• Journal of the Korean Society of Radiology
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• v.14 no.4
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• pp.345-351
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• 2020

In this study, a dose assessment was conducted on the exposure dose of thyroid, breast and sexual gland using a personal dosimeter in multiple CT examinations currently being conducted in health examinations. The dose assessment was measured by attaching TLD and EPD to the locations of the thyroid, breast and sexual gland during CT examinations of Brain, Brain + C-S, Brain + Low lung, Brain + L-S among CT items. The generated dose of equipment, CTDI_vol and DLP, was measured. The study found that effective doses were rated 41.7% higher for thyroid TLD in Brain + C-S CT examinations than for the general public, 156% higher for EPD, 10% for breast EPD in Brain + Low Lung CT examinations, 124.4% higher for reproductive TLD and 339.8% higher for Brain + L-S CT examinations. The CTDI_vol and DLP analysis results showed that C-S CTDI_vol values were higher than the diagnostic reference levels at 0.6%, Low Lung CTDI_vol values at 5.7%, DLP values at 11.8% and L-S CTDIvol values at 1.2%. In order to reduce the exposure dose of patients, indiscriminate examination is reduced and dose limit setting is needed in health examination.

• Journal of the Korean Society of Radiology
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• v.8 no.2
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• pp.75-79
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• 2014

The aim of this retrospective research was to investigate the influence of the patient's arm position on radiation dose and scanning during CT. Chest CT image created image degradation, artifact and overdose to the patient due to the difference of the chest thickness. Therefore, the patient's arm should up position during the CT chest examination. In 2012, 1,642 patients underwent chest CT examination in Seoul K hospital. 118 chest CT examination performed hands down position. The average DLP value of the CT chest arm up examination was 275 $mGy{\cdot}cm$. The average DLP value of the CT chest arm down examination was 312.46 $mGy{\cdot}cm$. In the retrospective study with same patient, The average DLP value of the CT chest examination arm up vigorously was 267.5 $mGy{\cdot}cm$. The average DLP value of the CT chest arm down examination was 307.5 $mGy{\cdot}cm$. Chest CT scan without raising arm created linear artifact due to the lack of X-ray photons which is the thickest part of the human body of shoulder area. In conclusion, arm positioning patients' arms above the shoulders at CT of the chest increases image quality and substantially reduces effective radiation dose.

• Progress in Medical Physics
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• v.20 no.3
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• pp.145-151
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• 2009

This study aims to evaluate CT (Computed Tomography) characteristics through the estimation of HU (Hounsfield Unit) and the corresponding variations using coefficient of variation values for various materials as a function of physical factor. HU values for various materials with varying densities as a function of physical factor were measured using MDCT (Siemens SOMATOM Sensation 4, Germany). The results showed that the HU values were decreased and increased as a function of kVp and material density, respectively. Especially, the HU values for bone and iodine at 140 kVp were 32% and 42% smaller than those at 80 kVp, respectively. In case of iodine, the HU values also decreased and increased as a function of kVp and concentration, respectively. While the HU values were fixed as a function of mAs. The decreased ratio of HU values between 80 keV and 140 keV was different at various concentration and maximum difference was shown as 1.73 at 3% concentration. These results indicated that it may be possible to separate composition of materials, e.g. iodine and bone, using single source CT. The results showed that dual energy techniques using single source CT can be applied to material separation and expand CT imaging techniques to other practical applications.

• The Korean Journal of Nuclear Medicine Technology
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• v.15 no.2
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• pp.53-59
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• 2011

Purpose: To evaluate the dosimetry and image of very low does CT attenuation correction for phantom using pediatric PET/CT. Materials and methods: three PET / CT scanners (Discovery STe, BiographTruepoint 40, Discovery 600) as a child-size acrylic phantom and ion chamber dosimeter (Unfous Xi CT, Sweden) using a CT image acquisition parameters (10, 20, 40, 80, 100, 160 mA; 80, 100, 120, 140 kVp) by varying the depth dose and evaluate $CTDI_{vol}$ value. And each attenuation corrected PET/CT images used NEMA PET Phantom$^{TM}$ (NU2-1994) was evaluated by SUV. Results: Abdominal diagnosis CT dose in general pediatric (about 10 ages) parameter (100 kVp, 100 mA) than very low dose CT parameter (80 kVp, 10 mA) at the depth dose was reduced approximately 92%, $CTDI_{vol}$ was reduced to about 88%. Each CT attenuation corrected parameters PET images showed no change in the value of SUV. Conclusion: for pediatric patients, PET/CT scan can be obtained with very low dose attenuation correction CT (80 kVp, 10 mA), and such attenuation correction CT dose was reduced 100 fold than diagnosis CT dose. PET / CT scan used very low dose CT attenuation correction in pediatric patients can be helpful in reducing radiation dose.

• Journal of the Korean Society of Radiology
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• v.17 no.6
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• pp.843-849
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• 2023

This study attempted to determine the optimal algorithm after quantitatively analyzing noise, SNR, and CNR measurements by reconstructing four algorithms (Standard, Soft, Bone, and Detail) from head and neck CT images of patients who underwent implant surgery. As an analysis method, pixel values were calculated through the region of interest in the reconstructed image using the Image J program. For noise, SNR, and CNR, the region of interest was measured at the location of the pharynx, masseter muscle, and parotid gland in the image, and the mean and SD values were obtained. The values of SNR and CNR were calculated based on the given formula. As a result, the standard algorithm showed the lowest noise and the highest SNR. CNR was highest in the Soft algorithm, but showed no significant difference from the Standard algorithm. Therefore, it is believed that the Standard algorithm is the optimal algorithm for examining patients wearing intraoral implants in head and neck CT examinations. We hope that the data from this study will be used as basic data for image evaluation in head and neck CT examinations, and that the quality of images will be further improved through various algorithm changes. It is believed that this will be an opportunity to do so.

• Progress in Medical Physics
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• v.25 no.1
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• pp.53-63
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• 2014

The objective of this study is to investigate the difference of ITV lengths and ITVs between 4DCT and Slow-CT images according to respiratory patterns using a respiratory motion phantom. The respiratory periods 1~4 s and target motion 1~3 cm were applied on each respiratory pattern. 4DCT and Slow-CT images were acquired for 3 times. 4DCT and Slow-CT ITVs were measured with contouring the target in the Eclipse RTP system. The measured ITV lenghts and ITVs in 4DCT and Slow-CT images were compared to the known values. For the ITV lengths and ITVs in the 4DCT, the difference of them were reduced as the respiratory period is longer and target motion is shorter. For the Slow-CT, there was same tendency with change in 4DCT ITV lengths and ITVs about target motion. However, the difference of ITV lengths and ITVs for the respiratory periods were the lowest in respiratory period 1 second and different slightly within respiratory period 2-4 seconds. According to the respiratory patterns, pattern A had the highest reproducibility. Pattern B, C and D were showed the difference similar to each other. However, for pattern E, the reproducibility was the lowest compared with other four patterns. The difference of ITV lengths and ITVs between Slow-CT and 4DCT was increased by increasing the respiratory periods and target motion for all respiratory patterns. When the difference of Slow-CT ITV lengths and ITVs were compared with that of 4DCT ITV lengths and ITVs, Slow-CT ITV lengths and ITVs were approximately 22 % smaller than 4DCT, and the representations of target were different in each pattern. In case of pattern A, B and C, length difference was 3 mm at S (superior) and I (inferior) direction, and the length difference of pattern D was 1.45 cm at only "I" direction whereas the length difference of pattern E was 5 mm longer in "S" direction than "I" direction. Therefore, the margin in SI directions should be determined by considering the respiratory patterns when the margin of Slow-CT is compensated for 4DCT ITV lengths. Afterward, we think that the result of this study will be useful to analyze the ITV lengths and ITVs from the CT images on the basis of the patient respiratory signals.

• Journal of the Korean Society of Radiology
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• v.83 no.6
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• pp.1312-1326
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• 2022

Purpose To investigate the added value of right down decubitus (RDD) CT when determining adjacent organ invasion in cases of advanced gastric cancer (AGC). Materials and Methods A total of 728 patients with pathologically confirmed T4a (pT4a), surgically confirmed T4b (sT4b), or pathologically confirmed T4b (pT4b) AGCs who underwent dedicated stomach-protocol CT, including imaging of the left posterior oblique (LPO) and RDD positions, were included in this study. Two radiologists scored the T stage of AGCs using a 5-point scale on LPO CT with and without RDD CT at 2-week intervals and recorded the presence of "sliding sign" in the tumors and adjacent organs and compared its incidence of appearance. Results A total of 564 patients (77.4%) were diagnosed with pT4a, whereas 65 (8.9%) and 99 (13.6%) patients were diagnosed with pT4b and sT4b, respectively. When RDD CT was performed additionally, both reviewers deemed that the area under the curve (AUC) for differentiating T4b from T4a increased (p < 0.001). According to both reviewers, the AUC for differentiating T4b with pancreatic invasion from T4a increased in the subgroup analysis (p < 0.050). Interobserver agreement improved from fair to moderate (weighted kappa value, 0.296-0.444). Conclusion RDD CT provides additional value compared to LPO CT images alone for determining adjacent organ invasion in patients with AGC due to their increased AUC values and improved interobserver agreement.

• The korean journal of orthodontics
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• v.40 no.1
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• pp.6-15
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• 2010

Objective: The aim of this study is to find the most helpful midsagittal reference plane for diagnosis in PA cephalometry compared with 3D CT. Methods: The subjects consisted of 25 adults who showed no facial asymmetry by gross inspection. 3D CT and posteroanterior cephalogram of the subjects were taken. To find the most helpful midsagittal reference plane in PA cephalometry, we considered five kinds of midsagittal planes from which the distances to five landmarks were measured and compared the result with that of 3D CT. The midsagittal plane for 3D CT was determined by the landmarks Nasion, Sella and Basion. Results: PA measurements using the midsagittal reference plane on a perpendicular plane lying through the midpoint of the right and left latero-orbitales was closest to those of 3D CT. Conclusions: It was considered that latero-orbitale perpendicular could be used as the helpful midsagittal reference plane to assess facial asymmetry in PA cephalometry.

• The Korean Journal of Nuclear Medicine Technology
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• v.22 no.1
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• pp.35-42
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• 2018

Purpose Standardized uptake value(SUV) has been widely used as a quantitative metric of uptake in PET/CT for diagnosis of malignant tumors and evaluation of tumor therapy response. However, the SUV depends on various factor including PET/CT scanner specifications and reconstruction parameter. The purpose of this study is to validate a EQ PET to evaluate SUV across different PET/CT systems. Materials and Methods First, NEMA IEC body phantom data were used to calculate the EQ filter for OSEM3D with PSF and TOF reconstruction from three different PET/CT systems in order to obtain EARL compliant recovery coefficients of each spheres. The Biograph true point 40 PET/CT images were reconstructed with a OSEM3D+PSF reconstruction, images of the Biograph mCT 40 and Biograph mCT 64 PET/CT scanners were reconstructed with a OSEM3D+PSF, OSEM3D+TOF, OSEM3D+PSF+TOF. Post reconstructions, the proprietary EQ filter was applied to the reconstruction data. Recovery coefficient can be estimated by ratio of measured to true activity concentration for spheres of different volume and coefficient variability(CV) value of RC for each sphere was compared. For clinical study, we compared SUVmax applying different reconstruction algorithms in FDG PET images of 61 patients with lung cancer using Biograph mCT 40 PET/CT scanner. Results For the phantom studied, the mean values of CV for OSEM3D, OSEM3D+PSF, OSEM3D+TOF and OSEM3D+PSF+TOF reconstructions were 0.05, 0.04, 0.04 and 0.03 respectively for RC. Application of the proprietary EQ filter, the mean values of CV for OSEM3D, OSEM3D+PSF, OSEM3D+TOF and OSEM3D+PSF+TOF reconstructions were 0.04, 0.03, 0.03 and 0.02 respectively for RC. Clinical study, there were no statistical significance of the difference applying EQ PET on SUVmax of 61 patients FDG PET image. (p=1.000) Conclusion This study indicates that CV values of RC in phantom were decreased after applying EQ PET for different PET/CT system and The EQ PET reduced reconstruction dependent variation in SUVs for 61 lung cancer patients, Therefore, EQ PET will be expected to provide accurate quantification when the patient is scanned on different PET/CT system.

• Journal of the Korean Society of Radiology
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• v.14 no.5
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• pp.669-676
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• 2020

The purpose of this study was to analyze the changes in the values of Hounsfield Unit (HU) according to the changes in monoenergy (keV) and dilution ratio of the contrast agent, using the spectral CT. Spectral CT was used as the testing device, while 20 cc syringe phantom was used to set a total of six dilution ratios of the contrast agent: 8:2, 7:3, 6:4, 5:5, 4:6, and 3:7. Here, the non-ionic iodine solution (350 mg/ml) was used as a contrast agent. The syringe axial image was reconstructed by adjusting the obtained data on nine MonoE levels; 40 keV, 45 keV, 50 keV, 55 keV, 60 keV, 65 keV, 70 keV, 75 keV, and 80 keV. The HU values were measured at the three points of the reconstructed syringe axial image. The measurements were taken 1,620 times in total. In the analysis of the HU values according to the changes in keV and dilution ratio of the contrast agent, the highest and lowest HU values were obtained from dilution ratio 8:2 and dilution ratio 3:7, respectively, across every MonoE in the comparison of HU according to dilution ratio per MonoE (p<0.05), while the highest and lowest HU values were obtained from 40 keV and 80 keV, respectively, across all dilution ratios in the comparison of HU according to MonoE per dilution ratio (p<0.05). For the correlation per each parameter, a negative correlation of -15.014 ± 0.298 was found for HU per keV (R²=0.519) and a negative correlation of -61.372 ± 3.608 was found for HU per dilution ratio (R²=0.152) (p<0.05). To conclude, an increase in keV or dilution ratio of the contrast agent was shown to decrease the HU, and the findings in this study are anticipated to serve as the basic data in the research of HU-related parameters in Spectral CT.