Bettina Heise

Dynamic optical studies in materials testing with spectral-domain polarization-sensitive optical coherence tomography

By combining dynamic mechanical testing with spectral-domain polarization-sensitive optical coherence tomography (SD-PS-OCT) performed at 1550 nm we are able to directly investigate for the first time changes within scattering technical materials during tensile and fracture tests. Spatially and temporally varying polarization patterns, due to defects and material inhomogeneities, were observed within bulk polymer samples and used to finally obtain--with the help of advanced image processing algorithms--quantitative maps of the evolving internal stress distribution. Furthermore, locally increased stress within fiber-reinforced composite materials was identified in situ with SD-PS-OCT to cause depolarizing sites of fiber-matrix debonding prior the onset of complete structural failure.

Imaging-based live cell yeast screen identifies novel factors involved in peroxisome assembly.

We describe an imaging-based method in intact cells to systematically screen yeast mutant libraries for abnormal morphology and distribution of fluorescently labeled subcellular structures. In this study, chromosomally expressed green fluorescent protein (GFP) fused to the peroxisomal targeting sequence 1, consisting of serine-lysine-leucine, was introduced into 4740 viable yeast deletion mutants using a modified synthetic genetic array (SGA) technology. A benchtop robot was used to create ordered high-density arrays of GFP-expressing yeast mutants on solid media plates. Immobilized live yeast colonies were subjected to high-resolution, multidimensional confocal imaging. A software tool was designed for automated processing and quantitative analysis of acquired multichannel three-dimensional image data. The study resulted in the identification of two novel proteins, as well as of all previously known proteins required for import of proteins bearing peroxisomal targeting signal PTS1, into yeast peroxisomes. The modular method enables reliable microscopic analysis of live yeast mutant libraries in a universally applicable format on standard microscope slides, and provides a step toward fully automated high-resolution imaging of intact yeast cells.

Generalized Analytic Signals in Image Processing: Comparison, Theory and Applications

This article is intended as a mathematical overview of the generalizations of analytic signals to higher-dimensional problems, as well as of their applications to and of their comparison on artificial and real-world image samples.

Flexible contrast for low-coherence interference microscopy by Fourier-plane filtering with a spatial light modulator

We propose a full-field low-coherence interference (LCI) microscope that can provide different contrast modes using Fourier-plane filtering by means of a spatial light modulator. By altering the phase and spatial frequencies of the backreflected wavefront from the sample arm of the interferometer, we are able to change the contrast in the depth-resolved LCI images. We demonstrate that different types of contrast modes, such as, e.g., spiral phase contrast, can successfully be emulated to provide specific enhancement of internal structures and edges and to reveal complementary details within the samples under investigation.

An automatic cell segmentation method for differential interference contrast microscopy

With the huge amount of cell images produced in bio-imaging, automatic methods for segmentation are needed in order to evaluate the content of the images with respect to types of cells and their sizes. Traditional PDE-based methods using level-sets can perform automatic segmentation, but do not perform well on images with clustered cells containing sub-structures. Furthermore, DIC images contain a phase gradient, which should be removed first. We present a method that removes this gradient, finds the cell centres and derives the relevant individual cells.

Spatially Resolved Stress Measurements in Materials With Polarisation‐Sensitive Optical Coherence Tomography: Image Acquisition and Processing Aspects

:  We demonstrate that polarisation-sensitive optical coherence tomography (PS-OCT) is suitable for mapping the stress distribution within materials in a contact-free and non-destructive way. In contrast to transmission photoelasticity measurements, the samples do not have to be transparent but can be of scattering nature. Denoising and analysis of fringe patterns in single PS-OCT retardation images are demonstrated to be the bases for a quantitative whole-field evaluation of the internal stress state of samples under investigation.

Full-field optical coherence microscopy with Riesz transform-based demodulation for dynamic imaging

We present dynamic full-field optical coherence microscope imaging using a scientific complementary metal oxide semiconductor camera in conjunction with a demodulation scheme based on the Riesz transform and monogenic signals. The potential of our approach is verified by a comparison with conventional phase-stepping as well as with an analytic reconstruction method and finally exemplified for dynamic mechanical testing of a polymer/fiber composite structure.

A Clustering Based Denoising Technique for Range Images of Time of Flight Cameras

A relatively new technique for measuring the 3D structure of visual scenes is provided by time of flight (TOF) cameras. Reflections of modulated light waves are recorded by a parallel pixel array structure. The time series at each pixel of the resulting image stream is used to estimate travelling time and thus range information. This measuring technique results in pixel dependent noise levels with variances changing over several orders of magnitude dependent on the illumination and material parameters. This makes application of traditional (global) denoising techniques suboptimal. Using free additional information from the camera and a clustering procedure we can get information about which pixels belong to the same object, and what their noise level is, which allows for locally adapted smoothing. To illustrate the success of this method, we compare it with raw camera output and a traditional method for edge preserving smoothing, anisotropic diffusion. We show that this mathematical technique works without individual adaptations on two camera systems with highly different noise characteristics.

Quantitative phase reconstruction for orthogonal-scanning differential phase-contrast optical coherence tomography

We present differential phase-contrast optical-coherence tomography (DPC-OCT) with two transversally separated probing beams to sense phase gradients in various directions by employing a rotatable Wollaston prism. In combination with a two-dimensional mathematical-reconstruction algorithm based on a regularized shape from shading method, accurate quantitative phase maps can be determined from a set of two orthogonal en-face DPC-OCT images, as exemplified on various technical samples.

Denoising techniques for raw 3D data of TOF cameras based on clustering and wavelets

In order to measure the 3D structure of a number of objects a comparably new technique in computer vision exists, namely time of flight (TOF) cameras. The overall principle is rather easy and has been applied using sound or light for a long time in all kind of sonar and lidar systems. However in this approach one uses modulated light waves and receives the signals by a parallel pixel array structure. Out of the travelling time at each pixel one can estimate the depth structure of a distant object. The technique requires measuring the intensity differences and ratios of several pictures with extremely high accuracy; therefore one faces in practice rather high noise levels. Object features as reflectance and roughness influence the measurement results. This leads to partly high noise levels with variances dependent on the illumination and material parameters. It can be shown that a reciprocal relation between the variance of the phase and the squared amplitude of the signals exists. On the other hand, objects can be distinguished using these dependencies on surface characteristics. It is shown that based on local variances assigned to separated objects appropriate denoising can be performed based on Wavelets and edge-preserving smoothing methods.