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Characterization of microfluidic circuits using speckle patterns in optical coherence tomography images

Grant number: 13/05492-9
Support Opportunities:Scholarships in Brazil - Master
Effective date (Start): October 01, 2013
Effective date (End): March 31, 2015
Field of knowledge:Engineering - Biomedical Engineering
Principal Investigator:Anderson Zanardi de Freitas
Grantee:Lucas Ramos de Pretto
Host Institution: Instituto de Pesquisas Energéticas e Nucleares (IPEN). Secretaria de Desenvolvimento Econômico (São Paulo - Estado). São Paulo , SP, Brazil


Optical Coherence Tomography (OCT) is a technique based on low coherence optical interferometry that produce cross sectional images of scattering material with high spatial resolution. The ability to perform OCT images of scattering materials and/or interfaces with different refractive indexes allows it to be used in the characterization of microfluidic devices consisting of microchannels. OCT images with speckle patterns are due to scattering characteristic of samples, which is regarded as a noise source degrading image quality, nevertheless the speckle pattern also carries information relating to the sample, similar to that used in imaging technique laser speckle, LSI (Laser Speckle Imaging), for example. In OCT images the speckle variance between sequential images has been used to enhance visualization of micro-vasculature in biological systems (svOCT - speckle variance Optical Coherence Tomography). For measurement of flow in biological systems and microfluidic circuits, techniques sensible to Doppler shift has been used, including Doppler OCT. However, we did not find any studies involving measurement of flow using speckle variance for this type of measurement, which is very important in the context of microfluidics and also biomedical engineering, where studies "in vivo" can analyze microcirculatory responses associated with a particular stimulus. Our group has demonstrated, using OCT, the ability to characterize microchannels in different types of materials, and also has demonstrated the ability to design and manufacture microcircuits being of interest to have a precise technique for characterization.In this context, we will perform the dimensional characterization of microchannels (width, depth and thus the volume) important parameter for various applications in microfluidic reactors, as well as the characterization of the microfluidic system. As a consequence of physical characterization dimensional, we can verify the uniformity of microchannels fabricated. Through computer simulations, will be determined "in silico" the applicability of the algorithms for analysis of speckle in simulated OCT images, evaluate their detection limits and then apply the developed algorithms for speckle pattern analysis in real OCT images, to characterize the fluid dynamics in microchannels, for example, the flow velocity and flow regime type.Therefore, we will study the limitations and applicability of methods originally developed for analysis of laser speckle surface to OCT images. Two of these methods will be discussed: (1) s-LASCA where the images acquired in function of time are grouped into a single image and will be evaluated the effectiveness of algorithm analysis using speckle windows of nxn (where n can be 3, 5, 7 and 9 pixels), running through the image, to calculate the speckle contrast parameter, and (2) t-LASCA, with analysis being performed on OCT images, and in this case there will be a temporal monitoring of the flow in microchannels. All experiments "in silico" (the simulated images with known parameters, simulators and algorithms to be tested) will be developed in LabView2010 programming environment. The flow images of microchannels system will be generated using microfluidic circuits already available and developed by the Centre for Lasers and Applications. The main expected results are: to adapt the speckle algorithms analysis to OCT images, detection and measurement of backscattering liquid flow velocities and microchannel geometry flow regime dependence. The results obtained here can be immediately applied in microcirculation flowmetry of biological systems.

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Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
DE PRETTO, LUCAS RAMOS; YOSHIMURA, TANIA MATEUS; RIBEIRO, MARTHA SIMOES; DE FREITAS, ANDERSON ZANARDI. Optical coherence tomography for blood glucose monitoring in vitro through spatial and temporal approaches. Journal of Biomedical Optics, v. 21, n. 8, . (13/09311-9, 13/05492-9, 14/02564-1)
DE PRETTO, LUCAS R.; NOGUEIRA, GESSE E. C.; FREITAS, ANDERSON Z.. Microfluidic volumetric flow determination using optical coherence tomography speckle: An autocorrelation approach. Journal of Applied Physics, v. 119, n. 16, . (13/09311-9, 13/05492-9)
Academic Publications
(References retrieved automatically from State of São Paulo Research Institutions)
PRETTO, Lucas Ramos de. Development of an optimized algorithm for the characterization of microflow using speckle patterns present in optical coherence tomography signal. 2015. Master's Dissertation - Universidade de São Paulo (USP). Instituto de Pesquisas Energéticas e Nucleares (IPEN/BT) São Paulo.

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