KEYWORDS: 3D scanning, 3D modeling, Liquid lenses, Liquids, Confocal microscopy, Clouds, Modulation, 3D image reconstruction, 3D image processing, Instrument modeling
We demonstrated a three-dimensional (3D) dental scanning apparatus based on structured illumination. A liquid lens was used for tuning focus and a piezomotor stage was used for shift of structured light. A simple algorithm, which detects intensity modulation, was used to perform optical sectioning with structured illumination. We reconstructed 3D point cloud, which represents the 3D coordinates of the digitized surface, of a dental gypsum cast by piling up sectioned images. We performed 3D registration of individual 3D point cloud, which includes alignment and merging the 3D point clouds, to exhibit a 3D model of the dental cast.
We propose an image reconstruction method of digital holography for getting more accurate reconstruction. Digital holography provides both the light amplitude and the phase of a specimen through recording the interferogram. Since the Fresenl diffraction can be efficiently implemented by the Fourier transform, zero padding technique can be applied to obtain more accurate information. In this work, we report the method of frequency domain zero padding (FDZP). Both in computer-simulation and in experiment made with a USAF 1951 resolution chart and target, the FDZD gave the more accurate rconstruction images. Even though, the FDZD asks more processing time, with the help of graphics processing unit (GPU), it can find good applications in digital holography for 3-D profile imaging.
We present a fiber-based dual-modal imaging system that combines non-contact photoacoustic tomography (NCPAT) and fluorescence imaging by using double cladding fiber (DCF). The NCPAT system utilizing an all-fiber heterodyne interferometer as an ultrasound detector measures the photoacoustic signal at the sample surface without physical contact. Fluorescence imaging system is composed of fiber-optics to deliver the excitation light and the emission light. For combined system the probe consists of a specially fabricated DCF coupler and a lensed fiber so that we can simultaneously acquire the signals of two systems with the same probe. The DCF has a core and two claddings, inner and outer, which allows two concentric light-guiding channels via the core and the inner cladding. The lensed fiber of the DCF probe is compactly fabricated to focus the interferometer light and the excitation light, and to efficiently collect the fluorescence signal. To demonstrate the feasibility of the proposed dual-modal system, we have conducted phantom experiments using tissue mimicking phantoms which contained a couple of tubes filled with fluorescein solution and black ink, respectively. The proposed imaging system is implanted with fiber-optic configurations so that it has the potential for minimally invasive and improved diagnosis and guided treatment of diseases.
We present the real-time stroboscopic full-field optical coherence tomography (FF-OCT) system that is based on graphics processing unit (GPU). The basic configuration of the proposed FF-OCT system was the Linnik interferometer. While scanning of a reference mirror in the axial direction, a series of the transverse sectional image was captured with a 2-dimensional CCD camera. To get a depth-resolved 3-D image, the light source of OCT was turned on and off like a stroboscope at the Doppler frequency of the OCT system. The CCD camera used in experiment operated at a rate of 200 frames per second, but the Doppler frequency was ~kHz. To overcome the slow operation of the CCD camera below the Doppler frequency, the light source was operated in the stroboscopic mode. In addition, lock-in detection technique was utilized in order to avoid the dissolution of the coherent signals during the integration time of the CCD camera. Furthermore, the Doppler frequency shift due to nonlinear scanning motion of the reference mirror was monitored by using an auxiliary interferometer and then fed back to the light source driver so that the strobe frequency was always matched with the Doppler frequency of the OCT system. For the real-time 3-D rendering, we used a graphics processing unit.
We propose and demonstrate a novel refractive index (RI) measurement by using the numerical-sample-motion based the
defocus correction method in full field optical coherence tomography (FF-OCT). Overcoming the general problem in FFOCT
that is the position of the focal plane is separated from the position of the image plane when imaging a deep region
inside a sample, we measure the separation distance from the position of the focal plane to the position of the image
plane. The RI is determined from the separation distance that is obtained by the numerically adjusted distance of a
sample position. With the proposed method, the depth resolved RIs of double layer materials are determined.
We propose the digital holographic technique that can mathematically reconstruct the distorted two dimensional en-face images obtained with full-field optical coherence tomography (FF-OCT). As a powerful biomedical imaging modality,
FF-OCT provides inner microstructure images of a biological sample noninvasively but with a submicron depth
resolution. The main advantage of the FF-OCT over other OCT techniques is that, it requires only depth scanning (C-scan)
without any transverse mechanical scanning (B-scan). In a FF-OCT system based on a Michelson interferometer,
not only the length of the reference arm should be matched with the length to the imaging plane in the sample arms, but
also the focal plane of the system should be matched with the imaging plane. When the sample has a very high refractive
index than the surrounding medium, in which the reference mirror is immersed, the mismatch between the imaging plane
and the focusing plane becomes a severe problem and results in degradation of OCT image. In this study, we confirm the
existence of the imaging and focusing plane mismatch problem in the FF-OCT system, and propose the method that can
retrieve the focused image from a defocused image with the help of digital holography. One of the major advantages of
the proposed technique is that it does not require any mechanical movement for refocusing. Only numerical calculation
based on the Fresnel diffraction theory is enough. The performance is demonstrated with the image of the USAF
resolution target. The image of the chromium coated pattern on the target was blurred with the existence of the glass
substrate, when the OCT image was taken through the substrate. The blurred image was digitally corrected to get on the
focused clear image of the pattern.
We present a tomographic imaging system that is applied a continuous phase shifting interferometry scheme to digital
holographic microscopy (DHM). The proposed scheme achieves en-face tomographic image from digitally recorded
original hologram by 2-D sensor array. Although images obtained at out-of-focus position, the application of integrating
four bucket technique to digital hologram produces refocused en-face image with showing clear field of view. The
proposed technique has advantages such as reduced phase errors and faster acquisition speed when it compared with
conventional discrete phase stepping method. The performance of the system is demonstrated with presenting of the
images on a scratched mirror surface and of an USAF resolution target. The reconstructed images are compared with
conventional microscopic images, which reveal good aggrements. We believe that the proposed method enables
tomographic imaging of biological samples with providing reduced noise level and improved imaging speed.
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