• Progress in Medical Physics
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• v.16 no.4
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• pp.161-165
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• 2005

The CT number corresponds to electron density and its influence on dose calculation was studied. Five kinds of CT scanners were used to obtain Images of electron density calibration phantom (Gammex RMI 467), Then the differences between CT numbers for each scanners were ${\pm}2\%$ In homogeneous medium and $9.5\%$ in high density medium. In order to Investigate the influence of CT number to dose calculation, patients' thoracic CT images were analyzed. The maximum dose difference was $0.48\%$ for each organ. It acquired the phantom Images inserted high density material in the water phantom. Comparing the doses calculated with CT Images from each CT scanner, the maximum dose difference was $2.1\%$ in 20 cm in depth. The exact density to CT number conversion according to CT scanner is required to minimize the uncertainty of dose depends on CT number Especially the each hospital with various CT scanners has to discriminate CT numbers for each CT scanner. Moreover a periodic quality assurance is required for reproducibility of CT number.

• Journal of the Korean Society of Radiology
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• v.16 no.3
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• pp.289-294
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• 2022

In this study, the accuracy and usefulness of volume measurement were investigated as a phantom experiment using CT and USG scan data and a clinical trial using patient scan data. As a result, there was no significant difference between the volume of the actual round phantom of various volumes for both the CT and ultrasound devices (p>0.05). As a result of statistical analysis, it was analyzed that there was no significant difference (p>0.05). Clinical application of this result requires more clinical trials, but if a CT or ultrasound device is selected and applied in consideration of patient radiation exposure, the examiner's scanning technology, and CT reconstruction experience, the basic data in terms of the usefulness of volume measurement using CT scan image is considered to have application value.

• Journal of radiological science and technology
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• v.30 no.2
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• pp.129-138
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• 2007

The Purpose of this study is to suggest the basic data for making good quality image and maintaining equipment homeostasis by accepting image quality evaluation and radiation dose evaluation in Multi-detector CT. In this study we surveyed 14 CT equipments in Seoul. The results obtained were as follows ; CT number was $0.56{\pm}0.70\;HU$. Noise was $0.39{\pm}0.09\;HU$. Uniformity was $1.08{\pm}0.52\;HU$. High contrast resolution was $0.48{\pm}0.05\;mm$ and low contrast resolution was $3.65{\pm}1.16\;mm$. For CTDI, the central part and the peripheral part of head phantom were $43.2{\pm}15.4\;mGy$ and $45.6{\pm}17.5\;mGy$, respectively. For body phantom, the central part and the peripheral part of head phantom were $13.5{\pm}4.5$ and $29.2{\pm}10.2\;mGy$, respectively. CTDIw was $44.8{\pm}16.8\;mGy$ and CTDIw/100 mAs was $18.8{\pm}5.3\;mGy$ using head phantom. CTDIW was $24.0{\pm}8.3\;mGy$ and CTDIw/100 mAs was $10.1{\pm}2.5\;mGy$ using body phantom. Therefore, CT number, noise, high contrast resolution, low contrast resolution, CTDI, CTDIw and CTDIw/100 mAs of MDCT were showed excellently in all equipments.

• Progress in Medical Physics
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• v.24 no.4
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• pp.205-212
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• 2013

Recent developments of image guided radiation therapy (IGRT), especially the On Board Imaging (OBI) system and the cone beam CT (CBCT), enable the radiation treatment more accurate and reliable. IGRT is widely used in the radiation therapy as a standard of care. Use of IGRT is even expected to increase in the near future. IGRT is only beneficial to patients when it is used with proper considerations of safety and appropriateness of the techniques. Institutional procedure should be developed based on the clinical need and the deep understanding of the system before applying the new technique to the clinic. Comprehensive QA program should be established before to the clinic and imaging dose should be considered when preparing the departmental practice guidelines for IGRT.

• Journal of Radiation Protection and Research
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• v.30 no.1
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• pp.9-15
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• 2005

This study was conducted to investigate the patient exposure dose during a CT examination and the present position in utilization of the CT equipments. To this end Questionnaire were sent out to 278 medical facilities registered at Korea Hospital Association and replies of 161 medical facilities were analyzed. The results were as follows ; 1) The distribution of CT examination was. Brain 40.7%, Abdomen 27.8%, Chest 15.7%, Spine 4.8%, Pelvis 4.1%, PNS 3.2%, Facial bone 2.5% and Extremity 1.1% respectively. 2) The statistics for dose index according to each part of examination were Brain 38.0mGy, Abdomen 12.0mGy for adults : Brain 13.6mGy, Abdomen 6.2mGy for infant. Our surveyed dose index appeared lower than the IAEA recommends. 3) Most medical facilities have selected the parameters for radiographic exposure in the range of $100{\sim}120kVp,\;100{\sim}250mA\;and\;1{\sim}2$ seconds.

• Journal of Biomedical Engineering Research
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• v.25 no.2
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• pp.97-102
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• 2004

We developed an x-ray cone-beam micro computed tomography (micro-CT) system for small-animal imaging. The micro-CT system consists of a 2-D flat-panel x-ray detector with a field-of-view (FOV) of 120${\times}$120 mm2, a micro-focus x-ray source, a scan controller and a parallel image reconstruction system. Imaging performances of the micro-CT system have been evaluated in terms of contrast and spatial resolution. The minimum resolvable contrast has been found to be less than 36 CT numbers at the dose of 95 mGy and the spatial resolution about 14 lp/mm. As small animal imaging results, we present high resolution 3-D images of rat organs including a femur, a heart and vessels. We expected that the developed micro-CT system can be greatly used in biomedical studies using small animals.

• Journal of the Korean Society of Radiology
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• v.15 no.3
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• pp.293-299
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• 2021

In order to reduce the irresistible radiation exposure of patients who perform periodic examinations using a CT among various scan parameters a method to reduce patient dose was investigated through changes in the tube voltage close to X-ray penetrating power. As a result of the experiment 100 kVp was applied instead of 120 kVp which is commonly used in clinical practice and CTDI decreased by about 41% during scan. In addition the degree of change in image quality was measured as 1046.1±3.7 HU for CT value and 71.4±7.9 for Pixel value and statistical analysis showed no significant difference (0.05

• Radiation Oncology Journal
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• v.26 no.2
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• pp.118-125
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• 2008

Purpose: On-line image guided radiation therapy(on-line IGRT) and(kV X-ray images or cone beam CT images) were obtained by an on-board imager(OBI) and cone beam CT(CBCT), respectively. The images were then compared with simulated images to evaluate the patient's setup and correct for deviations. The setup deviations between the simulated images(kV or CBCT images), were computed from 2D/2D match or 3D/3D match programs, respectively. We then investigated the correctness of the calculated deviations. Materials and Methods: After the simulation and treatment planning for the RANDO phantom, the phantom was positioned on the treatment table. The phantom setup process was performed with side wall lasers which standardized treatment setup of the phantom with the simulated images, after the establishment of tolerance limits for laser line thickness. After a known translation or rotation angle was applied to the phantom, the kV X-ray images and CBCT images were obtained. Next, 2D/2D match and 3D/3D match with simulation CT images were taken. Lastly, the results were analyzed for accuracy of positional correction. Results: In the case of the 2D/2D match using kV X-ray and simulation images, a setup correction within $0.06^{\circ}$ for rotation only, 1.8 mm for translation only, and 2.1 mm and $0.3^{\circ}$ for both rotation and translation, respectively, was possible. As for the 3D/3D match using CBCT images, a correction within $0.03^{\circ}$ for rotation only, 0.16 mm for translation only, and 1.5 mm for translation and $0.0^{\circ}$ for rotation, respectively, was possible. Conclusion: The use of OBI or CBCT for the on-line IGRT provides the ability to exactly reproduce the simulated images in the setup of a patient in the treatment room. The fast detection and correction of a patient's positional error is possible in two dimensions via kV X-ray images from OBI and in three dimensions via CBCT with a higher accuracy. Consequently, the on-line IGRT represents a promising and reliable treatment procedure.

• The Journal of Korean Society for Radiation Therapy
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• v.22 no.1
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• pp.1-10
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• 2010

Purpose: The effect of artifact was analyzed, which occurs from fiducial marker during the liver Image Guided Radiation Therapy (IGRT) using the fiducial marker. Materials and Methods: The size of artifact of fixed fiducial marker and length of mobile fiducial marker locus were measured using the On-Board Imager system (OBI) and CT simulator, and 2D-2D matching and 3D-3D matching were carried out, respectively, and at this time, the coordinates transition value of couch was analyzed. Results: The measurement of fixed fiducial marker artifact size indicated CT 4.90, 8.10, 12.90, 19.70 mm and OBI 5.60, 10.60, 14.70, 29.40 mm based on the reference CT slice thickness of 1.25, 2.50, 5.00, and 10.00 mm. Meanwhile, the measurement of mobile fiducial marker locus length indicated CT 42.00, 43.10, 46.50 mm, and OBI 43.40, 46.00, 49.30 mm. The coordinates transition of 1.00, 2.00, and 8.00 mm occurred between 2D-2D matching and 3D-3D matching. Conclusion: It was confirmed that the therapy error increased during IGRT due to the influence of artifact when CT slice thickness increased. Thus, it may be desirable to acquire the image less than 2.50 mm in slice thickness when IGRT is implemented using the fiducial marker.

• Journal of the Korean Society of Radiology
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• v.15 no.3
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• pp.301-306
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• 2021

The use of tin filters as a way to reduce the medical radiation in computed tomography (CT). However, due to the changed X-ray spectrum with the use of tin filters, disease diagnosis could be affected because it appears as images of different impressions from previous images. Therefore, this study evaluates the changes in images when using tin filter and high pitch in chest low-dose CT. In this study, images were acquired in groups of three for comparison. Group 1 did not apply to tin filter, and used the existing pitch 0.8. Group 2 used a tin filter, pitch 0.8, Group 3 used a tin filter, and pitch 2.5. To compare the image quality, the natural image quality evaluator (NIQE) and the blind/referenceless image quality evaluator (BRISQUE) were used among the blind quality evaluation factors depended on a no-reference basis. As a result, the NIQE values were low in the order of Group 1, Group 3, and Group 2. BRISQUE values were low in the order of Group 3, Group 2 and Group 1. This study confirms the superiority of images of tin filter and high pitch techniques in chest low-dose CT, which is considered to be a fundamental study for acquiring accurate images of patients with difficult breathing control.