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Identifier

000412688

Title

Exploitation of non-linear effects for the discrimination of absorbers in optical resolution photoacoustic microscopy using single wavelength excitation

Alternative Title

Αξιοποίηση μη γραμμικών φαινομένων για το διαχωρισμό απορροφητών στη φωτοακουστική μικροσκοπία οπτικής ανάλυσης με χρήση ενός μήκους κύματος διέγερσης

Author

Λεμονάκη, Κρυσταλία Σ.

Thesis advisor

Χαραλαμπίδης, Δημήτριος

Reviewer

Ζαχαράκης, Ιωάννης
Καφεσάκη, Μαρία

Abstract

Optical resolution photoacoustic microscopy (OR-PAM) is an effective in vivo functional imaging tool. During photoacoustic (PA) effect, light is absorbed by molecules and converted into heat. Subsequent thermoelastic expansion generates an acoustic wave, termed as the PA wave. Detection of PA waves provides quantitative information about the concentrations of multiple chromophores such as oxygenated and deoxygenated hemoglobin molecules in red blood cells and melanin. Generally, the amplitude of the PA signal is assumed to be linearly proportional to the excitation pulse fluence. However, as the excitation laser intensity increases, the temperature dependence of thermal expansion coefficient results in a measurable nonlinear dependence of the PA signal on the excitation pulse fluence. PA nonlinearity has recently been used in several applications such as quantifying picosecond absorption relaxation times with a nanosecond laser, differentiating optical absorbers, measuring oxygen saturation in vivo, and performing label-free PA nanoscopy of biological structures having undetectable fluorescence. In this work, we consider photoacoustic nonlinearity as a candidate mechanism to discriminate between two different types of optical absorbers. More specifically, we experimentally investigate nonlinear photoacoustic signal generation as a means of unmixing blood and ink, by employing pulsed laser radiation at 532 nm. Therefore, using this alternative approach, it was demonstrated that an accurate absorber differentiation can be achieved through single wavelength excitation, unlike the conventional linear unmixing methods requiring two different wavelengths for such a purpose. The proposed methodology could find several applications regarding the specific imaging of biological components presenting discrete nonlinear PA behavior, such as melanin and hemoglobin, upgrading significantly the potential of OR-PAM technique in a simple, low-cost and reliable manner.

Language

English

Subject

Μη γραμμικά φαινόμενα

Issue date

2017-11-22

Collection

School/Department--School of Sciences and Engineering--Department of Physics--Post-graduate theses

Type of Work--Post-graduate theses

Views

640

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