M.Sc Thesis

M.Sc StudentMerman Michal
SubjectVibration Measurements Using Spectrally-Encoded Endoscopic
Doppler Imaging
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Dvir Yelin
Full Thesis textFull thesis text - English Version


Spectrally-encoded endoscopy (SEE) is a recent development in miniature optical endoscopy: a system of a single fiber with miniature optics which uses interferometry for high resolution imaging. The endoscopic probe includes a transmission grating and a lens, which diffracts the beam to form a spectrally-encoded line. In this manner, every location along the x-axis is encoded by a narrow part of the spectrum, and information from a large number of image points is collected simultaneously, eliminating the need for complex beam-scanning mechanisms. Extensive experimental work has been published, which demonstrated SEE capabilities for high-resolution in-vitro and in-vivo structural imaging, as well as for functional Doppler imaging of vibrations and flow. Vibration imaging may be useful in diagnosis of various pathologies in the middle ear. Due to miniature probe size, spectrally-encoded miniature endoscopy could allow functional imaging within the middle ear, which is currently restricted by its remote location and small size.  

In this work, we have continued to explore the SEE imaging technique and further develop theoretical principles, which govern SEE imaging, as well as experimental techniques for improvement of imaging quality and extraction of additional information from the acquired data. We have thoroughly analyzed several key imaging parameters of SEE, derived explicit expressions which formulate its resolution and field of view geometries in three dimensions, and outlined the system’s unique optical aberrations. This analysis could be useful in understanding future system and probe designs, and would hopefully assist in the development of novel spectrally encoded imaging concepts. We have also formulated and demonstrated new means for adjusting the imaging plane in Fourier-domain SEE, effectively compensating for an inherent tilt of the field-of-view, that is characteristic for the traditional SEE probe design. The tilt of the field-of-view may cause parts of the sample to be positioned out of the effective range of the interferometric SEE imaging system; we have shown experimentally that using controlled optical dispersion we may adjust the field-of-view to achieve better sample coverage and avoid image artifacts. In addition, we have continued to develop the SEE Doppler method for vibration imaging. Applying phase analysis principles, we have experimentally demonstrated single- and multi-frequency waveform extraction and complex signals reconstruction from interferometric data recorded on the surface of a piezoelectric actuator and a bovine stapes attached to it. We have shown that Doppler SEE is a promising endoscopic technique, which is capable of simultaneous structural and functional imaging.