Mikhail Yu. Kirillin

Simulation of optical coherence tomography images by Monte Carlo modeling based on polarization vector approach.

Monte Carlo method is applied for simulation of 2D optical coherence tomography (OCT) images of skin-like model. Layer boundaries in skin model feature curved shape which agrees with physiological structure of human skin. The effect of coherence properties of probing radiation on OCT image formation and speckles in the detected OCT signal is considered. The developed model is employed for image simulation both for conventional and polarization dependent time-domain OCT modalities. Simulation of polarized OCT signal is performed using vector approach developed previously for modeling of electromagnetic field transfer in turbid media.

Simulation of polarization-sensitive optical coherence tomography images by a Monte Carlo method

We introduce a new Monte Carlo (MC) method for simulating optical coherence tomography (OCT) images of complex multilayered turbid scattering media. We demonstrate, for the first time of our knowledge, the use of a MC technique to imitate two-dimensional polarization-sensitive OCT images with nonplanar boundaries of layers in the medium like a human skin. The simulation of polarized low-coherent optical radiation is based on the vector approach generalized from the iterative procedure of the solution of Bethe-Saltpeter equation. The performances of the developed method are demonstrated both for conventional and polarization-sensitive OCT modalities.

Perspectives of mid-infrared optical coherence tomography for inspection and micrometrology of industrial ceramics

Optical coherence tomography (OCT) is a promising tool for detecting micro channels, metal prints, defects and delaminations embedded in alumina and zirconia ceramic layers at hundreds of micrometers beneath surfaces. The effect of surface roughness and scattering of probing radiation within sample on OCT inspection is analyzed from the experimental and simulated OCT images of the ceramic samples with varying surface roughnesses and operating wavelengths. By Monte Carlo simulations of the OCT images in the mid-IR the optimal operating wavelength is found to be 4 µm for the alumina samples and 2 µm for the zirconia samples for achieving sufficient probing depth of about 1 mm. The effects of rough surfaces and dispersion on the detection of the embedded boundaries are discussed. Two types of image artefacts are found in OCT images due to multiple reflections between neighboring boundaries and inhomogeneity of refractive index.

Differential diagnosis of human bladder mucosa pathologies in vivo with cross-polarization optical coherence tomography

Quantitative image analysis and parameter extraction using a specific implementation of polarization-sensitive optical coherence tomography (OCT) provides differential diagnosis of mucosal pathologies in in-vivo human bladders. We introduce a cross-polarization (CP) OCT image metric called Integral Depolarization Factor (IDF) to enable automatic diagnosis of bladder conditions (assessment the functional state of collagen fibers). IDF-based diagnostic accuracy of identification of the severe fibrosis of normal bladder mucosa is 79%; recurrence of carcinoma on the post-operative scar is 97%; and differentiation between neoplasia and acute inflammation is 75%. The promising potential of CP OCT combined with image analysis in human urology is thus demonstrated in vivo.

Speckle statistics in OCT images: Monte Carlo simulations and experimental studies

The speckle pattern of an optical coherence tomography (OCT) image carries potentially useful sample information that may assist in tissue characterization. Recent biomedical results in vivo indicate that the distribution of signal intensities within an OCT tissue image is well described by a log-normal-like (Gamma) function. To fully understand and exploit this finding, an OCT Monte Carlo model that accounts for speckle effects was developed. The resultant Monte Carlo speckle statistics predictions agree well with experimental OCT results from a series of control phantoms with variable scattering properties; the Gamma distribution provides a good fit to the theoretical and experimental results. The ability to quantify subresolution tissue features via OCT speckle analysis may prove useful in diagnostic photomedicine.

Optical coherence tomography for quality assessment of embedded microchannels in alumina ceramic

Large-scale and cost-effective manufacturing of ceramic micro devices based on tape stacking requires the development of inspection systems to perform high-resolution in-process quality control of embedded manufactured cavities, metal structures and defects. With an optical coherence tomography (OCT) system operating at 1.3 μm and a dedicated automated line segmentation algorithm, layer thicknesses can be measured and laser-machined channels can be verified in alumina ceramics embedded at around 100 μm depth. Monte Carlo simulations are employed to analyze the abilities of OCT in imaging of the embedded channels. The light scattering parameters required as input data for simulations are evaluated from the integrating sphere measurements of collimated and diffuse transmittance spectra using a reconstruction algorithm based on refined diffusion approximation approach.

Light Propagation in NIR Spectroscopy of the Human Brain

In study of the brain, oxygenation changes in the cerebral cortex are of great interest, since the concentrations of oxyhaemoglobin and deoxyhaemoglobin change due to coupling of hemodynamics to cortical neural activity. In order to non-invasively monitor oxygenation in the cerebral cortex by near-infrared spectroscopy (NIRS), light should penetrate into brain tissue to a depth of approximately 1-2 cm. Many studies show that by increasing the source-detector distance, illuminating light penetrates deeper into brain tissue. Using tissue-mimicking phantom measurements, forehead in vivo measurements, and Monte Carlo (MC) simulations, this paper estimates light propagation in the brain and the minimum source-detector distance to allow sensing of the cerebral cortex. We present optical sensing of a pulsating aqueous intralipid suspension in a vessel located at different depths within a multilayered phantom of the human forehead. Experimental results are compared with the MC simulations accounting for the optical properties of the phantom. The thickness and morphology of the different tissue layers were obtained from an anatomical magnetic resonance image of a test subjects head. Results from these three methods correlate with each other and show that the brain cortex can be sensed with optical methods based on NIRS.

Glucose sensing in aqueous Intralipid suspension with an optical coherence tomography system: experiment and Monte Carlo simulation

Peculiarities of light transport in IntralipidTM solutions and the effect of glucose on light scattering properties of the solution at two different IntralipidTM concentrations were studied with optical coherence tomography (OCT) technique in vitro. An open air OCT system using a superluminescent light source with center wavelength = 830 nm was used. 5% IntralipidTM solutions were used to simulate a biological tissue (skin) in our experiment. Glucose concentrations at the physiologically relevant level were added to IntralipidTM solutions. Increasing IntralipidTM concentration increases the scattering coefficient of the media meanwhile increasing glucose concentration increases the refractive index of the media and reduces the scattering coefficient of the media. The experimental data were compared to Monte Carlo simulations. We also made the simulations for 2% IntralipidTM solution. The results indicate that glucose added to 2 and 5% IntralipidTM solutions changes their scattering properties, which is manifested by a decrease in the slope of the OCT signal. This finding shows the ways of using OCT for sensing glucose and monitoring the alterations of its content in biotissues. Some discrepancies between measurements and simulations were found, which need further investigation.

Optical sensing of titanium dioxide nanoparticles within horny layer of human skin and their protecting effect against solar UV radiation

In the present paper the problem of protection of human skin against harmful UV solar rays using nano-sized spherical particles of titanium dioxide and sensing their concentration if embedded into skin is considered. Experimental tape-stripping method was used to reveal the in-depth distribution of the particles within the horny layer up to 20 µm. Computer simulations of optical coherence tomography (OCT) investigations of skin and, in particular, horny layer in vitro with and without titanium dioxide particles added were also performed in order to understand, if this modern non-invasive technique is applicable for skin study and revealing the distribution of nanoparticles within the horny layer. The effect of particles size (25-200 nm) and concentration on simulated OCT signals was analyzed. The increase of scattering in the sample (with increase of particles concentration or size) leads to increase of the OCT signal slope and decrease of rear border peak. We also performed simulations implementing the Monte Carlo technique to evaluate the protecting effect of titanium dioxide nanoparticles of different size. The most effective sizes were revealed. Computations were performed for the wavelength of 290.5 nm as the most harmful one. Dependencies of light intensities absorbed, backscattered, and transmitted through the whole horny layer (20 µm thick) on concentration of titanium dioxide particles (0-5%) were obtained and analyzed.

Optical coherence tomography : a potential tool for roughness assessment of free and embedded surfaces of laser-machined alumina ceramic

For an emerging market a mass and cost-effective production of non-silicon micro devices requires an in-process and accurate 3D monitoring to assure the quality. Optical coherence tomography (OCT) ...