• The Journal of Korean Society for Radiation Therapy
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• v.22 no.2
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• pp.135-144
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• 2010

Purpose: The purpose of this study is that through production of phantom for respiration gated radiotherapy, assessing appropriacy of exposure dose for the therapy using RPM (Real-time Position Management). Materials and Methods: We located measurement object on the phantom for respiration gated radiotherapy made of 2 linear actuator, acrylic panel, stanchion, iron plate ets. to drive (up, down, front, back). Using 4D CT scan, we analyzed patient's respiration and reproduced the movement by computer. On the phantom, we located a 2D-Array (PTW) and an White water phantom (4.5 cm) and used DMLC (interval 2 cm) in the field size $10{\times}10\;cm$, then exposed 21EX X-ray 100 MU, in the case of phantom was (1) static (2) moving (3) gated using RPM respectively gantry $0^{\circ}$ and $90^{\circ}$ We measured with a 0.125 CC ionization chamber (PTW) on the phantom (7.5 cm) in the same condition. Results: Ionization chamber: There were within 0.3% of error with gating respiration and approximately 2% of error without gating in the same condition. 2D-Array: Gantry $90^{\circ}$, field size $10{\times}10\;cm$, using DMLC. There were within 3% of error with gating respiration and approximately 16% of error without gating. Conclusion: The phantom for respiration gated radiotherapy makes plans considering patient's movement, quantitative analysis of exposure dose and proper assessment therapy for IMRT patients using RPM possible.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.1
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• pp.107-114
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• 2014

Purpose : The purpose of this study is evaluation for the applicability of O-MAR(Metal artifact Reduction for Orthopedic Implants)(ver. 3.6.0, Philips, Netherlands) in head & neck radiation treatment planning CT with metal artifact created by dental implant. Materials and Methods : All of the in this study's CT images were scanned by Brilliance Big Bore CT(Philips, Netherlands) at 120kVp, 2mm sliced and Metal artifact reduced by O-MAR. To compare the original and reconstructed CT images worked on RTPS(Eclipse ver 10.0.42, Varian, USA). In order to test the basic performance of the O-MAR, The phantom was made to create metal artifact by dental implant and other phantoms used for without artifact images. To measure a difference of HU in with artifact images and without artifact images, homogeneous phantom and inhomogeneous phantoms were used with cerrobend rods. Each of images were compared a difference of HU in ROIs. And also, 1 case of patient's original CT image applied O-MAR and density corrected CT were evaluated for dose distributions with SNC Patient(Sun Nuclear Co., USA). Results : In cases of head&neck phantom, the difference of dose distibution is appeared 99.8% gamma passing rate(criteria 2 mm / 2%) between original and CT images applied O-MAR. And 98.5% appeared in patient case, among original CT, O-MAR and density corrected CT. The difference of total dose distribution is less than 2% that appeared both phantom and patient case study. Though the dose deviations are little, there are still matters to discuss that the dose deviations are concentrated so locally. In this study, The quality of all images applied O-MAR was improved. Unexpectedly, Increase of max. HU was founded in air cavity of the O-MAR images compare to cavity of the original images and wrong corrections were appeared, too. Conclusion : The result of study assuming restrained case of O-MAR adapted to near skin and low density area, it appeared image distortion and artifact correction simultaneously. In O-MAR CT, air cavity area even turned tissue HU by wrong correction was founded, too. Consequentially, It seems O-MAR algorithm is not perfect to distinguish air cavity and photon starvation artifact. Nevertheless, the differences of HU and dose distribution are not a huge that is not suitable for clinical use. And there are more advantages in clinic for improved quality of CT images and DRRs, precision of contouring OARs or tumors and correcting artifact area. So original and O-MAR CT must be used together in clinic for more accurate treatment plan.

• The korean journal of orthodontics
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• v.36 no.6
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• pp.412-421
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• 2006

Objective: The result of finite element analysis depends on material properties, structural expression, density of element, and boundar or loading conditions. To represent proper elastic behavior, a finite element model was made using Hounsfield unit (HU) values in CT images. Methods: A 13 year 6 month old male was used as the subject. A 3 dimensional visualizing program, Mimics, was used to build a 3D object from the DICOM file which was acquired from the CT images. Model 1 was established by giving 24 material properties according to HU. Model 2 was constructed by the conventional method which provides 2 material properties. Protraction force of 500g was applied at a 45 degree downward angle from Frankfort horizontal (FH) plane. Results: Model 1 showed a more flexible response on the first premolar region which had more forward and downward movement of the maxillary anterior segment. Maxilla was bent on the sagittal plane and frontal plane. Model 2 revealed less movement in all directions. It moved downward on the anterior part and upward on the posterior part, which is clockwise rotation of the maxilla. Conclusion: These results signify that different outcomes of finite element analysis can occur according to the given material properties and it is recommended to use HU values for more accurate results.

• Progress in Medical Physics
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• v.25 no.4
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• pp.271-280
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• 2014

Recently, digital breast tomosynthesis (DBT) has been investigated to overcome the limitation of conventional mammography for overlapping anatomical structures and high patient dose with cone-beam computed tomography (CBCT). However incomplete sampling due to limited angle leads to interference on the neighboring slices. Many studies have investigated to reduce artifacts such as interference. Moreover, appropriate filters for tomosynthesis have been researched to solve artifacts resulted from incomplete sampling. The primary purpose of this study is finding appropriate filter scheme with FBP reconstruction for DBT system to reduce artifacts. In this study, we investigated characteristics of various filter schemes with simulation and prototype digital breast tomosynthesis under same acquisition parameters and conditions. We evaluated artifacts and noise with profiles and COV (coefficinet of variation) to study characteristic of filter. As a result, the noise with parameter 0.25 of Spectral filter reduced by 10% in comparison to that with only Ramp-lak filter. Because unbalance of information reduced with decreasing B of Slice thickness filter, artifacts caused by incomplete sampling reduced. In conclusion, we confirmed basic characteristics of filter operations and improvement of image quality by appropriate filter scheme. The results of this study can be utilized as base in research and development of DBT system by providing information that is about noise and artifacts depend on various filter schemes.

• The Journal of Korean Society for Radiation Therapy
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• v.16 no.2
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• pp.19-24
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• 2004

Introduction : The Vaginal, the urethra, the vulva and anal cancer avoid the many dose to femur head and the additional treatment is necessary in inguinal LN. The partial transmission block to use inguinal LN addition there is to a method which it treats and produce partial transmission block a method and the MLC which to it analyzes. Material & Methode : The Inguinal the LN treatment patient partial transmission it used block and the MLC in the object and with solid water phantom with the patient it reappeared the same depth. In order to analyze the error of the junction the EDR2 (Extended dose range, the Kodak and the U.S) it used the Film and it got film scanner it got the beam profile. The partial transmission block and the MLC bias characteristic, accuracy and stability of production for, it shared at hour and comparison it analyzed. Result : The partial the transmission block compares in the MLC and the block production is difficult and production hour also above 1 hours. The custom the block the place where it revises the error of the junction is a difficult problem. If use of the MLC the fabrication will be break and only the periodical calibration of the MLC it will do and it will be able to use easily. Conclusion : The Inguinal there is to LN treatment and partial transmission block and the MLC there is efficiency of each one but there is a place where the junction of block for partial transmission block the production hour is caught long and it fixes and a point where the control of the block is difficult. like this problem it transfers with the MLC and if it treats, it means the effective treatment will be possible.

• The Korean Journal of Nuclear Medicine Technology
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• v.23 no.1
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• pp.59-63
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• 2019

Purpose The motion due to respiration of patients undergoing PET/CT is a cause of artifacts in image and registration error between PET and CT images. The degree of displacement and distortion for tumor, which affects the measurement of Standard Uptake Value (SUV) and lesion volume, is especially higher for tumors that is small or located at the base of lungs. The purpose of this study was to evaluate the usefulness of prone position in the correction of image distortion due to respiration of patients in PET/CT. Materials and Methods The imaging equipment used in this study was PET/CT Discovery 600 (GE Healthcare, MI, USA). 20 patients whose lesions were identified in the middle and lower lungs from May to August 2018 were enrolled in this study. After acquiring whole body image in the supine position, additional images of the lesion area were obtained in the prone position with the same conditions. SUVmax, SUVmean, and volume of the lesion were measured for each image, and the displacement of the lesion on PET and CT images were measured, compared, and analyzed. Results The SUVmax, SUVmean, and volume, and displacement of the lesion were $4.72{\pm}2.04$, $3.10{\pm}1.38$, $4.68{\pm}3.20$, and $4.64{\pm}1.88$, respectively for image acquired in the supine position and $5.89{\pm}2.42$, $3.97{\pm}1.65$, $2.13{\pm}1.09$, and $2.24{\pm}0.84$, respectively for image acquired in the prone position, indicating that, for all the lesions imaged, SUVmax and SUVmean were higher and volume and displacement were smaller in the images acquired in prone position compared to those acquired in supine one(p<0.05). Conclusion These results showed that the prone position PET/CT imaging improves the quality of the image by increasing the SUV of the lesion and reducing the respiratory artifacts caused by registration error between PET and CT images. It is considered that the PET/CT imaging in the prone position is helpful in the diagnosis of the disease as an economical and efficient methods that correct registration error for the lesions in basal lung and reduce artifacts.

• Journal of the korean academy of Pediatric Dentistry
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• v.48 no.4
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• pp.467-475
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• 2021

The purpose of this study was to compare the effect of sodium fluoride(NaF) varnish and potassium iodide(KI) on remineralization efficacy of silver diamine fluoride(SDF) by measuring microhardness and evaluating surface morphology by scanning electron microscope(SEM). Artificial caries lesions were induced on extracted primary molars and vickers microhardness was measured. Specimens were randomly separated into 4 groups for treatment. The specimens in group I were treated with SDF, group II with NaF varnish after SDF, group III with KI after SDF and group IV with distilled water. After 8 days of pH cycling, vickers microhardness was measured and difference before and after treatment was calculated. For SEM, 2 samples were evaluated respectively after enamel polishing, lesion formation and after pH cycling. Group III showed highest increase in microhardness. Group I showed higher increase in microhardness than Group II but without statistical difference. Group IV showed lowest increase in microhardness value among 4 groups. On SEM image, group I, II and III showed smoother and less irregular surface compared to group IV. Amorphous crystal pellicles were observed in group III. In conclusion, SDF, SDF and NaF, SDF and KI groups showed smoother surface and increase in microhardness suggesting the possibility that remineralization effect might take place in oral conditions. In addition, in limited conditions of this study, applying NaF varnish after SDF did not increase the remineralization efficacy of SDF while KI significantly increased the remineralization efficacy of SDF. However, additional study considering various conditions that might affect demineralization and remineralization in clinical situations need to be conducted.

• Journal of the Korean Orthopaedic Association
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• v.55 no.5
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• pp.405-410
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• 2020

Purpose: Pedicle screw insertion has been traditionally used as a surgical treatment for degenerative lumbar spine disease. As an alternative, the cortical-bone trajectory screw allows less invasive posterior lumbar fixation and excellent mechanical stability, as reported in several biomechanical studies. This study evaluated the clinical and radiological results of a case of early failure of cortical-bone screw fixation in posterior fixation and union after posterior decompression. Materials and Methods: This study examined 311 patients who underwent surgical treatment from 2013 to 2018 using cortical orbital screws as an alternative to traditional pedicle screw fixation for degenerative spinal stenosis and anterior spine dislocation of the lumbar spine. Early fixation failure after surgery was defined as fixation failure, such as loosening, pull-out, and breakage of the screw on computed tomography (CT) and radiographs at a follow-up of six months. Results: Early fixation failure occurred in 46 out of 311 cases (14.8%), screw loosening in 46 cases (14.8%), pull-out in 12 cases (3.9%), and breakage in four cases (1.3%). An analysis of the site where the fixation failure occurred revealed the following, L1 in seven cases (15.2%), L2 in three cases (6.5%), L3 in four cases (8.7%), L4 in four cases (8.7%), L5 in four cases (8.7%), and S1 in 24 cases (52.2%). Among the distal cortical bone screws, fixation failures such as loosening, pull-out, and breakage occurred mainly in the S1 screws. Conclusion: Cortical-bone trajectory screw fixation may be an alternative with comparable clinical outcomes or fewer complications compared to conventional pedicle screw fixation. On the other hand, in case with osteoporosis and no anterior support structure particularly at L5-S1 fusion sites were observed to have result of premature fixation failures such as relaxation, pull-out, and breakage.

• Sleep Medicine and Psychophysiology
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• v.28 no.2
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• pp.78-85
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• 2021

Objectives: When elderly patients show depressive symptoms, discrimination between depressive disorder and prodromal phase of Alzheimer's disease is important. We tested whether a quantitative electroencephalogram (qEEG) marker was associated with cerebral amyloid-β (Aβ) deposition in older adults with depression. Methods: Non-demented older individuals (≥ 55years) diagnosed with depression were included in the analyses (n = 63; 76.2% female; mean age ± standard deviation 73.7 ± 6.87 years). The participants were divided into Aβ+ (n = 32) and Aβ- (n = 31) groups based on amyloid PET assessment. EEG was recorded during the 7min eye-closed (EC) phase and 3min eye-open (EO) phase, and all EEG data were analyzed using Fourier transform spectral analysis. We tested interaction effects among Aβ positivity, condition (EC vs. EO), laterality (left, midline, or right), and polarity (frontal, central, or posterior) for EEG alpha band power. Then, the EC-to-EO alpha reactivity index (ARI) was examined as a neurophysiological marker for predicting Aβ+ in depressed older adults. Results: The mean power spectral density of the alpha band in EO phase showed a significant difference between the Aβ+ and Aβ- groups (F = 6.258, p = 0.015). A significant 3-way interaction was observed among Aβ positivity, condition, and laterality on alpha-band power after adjusting for age, sex, educational years, global cognitive function, medication use, and white matter hyperintensities on MRI (F = 3.720, p = 0.030). However, post-hoc analyses showed no significant difference in ARI according to Aβ status in any regions of interest. Conclusion: Among older adults with depression, increased power in EO phase alpha band was associated with Aβ positivity. However, EC-to-EO ARI was not confirmed as a predictor for Aβ+ in depressed older individuals. Future studies with larger samples are needed to confirm our results.

• Journal of the Korean Society of Radiology
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• v.82 no.5
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• pp.1196-1206
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• 2021

Purpose To construct a standard dataset of contrast-enhanced CT images of liver tumors to test the performance and safety of artificial intelligence (AI)-based algorithms for clinical decision support systems (CDSSs). Materials and Methods A consensus group of medical experts in gastrointestinal radiology from four national tertiary institutions discussed the conditions to be included in a standard dataset. Seventy-five cases of hepatocellular carcinoma, 75 cases of metastasis, and 30-50 cases of benign lesions were retrieved from each institution, and the final dataset consisted of 300 cases of hepatocellular carcinoma, 300 cases of metastasis, and 183 cases of benign lesions. Only pathologically confirmed cases of hepatocellular carcinomas and metastases were enrolled. The medical experts retrieved the medical records of the patients and manually labeled the CT images. The CT images were saved as Digital Imaging and Communications in Medicine (DICOM) files. Results The medical experts in gastrointestinal radiology constructed the standard dataset of contrast-enhanced CT images for 783 cases of liver tumors. The performance and safety of the AI algorithm can be evaluated by calculating the sensitivity and specificity for detecting and characterizing the lesions. Conclusion The constructed standard dataset can be utilized for evaluating the machine-learning-based AI algorithm for CDSS.