• Applied Microscopy
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• v.42 no.4
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• pp.218-222
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• 2012

Modern aberration-corrected transmission electron microscope (TEM) with appropriate electron beam energy is able to achieve atomic resolution imaging of single and bilayer graphene sheets. Especially, atomic configuration of bilayer graphene with a rotation angle can be identified from the direct imaging and phase reconstructed imaging since atomic resolution Moir$\acute{e}$ pattern can be obtained successfully at atomic scale using an aberration-corrected TEM. This study boosts a reliable stacking order analysis, which is required for synthesized or artificially prepared multilayer graphene, and lets graphene researchers utilize the information of atomic configuration of stacked graphene layers readily.

• Bulletin of the Korean Mathematical Society
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• v.49 no.6
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• pp.1291-1302
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• 2012

In this paper, we introduce a new elliptic PDE: $$\{{\nabla}{\cdot}\(\frac{|{\gamma}^{\omega}(r)|^2}{\sigma}{\nabla}v_{\omega}(r)\)=0,\;r{\in}{\Omega},\\v_{\omega}(r)=f(r),\;r{\in}{\partial}{\Omega},$$ where ${\gamma}^{\omega}={\sigma}+i{\omega}{\epsilon}$ is the admittivity distribution of the conducting material ${\Omega}$ and it is shown that the introduced elliptic PDE can replace the standard elliptic PDE with conductivity coefficient in EIT imaging. Indeed, letting $v_0$ be the solution to the standard elliptic PDE with conductivity coefficient, the solution $v_{\omega}$ is quite close to the solution $v_0$ and can show spectroscopic properties of the conducting object ${\Omega}$ unlike $v_0$. In particular, the potential $v_{\omega}$ can be used in detecting a thin low-conducting anomaly located in ${\Omega}$ since the spectroscopic change of the Neumann data of $v_{\omega}$ is inversely proportional to thickness of the thin anomaly.

• Imaging Science in Dentistry
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• v.40 no.1
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• pp.15-23
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• 2010

Purpose : This study was designed to compare the effective doses from low-dose and standard-dose multi-detector CT (MDCT) scanning protocols and evaluate the image quality and the spatial resolution of the low-dose MDCT protocols for clinical use. Materials and Methods : 6-channel MDCT scanner (Siemens Medical System, Forschheim, Germany), was used for this study. Protocol of the standard-dose MDCT for the orthodontic analysis was 130 kV, 35 mAs, 1.25 mm slice width, 0.8 pitch. Those of the low-dose MDCT for orthodontic analysis and orthodontic surgery were 110 kV, 30 mAs, 1.25 mm slice width, 0.85 pitch and 110 kV, 45 mAs, 2.5 mm slice width, 0.85 pitch. Thermoluminescent dosimeters (TLDs) were placed at 31 sites throughout the levels of adult female ART head and neck phantom. Effective doses were calculated according to ICRP 1990 and 2007 recommendations. A formalin-fixed cadaver and AAPM CT performance phantom were scanned for the evaluation of subjective image quality and spatial resolution. Results : Effective doses in ${\mu}Sv$ ($E_{2007}$) were 699.1, 429.4 and 603.1 for standard-dose CT of orthodontic treatment, low-dose CT of orthodontic analysis, and low-dose CT of orthodontic surgery, respectively. The image quality from the low-dose protocol were not worse than those from the standard-dose protocol. The spatial resolutions of both standard-dose and low-dose CT images were acceptable. Conclusion : From the above results, it can be concluded that the low-dose MDCT protocol is preferable in obtaining CT images for orthodontic analysis and orthodontic surgery.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.350-350
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• 2011

The spin structure of Fe over layers on Cu (001), especially in region II is one of the unsolved problem for many years. We study the out - of - plane (OP) Fermi surfaces (FSs) of 7 monolayer Fe/Cu (001) films using angle resolved photo emission spectroscopy (ARPES). Ultrathin Fe was grown on Cu (001) substrate at room temperature and the experimental measurements were carried out at room temperature and low temperature. Fermi surfaces measured about $\frac{1}{4}$ of the Brillouin Zone (BZ) using photon energies ranging from 170 eV to 280 eV. Our results confirmed that ferromagnetic signal at 7 ML Fe on Cu (001) is nearly zero. These results are consistent with our recent x-ray magnetic circular dichroism (XMCD) and surface magneto - optic Kerr effect (SMOKE) experiments. Based on our observations we have made a simple model of this system, which explains all the experimental results.

• Journal of Cardiovascular Imaging
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• v.31 no.2
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• pp.108-115
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• 2023

BACKGROUND: Minimizing contrast dose and radiation exposure while maintaining image quality during computed tomography angiography (CTA) for transcatheter aortic valve replacement (TAVR) is desirable, but not well established. This systematic review compares image quality for low contrast and low kV CTA versus conventional CTA in patients with aortic stenosis undergoing TAVR planning. METHODS: We performed a systematic literature review to identify clinical studies comparing imaging strategies for patients with aortic stenosis undergoing TAVR planning. The primary outcomes of image quality as assessed by the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were reported as random effects mean difference with 95% confidence interval (CI). RESULTS: We included 6 studies reporting on 353 patients. There was no difference in cardiac SNR (mean difference, -1.42; 95% CI, -5.71 to 2.88; p = 0.52), cardiac CNR (mean difference, -3.83; 95% CI, -9.98 to 2.32; p = 0.22), aortic SNR (mean difference, -0.23; 95% CI, -7.83 to 7.37; p = 0.95), aortic CNR (mean difference, -3.95; 95% CI, -12.03 to 4.13; p = 0.34), and ileofemoral SNR (mean difference, -6.09; 95% CI, -13.80 to 1.62; p = 0.12) between the low dose and conventional protocols. There was a difference in ileofemoral CNR between the low dose and conventional protocols with a mean difference of -9.26 (95% CI, -15.06 to -3.46; p = 0.002). Overall, subjective image quality was similar between the 2 protocols. CONCLUSIONS: This systematic review suggests that low contrast and low kV CTA for TAVR planning provides similar image quality to conventional CTA.

• Journal of Radiation Protection and Research
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• v.43 no.1
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• pp.1-9
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• 2018

Background: In this study, we investigate the image quality of virtual monochromatic images synthesized from dual-energy computed tomography (DECT) at voltages of 80/140 kV and 100/140 kV. Materials and Methods: Virtual monochromatic images of a phantom are synthesized from DECT scans from 40 to 70 keV in steps of 1 keV under the two combinations of tube voltages. The dose allocation of dual-energy (DE) scan is 50% for both low- and high-energy tubes. The virtual monochromatic images are compared to single-energy (SE) images at the same radiation dose. In the DE images, noise is reduced using the 100/140 kV scan at the optimal monochromatic energy. Virtual monochromatic images are reconstructed from 40 to 70 keV in 1-keV increments and analyzed using two quality indexes: noise and contrast-to-noise ratio (CNR). Results and Discussion: The DE scan mode with the 100/140 kV protocol achieved a better maximum CNR compared to the 80/140 kV protocol for various materials, except for adipose and brain. Image noise is reduced with the 100/140 kV protocol. The CNR values of DE with the 100/140 kV protocol is similar to or higher than that of SE at 120 kV at the same radiation dose. Furthermore, the maximum CNR with the 100/140 kV protocol is similar to or higher than that of the SE scan at 120 kV. Conclusion: It was found that the CNR achieved with the 100/140 kV protocol was better than that with the 80/140 kV protocol at optimal monochromatic energies. Virtual monochromatic imaging using the 100/140 kV protocol could be considered for application in breast, brain, lung, liver, and bone CT in accordance with the CNR results.

• Korean Journal of Digital Imaging in Medicine
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• v.11 no.2
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• pp.101-107
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• 2009

With the recent development of diagnosis using radiation and increasing demand of the medical treatment, we need to minimize radiation exposure dose. So, This is the method which reduce patient dose by measuring surface dose of radiographic change factor and by comparing theoretical and actual dose, when we take an X-ray which is generally used. By changing the factor of kV, mAs, FSD, whose range is 60 to 120 kV, 20 to 100 mAs, 80 to 180 cm, we compared theoretical surface dose with actual surface dose calculated by the simple calculation program, Bit system, and NDD-M method As a result, when kV and mAs were higher, theoretical surface dose and actual surface dose were more increased. but the higher FSD was, the more decreased surface dose was. According to this, the error were measured about 0.1 to 0.2 mGy in low dose part and about 0.7 to 1.5 mGy in high dose part. Therefore, this shows that theoretical surface dose calculation method is more correct in low dose part than in high dose part. In conclusion, we will have to make constant efforts which can reduce patient and radiographer's exposure dose, studying methods which can predict patient's radiation exposure dose more exactly.

• Journal of the Korean Society of Radiology
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• v.9 no.4
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• pp.205-211
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• 2015

At a recent medical imaging technology, the major issue of X-ray diagnosis in breast cancer is the early detection of breast cancer and low patient's exposure dose. As one of studies to acquire a monochromatic X-ray, Technologies using multilayer mirror had been preceded. However, a uniform multilayer mirror that consists of uniform thin-film thickness can acquire a monochromatic X-ray only in the partial area corresponds to angle of incidence of white X-ray, so there are limits for X-ray imaging technology applications. In this study, we designed laterally graded multilayer mirror(below GML) that reflects same monochromatic X-ray over the entire area of thin-film mirror, which have the the thickness of the linear gradient that correspond to angle of incidence of white X-ray. By using ion-beam sputtering system added the mask control system we fabricated a GML which has size of $100{\times}100mm^2$. The GML is designed to achieve the monochromatic X-ray of 17.5kev energy and has thin-film thickness change from 4.62nm to 6.57nm(3.87nm at center). It reflects the monochromatic X-ray with reflectivity of more than 60 percent, FWHM of below 2.6keV and X-ray beam width of about 3mm. The monochromatic X-ray corresponded to 17.5keV using GML would have wide application in development of mammography system with high contrast and low dose.

• Journal of the Korean Society of Radiology
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• v.11 no.7
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• pp.663-669
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• 2017

In diagnostic medical imaging, it is essential to reduce the scattered radiation for the high medical image quality and low patient dose. Therefore, in this study, the influence of the scattered radiation on medical images was analyzed as the tube voltage increases. For this purpose, ANSI chest phantom was used to measure the scattering ratio, and the scattering effect on the image quality was investigated by RMS evaluation, RSD and NPS analysis. It was found that the scattering ratio with increasing x-ray tube voltage gradually increased to 48.8% at 73 kV tube voltage and to 80.1% at 93 kV tube voltage. As a result of RMS analysis for evaluating the image quality, RMS value according to increase of tube voltage was increased, resulting in low image quality. Also, the NPS value at 2.5 lp/mm spatial frequency was increased by 20% when the tube voltage was increased by 93 kV compared to the tube voltage of 73 kV. From this study, it can be seen that the scattering radiation have a significant effect on the image quality according to the increase of x-ray tube voltage. The results of this study can be used as basic data for the improvement of medical imaging quality.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.23
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• pp.10057-10059
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• 2015

Positron emission tomography (PET) as the functional component of current hybrid imaging (like PET/CT or PET/MRI) seems to dominate the horizon of medical imaging in coming decades. $^{18}$Flourodeoxyglucose ($^{18}FDG$) is the most commonly used probe in oncology and also in cardiology and neurology around the globe. However, the major capital cost and exorbitant running expenditure of low to medium energy cyclotrons (about 20 MeV) and radiochemistry units are the seminal reasons of low number of cyclotrons but mushroom growth pattern of PET scanners. This fact and longer half-life of $^{18}F$ (110 minutes) have paved the path of a centralized model in which $^{18}FDG$ is produced by commercial PET radiopharmacies and the finished product (multi-dose vial with tungsten shielding) is dispensed to customers having only PET scanners. This indeed reduced the cost but has limitations of dependence upon timely arrival of daily shipments as delay caused by any reason results in cancellation or rescheduling of the PET procedures. In recent years, industry and academia have taken a step forward by producing low energy, table top cyclotrons with compact and automated radiochemistry units (Lab-on-Chip). This decentralized strategy enables the users to produce on-demand doses of PET probe themselves at reasonably low cost using an automated and user-friendly technology. This technological development would indeed provide a real impetus to the availability of complete set up of PET based molecular imaging at an affordable cost to the developing countries.