Innovative experimental concepts for optical coherence tomography

Optical Coherence Tomography (OCT) is a recent biomedical imaging technique based on low-coherence interferometry that is capable of acquiring depth-resolved reflectivity maps of scattering tissues with high sensitivity. The conventionally employed imaging mode is to build up a cross sectional image by scanning the sample surface with a point illumination. In order to increase imaging speed, the concept of parallel detection has been introduced to OCT. Here, a whole sample line or even surface is imaged directly onto an array of photodetectors, making the lateral scanning motion obsolete. A customized detector array has been developed in our institute for parallel OCT imaging based on complimentary metal-oxide-semiconductor (CMOS) technology. It associates a signal processing circuit to each photosensitive area of the array, capable of demodulating the interferometric signal on-chip. In this manner, only the signal envelop has to be read out, allowing for a high dynamic range and high frame rates. At the beginning of the thesis, this device had only been tested for topographic measurements on reflective surfaces. As a direct continuation of this previous work, the initial objective of this thesis has been to extend its application to parallel OCT in scattering samples and to identify other uses of this technology in the field of OCT. Accordingly, the first part of this work is dedicated to parallel detection in OCT, using this customized CMOS detector array. The feasibility of the approach is shown experimentally on scattering samples. Reflective surfaces covered with scattering solutions of varying concentration and onion samples are studied. Furthermore, the initial goal of fast OCT imaging is pursued by using the detector at its technological limits and realizing video-rate, three-dimensional OCT acquisitions of a dynamically changing sample. The thermal deformations induced by the probing beam on a dark strand of human hair are imaged at 25 volume acquisitions per second. Identified as a possible new application for the CMOS detector array, the concept of wavelength de-multiplexing for spectroscopic OCT is investigated in the second part of this thesis. Wavelength de-multiplexing is an experimental method for realizing spectroscopically resolved, time-domain OCT measurements. In contrast to the currently employed numerical post-processing methods for extracting spectroscopic information, wavelength de-multiplexing relies on optical wavelength separatio