• Progress in Medical Physics
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• v.22 no.4
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• pp.163-171
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• 2011

The purpose of this study was to investigate the effect of various technical parameters for the dose optimization in pediatric chest radiological examinations by evaluating effective dose and effective detective quantum efficiency (eDQE) including the scatter radiation from the object, the blur caused by the focal spot, geometric magnification and detector characteristics. For the tube voltages ranging from 40 to 90 kVp in 10 kVp increments at the FDD of 100, 110, 120, 150, 180 cm, the eDQE was evaluated at the same effective dose. The results showed that the eDQE was largest at 60 kVp when compares the eDQE at different tube voltage. Especially, the eDQE was considerably higher without the use of an anti-scatter grid on equivalent effective dose. This indicates that the reducing the scatter radiation did not compensate for the loss of absorbed effective photons in the grid. When the grid is not used the eDQE increased with increasing FDD because of the greater effective modulation transfer function (eMTF). However, most of major hospitals in Korea employed a short FDD of 100 cm with an anti-scatter grid for the chest radiological examination of a 15 month old infant. As a result, the entrance surface air kerma (ESAK) values for the hospitals of this survey exceeded the Korean DRL (diagnostic reference level) of $100{\mu}Gy$. Therefore, appropriate technical parameters should be established to perform pediatric chest examinations on children of different ages. The results of this study may serve as a baseline to establish detailed reference level of pediatric dose for different ages.

• Progress in Medical Physics
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• v.19 no.1
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• pp.63-72
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• 2008

With recent advancement of the medical imaging systems and picture archiving and communication system (PACS), installation of digital radiography has been accelerated over past few years. Moreover, Computed Radiography (CR) which was well established for the foundation of digital x-ray imaging systems at low cost was widely used for clinical applications. This study analyzes imaging characteristics for two systems with different pixel sizes through the Modulation Transfer Function (MTF), Noise Power Spectrum (NPS) and Detective Quantum Efficiency (DQE). In addition, influence of radiation dose to the imaging characteristics was also measured by quantitative assessment. A standard beam quality RQA5 based on an international electro-technical commission (IEC) standard was used to perform the x-ray imaging studies. For the results, the spatial resolution based on MTF at 10% for Agfa CR system with I.P size of $8{\times}10$ inches and $14{\times}17$ inches was measured as 3.9 cycles/mm and 2.8 cycles/mm, respectively. The spatial resolution based on MTF at 10% for Fuji CR system with I.P size of $8{\times}10$ inches and $14{\times}17$ inches was measured as 3.4 cycles/mm and 3.2 cycles/mm, respectively. There was difference in the spatial resolution for $14{\times}17$ inches, although radiation dose does not effect to the MTF. The NPS of the Agfa CR system shows similar results for different pixel size between $100{\mu}m$ for $8{\times}10$ inch I.P and $150{\mu}m$ for $14{\times}17$ inch I.P. For both systems, the results show better NPS for increased radiation dose due to increasing number of photons. DQE of the Agfa CR system for $8{\times}10$ inch I.P and $14{\times}17$ inch I.P resulted in 11% and 8.8% at 1.5 cycles/mm, respectively. Both systems show that the higher level of radiation dose would lead to the worse DQE efficiency. Measuring DQE for multiple factors of imaging characteristics plays very important role in determining efficiency of equipment and reducing radiation dose for the patients. In conclusion, the results of this study could be used as a baseline to optimize imaging systems and their imaging characteristics by measuring MTF, NPS, and DQE for different level of radiation dose.

• Journal of Korean Ophthalmic Optics Society
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• v.18 no.3
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• pp.347-356
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• 2013

Purpose: To evaluate the visual acuity and visual performance after implantation of a aspheric multifocal (ReSTOR$^{(R)}$ SN6AD3) intraocular lens (IOL). Methods: Nineteen cataract patients (30 eyes) implanted with an aspheric multifocal IOL (ReSTOR$^{(R)}$ SN6AD3) either unilaterally or bilaterally were participated. Visual acuity (VA) and objective optical performance were evaluated at the time of preoperation, 1 week, 1 month, and 3 month after operation. At 3 month of post-operation, objective visual performance were measured and compared with the 38 eyes of 20 age-matched normal control. Distance VA was measured by using the ETDRS LCD chart and intermediate and near visual acuity were measured using Jaeger chart. Objective visual performance was assessed preoperatively and 1 week, 1 month and 3 month postoperatively using a double-pass system (Optical Quality Analysis System) with a 4-mm pupil diameter, the OSI (objective scatter index), MTF (modulation transfer function) cut off and strehl ratio. At 3 month of post-operation, visual acuity and visual performance compared with age matched normal control. Results: The uncorrected distance VA, OSI, MTF cut off and strehl ratio were significantly improved (p<0.05) until 1 month postoperatively. Visual performance of MTF cut off and strehl ratio after 3 month of operation were significantly improved compared to the normal control (p=0.063, p=0.103 respectively), however, OSI was higher than normal control. Patients implanted with aspheric multifocal IOL were satisfied with distance and near VA however, were unsatisfied with intermediate VA and reported glare and halos. Conclusions: The visual performance reaches to a stable condition in 1 month of implantation of aspheric multifocal IOL and improved to the level of age-mated normal patients. Also patients were satisfied with their quality of vision, however, intermediate VA, glare and halos were reported as complications.

• Journal of the Korean earth science society
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• v.23 no.7
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• pp.552-564
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• 2002

The data of satellite-observed Microwave Sounding Unit (MSU) channel 1 (Ch1) brightness temperature and General Circulation Model (GCM) reanalyses over the globe have been used to investigate low tropospheric hydrometeors and microwave surface emissivity during the period from January 1981 to December 1993. The average of GCM Ch1 temperature has been reconstructed from three kinds of reanalyses, based on the MSU weighting function. Since the GCM temperature mainly corresponds to the thermal state of the lower troposphere without the difference in the emissivity between ocean and land, it is higher in summer than in other seasons over the regions. The MSU temperature over the ocean shows its maximum at the ITCZ and the SPCZ due to hydrometeors. Over high latitude ocean, the temperature is enhanced because of sea ice emissivity, while it is reduced over the land. The seasonal displacement of the ITCZ and the SPCZ systematically appeared in the difference of Ch1 temperature between the GCM and the MSU. The difference values decrease in the regions of the ITCZ, the SPCZ, and the sea ice because of the increase of the MSU temperature. According to the local minima of the values, the ITCZ moves norhward to 9 N in fall, and the SPCZ moves southward to 12 S in boreal fall and winter. The sea ice in the northern hemisphere is extended southward to 53 N in winter, while the ice in the southern hemisphere, northward to 58 S in boreal summer. We also have discussed the separated contribution from hydrometeors and surface emissivity to the MSU Ch1 temperature, utilizing radiative transfer theory. The increase of 4-6K in the temperature over the ITCZ is inferred to result from hydrometeors of 1-1.5mm/day, and furthermore the increase of 10-30K over the high latitude ocean, ice emissivity of 0.6-0.9.

• Korean Journal of Remote Sensing
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• v.36 no.2_1
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• pp.155-165
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• 2020

In this present study, the sensitivity of O₄ Air Mass Factor (AMF) to Aerosol Peak Height (APH) has been investigated using radiative transfer model according to various parameters(wavelength (340 nm and 477 nm), aerosol type (smoke, dust, sulfate), aerosol optical depth (AOD), surface reflectance, solar zenith angle, and viewing zenith angle). In general, it was found that O₄ AMF at 477 nm is more sensitive to APH than that at 340 nm and is stably retrieved with low spectral fitting error in Differential Optical Absorption Spectroscopy (DOAS) analysis. In high AOD condition, sensitivity of O₄ AMF on APH tends to increase. O₄ AMF at 340 nm decreased with increasing solar zenith angle. This dependency isthought to be induced by the decrease in length of the light path where O₄ absorption occurs due to the shielding effect caused by Rayleigh and Mie scattering at high solar zenith angles above 40°. At 477 nm, as the solar zenith angle increased, multiple scattering caused by Rayleigh and Mie scattering partly leads to the increase of O₄ AMF in nonlinear function. Based on synthetic radiance, APHs have been retrieved using O₄ AMF. Additionally, the effect of AOD uncertainty on APH retrieval error has been investigated. Among three aerosol types, APH retrieval for sulfate type is found to have the largest APH retrieval error due to uncertainty of AOD. In the case of dust aerosol, it was found that the influence of AOD uncertainty is negligible. It indicates that aerosol types affect APH retrieval error since absorption scattering characteristics of each aerosol type are various.