Article

Paired-angle-rotation scanning optical coherence tomography forward-imaging probe

Department of Electrical Engineering, California Institute of Technology, California 91125, USA.
Optics Letters (Impact Factor: 3.18). 06/2006; 31(9):1265-7. DOI: 10.1364/OL.31.001265
Source: PubMed

ABSTRACT We report a novel forward-imaging optical coherence tomography (OCT), needle-probe paired-angle-rotation scanning OCT (PARS-OCT) probe. The probe uses two rotating angled gradient-index lenses to scan the output OCT probe beam over a wide angular arc (approximately 19 degrees half-angle) of the region forward of the probe. Among other advantages, this probe design is readily amenable to miniaturization and is capable of a variety of scan modes, including volumetric scans. To demonstrate the advantages of the probe design, we have constructed a prototype probe with an outer diameter of 1.65 mm and employed it to acquire four OCT images, with a 45 degrees angle between adjacent images, of the gill structure of a Xenopus laevis tadpole. The system sensitivity was measured to be 93 dB by using the prototype probe with an illumination power of 450 microW on the sample. Moreover, the axial and the lateral resolutions of the probe are 9.3 and 10.3-12.5 microm, respectively.

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    ABSTRACT: Coherence domain optical imaging techniques have been developing quickly in the past few decades after the invention of laser. In this thesis, I will report the imaging methods that constitute my research projects during these years of graduate studies, including paired-angle-rotation scanning (PARS) forward-imaging probe for optical coherence tomography (OCT), full-field phase imaging technique based on harmonically matched diffraction grating (G1G2 grating), and Fresnel zone plate (FZP) based optifluidic microscopy (OFM). Compared with conventional optical microscopy, the coherence domain optical imaging has many advantages and greatly extends the application of imaging techniques. OCT, based on low-coherence interferometry, is a high-resolution imaging technique that has been successfully applied to many biomedical applications. The development of various probes for OCT further made this technique applicable to endoscopic imaging. In the project of PARS-OCT probe, I have developed a forward-imaging probe based on two rotating angle-cut GRIN lenses. The diameter of the first prototype PARS-OCT probe that I made is 1.65 mm. My colleagues further built a probe with diameter of 0.82 mm. To our knowledge, this is the smallest forward-imaging probe that has been reported. The first prototype probe was characterized and successfully used to acquire OCT images of a Xenopus laevis tadpole. Full-field phase imaging techniques are important for metrology and can also obtain high-resolution images for biological samples, especially transparent samples such as living cells. We have developed a novel full-field phase imaging technique based on the G1G2 grating. The G1G2 interferometry uses the G1G2 grating as a beam splitter/combiner and can confer nontrivial phase shift between output interference signals. Thus the phase and intensity information of the sample can be obtained by processing the two direct CCD images acquired at the output ports of the G1G2 grating. The details of this technique are explained in this thesis, and the phase imaging results for standard phase objects and biological samples are also shown. OFM is a novel high-resolution and low-cost chip-level microscope developed by our group several years ago. Combining the unique imaging concept and microfluidic techniques, OFM system can be potentially useful to many biomedical applications, such as cytometry, blood parasite diagnosis, and water quality inspection. In the project of FZP-OFM, I applied the FZP to project the OFM aperture array onto an imaging sensor for OFM imaging. In this way, the sensor and the aperture array can be separated and will be useful for some situations. To demonstrate its capability, the FZP-OFM system was used to acquire OFM images of the protist Euglena gracilis. The studies in my research show the possibility of the application of various coherence domain optical imaging techniques in biomedical area, which is the primary objective of this thesis.