Abstract
Optical coherence tomography (OCT) is a reflection based imaging technique, with numerous applications, initially in medical diagnostics. Unlike ultrasound, another reflection imaging technique, OCT relies on light scattering in samples, low coherence near- infrared interferometry, and graphical image construction, to acquire 2D and 3D reflectogram images. OCT has resolution an order of magnitude greater than ultrasound, but its depth penetration is less than a few millimetres.
Axial resolution is a critical parameter in determining whether OCT can be used to resolve specific features in a sample image. Typically, measures of resolution have been attributed only to the light source’s characteristics, including its coherence length and the FWHM of its frequency spectrum’s inverse FT, or auto-correlogram. The need to cost effectively visualize the OCT-system-generated auto-correlograms, and OCT cross-correlograms (A-scan) (produced using many different OCT light sources), has necessitated the extrinsic-evolution of an OCT simulation model, presented in this thesis. This research indicated that empirical resolution in vivo is also strongly dependent on the optical characteristics of the tissue, including surface reflection. When the surface reflection is removed from the A-scan, the minimum stratum depth that can be resolved for the sub-surface strata, is significantly enhanced. Furthermore, this subtraction enhances the stratum depth resolution, so that it approaches more closely the light source’s resolution limit, compared to A-scans without the subtraction.
The time domain OCT’s optical delay line (ODL) and light source components were also reviewed to determine their affordability and functionality for engineering a portable, high resolution, but simple OCT modality. To this end, a stationary ODL, using a transmissive optical light valve array and a stepped mirrored structure (SMS), was characterised in ‘proof of principle’ experiments. Unfortunately, fabrication of the SMS, using four affordable techniques, proved unsuccessful; however, more promising techniques, based on the theoretical developments in this thesis, are envisaged. A stochastic pseudo-genetic algorithm (GAM), similar, but not exactly analogous to theoretical genetic intrinsic-evolution, was characterised and used to backwards-fit the solution set of strata depths and reflectivities of a selected OCT A-scan. Unfortunately, its speed in Matlab was not timely enough for e-medical application – though in c this GAM could run faster. This slowness is due to the GAM’s stochastic nature, prompting future investigation of other GAMs, which will eliminate the stochastic element so that more timely results can be achieved.
Related Publications
Jansz, P. V., Richardson, S., Wild, G., Hinckley, S., (2014). Characterising the resolvability of real superluminescent diode sources for application to Optical Coherence Tomography using a low coherence interferometry model. Journal of Biomedical Optics, (19)8. doi:10.1117/1.JBO.19.8.085003. Article available here.
Jansz, P. V., Richardson, S. J., Wild, G. , & Hinckley, S. (2012). Biomedical Image Signal Processing for Reflection-Based Imaging. In Radovan Hudak, Marek Penhaker and Jaroslav Majernik (Eds.). Biomedical Engineering - Technical Applications in Medicine (pp. 361-386). InTech. Link to the original chapter is available here.
Jansz, P. V., Wild, G. , Richardson, S. J., & Hinckley, S. (2012). Low Coherence Interferometry Modelling using Combined Broadband Gaussian Light Sources. Proceedings of Third Asia Pacific Optical Sensors Conference. (pp. 83510C1-7). Sydney, Australia. The Society of Photo-Optical Instrumentation Engineers. Link to the original article is available here.
Jansz, P. V., Richardson, S. J., Wild, G. , & Hinckley, S. (2012). Modelling of low coherence interferometry using broadband multi-Gaussian light sources. Photonic Sensors, 2(3), 247-258. Link to the original article is available here.
Jansz, P. V., Richardson, S. J., Wild, G., & Hinckley, S. (2011). An extended analytical model to simulate optical coherence tomography systems with a quasi-stationary optical delay line. Paper presented at the SPIE Smart Nano+Micro Materials and Devices. Melbourne, Australia. (pp. 82043G-1 – 13). Link to article available here.
Jansz, P. V. & Hinckley, S. (2011). Extrinsic evolution of the stacked gradient poly-homojunction photodiode genre. In G. F. D. Betta (Ed.), Advances in Photodiodes, (pp. 181 – 204). doi: 10.5772/15417. Link to chapter available here.
Jansz, P. V., Wild, G., Richardson, S. J., & Hinckley, S. (2011) Simulation of an optical delay lines for optical coherence tomography. Paper presented at the Incorporating the Australasian Conference on Optics, Lasers and Spectroscopy and the Australian Conference on Optical Fibre Technology. Sydney, Australia. (pp. 1400 – 1402). Link to original article available here.
Jansz, P. V., Hinckley, S. , & Wild, G. (2011). A stationary optical delay line for low coherence interferometry. Paper presented at the 6th IEEE International Symposium on Electronic Design, Test and Application, (DELTA), Queenstown, New Zealand. (pp. 162 – 167). doi: 10.1109/DELTA.2011.37 Link to article available here.
Jansz, P. V., Wild, G. , Hinckley, S. , Yang, Y., & Duncan, P. (2010). A Comparison of Grinding and Electric Discharge Machining to Fabricate a Stepped Mirror Structure for a Stationary Optical Delay Line. Proceedings of AIP/ACOFT 2010 (ACOFTAOS). Melbourne. (pp. 1-4). Link to the original article is available here.
Jansz, P. V., Wild, G., & Hinckley, S., (2008). A comparison of wet and dry etching to fabricate a micro-photonic structure for use in OCT. Proc. SPIE 7270, Biomedical Applications of Micro- and Nanoengineering IV and Complex Systems, 727016. doi:10.1117/12.810973
Jansz, P. V., Wild, G., & Hinckley, S. (2008). A micro-photonic stationary optical delay line for fibre optic time domain OCT. Proc. OECC ACOFT, 1 – 2. Link to original article here.
Jansz, P. V., Wild, G., Hinckley, S., (2008). Optical switching of a proposed stationary optical delay line for OCT. Proceedings of the . SPIE 7268, Smart Structures, Devices, and Systems IV, 72681J (pp. 1-10). Link to original article available here.
Jansz, P. V., Wild, G., & Hinckley, S., (2008). A proposed fibre optic time domain optical coherence tomography system using a micro-photonic stationary optical delay line. Proc. SPIE, 19th International Conference on Optical Fibre Sensors, 7004, 70045Y-1 – 4. Link to abstract available here.
Jansz, P. V., Wild, G., & Hinckley, S., (2008). Stepped mirrored structures for generating true time delays in stationary optical delay line proof-of-principle experiments for application to optical coherence tomography. In Z. Krolikowski, C. Soukoulis, P. K. Lam, T. Koy; Davis, S. Fan, & Y. S. Kivshar (Eds.). Photonics: Design, Technology, and Packaging III. Proceedings of the SPIE, Volume 6801, article id. 68011H. doi: 10.1117/12.759012 Link to article available here.
