• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.25-29
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• 2006

The object of this study is to develop new examination techniques for measuring the O-ring deformation behavior under the pressure condition. The extrusion lengths measured from the computed tomography were in good agreement with the results that measured from non-contact laser displacement sensor. The deformed shapes of O-ring measured by the computed tomography and evaluated by the FEM agreed well with the extrusion length and the expanded diameter. But the contact widths of the O-ring and steel measured by the computed tomography were a little larger than the results of the FEM.

• Journal of the Korean Society of Radiology
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• v.9 no.6
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• pp.403-408
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• 2015

Hard X-ray has been widely used in medical and industrial fields because it can be applied to observe the inside of a sample. Computed tomography provides sectional images of the sample through the reconstruction of the projection images. The quality of sectional images strongly depends on that of projection images. Ring artifact appeared on the seconal image can be made by the abnormal pixels of the detector used. In this study, we examine the ring artifact ratio in the circle phantom as a function of detection error of the detector used in computed tomography. The ring artifact increased with the increment of detection error under parallel and fan beam geometries and strongly increased near the center of rotation. The corrections, dead pixel and flat field corrections, for the images taken with the detector are required before the image reconstruction process to reduce the ring artifact in the computed tomography.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.1
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• pp.1-8
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• 2008

The object of this study is to develop the examination technique for measuring the O-ring deformation behavior under the pressure and the squeezed condition simultaneously. The O-ring deformation measuring device in which two grooves were dug to insert the two O-rings was manufactured to be not deformed under the high pressure and the 1 mm and 0.1 mm gap were designed to measure the extrusion lengths under the internal pressure. The beam hardening correction, the histogram analysis and the dead zone correction were executed to exactly measure the shape of O-ring deformation and the lengths of the O-ring deformation were measured by the LSF and the ERF. The computed tomography applied the pressure of 0, 1.378, 4.902, 9.804, 15.692 MPa at 22.3% squeezed condition and the expanded diameter, contact length and extrusion depth were measured in each pressure. The shape of O-ring deformation was evaluated by the FEM to verify the results of measuring by the computed tomography and the area of O-ring was mutually compared to the area measured by the computed tomography.

• Journal of the Korean Society of Radiology
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• v.83 no.1
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• pp.3-27
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• 2022

Cardiac CT has been proven to provide diagnostic and prognostic evaluation of coronary artery disease for cardiovascular risk stratification and treatment decision-making based on rapid technological development and various research evidence. Coronary CT angiography has emerged as a gateway test for coronary artery disease that can reduce invasive angiography due to its high negative predictive value, but the diagnostic specificity is relatively low. However, coronary CT angiography is likely to overcome its limitations through functional evaluation to identify the hemodynamic significance of coronary artery disease by analyzing myocardial perfusion and fractional flow reserve through cardiac CT. Recently, studies have been actively conducted to incorporate artificial intelligence to make this more objective and reproducible. In this review, functional imaging techniques of cardiac computerized tomography are explored.

• Journal of radiological science and technology
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• v.40 no.2
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• pp.253-259
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• 2017

The study examines changes in calcium volume on born by comparing two figures; one is measured by dual energy computed tomography(DECT) followed by applying variation in monochromatic energy selection(keV), material decomposition(MD), and material suppressed iodine(MSI) analysis, and the other is measured by conventional single source computed tomography(CSCT). For this study, based on CSCT images taken by using human mimicked phantom, 70, 100, 140 keV and MSI, MD material calcium weighting(MCW) and MD material iodine weighting(MIW) of DECT were applied respectively. Then calculated calcium volume was converted to Agatston score for comparison. Volume of human mimicked phantom was in inverse proportion to keV. The volume decreased while keV increased(p<0.05). The most similar DECT volumes were reconstructed at 70 keV, the difference was showed $35.8{\pm}12.2$ for rib, femur ($16.1{\pm}24.1$), pelvis($13.7{\pm}18.8$), and spine($179.0{\pm}61.8$). However, the volume of MSI was down for each organ; the volume of rib was 5.55%, femur(76.34%), pelvis(55.16%) and spine(87.58%). The volume of MSI decreased 55.9% for rib, femur(80.7%), pelvis(69.6%) and spine(54.2%) while MD MIW reduced for rib(83.51%), femur(87.68%), pelvis(86.64%), and spine(82.62%). With the results, the study found that outcomes were affected by the method which examiners employed. When using DECT, calcium volume of born dropped with keV increased. It also found that the most similar DECT images were reconstructed at 70 keV. The results of experiments implied that the users of MSI and MD should be cautious of errors as there are big differences in scores between those two methods.

• Journal of the Korean Society of Radiology
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• v.81 no.2
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• pp.250-271
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• 2020

Assessment of myocardial ischemia in patients with stable angina is important in deciding whether to treat coronary artery disease and in predicting clinical outcome. The fractional flow reserve is a standard reference for the diagnosis of myocardial ischemia, but this procedure has limitations because of its invasiveness. Coronary computed tomography angiography (CCTA) is now an established tool in the anatomic diagnosis of coronary artery disease; however, there are limits to the diagnosis of hemodynamically important stenosis that causes myocardial ischemia. In order to address this problem, studies using quantification of coronary atherosclerotic plaques, myocardial perfusion, and noninvasive calculation of fractional flow reserve based on CCTA have been actively conducted and recognized for their diagnostic value. In this review, several imaging techniques of CCTA used to assess myocardial ischemia are described.

• Journal of radiological science and technology
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• v.39 no.4
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• pp.543-547
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• 2016

Acute stroke is a one of common disease that require fast diagnosis and treatment to save patients life. however, the acute stroke may cause lifelong disability due to brain damage with no prompt surgical procedure. In order to diagnose the Stroke, brain perfusion CT examination and possible rapid implementation of 3D angiography has been widely used. However, a low-dose technique should be applied for the examination since a lot of radiation exposure to the patient may cause secondary damage for the patients. Therefore, the degradation of the measured CT images may interferes with a clinical check in that blood vessel shapes on the CT image are significantly affected by gaussian noise. In this study, we employed the spatio-temporal technique to analyze dynamic (brain perfusion) CT data to improve an image quality for successful clinical diagnosis. As a results, proposed technique could remove gaussian noise successfully, demonstrated a possibility of new image segmentation technique for CT angiography. Qualitative evaluation was conducted by skilled radiological technologists, indicated significant quality improvement of dynamic CT images. the proposed technique will be useful tools as a clinical application for brain perfusion CT examination.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7C
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• pp.601-609
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• 2012

In this paper, a limited-view CT image reconstruction method was studied to reduce the scan times and the X-ray dose for the patients. To reduce streak artifacts which is caused by insufficient number of views, we introduce a sinogram interpolation method based on image matching. Image matching is achieved using the characteristics of the neighboring views including intensity, gradient and distance between the pixels. Interpolation is performed using the image matching results.. A numerical phantom and Al-acryl phantom were used for evaluating the effectiveness of the proposed interpolation method. The results showed that streak artifacts were reduced in the reconstructed images while the details of the images were preserved. Moreover, maximum 5% improvements in terms of PSNR were observed.

• Journal of Radiation Protection and Research
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• v.30 no.3
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• pp.113-119
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• 2005

The computed tomogrpahy(CT) provides a high quality in images of human body but contributes to the relatively high patient dose. The frequency of CT examination is increasing and, therefore, the concerns about the patient dose are also increasing. In this study the experimental determination of patient dose was performed by using a physical anthropomorphic phantom and thermoluminescent dosimeter(TLD). The measurements were done for the both axial and spiral scan mode. As a result the effective doses for each scan mode were 17.78mSv and 10.01 mSv respectively and the fact that the degree of the reduction in the patient dose depends on the pitch scan parameter was confirmed. The measurement methods suggested in this study can be applied for the reassessment of the patient dose when the technique in CT equipment is developed or the protocol for CT scanning is changed.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.1
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• pp.20-30
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• 2010

In this paper, a new tomographic scan method with fixed installed detectors and rotating source from gamma projector was presented to diagnose the industrial plants which were impossible to be examined by conventional tomographic systems. Weight matrix calculation method which was suitable for volumetric detector and statistical iterative reconstruction method were applied for reconstructing the simulation and experimental data. Monte Carlo simulations had been performed for two kinds of phantoms. Lab scale experiment with a same condition as one of phantoms, had been carried out. Simulation results showed that reconstruction from photopeak counting measurement gave the better results than from the gross counting measurement although photopeak counting measurement had large statistical errors. Experimental data showed the similar result as Monte Carlo simulation. Those results appeared to be promising for industrial tomographic applications, especially for petrochemical industries.