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Identifier

000390606

Title

Development of an advanced system for in vivo -mouse optical neuro-imaging applications

Alternative Title

Ανάπτυξη ενός εξελιγμένου συστήματος in vivo- οπτικής νευροαπεικόνησης σε ποντίκια

Author

Bekollari, Marsida

Thesis advisor

Παπάζογλου, Δημήτρης

Reviewer

Ζαχαρόπουλος, Αθανάσιος

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Πανεπιστήμιο Κρήτης.

Abstract

Fluorescence Molecular Tomography (FMT) is an inexpensive, noninvasive, fast, three-dimensional (3D), in vivo optical imaging modality that has been well established in providing quantitative imaging of the distribution of fluorescence targets. This translates to information about gene expression and molecular function, in small animals and biological tissues where the transmission of light is diffusive. The recovery of this distribution in a tomographic fashion requires a model-based reconstruction and depends on an appropriate mathematical model that describes light propagation in tissue (forward model) and the solution of an image reconstruction algorithm (inverse problem) based on the forward. The highly diffusive nature of biological tissue leads to a challenging (ill-posed) inverse problem and effectively limits the resolution and the quantification accuracy achieved. A solution to these problems can be found by including a priory known information to the inversion that can improve the accuracy of the photon propagation (forward) model and restrict the inversion procedure to meaningful solutions, that is, to reduce the uncertainty of the inverse problem. The information could be for example, the distributions of optical parameters (absorption, scattering) in the relevant wavelengths through the tissue under investigation and an accurate geometric description of its boundaries. Purpose The aim of this project is to optimize the FMT imaging system, by adding prior information to the inversion procedure. This will be done by accessing two aspects of the problem. The first will be the recovery of the absorption and scattering distributions over the domain of the mouse and the second is the development of a profilometry device or 3D scanning procedure, to be included in the FMT apparatus, to acquire information on the shape of the mouse’s boundary. Methods To investigate the effect of optical properties, such as absorption and scattering, in the reconstruction problem in Diffuse Optical Tomography (DOT), we are going to use resin made phantoms with varying optical properties. To determine the optical characteristics of the materials used to fabricate the phantoms we employ Spectrophotometer measurements of Diffuse Reflectance and Diffuse Transmittance. From those we can then calculate the absorption and scattering parameters of the materials, by using the Kubelka-Munk model, according to the relevant literature. Since our main interest is neuro-imaging the specimens 4 used in this work represent separately the optical properties of the different tissue types of the mouse's head. Following, a procedure that would allow the estimation of the absorption and scattering distributions through the media by using the FMT apparatus and measurements, based on the Diffusion Equation, was attempted with the employment of a simple inversion solution. Simultaneously, a 3D shape extraction mechanism was fashioned to augment the existing FMT apparatus with the ability to obtain the surface scan of the samples under imaging. Results The results of the project consist of three parts. The first part includes the fabrication of specimens and the determination of their optical properties using a Spectrophotometer. In the second part a simple inversion from FMT measurements on the specimens is performed by using the simulation of the light propagation (forward). Finally, in the third part a 3D scanning procedure is presented in order to be used in 3D surface reconstruction. Conclusions Using prior information can be the solution to the problems arising from the highly diffusive nature of biological tissue and the ill-posedness of the inversion involved in the image reconstruction. We have demonstrated ways to create this prior information, using the existing FMT setup.

Language

English

Subject

3D scanning

Diffuse optical tomography

Fluorescence molecular tomography

Optical tomography

Scattering

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