KEYWORDS: 3D scanning, Laser scanners, 3D image processing, Optical coherence tomography, Teeth, 3D modeling, Scanners, Clouds, Microelectromechanical systems, 3D acquisition
We report fabrication and performance of the three-dimensional intraoral scanner based on optical coherence tomography (OCT) that enables three-dimensional structure images of tooth and diagnosis of the tooth through OCT images. The OCT system was configured the swept source OCT (SS-OCT), that is based on the swept source with center wavelength of 1310 nm, the scanner was built using MEMs mirror and optical collimator. The implemented SS-OCT based on MEMs scanner show axial resolution of 10 μm, scan length of 10 mm. With OCT system, OCT 2D images of the human tooth obtained by intraoral scanner based on OCT system. 3D OCT image of the human tooth was obtained by combining the 500 2D OCT images and also included internal information and structure of the human tooth. 3D images of a human tooth obtained were sequentially stitching using the iterative closet point (ICP). By equipping the implemented SS-OCT system with MEMs probe and using ICP algorithm, the intraoral scanner based on OCT system was constructed and used to demonstrate the feasibility of intraoral scanner, that is able to acquire the structure and function images of the human tooth, for intraoral scanner 3D image in dentistry.
We describe a non-invasive and non-contact viscosity measurement system using a compact optical fiber heterodyne interferometry. The proposed system consists of a fiber based pulse laser for surface acoustic wave (SAW) excitation and a lensed fiber for probing laser. When the pulsed laser illuminates onto the oil surface, the SAW is generated by photoacoustic effect and it propagates along the surface. The interference of probing laser reflected on the sample surface has the information of the surface movement. We can calculate the propagation velocity of SAW from the detected interference signal. The propagated SAW contains the information of liquid properties (viscosity and elasticity). For the preliminary measurements, an industrial engine oil and a polydimethylsiloxane (PDMS) are used. We can measure the viscosity of them without noncontact, successfully.
We report herein the fabrication and performance response of a three-dimensional (3-D) intraoral scan probe based on optical coherence tomography (OCT) that enables 3-D structural and functional diagnoses of the human teeth. The OCT system was configured using a swept-source OCT (SS-OCT) with a center wavelength of 1310 nm. The scan probe was built using an MEMS mirror and an optical collimator. The implemented SS-OCT equipped with the MEMS-based scan probe yielded an axial resolution of 10 μm and a scan range of 8 × 8 mm2. Two-dimensional (2-D) cross-sectional images of the teeth were acquired by the scan probe based on the OCT. The 3-D volume image was acquired by combining a series of 2-D images, which includes internal and structural information of the human teeth. To utilize the OCT system as an intraoral scanner, partially overlapped 3-D volume images were sequentially acquired and stitched. The 3-D stitching was implemented based on an iterative closest point algorithm. The feasibility of the intraoral scan probe is demonstrated based on its ability to image and characterize the structure and function of the human teeth.
We propose the noncontact measurement of elasticity by using an optical fiber heterodyne interferometer and laser ultrasonics. The surface acoustic wave (SAW), that is generated by the laser pulse irradiation on the sample surface and propagating along the surface, is optically monitored by the heterodyne interferometer without taking any contact with the sample. By taking several measurements with changing the relative distance between the excitation and the measurement points, the phase velocity of SAW was calculated and from which the elasticity of the sample could be obtained. This proposed method was experimentally evaluated by using PDMS samples having various mixing ratio of curing agent and PDMS. For the sample of a 12:1 mixing ratio, the phase velocity was measured as about 39.46 m/s and the Young’s modulus as about 1987 kPa. This technique is expected to detect the mechanical properties of biological tissues also.
We present an all optical fiber combined-imaging system that integrates non-contact photoacoustic tomography (NPAT) and optical coherence tomography (OCT) to simultaneously provide PA and OCT images. The fiber-based PAT system utilizing a Mach-Zehnder interferometer with a fiber laser of 1550 nm measures the photoacoustic signal at the sample surface. For the generation of a PA signal, a pulse train from a bulk type Nd:YAG laser illuminates the sample via a large core multimode optical fiber. The fiber-based OCT operating at a center wavelength of 1310 nm allowed is combined with the fiber-based PAT system by sharing the same optical fiber probe. The two lights from the fiber laser and the OCT source are guided into the probe through each port of a 2 by 2 optical fiber coupler. The back-reflected lights from the sample are guided to respective imaging systems by the same coupler. With these both NPAT and OCT images could be co-registered without physical contact with the sample. To demonstrate the feasibility of the proposed system, a phantom experiment has been carried out with a phantom composed of a black PET fiber and a fishing wire. The proposed all fiber-optic combined-imaging system has the potential for minimally invasive and improved diagnosis.
We present a photoacoustic microscopy (PAM) system based on a Fabry-Perot Interferometer (FPI) consisting of a transparent Polydimethylsiloxane (PDMS) thin film. Most of the PAM systems have limitations with the system alignment because the ultrasound transducers for detection are not transparent. Therefore, the excitation laser source should avoid the opaque transducer to illuminate the sample, which makes the system difficult to build-up. Especially, the system volume is highly limited to be compact. In our experiment, to solve these difficulties, a FPI based on the PDMS film has been implemented and applied to measure the acoustic wave signal. The system uses a FPI as an acoustic wave detector instead of a conventional ultrasound transducer. A tunable laser was used to choose the quadrature-point at which the signal has the highly sensitve and linear response to the acoustic wave. Also a 20Hz pulsed Nd:YAG laser was used to generate acoustic waves from a sample. When the acoustic waves arrive at the PDMS film, one of the surfaces of the film is modulated at the detecting point, which gives the tuned FPI interference signal. From the signal arriving time, the depth location of the sample is calculated. As a primary experiment using the PDMS thin film as an ultrasound transducer, a couple of narrow black friction tapes located in a water container were used as the samples. This proposed imaging method can be used in various applications for the detection and measurement of acoustic waves.
We present three-dimensional (3-D) in vivo photoacoustic (PA) images of the blood vasculature of a chicken chorioallantoic membrane (CAM) obtained by using a fiber-based noncontact PA tomography system. With a fiber-optic heterodyne interferometer, the system measures the surface displacement of a sample, induced by the PA wave, which overcomes the disadvantage of physical-contact of ultrasonic transducer in a conventional system. The performance of an implemented system is analyzed and its capability of in vivo 3-D bioimaging is presented. At a depth of 2.5 mm in a phantom experiment, the lateral and axial resolutions were measured as 100 and 30 μm, respectively. The lateral resolution became doubled at a depth of 7.0 mm; however, interestingly, the axial resolution was not noticeably deteriorated with the depth. With the CAM experiment, performed under the American National Standards Institute laser safety standard condition, blood vessel structures placed as deep as 3.5 mm were clearly recognized.
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 report an all-fiber heterodyne interferometer for the measurements of laser-induced thermoelastic deformation to estimate the Gruneisen coefficient and the optical attenuation depth of a sample. The system comprises a Q-switched Nd-YAG laser providing a nanosecond excitation pulse and an all-fiber heterodyne interferometer that measures the induced displacement of the sample surface. To evaluate the system, phantom experiments were carried out with various gelatin-based models. The results show that the attenuation depth and Gruneisen coefficient of the phantoms were about 4.256 mm and 0.568, respectively. In addition, increase of the weight fraction of gelatin led increase in the Gruneisen coefficient.
We propose the noncontact photoacoustic tomography system that reads the acoustic signal by using an optical fiberbased heterodyne interferometer. The surface displacement of a specimen, resulting from the acoustic wave generated by irradiation of a laser pulse and its absorption inside the specimen, is optically measured by the heterodyne interferometer. With the data set of the surface displacement, the photoacoustic image of the specimen is reconstructed by a Fourier transform based reconstruction algorithm. This proposed method is experimentally evaluated by using a phantom sample that contains PET fibers.
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