Development of Spectral Domain Optical Coherence Tomography for in Vivo Functional Imaging of Biological Tissues

Download or read book Development of Spectral Domain Optical Coherence Tomography for in Vivo Functional Imaging of Biological Tissues written by Lin An and published by . This book was released on 2013 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: Optical coherence tomography is a rapidly developing optical imaging modality capable of noninvasively providing depth resolved information of biological tissue at micrometer scale. Since its first report in 1991, it has made tremendous progress leading to successful applications in a number of fields, such as ophthalmology, gastroenterology, dermatology, dentistry, dermatology, cardiology, etc. According to [1], there are more than 15,000 OCT units that had been put into service in ophthalmic clinic by 2009, which represented approximately $1 billion market. The total amount paid by Medicare for OCT scans has increased from $1 billion per year in 2001 to $7 billion per year by 2008. The market size has kept growing in recent years. Reported in [2] by IBISWorld (an American research company), the OCT has achieved an annual growth rate of 27.4% since 2007. In 2012, the revenue is expected to be $478.4 million, which is 24.7% larger than last year. Despite the massive success, there are still several technical issues that need to be addressed, which could help the OCT technology to deliver even better imaging quality. In this thesis, we described several OCT technologies that can be used to double the imaging depth, realize functional vasculature imaging of biological tissue and increase the imaging speed of OCT system. Aim 1: Use of a scanner to introduce spatial frequency modulation to OCT spectral interferograms for in vivo full-range Fourier-domain optical coherence tomography. A novel method was developed that could easily introduce a modulation frequency onto the X-direction (i.e., B-scan) of the FDOCT scanning system, enabling full-range Fourier-domain Optical Coherence Tomography (frFDOCT). Compared to the conventional FDOCT system, the newly developed frFDOCT system can provide increased system sensitivity and deeper imaging depth. The previous technology that can achieve frFDOCT either needed multiple steps for data capturing, which is time consuming, or required additional components which increased the system's complexity. The newly developed method generates a modulation spatial frequency in the spectral interferogram by simply offsetting the probe beam at the X-scanner. In this way, the frFDOCT could be easily realized through applying a Hilbert transformation. Aim 2: Using optical micro-angiography to achieve in vivo volumetric imaging of vascular perfusion within human retina and choroids. Optical Micro-Angiography (OMAG) is a functional extension of FDOCT technology. It can achieve visualization of vasculature network of biological tissue. In order to apply the OMAG method to image vasculature map of human retina and choroid, a phase compensation algorithm was developed, which could minimize the motion artifacts generated by the movements of human eye and head. The original scanning protocol of OMAG method could only achieve ~2 mm x 2 mm scanning area on the retina, which is relatively small for clinical applications. To achieve large field of view of vasculature visualization of retina and choroid, multiple small areas of retina were sequentially scanned. After being processed, all the vasculature maps coming from small areas were stitched together to produce a vasculature map of the whole retina and choroid, which is comparable to Fluorescein Angiography. Aim 3: Developing ultrahigh sensitive optical micro-angiography to achieve micro vasculature imaging of biological tissue. Though the OMAG has been successfully applied for visualizing vasculature networks of different biological tissue, there are several problems that need to be solved, such as lower flow sensitivity, longer imaging time and so on. To improve the vasculature image quality, we developed ultrahigh sensitive OMAG (UHS-OMAG). Unlike conventional OMAG, UHS-OMAG applied the OMAG algorithm onto the slow direction of FDOCT scan (Y-direction). Because the time interval between adjacent B-frames is much longer than that between adjacent A-lines, UHS-OMAG can achieve much higher flow sensitivity compared to the conventional OMAG. In addition, the UHS-OMAG usually employed high frame rate (typically 300 frames per second) to achieve 3D scan, it cost much less time to finish one 3D scan compared to the traditional OMAG. However, when it was applied to visualize vasculature map of human tissue, the motion artifacts caused by the inevitable movements is still the biggest challenge. Based on the phase difference calculated from two adjacent B-frames, a new phase compensation algorithm was developed. The UHS-OMAG system was then applied onto human retina and skin to produce detailed micro vasculature networks. Aim 4: Developing ultrahigh speed Spectral Domain OCT system through sequentially controlling two high speed line scan CMOS cameras. Since the report of OCT technology, the imaging speed is always the hot topic along its development path. Though one branch of FDOCT technology, swept source OCT, can run at several megahertz, SSOCT is still not approved by FDA for human eye imaging. The development of spectral domain OCT is more attractive from a commercialization perspective. Two identical high speed line cameras were employed to build two home build high speed spectrometers. Through sequentially controlling the reading time period of two cameras, the imaging speed of the whole system could reach twice higher than the single camera system. The newly built 800 nm SDOCT system which can work at 500,000 Hz A-lines capturing speed was then used to achieve in vivo 3D imaging in both high speed and large field of view mode. In addition, through combining with the OMAG algorithm, the newly developed system is capable of providing detailed micro-vasculature imaging of human retina and optic nerve head.