Feature Of The Week 12/12/10: KAIST Researchers Demonstrate Novel Polarization-Sensitive SD-OCT System
Feature Of The Week 12/12/10: Researchers from the Korea Advanced Institute of Science and Technology (KAIST) recently published impressive results on the design and performance of novel Polarization-Sensitive Spectral-Domain Optical Coherence Tomography system using a multi-line signal camera spectrometer. Below is a summary of their recent work.
Recently developed polarization-sensitive spectral domain optical coherence tomography systems have some intrinsic limitations. Dual-camera based system has some difficulties in terms of the high-precision alignment of the spectrometers, the exact trigger timing and synchronization, and the system complexity. Most of single camera based system for avoiding these problems, also suffer from the reduced imaging speed or depth. We describe a PS SD-OCT technique using a single camera spectrometer that includes a custom-built multiplexed grating and a three-line CCD camera.
The spectrometer design is crucial in the proposed PS SD-OCT. The essential components of the spectrometer are the grating and the detection camera. The home-built spectrometer includes a multiplexed transmission custom grating (Wasatch Photonics), a three-element air-spaced camera lens, and a three-line CCD camera (Basler Vision Technology L301k). We utilize a CCD camera containing three lines (2098 pixels x 3 lines), and the center-to-center spacing between lines was 112 μm. Two types of VPHG were constructed and laminated together to produce the desired multiplexed grating. The diffraction efficiency is about 80%. Two-dimensional raw data (2048 x 1024 pixels/frame) from two orthogonal interference spectra were saved at a rate of about 8.98 frames per second (maximum line rate of 9.2 kHz) using a high-speed frame grabber (i2S, Horizon Link) or a camera link frame grabber (Solios 6M CL E, Matrox).
The novel spectrometer, composed of a single camera with more than two separated lines, can independently acquire two orthogonally polarized interference signals. Each polarization channel beam has a vertically different incident angle (0.0266°) on the multiplexed grating, while the incidence angles of two collimators are horizontally aligned at angles of ± 60°. The system configuration could help to utilize a camera’s full imaging speed and the increased depth range compared to previous studies. Without introducing a time delay, two orthogonally polarized interference beams were simultaneously read out by only a control signal. And the sharing components in the spectrometer reduce the system complexity compared to dual-camera based PS SD-OCT.
The axial resolution was experimentally determined to be 3.96 μm for the s-polarized beam and 3.89 μm for the p-polarized beam. The phase retardation image of the human palm tissue showed the presence of collagen in the dermis layers. Moreover, this PS SD-OCT system could discriminate the normal chest muscle and Lewis lung carcinoma (LLC) tissue from the DSred GFP mouse. Also, the differences between normal muscle and cancerous tissue were verified by complementary confocal microscopy study.
For more information see recent Articles. Courtesy Cheol Song.