Non-mechanical Axial Motion Compensation Using Master-Slave Optical Coherence Tomography

We present a novel technique for accurate, non-mechanical, axial motion compensation for OCT in both ophthalmology and dermal imaging through the combination of MS-OCT for imaging and a LCI for the motion detection

Full-Field Swept Source Master-Slave Optical Coherence Tomography

We apply the principle of master-slave (MS) interferometry to a full-field swept source optical coherence tomography (OCT) setup equipped with a fast 2-D camera. MS interferometry does not involve Fourier transformations and, therefore, eliminates the need for spectrum data resampling required by the conventional spectral domain OCT. Using this method in a full-field OCT setup, en face images are acquired in vivo from finger skin, Drosophila melanogaster larvae, and pupae, with no spectrum resampling and no mechanical scanning. The signal processing is based on a comparison operation of the shapes of channeled spectra for each camera pixel, with a set of reference signals (masks). In this way, en face OCT images can be obtained with no need for the volumetric assembly and software cutting the en face images from an image volume, which are required by the conventional spectral domain OCT method. We demonstrate that the sensitivity and axial resolution of the MS method in a full-field swept source OCT setup are similar to the values obtained using the conventional Fourier-transformation-based swept source OCT method in a full-field setup. Multiple en face images can be produced in parallel by using multiple stored shapes of channeled spectra for the depths of interest. The full-field MS-OCT method presented here opens the possibility of parallel processing for all image points in a 3-D volume of the object

Supercontinuum in the practice of Optical Coherence Tomography with emphasis on noise effects

Optical Coherence Tomography (OCT) is an imaging modality which has proven, since the early 1990s, its incredible potential. Nowadays, numerous fields of medical investigation, such as Ophthalmology, Dermatology or Cardiovascular imaging, would not be the same without the diagnostic tools bring by OCT. This tremendous development has been supported by industry support through improvement of dedicated components such as lasers, cameras and optics. A great example of this development is the evolution of Supercontinuum (SC) sources. Due to the extremely broad spectrum cover by SC sources, their high power density and high spatial coherence, it seems obvious to use them for driving OCT systems. However, an intensity noise issue arising from the SC sources has been reported as a limitation for OCT and needs to be addressed. The aim of the work presented in this thesis is to create a link between the world of Optical Coherence Tomography and Supercontinuum physics in order to understand the origins and the impact of SC source intensity noise into the OCT systems. This work is of importance as it helps to optimize the usefulness of the current generation of SC sources. Also, this work is a part of the work necessary for developing a new generation of SC sources which completely addresses the intensity noise limitations. More precisely, a part of the work presented deals with an optimization of the association SC source and OCT. The second part of the results is an attempt for improving this association by using a new SC source design

A study of the application of adaptive optics (AO) in optical coherence tomography (OCT) and confocal microscopy for the purpose of high resolution imaging

A problem is presented when imaging the eye in that optical aberrations are introduced by tissues of the anterior eye such as the cornea and lens. Adaptive optics (AO) and scanning laser ophthalmoscopy (SLO) have been combined to detect and compensate for these aberrations through the use of one or more correcting devices. Di erent corrector options exist, such as a liquid crystal lens or a deformable mirror (DM), such as that used in this thesis. This study seeks to use the ability of the DM to add focus/defocus aberrations to the closed loop AO system. This procedure could allow for dynamic focus control during generation of B-scan images using spectral domain optical coherence tomography (SD-OCT), where typically this is only possible using slower time domain techniques. The confocal gate scanning is controlled using the focus altering aberrations created by changing the shape of the deformable mirror. Using the novel master-slave interferometry method, multiple live en-face images can be acquired simultaneously. In this thesis, application of this method to an AO system is presented whereby en-face images may be acquired at multiple depths simultaneously. As an extension to this research, an OCT despeckle method is demonstrated. Further to this work is the investigation of the role in AO for optimisation of optical systems without the requirement for direct aberration measurement. Towards this end, genetic algorithms (GA) may be employed to control the DM in an iterative process to improve the coupling of light into fibre

Optical Fiber Interferometric Sensors

The contributions presented in this book series portray the advances of the research in the field of interferometric photonic technology and its novel applications. The wide scope explored by the range of different contributions intends to provide a synopsis of the current research trends and the state of the art in this field, covering recent technological improvements, new production methodologies and emerging applications, for researchers coming from different fields of science and industry. The manuscripts published in the Special issue, and re-printed in this book series, report on topics that range from interferometric sensors for thickness and dynamic displacement measurement, up to pulse wave and spirometry applications

Master/slave optical coherence tomography imaging of eyelid basal cell carcinoma

Optical coherence tomography (OCT) is fast emerging as an additional non-interventional modality for skin tumor detection and diagnosis. A master/slave flying spot OCT configuration was assembled to detect periocular basal cell carcinomas (BCC). A swept source at 1300 nm and sweeping speed of 50 kHz were used. A three-step process was involved. First, 384 channeled spectra using a mirror were stored for 384 optical path differences at the master stage. Then, the stored channeled spectra (masks) were correlated with the channeled spectrum from the BCC tissue to produce 384 en face OCT images (200×200200×200 pixels) for the optical path difference values used to acquire the masks. Finally, these en face slices were stacked to form a volume to cross-reference BCC tumor margins in the orthogonal plane. Per each eyelid sample, several en face images of 200×200200×200 lateral pixels are produced in the time to scan laterally a complete raster of 1.6 s. Combination of the en face views with the cross-sectioning views allow for better discrimination of BCCs comparable to using cross-sectional imaging alone, as previously reported using the conventional fast-Fourier-transform-based OCT techniques

Akinetic Tuneable Optical Sources with Applications

Optical Coherence Tomography (OCT) is a modern, non-invasive imaging technique in biomedical research and medical diagnostics. It was initially developed for clinical applications in ophthalmology, providing high-resolution, cross-sectional images of the retina, retinal nerve fibre layer and the optic nerve head. Today, OCT is used for in vivo imaging of almost every type of tissue and it also branched out in fields outside medicine, like industrial or pharmaceutical applications. OCT is a continuously improving imaging technique, benefiting from the development of advanced optical components and broadband optical sources. The objective of the work presented in the thesis was the development of both short and, respectively, long cavity akinetic optical devices, employing several types of dispersive optical fibre components in the cavity, like chirped fibre Bragg gratings, single mode or dispersion compensating fibre, and actively radio-frequency tuned semiconductor optical amplifiers, used as gain media. The use of external modulators, like Fabry-Perot assemblies, rotating mirrors and other mechanical devices is therefore completely eliminated, while versatility is added in the control of the coherence length, output bandwidth, repetition rate and power. The short cavity source was developed in the 1060 nm region, the output power and bandwidth showing a slow decay with the increase of repetition rate up to 250 kHz. Without any booster, the power achieved was 2 mW at 100 kHz. A novel dual-mode-locking mechanism was developed in order to tune an akinetic swept source based on dispersive cavities at a repetition rate close to, but different from the inverse of the cavity roundtrip. Several optical source configurations emitting in the 1060 nm or 1550 nm wavelength region were developed, characterised and tested in OCT applications. For the 1550 nm swept source employing a Faraday Rotating Mirror in a dispersive cavity, sweeping rates in the range of MHz were achieved, from 782 kHz to up to 5 times this value, with proportional decrease in the tuning bandwidth. Linewidths smaller than 60 pm and output powers exceeding 10 mW were measured. OCT topographic imaging was demonstrated. The thesis ends with a proposed broadband investigation of microresonators written in silica glass employing akinetic optical sources at 1550 nm. The work presented in this thesis resulted in several peer reviewed papers, one patent application and several conference presentations, listed after the final conclusions

Phase-Sensitive Optical Coherence Tomography for Dynamic Photothermal Detection And Imaging of Gold Nano-Rods in Scattering Media and Biological Tissue

Gold nanoparticles are particularly attractive agents in medical imaging and laser therapy due to their unique optical properties. This study seeks to propose and analyse solutions aimed at imaging the distribution of gold nanoparticles in scattering media and biological tissue using a photothermal modulation technique combined with phase sensitive Optical Coherence Tomography (OCT). In this thesis, a spectrometer based phase sensitive OCT system and a swept source based phase sensitive OCT system are developed separately to fulfil this goal. In each OCT system, a Ti:Sa laser beam is coaxially combined with the OCT probing beam. The photothermal detection of gold nano-rods in multiple layer of the sample is completed by fixing the combined beam on a single lateral position on the sample and modulating the frequency of the Ti:Sa beam to the sample. The photothermal imaging of gold nano-rods in multiple layers of the sample is achieved by raster scanning the combined beams over the sample, modulating the Ti:Sa beam to the sample and then generating high contrast en-face images displaying the phase values retrieved from the OCT signal. Using the recently developed Complex Master/Slave interferometry technique, en-face images can be acquired in real time. In this thesis, application of this technique to a swept source based OCT system is presented. A system is specifically developed to produce en-face phase images of multiple layers of the studied sample. By doing this, the phase sensitive function of the Complex Master/Slave interferometry technique is demonstrated for the first time