• 대한의용생체공학회:의공학회지
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• 제20권2호
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• pp.165-172
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• 1999

본 연구에서는 MRI 영상에서 위상을 조절하여 영상 대조를 증가 시키는 방법을 제안 하였다 영상하고자 하는 물체 자체가 갖는 위상에 따라 영상의 대조가 변하기 때문에 본 방법은 자화율 영상이나 유속 영상에 유용하게 쓰일 수가 있다. 본 논문에서는 위상 분포에 따른 영상의 대조를 증가 시키기 위하여 RF 펄스를 복셀 내에서 위상을 갖도록 디자인 하였다. 따라서 복셀에서의 신호의 크기는 물체자체의 위상과 RF 펄스에의하여 가해준 위상이 결합에 의하여 결정된다. 외부위상 변화에 따른 신호의 변화를 분석하였고 그때 디자인된 RF 펄스를 이용하여 자화율만의 영상과 유속만의 영상을 얻었다. 컴퓨터 시뮬레이션의 결과는 제안된 알고리즘이 복셀내에 위상을 갖는 물체의 영상에 유용하고 그런 물체만을 영상하는데 유용함을 보였다.

• Current Optics and Photonics
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• 제7권5호
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• pp.537-544
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• 2023

Differential phase contrast (DPC) microscopy, a central quantitative phase imaging (QPI) technique in cell biology, facilitates label-free, real-time monitoring of intrinsic optical phase variations in biological samples. The existing DPC imaging theory, while important for QPI, is grounded in paraxial diffraction theory. However, this theory lacks accuracy when applied to high numerical aperture (NA) systems that are vital for high-resolution cellular studies. To tackle this limitation, we have, for the first time, formulated a nonparaxial DPC imaging equation with a transmission cross-coefficient (TCC) for high NA DPC microscopy. Our theoretical framework incorporates the apodization of the high NA objective lens, nonparaxial light propagation, and the angular distribution of source intensity or detector sensitivity. Thus, our TCC model deviates significantly from traditional paraxial TCCs, influenced by both NA and the angular variation of illumination or detection. Our nonparaxial imaging theory could enhance phase retrieval accuracy in QPI based on high NA DPC imaging.

• Investigative Magnetic Resonance Imaging
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• 제23권1호
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• pp.1-16
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• 2019

Dynamic contrast enhanced (DCE) magnetic resonance (MR) imaging plays an important role in non-invasive detection and characterization of primary and metastatic lesions in the liver. Recently, efforts have been made to improve spatial and temporal resolution of DCE liver MRI for arterial phase imaging. Review of recent publications related to arterial phase imaging of the liver indicates that there exist primarily two approaches: breath-hold and free-breathing. For breath-hold imaging, acquiring multiple arterial phase images in a breath-hold is the preferred approach over conventional single-phase imaging. For free-breathing imaging, a combination of three-dimensional (3D) stack-of-stars golden-angle sampling and compressed sensing parallel imaging reconstruction is one of emerging techniques. Self-gating can be used to decrease respiratory motion artifact. This article introduces recent MRI technologies relevant to hepatic arterial phase imaging, including differential subsampling with Cartesian ordering (DISCO), golden-angle radial sparse parallel (GRASP), and X-D GRASP. This article also describes techniques related to dynamic 3D image reconstruction of the liver from golden-angle stack-of-stars data.

• 한국공작기계학회논문집
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• 제16권5호
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• pp.115-121
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• 2007

Phase contrast imaging in atomic force microscopy showed a promise as an effective tool for better understanding of micromechanical properties of surfaces at nano scale. A qualitative estimation model for phase contrast images obtained with a tapping mode AFM was developed. This investigation demonstrated the high efficiency of combined analysis of topography and phase contrast images for characterizing nanosurfaces. Phase contrast images allowed estimation of relative stiffness(elastic modulus) of the sample surface. The phase contrast images revealed a significant inhomogeneity of the nano scale worn surfaces. Phase contrast images are also capable of revealing the formation of tribofilms.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 춘계학술대회
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• pp.127-130
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• 1997

Phase-contrast(PC) methods have been used for quantitative measurements of velocity and volume flow rate. In addition, phase contrast cine magnetic resonance imaging (MRI) combines the flow dependent contrast of PC MRI with the ability of cardiac cine imaging to produce images throughout the cardiac cycle. In this method, the through-plane velocity has been encoded generally. However, the accuracy of the flow data can be reduced by the effect of flow direction, finite slice thickness, resolution, pulsatile flow pattern, and so on. In this study we calculated the error caused by misalignment of tomographic plane and flow directon. To reduce this error and encode the velocity for more complex flow, we suggested 3 directional velocity encoding method.

• 한국의학물리학회지:의학물리
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• 제28권3호
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• pp.83-91
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• 2017

In this work, we investigated the recently proposed phase-contrast x-ray imaging (PCXI) technique, the so-called single grid-based PCXI, which has great simplicity and minimal requirements on the setup alignment. It allows for imaging of smaller features and variations in the examined sample than conventional attenuation-based x-ray imaging with lower x-ray dose. We performed a systematic simulation using a simulation platform developed by us to investigate the image characteristics. We also performed a preliminary PCXI experiment using an established a table-top setup to demonstrate the performance of the simulation platform. The system consists of an x-ray tube ($50kV_p$, 5 mAs), a focused-linear grid (200-lines/inch), and a flat-panel detector ($48-{\mu}m$ pixel size). According to our results, the simulated contrast of phase images was much enhanced, compared to that of the absorption images. The scattering length scale estimated for a given simulation condition was about 117 nm. It was very similar, at least qualitatively, to the experimental contrast, which demonstrates the performance of the simulation platform. We also found that the level of the phase gradient of oriented structures strongly depended on the orientation of the structure relative to that of linear grids.

• KSTLE International Journal
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• 제1권2호
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• pp.69-75
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• 2000

The paper compares topography, phase contrast and force spectroscopy in atomic force microscopy data for evaluating the microheterogeneity of surface layer. The worn surface of ion-plated TiN coating was measured using both a laboratory-built and a commercial AFM. The results of analysis revealed structural and micromechanical heterogeneity of the worn surfaces. We demonstrated that the phase image allows relatively qualitative estimation of elastic modulus of the sample surface. The tribolayer formed in the worn surface possessed much lower stiffness than the original coating. It is shown that the most stable phase imaging is provided with a stiff cantilever. In this case, phase contrast is well conditioned, first of all, by microheterogeneity of elastic properties of the investigated surfaces. In this study an attempt was also made to correlate the results of phase imaging with that of the farce spectroscopy. The joint analysis of information on the surface properties obtained by the phase imaging and quantitative data measured with the force spectroscopy methods allows a better understanding of the nature of the surface micromechanical heterogeneity.

• Asian Pacific Journal of Cancer Prevention
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• 제16권6호
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• pp.2521-2526
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• 2015

Objective: The purpose of this study was to evaluate computed tomography (CT) virtual non-contrast (VNC) spectral imaging for gastric carcinoma. Materials and Methods: Fifty-two patients with histologically proven gastric carcinomas underwent gemstone spectral imaging (GSI) including non-contrast and contrast-enhanced hepatic arterial, portal venous, and equilibrium phase acquisitions prior to surgery. VNC arterial phase (VNCa), VNC venous phase (VNCv), and VNC equilibrium phase (VNCe) images were obtained by subtracting iodine from iodine/water images. Images were analyzed with respect to image quality, gastric carcinoma-intragastric water contrast-to-noise ratio (CNR), gastric carcinoma-perigastric fat CNR, serosal invasion, and enlarged lymph nodes around the lesions. Results: Carcinoma-water CNR values were significantly higher in VNCa, VNCv, and VNCe images than in normal CT images (2.72, 2.60, 2.61, respectively, vs 2.35, $p{\leq}0.008$). Carcinoma-perigastric fat CNR values were significantly lower in VNCa, VNCv, and VNCe images than in normal CT images (7.63, 7.49, 7.32, respectively, vs 8.48, p< 0.001). There were no significant differences of carcinoma-water CNR and carcinoma-perigastric fat CNR among VNCa, VNCv, and VNCe images. There was no difference in the determination of invasion or enlarged lymph nodes between normal CT and VNCa images. Conclusions: VNC arterial phase images may be a surrogate for conventional non-contrast CT images in gastric carcinoma evaluation.

• Korean Journal of Radiology
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• 제20권6호
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• pp.863-879
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• 2019

Hepatocellular carcinoma (HCC) can be noninvasively diagnosed on the basis of its characteristic imaging findings of arterial phase enhancement and portal/delayed "washout" on computed tomography (CT) and magnetic resonance imaging (MRI) in cirrhotic patients. However, different specific diagnostic criteria have been proposed by several countries and major academic societies. In 2018, major guideline updates were proposed by the Association for the Study of Liver Diseases, European Association for the Study of the Liver (EASL), Korean Liver Cancer Association and National Cancer Center (KLCA-NCC) of Korea. In addition to dynamic CT and MRI using extracellular contrast media, these new guidelines now include magnetic resonance imaging (MRI) using hepatobiliary contrast media as the first-line diagnostic test, while the KLCA-NCC and EASL guidelines also include contrast-enhanced ultrasound (CEUS) as the second-line diagnostic test. Therefore, hepatobiliary MR contrast media and CEUS will be increasingly used for the noninvasive diagnosis and staging of HCC. In this review, we discuss the emerging role of hepatobiliary phase MRI and CEUS for the diagnosis of HCC and also review the changes in the HCC diagnostic criteria in major guidelines, including the KLCA-NCC practice guidelines version 2018. In addition, we aimed to pay particular attention to some remaining issues in the noninvasive diagnosis of HCC.

• Applied Microscopy
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• 제33권3호
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• pp.169-178
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• 2003

영상이론과 회절 이론을 같은 비중으로 다루고 이들과의 관계를 나타내는 wave optics 이론을 소개하였다. 결맞는 파동 이론과 결 안맞는 파동이론 사이의 차이를 나타내고 Abbe이론과 여러 가지 phase contrast 이론들을 small angle 근사로 접근하였다. 마지막으로 다중 성분 시스템에 대한 파동 광학의 수학적인 방법의 적용을 소개하였다.