungen beruhen teilweise auf subjektiv erhobenen Kriterien. Hier wird beispielsweise die Rötung einer Hautläsion vom Arzt ohne objektive Messung eingeschätzt. Die Dokumentation erfolgt mit handelsüblichen Digitalkameras oder extra für die Hautuntersuchung entwickelten Auflichtmikroskopen, den sogenannten Dermatoskopen. Diese haben je nach Gerät und Behandlungsumgebung wechselnde Bildqualität. In der Dermatologie besteht besonders, aber nicht nur, im wissenschaftlichem Bereich ein erheblicher Bedarf an objektivierbaren Untersuchungsmethoden. Dafür bieten optische Lösungen als schnelle und nicht invasive, sogar berührungslose Verfahren erhebliche Vorteile. In dieser Arbeit wird ein Konzept einer dermatoskopischen Kamera vorgestellt, das an die Anforderung der Untersuchung von entzündlichen Hauterkrankungen angepasst ist. Das System ist in der Lage, makroskopische Bilder mit hoher Auflösung in einem, im Vergleich zum Stand der Technik, großem Abstand zum Patienten aufzunehmen. Hierbei wird die Herausforderung der notwendigen automatischen Fokussierung des Systems durch den Einsatz einer Flüssigkeitslinse gelöst. Gleichzeitig werden 3D-Übersichtsaufnahmen ermöglicht, auf denen sich die makroskopischen Aufnahmen verorten lassen. Die Beleuchtung für die Makroaufnahmen erlaubt es, Bilder mit gleichbleibender Bildqualität und Farbwiedergabe unabhängig von der Umgebungsbeleuchtung aufzunehmen. Um das Konzept zu evaluieren werden zwei Prototypen hergestellt. Ein Prototyp umfasst alle wesentlichen Elemente zur Aufnahme der makroskopischen Bilder. Der Andere umfasst zwei Kameras, die als Stereokamera zur Erzeugung der 3D-Übersichtsaufnahmen angeordnet sind. Um mögliche weitere objektive Messdaten zu erzeugen, wird das Potential polarimetrischer Messungen an der Haut evaluiert. Hierbei wird die sogenannte Müller Matrix (MM) gemessen. Diese enthält alle Informationen über die polarisationsverändernden Eigenschaften einer Probe. Diese Eigenschaften können Rückschlüsse auf die Orientierung von Strukturen wie beispielsweise Kollagen in der Haut zulassen. Um diesen Ansatz zu evaluieren, wird ein MM-Messsystem entwickelt und als Laborprototyp aufgebaut. Polymer-Fasermatten, die durch Elektrospinnen erzeugt werden, wurden verwendet um Proben mit unterschiedlicher Ausrichtung von Strukturen zu realisieren. Dieses Verfahren lässt das Einstellen unterschiedlicher Orientierungsgrade der Fasern in einer Vorzugsrichtung zu. Es werden Fasern mit unterschiedlichem Grad der Ausrichtung und unterschiedlicher Vorzugsrichtung gemessen. Es wird gezeigt, dass MM-Messungen den Ausrichtungsgrad der Fasern bestimmen können. Bei unbekannter Vorzugsrichtung der Faserausrichtung erlaubt das Errechnen des Stokes-Vektors der schnellen Achse der Verzögerung nach einer Polarzerlegung der MM Rückschlüsse auf diese. Um die Ergebnisse auf Hautmessungen zu übertragen, werden kollagenhaltige Proben gemessen. Hier kann die Richtung, in die das Kollagen ausgerichtet wird, bestimmt werden. In Zukunft kann das System durch die zusätzlich gemessenen, objektiven Informationen neue Standards für Bewertungskriterien in der Dermatologie liefern. Außerdem dient es als Grundlage für weitere wissenschaftliche Ergebnisse zu polarimetrischen Messungen von entzündlichen Hauterkrankungen

Assuring Quality of Scaffolds in Musculoskeletal Tissue Engineering Mueller Matrix Polarimetry and Transillumination Imaging

In order to achieve the high quality required in medical products, reliable characterization methods and quality management systems are necessary. In the field of musculoskeletal Tissue Engineering (mTE), electrospinning is utilized to manufacture fibre scaffolds as implant material. Depending on the application, in this case the regeneration of tendon-bone junctions, properties like the degree of fibre orientation, homogeneity of fibre throughout the scaffold and reaction to external mechanical load are of particular importance. Currently, destructive methods, like scanning electron microscopy (SEM), are widely used to determine these properties. In addition to the destruction of the samples, these methods often only allow the investigation of very small sections. In this study, we present two new methods for the fast, non-destructive and contactless characterization of electrospun fibre scaffolds for mTE. These methods are based on Transillumination Imaging (TI) and Mueller Matrix Polarimetry (MMP), utilizing low-power laser sources or LED light sources, respectively, to determine the relative homogeneity (TI) and the degree of fibre orientation (MMP) in electrospun fibre scaffolds

Mueller matrix-based approach for the ex vivo detection of riboflavin-treated transparent biotissue

Corneal collagen cross-linking is an established procedure for the treatment of certain eye diseases which is applied to enhance the mechanical stability of such biotissue without deteriorating its functionality. However, being transparent, the optical analysis of the outcome of such treatments is cumbersome and relies on relatively expensive experimental equipment. We aim to apply the Mueller matrix polarimetry for the detection of photo-induced collagen cross-linking in transparent biotissue after treatment with riboflavin and UV irradiation. A simple Mueller matrix polarimetry setup could provide a fast and non-invasive analysis of transparent media to sensitively detect small photo-induced cross-linking effects in biotissue. We demonstrated the current capabilities of the approach on non-planar porcine cornea samples ex vivo. We reported the distinction between untreated and riboflavin-treated samples. The differences observed were correlated with the variation of certain Mueller matrix elements and parameters derived from the decomposition. The measurement data show variation in the cross-linked and non-cross-linked samples, although the effect of the UV treatment on the riboflavin-treated samples was not at the same level of significance yet and needs further investigation. The Mueller matrix measurement represents a promising approach for the detection of the effects of corneal collagen cross-linking. Further studies with a larger sample number are required to validate this approach. In the future, this could enable the reliable and non-invasive detection of photo-induced effects in biotissue and open the possibility for in vivo application, e.g., in eye disease treatment or the detection of scar collagen development. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Mueller Matrix Measurement of Electrospun Fiber Scaffolds for Tissue Engineering

Electrospun fiber scaffolds are gaining in importance in the area of tissue engineering. They can be used, for example, to fabricate graded implants to mimic the tendon bone junction. For the grading of the tensile strength of the fiber scaffolds, the orientation of the fibers plays a major role. This is currently measured by hand in scanning electron microscope (SEM) images. In this work, a correlation between polarimetric information generated by measuring the Mueller matrix (MM) and the orientation of the fibers of electrospun fiber scaffolds is reported. For this, the MM of fiber scaffolds, which were manufactured with different production parameters, was measured and analyzed. These data were correlated with fiber orientation and mechanical properties, which were evaluated in an established manner. We found that by measurement of the MM the production parameters as well as the relative orientation of the fibers in space can be determined. Thus, the MM measurement is suitable as an alternative tool for non-contact, non-destructive determination of the production parameters and, thus, the degree of alignment of electrospun fiber scaffolds

Mueller Matrix Measurement of Electrospun Fiber Scaffolds for Tissue Engineering

Electrospun fiber scaffolds are gaining in importance in the area of tissue engineering. They can be used, for example, to fabricate graded implants to mimic the tendon bone junction. For the grading of the tensile strength of the fiber scaffolds, the orientation of the fibers plays a major role. This is currently measured by hand in scanning electron microscope (SEM) images. In this work, a correlation between polarimetric information generated by measuring the Mueller matrix (MM) and the orientation of the fibers of electrospun fiber scaffolds is reported. For this, the MM of fiber scaffolds, which were manufactured with different production parameters, was measured and analyzed. These data were correlated with fiber orientation and mechanical properties, which were evaluated in an established manner. We found that by measurement of the MM the production parameters as well as the relative orientation of the fibers in space can be determined. Thus, the MM measurement is suitable as an alternative tool for non-contact, non-destructive determination of the production parameters and, thus, the degree of alignment of electrospun fiber scaffolds

Non-Contact Dermatoscope with Ultra-Bright Light Source and Liquid Lens-Based Autofocus Function

Dermatoscopes are routinely used in skin cancer screening but are rarely employed for the diagnosis of other skin conditions. Broader application is promising from a diagnostic point of view as biopsies for differential diagnosis may be avoided but it requires non-contact devices allowing a comparably large field of view that are not commercially available today. Autofocus and color reproducibility are specific challenges for the development of dermatoscopy for application beyond cancer screening. We present a prototype for such a system including solutions for autofocus and color reproducibility independent of ambient lighting. System performance includes sufficiently high feature resolution of up to 30 µm and feature size scaling fulfilling the requirements to apply the device in regular skin cancer screening

Mueller Matrix Analysis of Collagen and Gelatin Containing Samples Towards More Objective Skin Tissue Diagnostics

Electrospun polycaprolactone:gelatin (PCL:GT) fibre scaffolds are widely employed in the field of tissue implants. Here, the orientation of fibres plays an important role in regard to implantation due to the impact on the mechanical properties. Likewise, the orientation of collagen fibres in skin tissue is relevant for dermatology. State-of-the-art fibre orientation measurement methods like electron microscopy are time consuming and destructive. In this work, we demonstrate polarimetry as a non-invasive approach and evaluate its potential by measuring the Mueller matrix (MM) of gelatin and collagen containing samples as simple skin tissue phantoms. We demonstrate that it is possible to determine the orientation of PCL:GT fibre scaffolds within one MM measurement. Furthermore, we determine the structural orientation in collagen film samples. Currently, the diagnosis of skin diseases is often performed by image analysis or histopathology respectively, which are either subjective or invasive. The method presented, here, provides an interesting alternative approach for such investigations. Our findings indicate that the orientation of collagen fibres within skin lesions might be detectable by MM measurements in the future, which is of interest for skin diagnostics, and will be further investigated during the next step

Mueller Matrix-Based Approach for the Ex Vivo Detection of Riboflavin-Treated Transparent Biotissue

Corneal collagen cross-linking is an established procedure for the treatment of certain eye diseases which is applied to enhance the mechanical stability of such biotissue without deteriorating its functionality. However, being transparent, the optical analysis of the outcome of such treatments is cumbersome and relies on relatively expensive experimental equipment. We aim to apply the Mueller matrix polarimetry for the detection of photo-induced collagen cross-linking in transparent biotissue after treatment with riboflavin and UV irradiation. A simple Mueller matrix polarimetry setup could provide a fast and non-invasive analysis of transparent media to sensitively detect small photo-induced cross-linking effects in biotissue. We demonstrated the current capabilities of the approach on non-planar porcine cornea samples ex vivo. We reported the distinction between untreated and riboflavin-treated samples. The differences observed were correlated with the variation of certain Mueller matrix elements and parameters derived from the decomposition. The measurement data show variation in the cross-linked and non-cross-linked samples, although the effect of the UV treatment on the riboflavin-treated samples was not at the same level of significance yet and needs further investigation. The Mueller matrix measurement represents a promising approach for the detection of the effects of corneal collagen cross-linking. Further studies with a larger sample number are required to validate this approach. In the future, this could enable the reliable and non-invasive detection of photo-induced effects in biotissue and open the possibility for in vivo application, e.g., in eye disease treatment or the detection of scar collagen development

Non-Contact Dermatoscope with Ultra-Bright Light Source and Liquid Lens-Based Autofocus Function

Dermatoscopes are routinely used in skin cancer screening but are rarely employed for the diagnosis of other skin conditions. Broader application is promising from a diagnostic point of view as biopsies for differential diagnosis may be avoided but it requires non-contact devices allowing a comparably large field of view that are not commercially available today. Autofocus and color reproducibility are specific challenges for the development of dermatoscopy for application beyond cancer screening. We present a prototype for such a system including solutions for autofocus and color reproducibility independent of ambient lighting. System performance includes sufficiently high feature resolution of up to 30 µm and feature size scaling fulfilling the requirements to apply the device in regular skin cancer screening