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Title: Focal Modulation Microscopy: A Novel Optical Imaging Method
Keywords: microscopy, focal modulation, medical optics, imaging system,scattering,deep tissue imaging
Issue Date: 25-Nov-2009
Citation: WONG CHEE HOWE (2009-11-25). Focal Modulation Microscopy: A Novel Optical Imaging Method. ScholarBank@NUS Repository.
Abstract: This thesis proposes a novel method for improving the imaging depth of a microscope based on focal modulation. The usual method for improving imaging depth often relies on the use of a long wavelength light source. Light with a spectrum closer to red, generally suffers lower extinction due to reduced scattering in the water-predominant tissue environment. However, this often precludes the usage of the current fluorescence dye suite and inhibits long wavelength source usage proliferation. The focal modulation approach aims to circumvent the above inhibition while affording the advantage of improved imaging depth without usage of a long wavelength source. Focal modulation is a method in which the focal point intensity is modulated via interference between a reference and a frequency phase modulated beam. Due to the sinusoidal frequency modulation of these interfered beams, the focal point intensity profile is constantly varying, with the main central lobe and the side lobes intensity varying from maximum to minimum periodically. On a fluorescence labelled specimen sample, the resultant fluorescence intensity will be modulated with the excitation beam, though the time-averaged fluorescence intensity will be equivalent to that of a conventional confocal microscope. The detector plane pinhole subsequently acts as a filter, blockading the side lobe intensity contribution and allow for retrieval of the modulated intensity. A prototype optical system which resembles closely to a conventional confocal microscope, is constructed to verify the concept. A pair of mirrors, each forming a half of the aperture and on which a piezoshifter is attached to one of them, is used to form the illumination aperture of the system. A sinusoidal control signal is supplied to the piezoshifter and the fluorescence light is then gathered via fiber optics attached to a PMT. Three different types of specimen (fluospheres, Schefflera arboricola and chicken cartilage) were used to study the proposed idea. From the experimental results, an improved sectioning effect is observed in the focal modulation microscope over the confocal microscope. Hence it is proposed that the focal modulation microscope provides a method in which the imaging depth is improved, yet at a minimal installation cost in terms of hardware and manpower.
Appears in Collections:Ph.D Theses (Open)

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