• Journal of Biomedical Engineering Research
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• v.30 no.3
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• pp.233-240
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• 2009

Using a spatial compound imaging technique in a medical ultrasound imaging system, the average speed of sound in a medium of interest is measured, and imaging of its distribution is implemented. When the brightness reaches the highest level in an ultrasonic image obtained as the speed of sound used in focusing is varied, it turns out that the focusing has been accomplished satisfactorily and that the speed of sound which has been adopted becomes the sought-after average speed of sound. Because spatial compound imaging provides many different views of the same object, the adverse effect of erroneous speed-of-sound estimation tends to be more severe in compound imaging than in plain B-mode imaging. Thus, in compound imaging, the average speed of sound even in the case of speckled images can be accurately estimated by observing the brightness change due to different speeds of sound employed. Using this new method that offers spatial diversity, we can construct an image of the speed of sound distribution in a phantom embedded with a 10-mm diameter plastic cylinder whose speed of sound is different from that of the background. The speed of sound in the cylinder is found to be different from that of the surrounding medium.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.18-19
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• 2001

일반적으로 weakly guiding되는 waveguide의 mode field profile을 측정하기 위해서는 CCD 카메라와 imaging lens를 사용하여 field distribution을 측정한다. 하지만, 이러한 방법은 빛의 회절한계 현상 때문에 특수 광섬유에서 guiding되는 빛을 높은 분해능으로 측정 할 수 없다는 단점이 있다. 따라서 빛의 회절현상을 극복하기 위해서는 빛이 회절 되기 전의 근접장 영역에서 mode field profile을 측정하는 방법이 필요하다. (중략)

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.6
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• pp.54-62
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• 2007

In this paper, we significantly reduces the amount of computation for intra 16$\times$16 mode decision in H.264 by applying the fast algorithm, which obtains the transformed prediction residual with fewer computations. By extending the existing intra 4$\times$4 mode decision, we propose the new algorithm for fast intra 16$\times$16 mode decision. The proposed algorithm uses partial transform coefficients which consist of one DC and three adjacent AC coefficients after 4$\times$4 transform in the intra 16$\times$16 mode decision. Theoretical analysis and experimental results show that the proposed algorithm can reduce computations up to 50% in the intra 16$\times$16 mode decision process with unnoticeable degradation.

• Journal of the Optical Society of Korea
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• v.10 no.1
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• pp.42-47
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• 2006

M-mode imaging of the in vivo murine myocardium using optical coherence tomography (OCT) is described. Application of conventional techniques (e.g. MRI, Ultrasound imaging) for imaging the murine myocardium is problematic because the wall thickness is less than 1.5 mm (20 g mouse), and the heart rate can be as high as six hundred beats per minute. To acquire a real-time image of the murine myocardium, OCT can provide sufficient spatial resolution ($10{\mu}m$) and imaging speed (1000 A-scans/s). Strong light scattering by blood in the heart causes significant light attenuation, which makes delineation of the endocardium-chamber boundary problematic. To measure the thickness change of the myocardium during one heart beat cycle, a myocardium edge detection algorithm is developed and demonstrated.

• Imaging Science in Dentistry
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• v.43 no.3
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• pp.145-151
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• 2013

Purpose: This study was performed to evaluate and compare the radiopacity of dentin, enamel, and 8 restorative composites on conventional radiograph and digital images with different resolutions. Materials and Methods: Specimens were fabricated from 8 materials and human molars were longitudinally sectioned 1.0 mm thick to include both enamel and dentin. The specimens and tooth sections were imaged by conventional radiograph using #4 sized intraoral film and digital images were taken in high speed and high resolution modes using a phosphor storage plate. Densitometric evaluation of the enamel, dentin, restorative materials, a lead sheet, and an aluminum step wedge was performed on the radiographic images. For the evaluation, the Al equivalent (mm) for each material was calculated. The data were analyzed using one-way ANOVA and Tukey's test (p<0.05), considering the material factor and then the radiographic method factor, individually. Results: The high speed mode allowed the highest radiopacity, while the high resolution mode generated the lowest values. Furthermore, the high resolution mode was the most efficient method for radiographic differentiation between restorative composites and dentin. The conventional radiograph was the most effective in enabling differentiation between enamel and composites. The high speed mode was the least effective in enabling radiographic differentiation between the dental tissues and restorative composites. Conclusion: The high speed mode of digital imaging was not effective for differentiation between enamel and composites. This made it less effective than the high resolution mode and conventional radiographs. All of the composites evaluated showed radiopacity values that fit the ISO 4049 recommendations.

• Journal of Welding and Joining
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• v.34 no.5
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• pp.26-32
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• 2016

In this study, Hot-wire laser welding (HWLW) without keyhole which deposits filler material by feeding hot wire into the process zone has been performed to increase process performance. From the analysis of High Speed Imaging (HSI), for higher voltage, the process is prone to arc formation and drop transfer, which is disagreeable transfer mode. It is necessary that arc formation and drop (globular) transfer should be avoided by lower voltage. Therefore, continuous wire melting and transfer mode is preferred when adopting this process. The HWLW technique has high potential in terms of performance, precision, robustness and controllability for thick section of narrow gap.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.796-804
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• 1994

This paper presents Inverse SAR imaging algorithm for a unknown velocity target and a real ISAR data is processed and applied to the algorithm. The real ISAR data is obtained by transmitting a number of pulse modulated by a stepped-frequency method and the received data are undersampled. We present a method applicable for the case of a undersampled data base. In this method, the original echoed signal is mixed with a reference signal to make it unaliased, followed by being interpolated. Target`s velocity required for the algorithm is estimated via subaperture processing and after the coordinate transformation into squint-mode SAR with the estimated velocity, a recently proposed SAR/ISAR imaging algorithm derived without any approximation is utilized to produce the output image. We also propose an ISAR image scheme that is usable when a target changes its velocity during ISAR data acquisition time.

• Journal of Satellite, Information and Communications
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• v.1 no.1
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• pp.26-39
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• 2006

A synthetic aperture radar (SAR) system can provide all-weather, day and night imaging capability, and thus, is very useful in surveillance for both civil and military applications. In this paper, the X-band spaceborne SAR system design procedure is introduced with the key design parameters for mission and system requirements characterized by the small satellite platform. The SAR imaging mode design technique is presented, and the design results are analyzed for standard mode performance evaluation. In line with the system requirements, the X-band SAR payload and ground reception/processing sub-systems are presented with the key design results and image applications examples. The designed small satellite SAR system shows the wide range of imaging capability, and proves to be an effective surveillance system in light-weight, high-performance and cost-effective points of view.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.3
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• pp.261-270
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• 2010

This paper presents an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves. We first consider the flexural wave (A0 mode) propagation in a plate containing a defect, and reception and time reversal process of the output signal at the receiver. The received output signal is then composed of two parts: a directly propagated wave and a scattered wave from the defect. The time reversal of these waves recovers the original input signal, and produces two additional side bands that contain the time-of-flight information on the defect location. One of the side band signals is then extracted as a pure defect signal. A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors. The simulation results show that the proposed scheme enables the accurate, baseline-free detection of a defect, so that experimental studies are needed to verify the proposed method and to be applied to real structure.

• Imaging Science in Dentistry
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• v.43 no.3
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• pp.171-177
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• 2013

Purpose: The purpose of this study was to compare the efficacy of two imaging modes in a cone beam computed tomography (CBCT) system in detecting root fracture in endodontically-treated teeth with fiber posts or screw posts by selecting two fields of view. Materials and Methods: In this study, 78 endodontically-treated single canal premolars were included. A post space was created in all of them. Then the teeth were randomly set in one of 6 artificial dental arches. In 39 of the 78 teeth set in the 6 dental arches, a root fracture was intentionally created. Next, a fiber post and a screw post were cemented into 26 teeth having equal the root fractures. High resolution (HiRes) and standard zoom images were provided by a CBCT device. Upon considering the reconstructed images, two observers in agreement with each other confirmed the presence or absence of root fracture. A McNemar test was used for comparing the results of the two modes. Results: The frequency of making a correct diagnosis using the HiRes zoom imaging mode was 71.8% and in standard zoom was 59%. The overall sensitivity and specificity in diagnosing root fracture in the HiRes mode were 71.79% and 46.15% and in the standard zoom modes were 58.97% and 33.33%, respectively. Conclusion: There were no significant differences between the diagnostic values of the two imaging modes used in the diagnosis of root fracture or in the presence of root canal restorations. In both modes, the most true-positive results were reported in the post space group.