• Journal of Periodontal and Implant Science
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• v.48 no.4
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• pp.202-212
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• 2018

Purpose: Bone-to-implant contact (BIC) is difficult to measure on micro-computed tomography (CT) because of artifacts that hinder accurate differentiation of the bone and implant. This study presents an advanced algorithm for measuring BIC in micro-CT acquisitions using a spiral scanning technique, with improved differentiation of bone and implant materials. Methods: Five sandblasted, large-grit, acid-etched implants were used. Three implants were subjected to surface analysis, and 2 were inserted into a New Zealand white rabbit, with each tibia receiving 1 implant. The rabbit was sacrificed after 28 days. The en bloc specimens were subjected to spiral (SkyScan 1275, Bruker) and round (SkyScan 1172, SkyScan 1275) micro-CT scanning to evaluate differences in the images resulting from the different scanning techniques. The partial volume effect (PVE) was optimized as much as possible. BIC was measured with both round and spiral scanning on the SkyScan 1275, and the results were compared. Results: Compared with the round micro-CT scanning, the spiral scanning showed much clearer images. In addition, the PVE was optimized, which allowed accurate BIC measurements to be made. Round scanning on the SkyScan 1275 resulted in higher BIC measurements than spiral scanning on the same machine; however, the higher measurements on round scanning were confirmed to be false, and were found to be the result of artifacts in the void, rather than bone. Conclusions: The results of this study indicate that spiral scanning can reduce metal artifacts, thereby allowing clear differentiation of bone and implant. Moreover, the PVE, which is a factor that inevitably hinders accurate BIC measurements, was optimized through an advanced algorithm.

• Investigative Magnetic Resonance Imaging
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• v.12 no.1
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• pp.27-32
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• 2008

Purpose : We developed a 3D CSI (chemical shift imaging) sequence that uses the PRESS (point resolved spectroscopy) excitation scheme and spiral-based readout gradients. Materials and Methods : We implemented constant-density spirals ($32{\times}32$ matrix, $24{\times}24\;cm$ FOV) which use analytic equations to enable real-time prescription on the scanner. In-vivo data from the brain were collected and reconstructed using the gridding algorithm. Results : Data illustrate that with our imaging sequence, the benefits of the PRESS technique, which include elimination of lipid artifacts, remain intact while flexible scan time versus resolution tradeoffs can be achieved using the constant-density spirals. Volumetric high resolution 3D CSI covering 5760 cm3 could be obtained in 12.5 minutes. Conclusion : Spiral-based readout gradients offer a flexible tradeoff between scan time versus resolution. By combining this feature with PRESS based excitation, efficient methods of volumetric spectroscopic imaging can be accomplished by obtaining whole brain coverage while eliminating lipid contamination.

• Proceedings of the KSMRM Conference
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• 2006.11a
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• pp.70-70
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• 2006

• Proceedings of the KSMRM Conference
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• 1996.10a
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• pp.14-14
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• 1996

• Proceedings of the KSMRM Conference
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• 2006.11a
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• pp.68-68
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• 2006

• Proceedings of the KSMRM Conference
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• 1999.11a
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• pp.89-89
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• 1999

• Proceedings of the KSMRM Conference
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• 2006.11a
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• pp.69-69
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• 2006

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1920-1921
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• 2007

본 논문에서는 나선주사 영상에서 발생하는 off-resonance 현상에 의한 영상의 번짐을 보정하는 새로운 알고리즘을 제안하였다. 공간상에서의 inhomogeneity와 chemical-shift 현상으로 생기는 off-resonance 효과는 공간의 자장의 세기에 비례한다. 현재 사용되고 있는 보정 방법에서의 절차를 간소화 하고 보다 효과적인 보정 알고리즘을 적용함으로써 보다 나은 Spiral scan 영상을 얻고자 하였다.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.2885-2887
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• 1999

초고속 영상 기법의 Echo Planar Imaging과 Spiral Scan Imaging 기법은 자기장의 inhomogeneity에 영향을 많이 받게 된다. 본 논문에서는 자기장의 inhomogeneity를 보정하는 기능인 shimming 기능을 자동으로 실행할 수 있는 알고리즘을 구현하였다. 자기장의 inhomogeneity를 보정하기 위해서 자기장에 생성될 수 있는 spherical harmonic function중 1차에 대해 보정을 시도하였고, 기존의 알고리즘보다 뛰어난 결과를 얻을 수 있었다.

• 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.