Akademik Veri Yönetim Sistemi
Tozburun S. (Yürütücü), Pekkan K.
TÜBİTAK Projesi, 2017 - 2020
The aim of the Project is to develop and build an original, prototype, Optical-domain subsampled Optical Coherence Tomography (OCT) imaging system that utilizes a wavelength-stepped laser with the state-of-the-art wavelength stepping method. We envision that this new generation OCT design will be able to provide promising steps towards measuring the volumetric blood flow and the volumetric angiography from the extended imaging depth at video rate by applying the inter-volume Doppler OCT and the inter-volume phase-variance OCT angiography techniques, respectively. In order to strive this envision in future studies with a clinical application, which would be the measurement of elasticity in capillaries, we aim to complete three main goals, which are underlined within the proposed project, including: Goal 1: Building, characterization and optimization of a chromatic dispersion between two phase modulator based wavelength-stepped laser system. Goal 2: Building and characterization of the optical-domain subsampled OCT system. Goal 3: Characterization and validation of the OCT system for Doppler OCT measurements in a phantom study with the use of conventional data acquisition card (DAQ) and without the need of either individual A-line trigger signals during the acquisition or post-processing phase calibration algorithms.
Optical Coherence Tomography, which was introduced for the first time to the field by Huang et al in 1991, is a new non-invasive imaging technique. The principle of OCT is based on interferometry technique of first scattered laser light from both the sample and the reference arms. It is possible to provide real-time, cross-sectional images from biological samples in a resolution range of 1-15 μm with this new imaging technique. Due to the intense demands of high speed imaging with high resolution for 3D imaging and for promising future potentials in clinical application sites, Swept-source OCT, which is one of the subtypes of Fourier-domain OCT, has been recently introduced to the attention of the researchers in the field. One of the interesting points in these imaging systems is the laser source called wavelength-swept lasers. Many technologies have been used in the development of wavelength-swept sources for Swept-source OCT and it is still an active field of research. In the recently developed laser sources, spectral-tuning was achieved with either a mechanical actuators/mirrors placed in the cavity or dispersion mode-locking techniques. Particularly, swept-source OCT devices using these laser designs have been utilized in Doppler OCT studies with the use individual A-line triggers or post-processing phase calibration algorithms. In addition to all, as a result of the current developments in the optical components of OCT devices, especially in the laser sources, the need of data acquisition cards with gigahertz sampling rate for digitalizing fast interference signals (OCT signals) has clearly appeared. This requirement has become a limitation point of the OCT technology due to the continuous dependency on the developments of DAQ card technology. Optical-domain subsampled OCT technique, which has begun developing in the recent years and the principal investigator of the project participated in innovative research and development studies of, was introduced as a solution site. With this new technique that uses laser output with discrete wavelength spectrum instead of continuous-wave optical spectrum, the required sampling bandwidth to catch the fast OCT signals is reduced to a level (~3 GS/s) where current DAQ cards easily provide. In the proposed project, a new generation optical-domain subsampled OCT device is introduced. The specific novelties of the imaging device having a new design laser are listed as following: i) opposite chromatic dispersion based phase modulated wavelength stepping module, ii) high sensitivity level (> 100 dB) in optically subsampled OCT devices, iii) intrinsically phase stable system structure.
In this perspective firstly, a laser composed of semiconductor optical amplifier (SOA), Fabry-Perot etalon, and wavelength stepping module will be developed. SOA will produce laser radiation at the center wavelength of 1.3-μm and will provide optical bandwidth of approximately 90-nm at the optical gain of 3 dB. Comb spectrum structure (or in other words, optical-domain subsampling model) will be achieved by a free-space Fabry-Perot. Module will consists of two-phase-modulators and two-chirped-fiber-Bragg-grating with two opposite dispersion (one applies positive chromatic dispersion and one applies negative chromatic dispersion). This will be a module that provides laser wavelength stepping in time without using any mechanic tool/mirror. Preliminary data showing the proof of concept and verification of the working principle of this module that is one of the novel parts of the laser is introduced in this proposal as well. Prototype OCT device will be built by combining the laser with a fiber optics interferometer having a 2D MEMS scanner in the sample arm. Device will be characterized under several subjects including absolute group delay measurement, noise and jitter measurement, polarization mode dispersion, coherence length, axial resolution and sensitivity measurements, and phase stable structure measurement. Lastly, an intralipit flow phantom study will be performed to validate the device’s inter-volume Doppler OCT and inter-volume phase variance OCT angiography claims without the need for individual A-line triggers or post-processing phase calibration algorithms.
As it is described in the general frame of TUBITAK Biomedical Instrumentation Call (1003-SAB-BMED-2016-1 Bioinstrumentation Systems) program, “the development of national, scientific and technologic potentials that is required for the development of new medical technologies in the field of biomedical equipment is needed.” In this call, “it is primarily aimed that after the end of the project, technology, prototype or product outcomes should be in the level of competition with similar world-class competitors.” Furthermore, the subject called the development of the medical imagine technologies holds a place within the scope of the program that is in the aim and goals section of the call text. When considered from this point, it is evaluated that the aim od the proposed project contributes to forming Turkey’s national innovator and competitive sites in the international platform, particularly in the field of medical imaging and the goals of the project exactly match with the call program.