Optoacoustic inversion via convolution kernel reconstruction in the paraxial approximation and beyond.

In this article we address the numeric inversion of optoacoustic signals to initial stress profiles. Therefore we study a Volterra integral equation of the second kind that describes the shape transformation of propagating stress waves in the paraxial approximation of the underlying wave-equation. Expanding the optoacoustic convolution kernel in terms of a Fourier-series, a best fit to a pair of observed near-field and far-field signals allows to obtain a sequence of expansion coefficients that describe a given "apparative" setup. The resulting effective kernel is used to solve the optoacoustic source reconstruction problem using a Picard-Lindelöf correction scheme. We verify the validity of the proposed inversion protocol for synthetic input signals and explore the feasibility of our approach to also account for the shape transformation of signals beyond the paraxial approximation including the inversion of experimental data stemming from measurements on melanin doped PVA hydrogel tissue phantoms.

Development of a combined OCT-Raman probe for the prospective in vivo clinical melanoma skin cancer screening.

A combined optical coherence tomography (OCT)-Raman probe was designed and built into a spectral domain OCT head, and its performance was evaluated and compared to the most common Raman probe setups, based on a fiber bundle and confocal free space optics. Due to the use of the full field of view of an OCT scanning lens, the combined probe has a superior performance within maximum permissible exposure limits, compared to the other two probes. Skin Raman spectra, recorded in vivo, further prove the feasibility of the OCT-Raman probe for the future in vivo clinical applications in skin cancer screening.

Effective one-dimensional approach to the source reconstruction problem of three-dimensional inverse optoacoustics.

The direct problem of optoacoustic signal generation in biological media consists of solving an inhomogeneous three-dimensional (3D) wave equation for an initial acoustic stress profile. In contrast, the more defiant inverse problem requires the reconstruction of the initial stress profile from a proper set of observed signals. In this article, we consider an effectively 1D approach, based on the assumption of a Gaussian transverse irradiation source profile and plane acoustic waves, in which the effects of acoustic diffraction are described in terms of a linear integral equation. The respective inverse problem along the beam axis can be cast into a Volterra integral equation of the second kind for which we explore here efficient numerical schemes in order to reconstruct initial stress profiles from observed signals, constituting a methodical progress of computational aspects of optoacoustics. In this regard, we explore the validity as well as the limits of the inversion scheme via numerical experiments, with parameters geared toward actual optoacoustic problem instances. The considered inversion input consists of synthetic data, obtained in terms of the effectively 1D approach, and, more generally, a solution of the 3D optoacoustic wave equation. Finally, we also analyze the effect of noise and different detector-to-sample distances on the optoacoustic signal and the reconstructed pressure profiles.

Detection, numerical simulation and approximate inversion of optoacoustic signals generated in multi-layered PVA hydrogel based tissue phantoms.

Optoacoustic (OA) measurements can not only be used for imaging purposes but as a more general tool to "sense" physical characteristics of biological tissue, such as geometric features and intrinsic optical properties. In order to pave the way for a systematic model-guided analysis of complex objects we devised numerical simulations in accordance with the experimental measurements. We validate our computational approach with experimental results observed for layered polyvinyl alcohol hydrogel samples, using melanin as the absorbing agent. Experimentally, we characterize the acoustic signal observed by a piezoelectric detector in the acoustic far-field in backward mode and we discuss the implication of acoustic diffraction on our measurements. We further attempt an inversion of an OA signal in the far-field approximation.

[Thin layer chromatographic test for the indirect and direct detection of the enzyme defect in histidinemia]. / Indirekter und direkter dünnschichtchromatographischer Nachweis des Enzymdefektes bei der Histidinämie.

A thin layer chromatographic method for the direct and indirect detection of the enzyme defect in histidineemia is described. Histidin and urocanic acid are analyzed in 0,2-1 mg stratum corneum for specific screening. 5-10 mg skin biopsy material is needed for the direct measurement of the enzyme activity. This simple metabolic test is convenient even in normal hospital laboratories.

[Creatinine concentration, osmolar concentration and blank color as basis for concentration dependent values in urine (author's transl)]. / Kreatininkonzentration, Osmolalität und Eigenfarbe als Bezugsgrössen für Konzentrationsangaben im Urin

The correlation between Creatinine concentration, osmolality and blank color of urines was investigated. Only values of creatinine concentration and osmolality allow an approximative inter-conversion. For urine analysis, especially in cases of a very high creatinine concentration, we recommend to measure osmolality as a control.