• The Korean Journal of Nuclear Medicine
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• v.32 no.1
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• pp.32-49
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• 1998

For estimation of regional myocardial blood flow with O-15 water PET, a few modifications considering partial volume effect based on single compartment model have been proposed. In this study, we attempted to quantify the degree of heterogeneity and to show the effect of tissue flow heterogeneity on partition coefficient(${\lambda}$) and to find the relation between perfusable tissue index(PTI) and ${\lambda}$ by computer simulation using two modified models. We simulated tissue curves for the regions with homogeneous and heterogeneous blood flow over a various flow range(0.2-4.0ml/g/min). Simulated heterogeneous tissue composed of 4 subregions of the same or different size of block which have different homogeneous flow and different degree of slope of distribution of blood flow. We measured the index representing heterogeneity of distribution of blood flow for each heterogeneous tissue by the constitution heterogeneity(CH). For model I, we assumed that tissue recovery coefficient ($F_{MME}$) was the product of partial volume effect($F_{MMF}$) and PTI. Using model I, PTI, flow, and $F_{MM}$ were estimated. For model II, we assumed that partition coefficient was another variable which could represent tissue characteristics of heterogeneity of flow distribution. Using model II, PTI, flow and ${\lambda}$ were estimated. For the simulated tissue with homogeneous flow, both models gave exactly the same estimates, of three parameters. For the simulated tissue with heterogeneous flow distribution, in model I, flow and $F_{MM}$ were correctly estimated as CH was increased moderately. In model II, flow and ${\lambda}$ were decreased curvi-linearly as CH was increased. The degree of underestimation of ${\lambda}$ obtained using model II, was correlated with CH. The degree of underestimation of flow was dependent on the degree of underestimation of ${\lambda}$. PTI was somewhat overestimated and did not change according to CH. We conclude that estimated ${\lambda}$ reflect the degree of tissue heterogeneity of flow distribution. We could use the degree of underestimation of ${\lambda}$ to find the characteristic heterogeneity of tissue flow and use ${\lambda}$ to recover the underestimated flow.

• Progress in Medical Physics
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• v.21 no.2
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• pp.165-173
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• 2010

In this paper, we evaluated the performance of 3D CRT, IMRT and three kind of RA plannings to investigate the clinical effect of RA with liver cancer case. The patient undergoing liver cancer of small volume and somewhat constant motion were selected. We performed 3D CRT, IMRT and RA plannings such as 2RA, limited triple arcs (3RA) and 3MRA with Eclipse version 8.6.15. The same dose volume objectives were defined for only CTV, PTV and body except heart, liver and partial body in IMRT and RA plannings. The steepness of dose gradient around tumor was determined by the Normal Tissue Objective function with the same parameters in place of respective definitions of dose volume objectives for the normal organs. The approach between the defined dose constraints and the practical DVH of CTV, PTV and Body was the best in 3MRA and the worst in IMRT. The DVHs were almost the same among RAs. Plans were evaluated using Conformity Index (CI), Homogeneity Index (HI) and Quality of coverage (QoC) by RTOG after prescription with dose level surrounding 98% of PTV in the respective plans. As a result, 3MRA planning showed the better favorable indices than that of the others and achieved the lowest MUs. In this study, RA planning is a technique that is possible to obtain the faster and better dose distribution than 3D CRT or IMRT techniques. Our result suggest that 3MRA planning is able to reduce the MUs further, keeping a similar or better targer dose homogeneity, conformity and sparing normal tissue than 2RA or 3RA.

• The Korean Journal of Nuclear Medicine
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• v.29 no.1
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• pp.48-53
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• 1995

This study investigates a simple mathematical model for the quantitative estimation of regional myocardial blood flow in experimental canine coronary artery thrombosis using Rb-82 dynamic myocardial positron emission tomography. The coronary thrombosis was induced using the new catheter technique by narrowing the lumen of coronary vessel gradually, which finally led to partial obstruction of coronary artery. Ten Rb-82 dynamic myocardial PET scans were performed sequentially for each experiment using our 5, 10 and 20 second acquisition protocol, respectively, and three regions of interest were drawn on the transaxial slices, one on left ventricular chamber for input function and the other two on normal and decreased perfusion segments for the flow estimation in those regions. Single compartment model has been applied to the measured sets of regional PET data, and the rate constants of influx to myocardial tissue were calculated for regional myocardial flow estimates with the three parameter fits of raw data by the Levenberg-Marquardt method. The results showed that, (1) single compartment model suggested by Kety-Schmidt could be used for the simple estimation of regional myocardial blood flow, (2) the calculated regional myocardial blood flow estimates were dependent on the selection of input function, which reflected partial volume effect and left ventricular wall motion, and (3) mathematically fitted input and tissue time activity curves were more suitable than the direct application of the measured data in terms of convergence.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.1-7
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• 2018

This study examined the effect of binder-to-soil ratio(B/S) and water-to-binder ratio(W/B) on the flow and compressive strength development of soil concrete using high-volume supplementary cementitious materials. As a partial replacement of ordinary portland cement, 10% by-pass dust, 40% ground granulated blast-furnace slag, and 25% circulating fluidized bed combustion fly ash were determined in the preliminary tests. Using the low-cement binder incorporated with clay soil or sandy soil, a total of 18 soil concrete mixtures was prepared. The flow of the soil concrete tended to increase with the increase in W/B and B/S, regardless of the type of soils. The compressive strength was commonly higher in sandy soil concrete than in clay soil concrete with the same mixture condition. Considering the high-workability and compressive strength development, it could be recommended for low-cement soil concrete to be mixed under the following condition: B/S of 0.35 and W/B of 175%.

• Journal of Biomedical Engineering Research
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• v.26 no.2
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• pp.73-86
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• 2005

We need to flatten the brain cortex to smooth surface, sphere, or 2D plane in order to view the buried sulci. The rendered 3D surface of the segmented white matter and gray matter does not have the topology of a sphere due to the partial volume effect and segmentation error. A surface without correct topology may lead to incorrect interpretation of local structural relationships and prevent cortical unfolding. Although some algorithms try to correct topology, they require heavy computation and fail to follow the deep and narrow sulci. This paper proposes a method that corrects topology of the rendered surface fast, accurately, and automatically. The proposed method removes fractions beside the main surface, fills cavities in the inside of the main surface, and removes handles in the surface. The proposed method to remove handles has three-step approach. Step 1 performs smoothing operation on the rendered surface. In Step 2, vertices of sphere are gradually deformed to the smoothed surfaces and finally to the boundary of the segmented white matter and gray matter. The Step 2 uses multi-resolutional approach to prevent the deep sulci from geometrical intersection. In Step 3, 3D binary image is constructed from the deformed sphere of Step 2 and 3D surface is regenerated from the 3D binary image to remove intersection that may happen. The experimental results show that the topology is corrected while principle sulci and gyri are preserved and the computation amount is acceptable.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.757-758
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• 2010

At the time of medical treatment and surgical operation, halogen lamp and plasma lamp were mainly used as luminous source for lighting. These two luminous sources have drawbacks that the life of lamps are not long, various problems are brought about due to excessive heat generation and its volume is very big because of cooling device. Accordingly, in this research a ring light was developed so that a partial shadowless shooting for the patient's affected area at the medical treatment room and surgical operation room using high luminance LED for which attention is being paid as new lighting parts for medical purpose. LED which was applied to the development used high luminance three color LED for full color for which various color materialization and the adjustment of radiation intensity are possible and we can get white light in order to emphasize the delicate expression for generic tone of shooting object, strong highlight, simple shadow and three dimensional effect at the time of close-up shadowless shooting of the affected area.

• Advances in concrete construction
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• v.9 no.2
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• pp.207-215
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• 2020

This paper describes the experimental studies carried out to determine the properties of fresh and hardened concrete with Recycled Plastic Waste (RPW) as a partial replacement material for fine aggregates. In the experimental study, RPW was used for replacing river sand and manufactured sand (M sand) aggregates in concrete. The replacement level of fine aggregates was ranging from 5% to 20% by volume with an increment of 5%. M40 grade of concrete with water cement ratio of 0.40 was used in this study. Two different types of RPW were used, and they are (i) un-activated RPW and (ii) activated RPW. The activated RPW was obtained by alkali activation of un-activated RPW using NaOH solution. The hardened properties of the concrete determined were dry density, compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity (UPV). The properties of the concrete with river sand, M sand, activated RPW and un-activated RPW were compared and inferences were drawn. The effect of activation using NaOH solution was investigated using FT-IR study. The micro structural examination of hardened concrete was carried out using Scanning Electron Microscopy (SEM). The test results show that the strength of concrete with activated RPW was more than that of un-activated RPW. From the results, it is evident that it is feasible to use 5% un-activated RPW and 15% activated RPW as fine aggregates for making concrete without affecting the strength properties.

• Investigative Magnetic Resonance Imaging
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• v.24 no.3
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• pp.95-122
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• 2020

In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). High-quality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B₁|) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B₁| region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B₁|-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1668-1670
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• 2002

Since more than two decades, the conventional PD detecting systems have been employed in order to detect the partial discharges occurring inside the HV power apparatus for their diagnosis by use of different type of detection such as acoustic and UHF detection method. Regardless of their wide on-site application, a certain number of technical inconveniences have been disclosed as follows : multistage amplification. large volume, susceptible to external noise and high price. In this respect, the optical measurement techniques are widely proposed in these days in this concerned field ascribed to the following advantages : immune to external EMI noise and broad band response of the Pockels cell covering from DC to GHz. However, the reliability of several proposed techniques enabling to measure the electric field inside the large high power apparatus has not yet been well approved In this work, an optical measuring system, based on the Pockels effect, has been developed for measuring the field variation due to the corona discharges occurring in air and in oil. This system consists of He-Ne laser, single mode optical fiber, multi mode optical fiber, polarizing film, Y-cut LiNbO3 cell, photo detector, digital oscilloscope and personal computer with GPIB. For this purpose, optical probe has been specially designed and realized and put into the needle-plane electrode. Afterward, same measurement is carried out in oil. We demonstrate the characteristic of the optical measuring system and the measurement results.

• Composites Research
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• v.24 no.6
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• pp.7-11
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• 2011

Polyurethane oligomers (PUOs) such as UA8297, UP127 and EB8200 were utilized to enhance the anti-bullet property of Dyneema$^{(R)}$/vinylester composites. First, prepregs of PUO and vinylester (XSR10) were prepared via spray coating on Dyneema$^{(R)}$ fabric at 21 % resin content (by volume). In addition, spray coating and film lamination were also carried out with a mixture of XSR10/PUO for selected PUOs. Next, the prepregs were dried at RT for 1-2 h and then at $100^{\circ}C$ for 30 min to remove the solvent and to provide partial cure when necessary. The prepregs were stacked in 24 layers and cured at $120^{\circ}C$ for 5 min under the contact pressure and for additional 25 min at 150 $kg/cm^2$. Finally, the anti-bullet properties of composite samples were evaluated by measuring $V_{50}$ with simulated fragment projectile (SFP, 17 gr). The results showed a 6.5 and 9.0 % increase of $V_{50}$ with UP127 and EB8200, respectively.