Ervin Nippolainen

Uniersity of Eastern Finland, Kuopio, Finland · Department of Applied Physics

italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Objective: The key characteristics of light propagation are the average penetration depth, average maximum penetration depth, and average path length of photons. These parameters depend on tissue optical properties and, thus, on the pathological state...

Objective A prototype infrared attenuated total reflection (IR-ATR) laser spectroscopic system designed for in vivo classification of human cartilage tissue according to its histological health status during arthroscopic surgery is presented. Prior to real-world in vivo applications, this so-called osteoarthritis (OA) scanner has been tested at in...

This work demonstrates for the first time a possibility of assessing changes in the parameters of cortical blood flow in mice through the intact cranial bone during pharmacological tests using the method of imaging photoplethysmography with illumination in the green region of the spectrum. This makes it possible to evaluate the effect of tests on h...

Significance Articular cartilage exhibits a zonal architecture, comprising three distinct zones: superficial, middle, and deep. Collagen fibers, being the main solid constituent of articular cartilage, exhibit unique angular and size distribution in articular cartilage zones. There is a gap in knowledge on how the unique properties of collagen fibe...

Optical properties of biological tissues, such as refractive index, are fundamental properties, intrinsically linked to a tissue’s composition and structure. This study aims to investigate the variation of refractive index (RI) of human articular cartilage along the tissue depth (via collagen fibril orientation and optical density) and integrity (b...

Non-destructive assessments are required for the quality control of tissue-engineered constructs and the optimization of the tissue culture process. Near-infrared (NIR) spectroscopy coupled with machine learning (ML) provides a promising approach for such assessment. However, due to its nonspecific nature, each spectrum incorporates information on...

Among numerous approaches to the study of migraine, the nitroglycerin (NTG) model occupies a prominent place, but there is relatively insufficient information about how NTG affects intracranial vessels. In this study we aim to assess the effects of NTG on blood-flow parameters in meningeal vessels measured by imaging photoplethysmography (iPPG) in...

Mid-infrared spectroscopy (MIR), near-infrared spectroscopy (NIR), and Raman spectroscopy are all well-established analytical techniques in biomedical applications. Since they provide complementary chemical information, we aimed to determine whether combining them amplifies their strengths and mitigates their weaknesses. This study investigates the...

Osteoarthritis degenerates cartilage and impairs joint function. Early intervention opportunities are missed as current diagnostic methods are insensitive to early tissue degeneration. We investigated the capability of visible light-near-infrared spectroscopy (Vis-NIRS) to differentiate normal human cartilage from early osteoarthritic one. Vis-NIRS...

Objective To differentiate healthy from artificially degraded articular cartilage and estimate its structural, compositional, and functional properties using Raman spectroscopy (RS). Design Visually normal bovine patellae ( n = 12) were used in this study. Osteochondral plugs ( n = 60) were prepared and artificially degraded either enzymatically (...

There is increasing research on the potential application of diffuse optical spectroscopy and hyperspectral imaging for characterizing the health of the connective tissues, such as articular cartilage, during joint surgery. These optical techniques facilitate the rapid and objective diagnostic assessment of the tissue, thus providing unprecedented...

Injuries to the ligaments of the knee commonly impact vulnerable and physically active individuals. These injuries can lead to the development of degenerative diseases such as post-traumatic osteoarthritis (PTOA). Non-invasive optical modalities, such as infrared and Raman spectroscopy, provide means for quantitative evaluation of knee joint tissue...

Preclassification of raw infrared spectra has often been neglected in scientific literature. Separating spectra of low spectral quality, due to low signal-to-noise ratio, presence of artifacts, and low analyte presence, is crucial for accurate model development. Furthermore, it is very important for sparse data, where it becomes challenging to visu...

Objective To evaluate the feasibility of Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy to detect cartilage degradation due to osteoarthritis and to validate the methodology with osteochondral human cartilage samples for future development towards clinical use. Design Cylindrical (d = 4 mm) osteochondral samples (n...

The aim of the study was to optimize preprocessing of sparse infrared spectral data. The sparse data were obtained by reducing broadband Fourier transform infrared attenuated total reflectance spectra of bovine and human cartilage, as well as of simulated spectral data, comprising several thousand spectral variables into datasets comprising only se...

Objective Joint injuries may lead to degeneration of cartilage tissue and initiate development of posttraumatic osteoarthritis. Arthroscopic surgeries can be used to treat joint injuries, but arthroscopic evaluation of articular cartilage quality is subjective. Fourier transform infrared spectroscopy combined with fiber optics and attenuated total...

Optical properties of biological tissues in the NIR spectral range have demonstrated significant potential for in vivo diagnostic applications and are critical parameters for modelling light interaction in biological tissues. This study aims to investigate the optical properties of articular cartilage as a function of tissue depth and integrity. Th...

Near-infrared (NIR) spectroscopy is a powerful analytical method for rapid, non-destructive and label-free assessment of biological materials. Compared to mid-infrared spectroscopy, NIR spectroscopy excels in penetration depth, allowing intact biological tissue assessment, albeit at the cost of reduced molecular specificity. Furthermore, it is rela...

Raman spectroscopy is promising in vivo tool in various biomedical applications; moreover, in recent years, its use for characterizing articular cartilage degeneration has been developing. It has also shown potential for scoring the severity of cartilage lesions, which could be useful in determining the optimal treatment strategy during cartilage r...

This study aimed to quantify the long‐term progression of blunt and sharp cartilage defects and their effect on joint homeostasis and function of the equine carpus. In nine adult Shetland ponies, the cartilage in the radiocarpal and middle carpal joint of one front limb was grooved (blunt or sharp randomized). The ponies were subjected to an 8‐week...

Objective To assess the potential of near-infrared spectroscopy (NIRS) for in vivo arthroscopic monitoring of cartilage defects. Method Sharp and blunt cartilage grooves were induced in the radiocarpal and intercarpal joints of Shetland ponies and monitored at baseline (0 weeks) and at three follow-up time points (11, 23, and 39 weeks) by measurin...

Absorption and reduced scattering coefficients ( ${\mathrm{\mu}_\textrm{a}},\mathrm{\mu}_\textrm{s}^{\prime}$ μ a , μ s ′ ) of biological tissues have shown significant potential in biomedical applications. Thus, they are effective parameters for the characterization of tissue integrity and provide vital information on the health of biological tiss...

Articular cartilage (AC) is a soft connective tissue that covers the ends of articulating bones. Joint injuries may lead to degeneration of cartilage tissue and initiate development of post-traumatic osteoarthritis (OA). Arthroscopic surgeries can be used to treat joint injuries, but arthroscopic evaluation of cartilage quality is subjective. There...

This study evaluates the feasibility of near infrared (NIR) spectroscopy to distinguish between different cartilage injury types associated with post-traumatic osteoarthritis and idiopathic osteoarthritis (OA) induced by mechanical and enzymatic damages. Bovine osteochondral samples (n = 72) were subjected to mechanical (n = 24) and enzymatic (n =...

We introduce classification models based on partial least squares discriminant-analysis (PLS-DA) for estimating cartilage integrity (assessed by OARSI grade) based on mid-infrared spectra of cartilage matrix. The best model achieved accuracy of 84%.

In this study, we demonstrate the potential of mid-infrared (MIR) and near infrared (NIR) spectroscopies to reveal and differentiate between superficial changes in articular cartilage (AC) after mechanical or enzymatic degradation.

Osteoarthritis (OA) is a musculoskeletal disease characterized by progressive degeneration of articular cartilage (AC) structure and function. AC consists mainly of interstitial fluid, extracellular matrix (ECM) and chondrocytes. The main molecular components of ECM are collagens and proteoglycans along with lesser amount of non-collagenous protein...

In this report we present the experimental study of imaging photoplethysmography in the area of the palm and wrist of fifty-six healthy subjects. We found that the amplitude of the PPG waveform is unevenly distributed over the studied area forming the hot spots with the elevated amplitude. There is clear tendency of the amplitude increasing in the...

Photoplethysmography (PPG) is a noninvasive optical method accepted in the clinical use for measurements of arterial oxygen saturation. It is widely believed that the light intensity after interaction with the biological tissue in vivo is modulated at the heartbeat frequency mainly due to pulsatile variations of the light absorption caused by arter...

We report a novel scheme of an adaptive optical microphone (AOM) based on two-wave mixing in a photorefractive crystal. The sensitive element of the microphone is a thin metal membrane which receives acoustic waves and modulates a light phase that is demodulated by means of a dynamic hologram continuously recorded in a photorefractive CdTe crystal....

Blood pulsation imaging (BPI) is a non-invasive optical method based on photoplethysmography (PPG). It is used for the visualization of changes in the spatial distribution of blood in the microvascular bed. BPI specifically allows measurements of the relative phase of blood pulsations and using it we detected a novel type of PPG fast waveforms, whi...

Cortical spreading depression (CSD) is a slowly propagating wave of depolarization of neurons and glia and has a less characterized vascular component. CSD is a commonly used phenomenon to test new methods of live brain imaging. Application of a blood pulsations imaging (BPI) technique to study of CSD induced with high-potassium solution in rat cor...

We investigated the propagation of kink waves in thin and isothermal expanding flux tubes in cylindrical geometry. By using the method of radial expansion for fluctuating variables we obtained a new kink wave equation. We show that including the radial component of the tube magnetic field leads to cutoff-free propagation of kink waves along thin fl...

Asymmetrical changes in blood perfusion and asynchronous blood supply to head tissues likely contribute to migraine pathophysiology. Imaging was widely used in order to understand hemodynamic variations in migraine. However, mapping of blood pulsations in the face of migraineurs has not been performed so far. We used the Blood Pulsation Imaging (BP...

A new method for quantitative estimation of 2D-distribution of blood pulsations amplitude in cutaneous vessels and quantitative analysis of their reaction on occlusion is presented. The technique is based on synchronous amplification of video recordings.

A novel method for fast mapping of surface defects using spatially filtered dynamic speckles is presented. It possesses high fidelity and versatility. The factors defining resolution of the proposed technique and ways of its improvement are discussed.

The non-invasive assessment of blood flow is invaluable for the diagnostic and monitoring treatment of numerous vascular and neurological diseases. We developed a non-invasive and non-contact method of blood pulsation imaging capable of visualizing and monitoring of the two-dimensional distribution of two key parameters of peripheral blood flow: th...

We present novel experimental method for estimation of the light penetration depth (LPD) in turbid media based on the analysis of the cross-correlation function of speckle patterns. Under certain illumination conditions, the amplitude of the correlation function is strongly dependent on the penetration depth. Presented theoretical model based on th...

In this paper we propose novel method possessing high fidelity and versatility for surface defect detection based on the spatially filtered dynamic speckles. It is shown that resolution of proposed method depends on the geometrical parameters of the optical system. The feasibility of the novel method for surface defect detection is demonstrated by...

We present novel experimental method for estimation of the light penetration depth (LPD) in turbid media based on the analysis of the speckle pattern structure. Under the certain illumination conditions this structure is strongly dependent on the penetration depth. Presented theoretical model based on the Bragg diffraction from the thick holograms...

We present novel experimental method for estimation of the light penetration depth (LPD) in turbid media based on the analysis of the speckle pattern structure. Under the certain illumination conditions this structure is strongly dependent on the penetration depth. Presented theoretical model based on the Bragg diffraction from the thick holograms...

We demonstrate excitation of the linear photogalvanic current in a Bi12TiO20 crystal by two orthogonally polarized femtosecond laser pulses with detecting the electrical current via charge accumulation on the sample electrodes. Such a setup was used to implement an interferometric autocorrelation technique for characterization of ultrashort light p...

We present a study of parameters that affect the accuracy of a reflectance spectrum recovery from the compressed data obtained in a multispectral imaging (MSI) system consisting of a computer-controlled set of light-emitting diodes (LEDs) synchronously switched with a digital monochrome camera. The system allows recovery of a two-dimensional distri...

We present a novel method for small surface defect detection based on the spatially filtered dynamic speckles. This method possesses high fidelity and versatility. Factors defining resolution of the proposed method is estimated and it is shown that resolution depends solely on the geometrical parameters of the optical system. Experimental results d...

Everybody knows that that blood volume circulated in a capillary bed is modulated in time with the rate of heart beatings. Light interaction with biological tissue in vivo results in the intensity modulation which occurs synchronously with each heartbeat. Generally, the time-varying component of the reflected light provides a signal proportional to...

Multispectral imaging systems play more and more important role in many domains such as medicine, life science and industry. Fast acquisitions of two dimensional (2D) reflectance spectra images with high spatial resolution allow monitoring not only complicate structure of object under study but also its dynamic changes in time [1]. Unfortunately, f...

We present a new method of formation photoplethysmographic images with high spatial resolution from video recordings of a living body in the reflection geometry. The method (patent pending) is based on lock-in amplification of every pixel of the recorded video frames. A reference function required for synchronous detection of cardiovascular pulse w...

We describe a new approach for noncontact measurements od ingredients concentration (as well as their spatial distribution) of pharmaceutical tablets. These measurements are preformed by using an optoelectronic system capable for fast acquisition of two-dimensional distribution of reflectance spectra. The system is based on a vector subspace model...

Recently we proposed a multispectral imaging system which is capable for fast acquisition of two-dimensional distribution of vectorial representation of reflectance spectra. The system operates on the base of the subspace vector model of surface reflection, which gives possibility to represent any reflectance spectrum in the compressed form with hi...

Performance of recently proposed multispectral imaging system for fast acquisition of two dimensional distribution of reflectance spectrum is experimentally studied. The system operation is based on a subspace vector model in which any reflectance spectrum is described in the compressed form as a linear combination of few spectral functions. A key...

Performance of novel optical system for fast acquisition of two-dimensional distribution of reflectance spectra with spatial resolution is experimentally studies. The system consists of a computer controlled light source and a monochrome CMOS camera. The light source is a composition of light-emitting diodes (LEDs) whic provides illumination of the...

A non-contact, non-destructive technique for estimating of ingredients concertration is presented. The technique is based on an optoelectronic system capable for fast acquistion of two-dimensional distribution of reflection spectral with high spatial resolution by using a subspace vector model of surface reflection. The measured spectral data are c...

A non-contact, non-destructive technique for estimating the dye concentration of a tablet is presented. These measurements are performed by an optoelectronic system capable for fast acquisition of two-dimensional distribution of reflection spectra with high spatial resolution by using a subspace vector model of surface reflection. Vector components...

We present novel optical system capable for fast acquisition of two-dimensional distribution of reflection spectra with high spatial resolution. It is based on a subspace vector model of surface reflections. The system consists of a computer controlled set of light-emitting diodes (LED) and a monochrome CCD camera. Spatial distribution of reflectio...

A multispectral imaging system with computer controlled light source of 16 light emitting diodes is applied for measuring of tablet porosity. The system is based on a subspace vector model of surface reflection. The measured spectral data are compressed on the stage of measurement and used directly for the discrimination of tablets with different p...

We present a novel architecture of dynamic-speckles distance sensors with a deflecting mirror in a Micro-Electro-Mechanical System (MEMS) for surface scanning. Due to sinusoidal oscillations of MEMS mirror, the speed of scanning is varying. Nevertheless, it does not affect the accuracy of the distance measurements. Signal processing using zero-cros...

Real-time distance monitoring and thickness measurements of production lines are typical tasks of the manufacturing process. We demonstrate a novel optical sensor prototype capable of providing accurate distance measurements of fast moving objects. The principle of sensor operation is based on spatial filtering of dynamic speckles generated with a...

Measuring the reflectance spectrum of an object can be accomplished in numerous ways, including a single-point spectrometer coupled to a twodimensional scanning system, a linescan spectrograph combined with a digital camera, a colored filter wheel and a monochrome camera, or a digital camera and a liquid-crystal tunable filter, among others. These...

Noncontact methods of distance measurements to a moving surface using laser light are relevant for many industrial applications, such as surface profile and position monitoring, thickness measurements, and wear estimation. Application of existing methods (e.g., triangulation) is limited especially for nonhomogeneous, semitransparent and rough mater...

We analyze a recently proposed technique for fast acquisition of the two-dimensional (2D) spatial distribution of reflectance spectra to figure out how much its ability of distinguishing almost similar spectra declines with increase of the spectral line bandwidth of the light source. This analysis was carried out using the experimentally measured r...

Tablets color (reflection spectrum) is an important characteristic which depends on pigmentation of tablets, their density, and coatings. Consequently, fast and precise measurements of two-dimensional distribution of the reflection spectra with high spatial resolution could be an excellent tool for online control of the tablets quality. However, im...

Diffraction-limited accuracy is estimated for measuring systems exploiting dynamic speckles. Statistical properties of the signal in the systems with spatial filtering are used to evaluate the signal frequency with precision sufficient to achieve the diffraction-limited accuracy. The results of the analysis allow for designing an optimal measuring...

Recently novel nonlinear optical phenomenon, optical orientation of dipolar centers (OODC), was firstly predicted theoretically and then found experimentally. From the phenomenological point of view the OODC-effect can be considered as a kind of optical rectification and consequently observed in any noncentrosymmetric crystals. However, unlike the...

We present an analysis of statistical properties of dynamic speckles to estimate the limiting accuracy of measurements achievable in a distance sensor using spatially filtered dynamic speckles. The main reason for inaccurate measurements using dynamic speckles is their stochastic nature. It is shown that the average lifetime of dynamic speckles is...

We present the experimental study of color-vector representation for accurate and fast analysis of 2D distribution of colours over an object surface, which is performed by use computer controlled light source.

Statistics of dynamic speckles generated with a scanning laser beam differs from that of created by a moving surface. Proper analysis of the correlation parameters allows us to optimize performance of the speckle distance sensor.

We present a novel approach that enables online, real-time and non-contact measurements of thickness of protective coatings. The proposed technique based on spatial filtering of dynamic speckles generated by rapidly deflected laser beam. An advantageous feature of the technique is that it is capable for very fast measurement of coating thickness wi...

In this paper, we report theoretical description and first experimental observation of recently predicted phenomenon called optical orientation of local centers with permanent dipole moment. An electrical current arising at periodical modulation of the polarization of incident light was observed in a crystal of Bi 12 SiO 20 grown in the argon atmos...

The system presented in this paper is able to classify the colors in accurate and fast way. This approach is completely new, because nowadays no system has the ability to be both fast and precise in the recognition of colors.

Measurement of the reflectance spectrum at each spatial point of an object surface certainly provides high accuracy for color classification and recognition but it takes time and requires huge computer resource. The method of principal components analysis allows us to find an optimal (low-dimensional) set of basic spectra with which any reflectance...

In this paper statistical properties of spatially filtered dynamic speckles are considered. This phenomenon was not sufficiently studied yet while spatial filtering is an important instrument for speckles velocity measurements. In case of spatial filtering speckle velocity information is derived from the modulation frequency of filtered light powe...

We analyze statistical properties of dynamic speckles formed when an optically rough surface is illuminated by a fast-deflecting laser beam. The modified space-time correlation function of the light-intensity fluctuations has been introduced to estimate the correlation parameters of a dynamic speckle pattern. Dynamic speckles are considered in thei...

We propose a novel approach for fast acquisition of multispectral images. Key-element of the proposed approach is the computer-controlled light source. It consists of a set of the light-emitting diodes and generates any predefined basic spectrum with possibility of fast switching from one spectrum to another. The feasibility of the proposed system...

We propose a novel approach for measurements of two-dimensional distribution of the reflection spectra with high spatial resolution. It is based on a subspace vector model of surface reflections and includes sequential illumination of the object by basis functions preliminary calculated with principal component analysis. A simple optical system con...

Online control of thickness of as-deposited coatings is of great importance because it directly affects the quality of protective coatings. We present a novel approach that enables online, real-time and non-contact measurements thickness of thermally sprayed coatings. The proposed technique uses dynamic speckles generated by rapidly deflecting lase...

We report discovery of recently predicted phenomenon, optical orientation by polar way of local centers with permanent dipole moment. In a crystal of Bi(12)SiO(20) grown in the argon atmosphere electrical current arises when the polarization of incident light is periodically modulated. Dependence of the current amplitude on the modulation frequency...

Distance measurements are of great importance in modern industry. With the increasing speed of industrial production lines, there is a need for fast distance sensors enabled for online control of as-deposited coating thickness, monitoring surface profile (and its dynamic variations and vibrations), and online thickness measurements of paper, metall...

An adaptive fiber-optical interferometer, which is based on dynamic reflection hologram recorded in the photorefractive crystal of cubic symmetry without applying any electrical field, is developed. Adaptive properties of dynamic hologram enable the solution of an interferometer's working point uncontrollable drift problem caused by external factor...

Accurate color classification by vector subspace method was implemented by simple optical system including computer controlled set of light-emitting diodes and a photo-receiver operating in the integration regime. The technique is capable for fast and precise classification of color distribution within two-dimensional frame with high spatial resolu...

A comparative study of two acousto-optic deflectors with different speeds of acoustic wave is presented in their application to optical distance measurements by using dynamic speckles. It is shown that the fast deflector allows us to achieve higher modulation frequency, thus diminishing the response time of the distance sensor. However, the increas...