Dieter Dirksen

Autofocusing in digital holographic phase contrast microscopy on pure phase objects for live cell imaging

Digital holography enables a multifocus quantitative phase microscopy for the investigation of reflective surfaces and for marker-free live cell imaging. For digital holographic long-term investigations of living cells an automated (subsequent) robust and reliable numerical focus adjustment is of particular importance. Four numerical methods for the determination of the optimal focus position in the numerical reconstruction and propagation of the complex object waves of pure phase objects are characterized, compared, and adapted to the requirements of digital holographic microscopy. Results from investigations of an engineered surface and human pancreas tumor cells demonstrate the applicability of Fourier-weighting- and gradient-operator-based methods for robust and reliable automated subsequent numerical digital holographic focusing.

Automated three-dimensional tracking of living cells by digital holographic microscopy.

Digital holographic microscopy (DHM) enables a quantitative multifocus phase contrast imaging that has been found suitable for technical inspection and quantitative live cell imaging. The combination of DHM with fast and robust autofocus algorithms enables subsequent automated focus realignment by numerical propagation of the digital holographically reconstructed object wave. In combination with a calibrated optical imaging system, the obtained propagation data quantify axial displacements of the investigated sample. The evaluation of quantitative DHM phase contrast images also enables an effective determination of lateral cell displacements. Thus, 3-D displacement data are provided. Results from investigations on sedimenting red blood cells and HT-1080 fibrosarcoma cells in a collagen tissue model demonstrate that DHM enables marker-free automated quantitative dynamic 3-D cell tracking without mechanical focus adjustment.

Clinical anatomy and palpability of the inferior lateral pterygoid muscle

STATEMENT OF PROBLEM The intraoral palpation technique of the inferior belly of the inferior lateral pterygoid (ILP) muscle is a standard diagnostic examination method for temporomandibular joint dysfunction syndrome, although different studies have revealed inconsistent results. PURPOSE This study assessed the feasibility of the ILP muscle palpation by a simulated clinical setting. MATERIAL AND METHODS Three dentists performed a bilateral palpation of the ILP muscle in 53 fresh and unfixed human cadavers and decided whether the muscle was palpable or unpalpable. In a second step, it was observed through the dissected infratemporal fossa, whether the examiners finger did or did not touch the ILP muscle by simulating the performed palpation. Palpatory findings were supplemented by 1-dimensional measurements for determination of topographic relations of the ILP muscle within the infratemporal fossa. For statistical analysis, sensitivity, specificity, and negative and positive predictive values of the palpation technique were calculated. Interexaminer agreement was estimated with the kappa value. RESULTS In 86 of 106 dissected specimens, a superficial fascicle of the medial pterygoid muscle was found in direct proximity to the ILP muscle. In these cases, a residual distance of 7.8 +/- 3.2 mm remained between the ILP muscle and buccinator fascia indented by the tip of the examiners finger. In 10 of 20 specimens with an absent superficial fascicle, the finger was able to reach the ILP muscle. CONCLUSION It is recommended that the ILP muscle palpation technique should no longer be considered as a standard clinical procedure because it is nearly impossible to palpate the ILP muscle anatomically and because the risk of false-positive findings (by palpation of the medial pterygoid muscle) is high.

Holographic double-exposure interferometry in near real time with photorefractive crystals

A holographic interferometric technique based on fast sequences of double exposures in photorefractive crystals for the dynamic analysis of reflection-type objects is presented. Methods for optimizing the diffraction efficiency and the decay time of the holographic gratings recorded at short exposure times are discussed. Special attention is paid to the use of external electrical fields. The maximization of fringe contrast in double-exposed interferograms is investigated both theoretically and experimentally. Finally, the automatic evaluation of interferograms is demonstrated by use of a sample sequence of interferograms.

Lensless Fourier holography for digital holographic interferometry on biological samples

Abstract Digital holography as a tool for highly sensitive, interferometric non-destructive testing has several advantages compared to holographic measurements based on conventional storage media like an all-digital processing and a direct access to the phase of the object wave. Experimental results of interferometric investigations of heart valve bio-prostheses with a setup for lensless Fourier holography are presented which demonstrate that this technique is applicable to such biological samples with their wet and unstable surfaces. Limitations on size and resolution of the reconstructed object caused by the properties of the CCD sensor are discussed.

Endoscopic double-pulse electronic-speckle-pattern interferometer for technical and medical intracavity inspection.

An endoscope electronic-speckle-pattern interferometer (ESPI) camera system is presented that can be applied to examinations of technical objects as well as for in vitro and in vivo minimal invasive medical diagnostics. Integration of optical fibers for the guidance of a cw-laser beam and an endoscopic imaging system yield a compact ESPI system that opens up new possibilities for highly sensitive interferometric intracavity inspection under handheld conditions. A CCD camera in combination with a fast frame-grabber system allows dynamic image subtractions at a frequency rate of as much as 25 Hz with high fringe contrast. Results from investigations of technical objects and biological objects in vitro and in vivo are obtained. In endoscopic minimal invasive therapy this method could substitute for the missing operators tactile contact with the treated tissue by replacing it with visual information (endoscopic taction).

Optimization of spatial phase shifting in endoscopic electronic speckle pattern interferometry

Endoscopic electronic speckle pattern interferometry (endoscopic ESPI) is a versatile tool for the inspection of technical and biological cavities. By the utilization of spatial phase shifting (SPS) methods, it is possible to obtain quantitative information about movements and displacements. An important quality parameter for such phase measurement techniques is a minimized noise of the phase difference. In this paper, a geometry for digital Fourier holographic reconstruction of the exit aperture of the endoscope imaging system is presented to adjust precisely and reliably the phase gradient between object wave and reference wave. Thus, the noise of the phase difference measured by endoscope SPS ESPI systems is reduced. Furthermore, the experimental setup can be simply integrated into an endoscope ESPI system with the advantage that no additional aperture in the optical path is needed.

Phase shifting holographic double exposure interferometry with fast photorefractive crystals

Abstract A technique for quasi real-time holographic interferometry with reflection type objects is presented. It is based on fast sequences of holographic double exposure interferograms recorded in sillenite-type photorefractive BTO crystals. The application of the phase shifting method for automatic quantitative evaluation of the obtained interferograms under the special constraint of short storage times in fast photorefractive crystals is investigated. Approaches to overcome this difficulty by applying a time dependent external electric field are discussed. Experimental results for dynamic analysis of reflecting type objects are presented.

Quantification of facial asymmetry by 2D analysis – A comparison of recent approaches

INTRODUCTION Symmetry has been found to play a crucial role in attractiveness assessment and so its restoration is an essential problem in oral maxillofacial surgery. This paper presents an overview of recent 2D asymmetry analysis techniques. These are techniques which are based on the evaluation of two-dimensional data, like photos. The aim of this paper is to find the most precise and practical techniques to investigate facial asymmetry. MATERIALS AND METHODS For this purpose studies addressing symmetry investigations are collected and categorized by the type of data they extract from the photos. The reference points on the facial surface, which are frequently used in these studies, are presented and calculation methods are described. RESULTS Three kinds of techniques using vertical or horizontal reference lines or centres of bilateral points appear to be most appropriate. Recommendations are made, which aspects should be taken into account when calculating symmetry/asymmetry indices from photos. Advantages and disadvantages of the three selected methods are summarized in a table. CONCLUSIONS Using one of the three recommended approaches denoted by FA, AI and z-score allows calculating meaningful asymmetry values. The proper selection and identification of reference points is crucial. For highest accuracy, a sufficient number of evenly distributed and reproducible reference points should be used.

Quantitative determination of out-of-plane displacements by endoscopic electronic-speckle-pattern interferometry

The combination of endoscopes and electronic-speckle-pattern interferometry requires a more detailed consideration of their imaging properties with respect to interferometric fringe formation, if a quantitative analysis of the observed deformation is desired. Due to a relatively small distance between the illuminating and the imaging optical elements and to strongly divergent beams, the sensitivity vector may not be regarded as constant, and image distortions caused by the endoscope optics must be taken into account. A simplified model that deals with the situation of a plane object perpendicular to the optical axes of the endoscope is presented and verified by experimental results.