• Investigative Magnetic Resonance Imaging
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• v.13 no.1
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• pp.15-21
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• 2009

Purpose : A method to estimate a real k-space trajectory based on a circuit model of the gradient system is proposed for spiral imaging. The estimated k-space trajectory instead of the ideal trajectory is used in the reconstruction to improve the image quality in the spiral imaging. Materials and Methods : Since the gradient system has self resistance, capacitance, and inductance, as well as the mutual inductance between the magnet and the gradient coils, the generated gradient fields have delays and transient responses compared to the input waveform to the gradient system. The real gradient fields and their trajectory in k-space play an important role in the reconstruction. In this paper, the gradient system is modeled with R-L-C circuits, and real gradient fields are estimated from the input to the model. An experimental method to determine the model parameters (R, L, C values) is also suggested from the quality of the reconstructed image. Results : The gradient fields are estimated from the circuit model of the gradient system at 1.5 Tesla MRI system. The spiral trajectory obtained by the integration of the estimated gradient fields is used for the reconstruction. From experiments, the reconstructed images using the estimated trajectory show improved uniformity, reduced overshoots near the edges, and enhanced resolutions compared to those using the ideal trajectory without model. Conclusion : The gradient system was successfully modeled by the R-L-C circuits. Much improved reconstruction was achieved in the spiral imaging using the trajectory estimated by the proposed model.

• Proceedings of the KOSOMBE Conference
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• v.1985 no.06
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• pp.22-25
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• 1985

본고에서, "나선형 주사 방법에 의한 고속 NMR 영상화" 방법을 제안하고 그에 따른 실험 결과를 보였다. 이것은 2차원 FID 영역을 나선형 궤적으로 스캐닝하며 데이타를 받을 수 있도록 경사 자계 파형 (gradient pulse)을 가하여 빠른 시간에 (수십 msec - 수초)내에 영상 정보를 얻어낸 후, 재구성 알고리즘을 씀으로써 영상을 얻어내는 방법이다. 이 방법의 장점은 첫째로 $T_2$ 감쇄에 의한 PSF (Point Spread Function)가 윈형 대칭으로 주어지므로 영상화 했을때 물체의 구조 식별이 기존의 EPI (Echo Planar Imaging) 방법에 비해서 선명하며, 둘째로 나선형 궤적을 구현하기 의한 경사 자계 파형에서 불연속 점을 없앰과 동시에 파형의 세기가 점차로 증가하는 형태이므로, 기존의, 파형 왜곡에 의해 영상에 미치는 영향을 최소화 할 수가 있으며, 세째로 나선형 스캔을 사이 사이에 끼워 넣는 방법을 씀으로써 해상도를 향상시킬 수가 있다.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.2
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• pp.110-119
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• 1994

The Robust Controller for scan-loop is designed using LQG/LTR Methodology. The design and analysis of spiral, rosette and conical scan patterns are discussed. The perfermance and robustness of the LQG/LTR controller are analyzed through experiments and cpmpared with those of the P-controller. Especially to improve the scan performance at large look angle, the cage coil output is linearized using a binomial equation. It is demonstrated that the scan-loop system by the LQG/LTR control is very robust to phase uncertainties.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.3
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• pp.174-178
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• 2013

A modified driving waveform is proposed to improve the address discharge characteristics using wall charge on the common electrodes in plasma display panel. In the driving scheme of plasma display, after a reset period, the negative charge are accumulated on two front electrodes and positive wall charge are accumulated on the address electrode. As the address discharge during an address period is produced when the scan and address pulses are applied at the same time, negative charge on the scan electrodes and positive charge on the address electrodes are mainly used. On the other hand, as the voltage are only maintained without applying the waveform during an address period on the common electrodes, the wall charge is not used on the common electrodes. In this paper, the address discharge characteristics are investigated with changing pulse applying time and applied voltage amplitude on the common electrodes and consequently the producing time of an address discharge are shortened about 200 ns compared with the conventional driving waveform.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.1
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• pp.179-184
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• 2014

The discharge characteristics of an open dielectric structure were investigated, especially such as a firing voltage and related wall voltage, compared with conventional panel structure based on the Vt close curve measurement in AC plasma display panel. While the front panel of the conventional structure in AC plasma display panel was composed of the glass, electrodes, and dielectric, the open dielectric structure could easily produce the discharge between the scan and the sustain electrodes by erasing the dielectric layer between two electrodes. As the open dielectric structure differ from the conventional structure, various problems were produced when driving with the conventional driving waveform. Especially, due to the changes in the discharge firing characteristics of the open dielectric structure between the scan and the sustain electrodes on the front panel, the conventional reset waveform including the address waveform needed to be modified. In this study, the Vt close curves were measured to compare the discharge firing voltages on three electrodes in the conventional and open dielectric structure and based on the Vt close curve analysis, the modified driving waveform suitable for the open dielectric structure was proposed.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.229-232
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• 2003

AC PDP의 ADS 추동 방식은 구동 방법이 간단하여 구현하기가 용이할 뿐만 아니라 가장 안정적인 구동 방식으로 널리 사용되고 있다 [1]. 그러나 ADS 구동 방식은 주사선의 수가 늘어남에 따라 어드레싱에 필요한 시간이 증가하게 되고 유지방전 구간에 할애할 시간이 상대적으로 감소하게 되어 휘도가 저하되게 되는 문제점을 갖고 있다. 이러한 문제를 해결하기 위하여 어드레싱 시간을 최소화하기 위한 고속 어드레싱 기술에 대한 연구가 계속하여 진행되고 있다 [2-10]. 본 논문에서는 고속 구동 시에 나타나는 불안정한 어드레싱으로 인한 화질의 저하문제를 해결하기 위한 개선된 ADS 구동파형을 제시한다. 초기화 구간의 Reset 파형은 어드레싱 추간의 특성에 중요한 영향을 미치게 되는데, Reset 구간에서 생성된 벽전하를 어드레싱 방전구간 동안 지속적으로 유지되게 함으로서 어드레싱 방전전압을 줄이고 안정적인 어드레싱이 유지될 수 있도록 하였다. 본 논문에서는 Priming Effect의 영향이 급격히 감소하는 80us 이후, 벽전하의 생성을 돕는 Wall Charge Acceleration Pulse를 적용함으로서 불안정한 어드레싱 문제를 해결할 수 있는 방법을 제시하였고 휘도의 불균등화로 인한 화질 저하의 문제를 해결하였다.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.05a
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• pp.130-134
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• 2007

단일 구동회로를 사용하여 패널전체를 동시에 방전시킬 수 있는 새로운 priming 방전기술을 고안하였다. 그리고 이 기술을 사용하여 1080개의 수평주사선수를 가지는 full-HDTV PDP를 고휘도로 구동할 수 있는 새로운 고속 구동방식을 제안하였다. 이 priming 방전기술을 사용하면 구동방식에 상관없이 priming 기간을 sustain 기간에 중첩시키고 ramp 파형을 가지는 priming pulse를 인가하는 것이 가능하다. 실험결과로부터 sustain 방전이 없는 경우에만 priming 방전이 일어났다. 그리고 sustain 방전은 priming 펄스의 영향을 거의 받지 않는다는 것이 확인되었다. 새로운 PDP 구동기술로 $0.7{\mu}s$의 address 펄스폭을 가지는 고속 address를 실현하였다. 그리고 40V의 넓은 address 동작마진을 얻었다. 이 기술들은 상용의 driver IC를 사용할 수 있도록 설계되어있으므로 상용화 가능성도 높다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.5
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• pp.455-461
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• 2009

In a scanning electron microscopy, image distortion is a critical issue and it is needed to be eliminated by some kinds of schemes. In this work, scanning frequency and scanning wave form are adjusted to have an improved image. The relationship between scan coil and its driver is investigated and appropriate frequency and wave form are suggested. It is proved that the selected frequency and wave form showed an enhanced image with less distortion, which were done by experiments. In addition, a noise elimination is addressed, providing improved image with a GROUND signal integration with the amplifier and the scan driver.

• Investigative Magnetic Resonance Imaging
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• v.10 no.2
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• pp.108-116
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• 2006

Purpose : High-resolution spiral-scan imaging is performed at 3 Tesla MRI system. Since the gradient waveforms for the spiral-scan imaging have lower slopes than those for the Echo Planar Imaging (EPI), they can be implemented with the gradient systems having lower slew rates. The spiral-scan imaging also involves less eddy currents due to the smooth gradient waveforms. The spiral-scan imaging method does not suffer from high specific absorption rate (SAR), which is one of the main obstacles in high field imaging for rf echo-based fast imaging methods such as fast spin echo techniques. Thus, the spiral-scan imaging has a great potential for the high-speed imaging in high magnetic fields. In this paper, we presented various high-resolution images obtained by the spiral-scan methods at 3T MRI system for various applications. Materials and Methods : High-resolution spiral-scan imaging technique is implemented at 3T whole body MRI system. An efficient and fast higher-order shimming technique is developed to reduce the inhomogeneity, and the single-shot and interleaved spiral-scan imaging methods are developed. Spin-echo and gradient-echo based spiral-scan imaging methods are implemented, and image contrast and signal-tonoise ratio are controlled by the echo time, repetition time, and the rf flip angles. Results : Spiral-scan images having various resolutions are obtained at 3T MRI system. Since the absolute magnitude of the inhomogeneity is increasing in higher magnetic fields, higher order shimming to reduce the inhomogeneity becomes more important. A fast shimming technique in which axial, sagittal, and coronal sectional inhomogeneity maps are obtained in one scan is developed, and the shimming method based on the analysis of spherical harmonics of the inhomogeneity map is applied. For phantom and invivo head imaging, image matrix size of about $100{\times}100$ is obtained by a single-shot spiral-scan imaging, and a matrix size of $256{\times}256$ is obtained by the interleaved spiral-scan imaging with the number of interleaves of from 6 to 12. Conclusion : High field imaging becomes increasingly important due to the improved signal-to-noise ratio, larger spectral separation, and the higher BOLD-based contrast. The increasing SAR is, however, a limiting factor in high field imaging. Since the spiral-scan imaging has a very low SAR, and lower hardware requirements for the implementation of the technique compared to EPI, it is suitable for a rapid imaging in high fields. In this paper, the spiral-scan imaging with various resolutions from $100{\times}100$ to $256{\times}256$ by controlling the number of interleaves are developed for the high-speed imaging in high magnetic fields.

• Journal of Veterinary Clinics
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• v.19 no.3
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• pp.277-282
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• 2002

This study was designed to evaluate the effects of anesthetics on waveform of SEPs and to authorize possible anesthetic protocol for measurement of the somatosensory evoked potentials (SEPs). Thirteen anesthetic methods were used. The SEPs were recorded on two channels (between the 5th and 6th lumbar vertebra as the channel 1 and between the 11th and 12th thoracic vertebra as the channel 2) following stimulation of posterior tibial nerve. ID analyze SEPs wave, latency and conduction velocity were measured. Among thirteen anesthetic methods, standard SEPs waveforms were observed in dogs anesthetized with following six methods: Acepromazine + Thiepfntal Na + Isoflurane, Acepronazine + Propofol + Isoflurane, Diazepam + Xylazine, Xylazine + Ketamine, Acepromazine + Propofol infusion and Propofol infusion. Above six methods could be used with sufficient anesthetic depth. The differences of latency and conduction velocity among six groups were minimal compared to general waveform of SEPs. These results indicate that the six anesthetic methods can be used for recording SEPs in the dog. In particular, Diazepam + Xylazine and XylaBine + Ketamine as injectable anesthesia are considered more convenient than other four methods in veterinary medicine.