In-vivo multilaboratory investigation of the optical properties of the human head

The in-vivo optical properties of the human head are investigated in the 600–1100 nm range on different subjects using continuous wave and time domain diffuse optical spectroscopy. The work was performed in collaboration with different research groups and the different techniques were applied to the same subject. Data analysis was carried out using homogeneous and layered models and final results were also confirmed by Monte Carlo simulations. The depth sensitivity of each technique was investigated and related to the probed region of the cerebral tissue. This work, based on different validated instruments, is a contribution to fill the existing gap between the present knowledge and the actual in-vivo values of the head optical properties

Bestimmung der optischen Eigenschaften trüber Medien mittels nichtinvasiver Remissionsmessungen

In this thesis two techniques for determination of the absorption- and reduced scattering coefficients of turbid media were introduced. The fundamentals of the spatially resolved reflectance method, measured with a CCD-Camera, were investigated and optimized. Further a new method, which measures the total reflectance of a sample, was developed and verified. Using both methods the optical properties of several biological samples could be determined with high spectral resolution. The compliance of both methods ensures the determination quality of the optical properties. For data analysis the light propagation in turbid media was described theoretically using the radiative transfer theory and the diffusion theory. The inverse problem for the determination of the optical properties was solved using a nonlinear least squares algorithm. The systematic errors in the determination of the optical properties caused by using the different theories were investigated. The method was validated using liquid phantoms and the measurement range was specified. The performance of both methods could be shown by determination of the optical properties of different biological samples. The absorption- and reduced scattering coefficients of these samples were determined and, thus, the ingredients of the media could be identified. This work enables the determination of the optical properties of a variety of turbid media which can be used for a lot of applications in the field of process control or medical diagnostics and therapy

Continuous Sizing and Identification of Microplastics in Water

The pollution of the environment with microplastics in general, and in particular, the contamination of our drinking water and other food items, has increasingly become the focus of public attention in recent years. In order to better understand the entry pathways into the human food chain and thus prevent them if possible, a precise characterization of the particles concerning their size and material is indispensable. Particularly small plastic particles pose a special challenge since their material can only be determined by means of large experimental effort. In this work, we present a proof of principle experiment that allows the precise determination of the plastic type and the particle size in a single step. The experiment combines elastic light scattering (Mie scattering) with inelastic light scattering (Raman scattering), the latter being used to determine the plastic type. We conducted Monte Carlo simluations for the elastically scattered light for different kinds of plastics in a microfluidic cuvette which we could reproduce in the experiment. We were able to measure the Raman signals for different microplastics in the same measurement as the elastically scattered light and thereby determine their material. This information was used to select the appropriate Monte Carlo simulation data and to assign the correct particle size to different materials with only one calibration measurement

Ex Vivo Determination of Broadband Absorption and Effective Scattering Coefficients of Porcine Tissue

A novel approach for precise determination of the optical scattering and absorption properties of porcine tissue using an optimized integrating sphere setup was applied. Measurements on several sample types (skin, muscle, adipose tissue, bone, cartilage, brain) in the spectral range between 400 nm and 1400 nm were performed. Due to the heterogeneity of biological samples, measurements on different individual animals as well as on different sections for each sample type were carried out. For all samples, we used an index matching method to reduce surface roughness effects and to prevent dehydration. The derived absorption spectra were used to estimate the concentration of important tissue chromophores such as water, oxy- and deoxyhemoglobin, collagen and fat