Fiber-based Optical Coherence Tomography System Research Articles

Dual Modality Noncontact Photoacoustic and Spectral Domain OCT Imaging.

We developed a multimodal imaging system, combining noncontact photoacoustic imaging and optical coherence tomography (OCT). Photoacoustic signals are recorded without contact to the specimens’ surface by using an interferometric technique. The interferometer is realized within a fiber-optic network using a fiber laser at 1550 nm as source. The fiber-optic network allows the integration of a fiber-based OCT system operating at a wavelength region around 1310 nm. Light from the fiber laser and the OCT source are multiplexed into one fiber using wavelength-division multiplexing. The same focusing optics is used for both modalities. Back-reflected light from the sample is demultiplexed and guided to the respective imaging systems. As the same optical components are used for OCT and photoacoustic imaging, the obtained images are co-registered intrinsically in lateral direction. Three-dimensional imaging is implemented by hybrid galvanometer and mechanical scanning. To allow fast B-scan measurements, scanning of the interrogation beam along one dimension is executed by a galvanometer scanner. Slow-axis scanning, perpendicular to the fast axis, is performed utilizing a linear translational stage. We demonstrate two-dimensional and three-dimensional imaging on agarose phantoms.

Characterization of Optical Coherence Tomography Images Acquired at Large Distances With Large-Diameter Beams

We tested the imaging capabilities for variants of a 1550-nm swept-source fiber-based optical coherence tomography system with a telecentric system incorporated at the end of its sample arm. The system was designed for in vivo imaging of burns; therefore, we acquired images from samples located at distances greater than 24 cm from the exit of the telecentric system. Each system variation had a specific combination of diameters for the reference and sample beams. In the reference arm, we used, alternately, two collimated beams with diameters of 1.5 and 14 mm, respectively. In the sample arm, we tested collimated beams with the following diameters: 1.5, 3.5, 5.7, 8.4, and 14 mm. A galvanometric mirror system scanned the collimated sample beam across the entrance pupil of the telecentric system. The sample beam exited the telecentric system parallel with its optical axis and convergent onto the sample. Depending on the collimator used in the sample arm, images were acquired with beams focused to waist diameters ranging from 40 to 240 μm. We acquired images with the sample at different locations within a ±30 mm range centered about the sample beam waist. Furthermore, we used the signal-to-noise ratio, the detected signal intensity, and the visual appearance to compare images acquired with different sample/reference beam configurations.

Fiber-based optical coherence tomography for biomedical imaging, sensing, and precision measurements

Recently published studies on fiber-based optical coherence tomography (OCT) are reviewed mainly in relation to applications within the fields of biomedical imaging and precision measurement. A succinct introduction to fiber-based OCT system configurations is described including history, related core components, and functional characteristics. Then, an overview of fiber-optic probes is presented in terms of actuating method, scanning direction, and functionality. In order to verify the performance of fiber-optic OCT systems, fiber-based OCT images of several biological samples including pearls, fingers, teeth, and tumor tissues are presented. A multi-functional modality combined with laser induced fluorescence spectroscopy is also presented to distinguish between similar samples. Finally, some interesting fiber-optic OCT studies are briefly presented to measure various physical, chemical, and biological parameters. In particular, simultaneous refractive index and thickness measurement systems with self-referencing and dual probing techniques are introduced. Also, high precision measurement using a common-path OCT configuration is demonstrated with the help of Fourier domain phase analysis.

Quantification of molecular diffusion in arterial tissues with optical coherence tomography and fluorescence microscopy

Alternations in vascular permeability for different molecules, drugs, and contrast agents might be a significant early marker of development of various diseases such as atherosclerosis. However, up to date experimental studies of molecular diffusion across vascular wall have been limited. Recently, we demonstrated that the Optical Coherence Tomography (OCT) technique could be applied for noninvasive and nondestructive quantification of molecular diffusion in different biological tissues. However, the viability of the OCT-based assessment of molecular diffusion should be validated with established methods. This study focused on comparing molecular diffusion rates in vascular tissues measured with OCT and standard fluorescent microscopy. Noninvasive quantification of tetramethylrhodamine (fluorescent dye) permeability in porcine vascular tissues was performed using a fiber-based OCT system. Concurrently, standard histological examination of dye diffusion was performed and quantified with fluorescent microscopy. The permeability of tetramethylrhodamine was found to be (2.08 ± 0.31) × 10−5 cm/s with the fluorescent technique (n = 8), and (2.45 ± 0.46) × 10−5 cm/s with the OCT (n = 3). Good correlation between permeability rates measured by OCT and histology was demonstrated, suggesting that the OCT-based method could be used for accurate, nondestructive assessment of molecular diffusion in multilayered tissues.

Dispersion Compensation in Optical Coherence Tomography with a Prism in a Rapid-Scanning Optical Delay Line

We demonstrate the theoretical and experimental results of using a single prism in the rapid-scanning optical delay line of an optical coherence tomography (OCT) system for compensating the mismatches of the first- and second-order group delay dispersion (GDD) between the reference and sample arms. The analytical expressions for the first- and second-order GDD are derived based on the typically designed system configuration. Numerical results in varying various parameters are shown. An optimized set of parameters for efficient dispersion compensation in a practical fiber-based OCT system is obtained. The numerical result of the dispersion compensation is demonstrated. Also, the experimental implementation of such a dispersion compensation method is illustrated with the conditions similar to the numerical calculations. The compensation result is quite satisfactory

Three-dimensional optical coherence tomography employing a 2-axis microelectromechanical scanning mirror

We present a three-dimensional (3-D) optical coherence tomography (OCT) system based on a dual axis microelectromechanical system (MEMS) mirror. The MEMS mirror provides high-speed, high resolution 2-axis scanning while occupying a very small volume with extremely low power consumption. The dimensions of the mirror are 600/spl times/600 /spl mu/m, and both axes are capable of scanning up to 30 degree angles at frequencies greater than 3 kHz with good linearity. A 3-D image set is acquired when the MEMS mirror is integrated with the fiber-based OCT system. Via 2-axis lateral scanning, combined with an axial scan, a volume (2/spl times/2/spl times/1.4 mm) image of tissue, including a cancerous region, from a hamster cheek pouch was obtained. Using a signal processing technique, image data is normally presented by 3-volume showing views at arbitrary angles and locations. The objective of this work is to show the capabilities of a 3-D OCT system utilizing a MEMS scanner as this technology can readily by applied to realize OCT beam delivery systems such as hand held scanners and endoscopic probes. A MEMS based 3-D OCT system employing a high speed, small volume scanner may have the potential to expand the application area of OCT and revolutionize areas of clinical medicine as well as medical research.

Micromachined array tip for multifocus fiber-based optical coherence tomography.

High-resolution optical coherence tomography demands a large detector bandwidth and a high numerical aperture for real-time imaging, which is difficult to achieve over a large imaging depth. To resolve these conflicting requirements we propose a novel multifocus fiber-based optical coherence tomography system with a micromachined array tip. We demonstrate the fabrication of a prototype four-channel tip that maintains a 9-14-microm spot diameter with more than 500 microm of imaging depth. Images of a resolution target and a human tooth were obtained with this tip by use of a four-channel cascaded Michelson fiber-optic interferometer, scanned simultaneously at 8 kHz with geometric power distribution across the four channels.

Optical Coherence Tomography Premiere in Korea

Optical Coherence Tomography (OCT) is considered as fundamentally new image modality having advantages such as high-speed, real-time cross sectional imaging with non-invasive in vivo investigation of biological tissue and its potential for clinical application is highly evaluated. In spite of these merits, the research activity in OCT has not taken much attention until recently. However the situation in Korea is gradually changing due to understanding of its versatile applications. Active research and commercialization are underway. Bulk optics-based OCT system is changed into alignfree fiber-optics system. With our expertise in the fabrication of fiber grating devices and strong background in control of fiber based system, we hope to contribute in developing simplified all-fiber OCT system with better performance. As a leading research group, working on OCT, we have firstly implemented fiber-based OCT system in Korea and demonstrated the imaging performance with glass plate and onion.