Irina Schelkanova

Independent component analysis of broadband near-infrared spectroscopy data acquired on adult human head

The goal of this study was to investigate the ability of independent component analysis in the time-spectral domain to isolate physiological sources of functional near infrared spectroscopy signals. We apply independent component analysis to the broadband fNIRS data acquired on the human forehead at 650 different wavelengths between 700 nm and 950 nm. To induce cerebral oxygenation changes we use the breath holding paradigm. We found one major independent component during baseline and two major components during exercise. Each independent component corresponds to one oxy-hemoglobin and one deoxy-hemoglobin time courses. The corresponding characteristic spectra of changes in optical absorption suggested that one component represented vasodilation of cerebral arterioles while the delayed component represented the washout of deoxyhemoglobin either in cerebral capillaries and venules or in extra cerebral tissue. We found that both broadband and isolated wavelength data can produce similar independent components.

Optimal quantitation of the cerebral hemodynamic response in functional near-infrared spectroscopy.

We have compared cerebral hemodynamic changes measured by near-infrared spectroscopy (NIRS) with simultaneously acquired BOLD fMRI signals during breath hold challenge in humans. The oxy- and deoxyhemoglobin concentration changes were obtained from the same broadband NIRS data using four different quantitation methods. One method used only two wavelengths (690 nm and 830 nm), and three other methods used broadband data with different spectral fitting algorithms. We found that the broadband techniques employing spectral derivatives were significantly superior to the multi-wavelength methods in terms of the correlation with the BOLD signals. In two cases out of six we found that the time courses of the deoxyhemoglobin changes produced by the two-wavelength method were qualitatively inconsistent with the BOLD fMRI signals.

The response of tissue to laser light

Abstract: In our chapter we describe the main mechanisms of interaction between laser light and biological tissues including both diagnostic and therapeutical applications. Various types of biotissue have been considered in terms of the tissue structure, light distribution in biostructures and tissue properties modification under laser irradiation.

Spatially resolved, diffuse reflectance imaging for subsurface pattern visualization toward development of a lensless imaging platform: phantom experiments

Abstract. A portable, spatially resolved, diffuse reflectance lensless imaging technique based on the charge-coupled device or complementary metal-oxide semiconductor sensor directly coupled to the fiber optic bundle is proposed for visualization of subsurface structures such as superficial microvasculature in the epithelium. We discuss an experimental method for emulating a lensless imaging setup via raster scanning a single fiber-optic cable over a microfluidic phantom containing periodic hemoglobin absorption contrast. To evaluate the ability of the technique to recover information about the subsurface linear structures, scattering layers formed of the Sylgard® 184 Silicone Elastomer and titanium dioxide were placed atop the microfluidic phantom. Thickness of the layers ranged from 0.2 to 0.7 mm, and the values of the reduced scattering coefficient (μs′) were between 0.85 and 4.25  mm−1. The results demonstrate that fiber-optic, lensless platform can be used for two-dimensional imaging of absorbing inclusions in diffuse reflectance mode. In these experiments, it was shown that diffuse reflectance imaging can provide sufficient spatial sampling of the phantom for differentiation of 30  μm structural features of the embedded absorbing pattern inside the scattering media.

Evaluation of spatially resolved diffuse reflectance imaging for subsurface pattern visualization towards applicability for fiber optic lensless imaging setup: phantom experiments and simulation

A portable, spatially resolved diffuse reflectance (SRDR) lensless imaging technique based on the charge coupled device (CCD), or complementary metal-oxide semiconductor (CMOS) sensor directly coupled with fiber optic bundle can be proposed for visualization of subsurface structures such as intrapapillary capillary loops (IPCLs). In this article, we discuss an experimental method for emulating a lensless imaging setup via raster scanning a single fiberoptic cable (where image is relayed onto the sensor surface through a fiber-optic cable equivalent to coupling a fiber optic conduit directly onto the sensor surface without any lenses) over a microfluidic phantom containing periodic hemoglobin absorption contrast. For mimicking scattering properties of turbid media, a diffusive layer formed of polydimethylsiloxane (PDMS) and titanium dioxide (TiO2) was placed atop of the microfluidic phantom. Thickness of the layers ranged from 0.2-0.7mm, and the μs` value of the layers were in the range of 0.85 mm-1 – 4.25mm-1. The results demonstrate that a fiber-optic bundle/plate coupled lensless imaging setup has a high potential to recover intensity modulations from the subsurface patterns. Decreasing of the interrogation volumes leads to enhanced spatial resolution of diffuse reflectance imaging, and hence, can potentially overcome the scattering caused blurring.

Diffuse reflectance measurements using lensless CMOS imaging chip

To assess superficial epithelial microcirculation, a diagnostic tool should be able to detect the heterogeneity of microvasculature, and to monitor qualitative derangement of perfusion in a diseased condition. Employing a lensless CMOS imaging chip with an RGB Bayer filter, experiments were conducted with a microfluidic platform to obtain diffuse reflectance maps. Haemoglobin (Hb) solution (160 g/l) was injected in the periodic channels (grooves) of the microfluidic phantom which were covered with ~250 μm thick layer of intralipid to obtain a diffusive environment. Image processing was performed on data acquired on the surface of the phantom to evaluate the diffuse reflectance from the subsurface periodic pattern. Thickness of the microfluidic grooves, the wavelength dependent contrast between Hb and the background, and effective periodicity of the grooves were evaluated. Results demonstrate that a lens-less CMOS camera is capable of capturing images of subsurface structures with large field of view.

Hyperspectral functional imaging of the human brain

We performed the independent component analysis of the hyperspectral functional near-infrared data acquired on humans during exercise and rest. We found that the hyperspectral functional data acquired on the human brain requires only two physiologically meaningful components to cover more than 50% o the temporal variance in hundreds of wavelengths. The analysis of the spectra of independent components showed that these components could be interpreted as results of changes in the cerebral blood volume and blood flow. Also, we found significant contributions of water and cytochrome c oxydase into changes associated with the independent components. Another remarkable effect of ICA was its good performance in terms of the filtering of the data noise.

Principal and independent component analysis of concomitant functional near infrared spectroscopy and magnetic resonance imaging data

Although near infrared spectroscopy (NIRS) is now widely used both in emerging clinical techniques and in cognitive neuroscience,4 the development of the apparatuses and signal processing methods for these applications is still a hot research topic. The main unresolved problem in functional NIRS is the separation of functional signals from the contaminations by systemic and local physiological fluctuations. This problem was approached by using various signal processing methods, including blind signal separation techniques.2 In particular, principal component analysis (PCA) and independent component analysis (ICA)3 were applied to the data acquired at the same wavelength and at multiple sites on the human or animal heads7 during functional activation. These signal processing procedures resulted in a number of principal or independent components that could be attributed to functional activity but their physiological meaning remained unknown. On the other hand, the best physiological specificity is provided by broadband NIRS.5 Also, a comparison with functional magnetic resonance imaging (fMRI) allows determining the spatial origin of fNIRS signals.5 In this study we applied PCA and ICA to broadband NIRS data to distill the components correlating with the breath hold activation paradigm and compared them with the simultaneously acquired fMRI signals. Breath holding was used because it generates blood carbon dioxide (CO2) which increases the blood-oxygen-level-dependent (BOLD) signal as CO2 acts as a cerebral vasodilator. Vasodilation causes increased cerebral blood flow which washes deoxyhaemoglobin out of the cerebral capillary bed thus increasing both the cerebral blood volume and oxygenation. Although the original signals were quite diverse, we found very few different components which corresponded to fMRI signals at different locations in the brain and to different physiological chromophores.

Non-labeled lensless micro-endoscopic approach for cellular imaging through highly scattering media

We describe an imaging approach based on an optical setup made up of a miniature, lensless, minimally invasive endoscope scanning a sample and matching post processing techniques that enable enhanced imaging capabilities. The two main scopes of this article are that this approach enables imaging beyond highly scattering medium and increases the resolution and signal to noise levels reaching single cell imaging. Our approach has more advantages over ordinary endoscope setups and other imaging techniques. It is not mechanically limited by a lens, the stable but flexible fiber can acquire images over long time periods (unlike current imaging methods such as OCT etc.), and the imaging can be obtained at a certain working distance above the surface, without interference to the imaged object. Fast overlapping scans enlarge the region of interest, enhance signal to noise levels and can also accommodate post-processing, super-resolution algorithms. Here we present that due to the setup properties, the overlapping scans also lead to dramatic enhancement of non-scattered signal to scattered noise. This enables imaging through highly scattering medium. We discuss results obtained from in vitro investigation of weak signals of ARPE cells, rat retina, and scattered signals from polydimethylsiloxane (PDMS) microchannels filled with hemoglobin and covered by intralipids consequently mimicking blood capillaries and the epidermis of human skin. The development of minimally invasive procedures and methodologies for imaging through scattering medium such as tissues can vastly enhance biomedical diagnostic capabilities for imaging internal organs. We thereby propose that our method may be used for such tasks in vivo.

Contrast enhancement for diffuse reflectance imaging by microbubbles

Microbubble contrast agents can potential improve optical imaging diagnostics based on increasing light scattering. Detection and quantification of microcirculation have been improved in diffuse reflectance imaging by administrating microbubbles