Full-field optical coherence tomography (FF-OCT) capable of in vivo cellular-level imaging is demonstrated for nonscanning horizontal cross-sectional imaging. The system is based on a white light interference microscope illuminated by a thermal light source. A dual-channel two-dimensional (2-D) detection technique incorporated with a pair of CCD cameras has been developed, where a pair of interferometric images with phase difference of /2 are simultaneously captured using an achromatic phase shifter. By acquiring an additional pair of images with a conventional phase shift method, a horizontal cross section is derived from every two consecutive CCD frames, enabling OCT imaging at the video rate. Using an ultrabroad bandwidth illumination incorporated with relatively high NA (0.8 NA) water immersion objectives, an axial resolution of 0.8 µm and a transverse resolution of 0.7 µm are experimentally confirmed. A field of view of 215 µm×215 µm is covered by the 500×500 pixel CCD cameras. We demonstrate, for what is believed to be the first time, in vivo cellular-level blood flow imaging of a Xenopus laevis tadpole by FF-OCT.
Retinal and choroidal imaging by using swept-source optical coherence tomography (SS-OCT) with a 1-μm band probe light, and high-contrast and three-dimensional (3D) imaging of choroidal vasculature are presented. This SS-OCT has a measurement speed of 28,000 A-lines/s, a depth resolution of 10.4 μm in tissue, and a sensitivity of 99.3 dB. A software-based algorithm for scattering optical coherence angiography (S-OCA) is developed for the high-contrast and 3D imaging of the choroidal vessels. This OCT is employed for the investigation of age related macular degeneration and visualizes structures beneath the retinal pigment epithelial detachment.
A feasibility study of ultrahigh-resolution full-field optical coherence tomography (FF-OCT) for a subcellular-level imaging of human donor corneas is presented. The FF-OCT system employed in this experiment is based on a white light interference microscope, where the sample is illuminated by a thermal light source and a horizontal cross-sectional (en face) image is detected using a charge coupled device (CCD) camera. A conventional four-frame phase-shift detection technique is employed to extract the interferometric image from the CCD output. A 95-nm-broadband full-field illumination yields an axial resolution of 2.0 µm, and the system covers an area of 850 µm×850 µm with a transverse resolution of 2.4 µm using a 0.3-NA microscope objective and a CCD camera with 512×512 pixels. Starting a measurement from the epithelial to the endothelial side, a series of en face images was obtained. From detected en face images, the epithelial cells, Bowman's layer, stromal keratocyte, nerve fiber, Descemet's membrane, and endothelial cell were clearly observed. Keratocyte cytoplasm, its nuclei, and its processes were also separately detected. Two-dimensional interconnectivity of the keratocytes is visualized, and the keratocytes existing between collagen lamellaes are separately extracted by exploiting a high axial resolution ability of FF-OCT.
A real-time, ultrahigh resolution full-field (FF) optical coherence tomography (OCT) system has been developed using a
dual-channel detection technique. Our FF-OCT system is based on a white-light interference microscope combined with
a polarization sensitive dual-channel detection technique using a pair of CCD cameras, where a pair of images with 90-
degree phase difference are simultaneously captured with an achromatic phase shifter. By acquiring an additional pair of
images using a conventional phase shift method, an inphase and a quadrature component of FF-OCT image are acquired
by calculating the differences every two consecutive CCD frames. Sum of their squares then yields FF-OCT image. Using
the ultrabroad bandwidth of halogen lamp and relatively high-NA objectives, an axial resolution of 1.2 &mgr;m and a transverse resolution of 1.7 &mgr;m have been achieved. Sub-cellular imaging results of porcine conjunctiva and esophagus recorded as fast as 40 ms are presented.
A two- and three- dimensional swept source optical coherence tomography (SS-OCT) system which uses a ready-to-ship scanning light source is demonstrated. The light source has the center wavelength of 1.31 μm, the -3 dB wavelength range of 110 nm, the scanning rate of 20 KHz and high linearity of frequency scanning. A simple calibration method using a fringe analysis technique for spectral rescaling is presented. This SS-OCT is capable of realtime display of two-dimensional OCT, and can take three-dimensional OCT with the measurement time of 2 s. In vivo human anterior eye segments are investigated both two- and three- dimensionally. The system sensitivity is experimentally determined as 113 dB.
We have demonstrated video-rate horizontal cross-sectional (en-face) OCT imaging using a parallel heterodyne detection technique. This technique is based on a dual-channel frequency synchronous detection technique that operates a pair of CCD cameras as two-dimensional heterodyne sensor arrays. Using this technique a series of full-field en-face OCT images are acquired at a rate of 100 frames/s during a single longitudinal scan. Results of en-face OCT imaging are reported.
En-face optical coherence tomography (OCT) employing parallel heterodyne detection technique is demonstrated for three-dimensional microscopy. To enable the use of commercially available CCD cameras as two-dimensional heterodyne detector arrays in OCT imaging, a frequency synchronous detection method is employed. Depth-resolved, full-field images are acquired at 30 Hz video-rate without lateral scanning.
Fluorescent x-ray computed tomography (FXCT) is being developed to detect non-radioactive contrast materials in living specimens. The FXCT systems consists of a silicon channel cut monochromator, an x-ray slit and a collimator for detection, a scanning table for the target organ and an x-ray detector for fluorescent x-ray and transmission x-ray. To reduce Compton scattering overlapped on the K(alpha) line, incident monochromatic x-ray was set at 37 keV. At 37 keV Monte Carlo simulation showed almost complete separation between Compton scattering and the K(alpha) line. Actual experiments revealed small contamination of Compton scattering on the K(alpha) line. A clear FXCT image of a phantom was obtained. Using this system the minimal detectable dose of iodine was 30 ng in a volume of 1 mm<SUP>3</SUP>, and a linear relationship was demonstrated between photon counts of fluorescent x-rays and the concentration of iodine contrast material. The use of high incident x-ray energy allows an increase in the signal to noise ratio by reducing the Compton scattering on the K(alpha) line.
We describe a new system of fluorescent x-ray computed tomography applied to image nonradioactive contrast materials in vivo. The system operates on the basis of computed tomography (CT) of the first generation. The experiment was also simulated using the Monte Carlo method. The research was carried out at the BLNE-5A bending-magnet beam line of the Tristan Accumulation Ring in Kek, Japan. An acrylic cylindrical phantom containing five paraxial channels of 5 and 4 mm diameters was imaged. The channels were filled with a diluted iodine-based contrast material, with iodine concentrations of 2 mg/ml and 500 (mu) g/ml. Spectra obtained with the system's high purity germanium (HPGe) detector separated clearly the K<SUB>(alpha</SUB> ) and K<SUB>(beta</SUB> 1) x-ray fluorescent lines, and the Compton scattering. CT images were reconstructed from projections generated by integrating the counts in these spectral lines. The method had adequate sensitivity and detection power, as shown by the experiment and predicted by the simulations, to show the iodine content of the phantom channels, which corresponded to 1 and 4 (mu) g iodine content per pixel in the reconstructed images.