Jerzy Pluciński

New aspects in assessment of changes in width of subarachnoid space with near-infrared transillumination/ backscattering sounding, part 2: clinical verification in the patient

The study presents comparison of near-infrared light propagation and near-infrared backscattered radiation power, as simulated with numerical modeling and measured live in a patient in clinical conditions with the use of the near-infrared transillumination-backscattering sounding (NIR-TBSS) technique. A unique chance for such precise comparative analysis was available to us in a clinical case of a female patient with scalp removed from one half of the head due to injury. The analysis performed indicates that the difference between the intensity of the signals in numerical modeling and live measurements is less than 4 dB. Analysis of the theoretical model also provides hints on the positioning of the two detectors relative to the source of radiation. Correctness of these predicted values is confirmed in practical application, when changes of signals received by the detectors are recorded, along with changes of the width of the subarachnoid space. What is more, the power distribution of the spectrum of near-infrared backscattered radiation returning to the detectors is confirmed in the real recording in the patient. An abridged description of the new method of NIR-TBSS is presented.

New aspects in assessment of changes in width of subarachnoid space with near-infrared transillumination/backscattering sounding, part 1: Monte Carlo numerical modeling

A modified Monte Carlo method was used for numerical modeling of the propagation of near-infrared radiation (NIR) within the anatomical layers of the human head. The distribution of NIR transmission between particular anatomical layers in the measurement region (frontal tubers) of the head was obtained. The study demonstrates the effect of the cardiac pump function-dependent changes in the width of the subarachnoid space (SAS) on the intensity of the backscattered radiation. It was proved that the influence of this factor increases with increasing distance between the observation point and the location of the NIR source placed on the surface of the head. Moreover, with sufficiently small NIR detector-source distance, the contribution of the optic radiation propagated within the SAS to the total signal received is negligibly low, which gives a basis for estimation of the modulatory influence of blood circulation within the superficial skin layer on the total intensity of the backscattered radiation. The dimensions of anatomical layers used in the study are real values measured in a female patient, in whom--due to unique circumstances--it was possible to make measurements followed by recordings in clinical conditions, a situation essential for verification of the results of numerical modeling.

Measurements of glucose content in scattering media with time-of-flight technique: comparison with Monte Carlo simulations

Scattering effect of the media can be seen as a pulse broadening and time delay of the pulse maximum relatively to the initial pulse. The purpose of this paper is to study the applicability of the time-of-flight measurement technique for glucose detection in 2% Intralipid solutions in vitro. Glucose samples with concentrations of 100, 200, 300, 500, 1000, 2000, 4000, and 8000 mg/dl are studied. Laser pulses with = 906 nm and FWHM λ = 30 ps are used in the experiments to investigate scattering properties of Intralipid . 1 - 5% suspensions are used to simulate scattering properties of different skin layers in the NIR spectrum region. Measurements are conducted with a slab cuvette, with 300-μm step index type fibers, and with 100-μm gradient index type fibers. Light propagation in the aqueous solutions is also studied by the Monte Carlo simulation. The simulations and the measurement results seem to correlate quite well for Intralipid suspensions. A clear correlation of pulse parameters as a function of Intralipid concentration was found. Slight changes of time delays of pulse maxima and the pulse broadening as a function of glucose concentration were revealed. Gradient index type fibers are found to be better choice for sensing glucose than the step index type fibers.

Multilayered structures examination using polarization sensitive optical coherence tomography

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Spectral measurement of birefringence using particle swarm optimization analysis.

Measurement of birefringence is useful for the examination of technical and biological objects. One of the main problems, however, is that the polarization state of light in birefringent media changes periodically. Without knowledge of the period number, the birefringence of a given medium cannot be reliably determined. We propose to analyze the spectrum of light in order to determine the birefringence. We use a particle swarm optimization algorithm for an automatic processing spectra of light transmitted through birefringent material for two orthogonal states of polarization. We have tested the described algorithm on a liquid crystal cell with varying effective birefringence. The proposed method can be used for the measurement of uniaxial positive birefringence without knowing the number of retardation periods or an approximate value of the measurement result. This fact makes the proposed method useful for automatic measurements, when hundreds or thousands of spectra need to be analyzed.

Time-frequency analysis in optical coherence tomography for technical objects examination

Optical coherence tomography (OCT) is one of the most advanced optical measurement techniques for complex structure visualization. The advantages of OCT have been used for surface and subsurface defect detection in composite materials, polymers, ceramics, non-metallic protective coatings, and many more. Our research activity has been focused on timefrequency spectroscopic analysis in OCT. It is based on time resolved spectral analysis of the backscattered optical signal delivered by the OCT. The time-frequency method gives spectral characteristic of optical radiation backscattered or backreflected from the particular points inside the tested device. This provides more information about the sample, which are useful for further analysis. Nowadays, the applications of spectroscopic analysis for composite layers characterization or tissue recognition have been reported. During our studies we have found new applications of spectroscopic analysis. We have used this method for thickness estimation of thin films, which are under the resolution of OCT. Also, we have combined the spectroscopic analysis with polarization sensitive OCT (PS-OCT). This approach enables to obtain a multiorder retardation value directly and may become a breakthrough in PS-OCT measurements of highly birefringent media. In this work, we present the time-frequency spectroscopic algorithms and their applications for OCT. Also, the theoretical simulations and measurement validation of this method are shown.

Novel approach to modeling spectral-domain optical coherence tomography with Monte Carlo method

Numerical modeling Optical Coherence Tomography (OCT) systems is needed for optical setup optimization, development of new signal processing methods and assessment of impact of different physical phenomena inside the sample on OCT signal. The Monte Carlo method has been often used for modeling Optical Coherence Tomography, as it is a well established tool for simulating light propagation in scattering media. However, in this method light is modeled as a set of energy packets traveling along straight lines. This reduces accuracy of Monte Carlo calculations in case of simulating propagation of dopeds. Since such beams are commonly used in OCT systems, classical Monte Carlo algorithm need to be modified. In presented research, we have developed model of SD-OCT systems using combination of Monte Carlo and analytical methods. Our model includes properties of optical setup of OCT system, which is often omitted in other research. We present applied algorithms and comparison of simulation results with SD-OCT scans of optical phantoms. We have found that our model can be used for determination of level of OCT signal coming from scattering particles inside turbid media placed in different positions relatively to focal point of incident light beam. It may improve accuracy of simulating OCT systems.

Dispersion compensation in optical coherence tomography

Dispersion of optical elements and sample in optical coherence tomography (OCT) system introduce a wavelength dependent phase distortion to the light beam propagating in OCT system. This causes blurring of the image in high resolution OCT using broadband light sources. Also decreased resolution with the depth of a sample is observed. To avoid this, the overall dispersion of the system can be compensated using a dispersive material in the reference arm of a system. Unfortunately, the dispersion is changed in the system with the probing depth. Overcome to this problem is numerical dispersion compensation technique. Calculations can be made after the measurements have been taken to provide depth dependent compensation. Various techniques and their possibilities are presented.

Modeling of broadband light source to use with optical coherent tomography system

The spectral shape of a light source in optical coherence tomography imaging is of prime importance because it determines resolution and quality of the image. Spectra and axial point spread function of photonic crystal fiber light source TB-1550 from Menlosystems GmbH before and after optical spectral shaping are presented. Low-pass and high-pass filters are simulated to shape the irregularities in light spectra of the source. Full-spectrum shaping results with use of spectral processor are calculated. Results show that shaping of a light source improves meaningly axial resolution and inhibits sidelobes of the point spread function.

An optical low-coherence system for 2-dimensional visualization of thin polymer layers

An Optical Low-Coherence Tomography (OCT) is a novel optical measurement technique, which enables non-destructive and non-contact investigation of multilayer structures. Nowadays, this method is highly applied in medical diagnostics. Despite of great progress in optoelectronics and optical measurement methods there is lack of studies on the OCT for non-medical application. In this paper authors present a laboratory OCT system for surface and subsurface investigation of scattering technical objects such as polymer layers. Preliminary test results on subsurface technical objects investigation using OCT system have been presented and discussed.