• Title, Summary, Keyword: CT number

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Evaluation of CT Number Difference between Radiation Therapeutic CT Simulator and Conventional CT (방사선치료용 CT simulator와 진단용 CT의 구조 차이에 의한 CT number의 비교 평가)

  • Seo, Jeong Min;Rhim, Jae Dong;Kim, Chan Hyeong
    • Journal of the Korea Safety Management & Science
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    • v.17 no.3
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    • pp.215-219
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    • 2015
  • The purpose in this study is to investigate CT number difference between conventional CT and CT simulator. It shows good correlation in CT number on the muscle, bone, and air. However, in the liver, lungs and water, the low correlation was detected. This result can become the good index for the direction of the distribution of dose difference research between CT equipment for using the computerized radiation therapy planning system.

The Analysis of CT Number Rate of Change of Applying The Iterative Metallic Artifact Reduction Algorithm for CT Reconstruction Image (Iterative Metallic Artifact Reduction 알고리즘 적용 CT 재구성영상의 CT Number 변화율 분석)

  • Kim, Hyeonju;Yoon, Joon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.7
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    • pp.84-91
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    • 2017
  • This study was performed using Somatom Definition Flash (Siemens, Enlarge, Germany) and GE 64-MDCT (Discovery 750 HD, GE HEALTHCARE, Milwaukee, USA.) using high-density medical materials that (are indispensable to?) computed tomography. We analyzed quantitatively the rate of change of the CT number of the CT reconstruction images by means of the IMAR and MAR algorithms using the phantom images acquired after scanning and previously captured raw data images. As a result, it was shown that the IMAR and MAR algorithms provided if ferent phantom images in the case of all medical high-density materials (p <0.05). The black streak artifacts were analyzed using the MAR and IMAR algorithms to determine if they corresponded to stainless steel materials (p>0.05). Also, it was found that the application of the IMAR algorithm affects the attenuation deviation, because there is a change in the image CT number compared to that before. The results suggest that, in the future, after the implant procedure, it would be useful to observe the surgical site and surrounding tissues during follow-up CT scans.

The Effect of the CT Number for Each CT on Dose Calculation (CT 기종에 따른 CT 수의 변화가 선량계산에 미치는 영향)

  • Cho Kwang Hwan;Lee Suk;Cho Sam Ju;Lim Sangwook;Huh Hyun Do;Min Chul Kee;Cho Byung-Chul;Kim Yong Ho;Choi Doo Ho;Kim Eun Seog;Kwon Soo Il
    • 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.

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The Dependence of CT Scanning Parameters on CT Number to Physical Density Conversion for CT Image Based Radiation Treatment Planning System (CT 영상기반 방사선치료계획시스템을 위한 CT수 대 물리적 밀도 변환에 관한 CT 스캐닝 매개변수의 의존성)

  • Baek, Min Gyu;Kim, Jong Eon
    • Journal of the Korean Society of Radiology
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    • v.11 no.6
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    • pp.501-508
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    • 2017
  • The dependence of CT scanning parameters on the CT number to physical density conversion from the CT image of CT and CBCT electron density phantom acquired by the CT scanner using in radiotherapy were analyzed by experiment. The CT numbers were independent of the tube current product exposure time, slice thickness, filter of image reconstruction, field of view and volume of phantom. But the CT numbers were dependent on the tube voltage and cross section of phantom. As a result, for physical density range above 0, the maximum CT number difference observed at the tube voltage between 90 and 120 kVp was 27%, and the maximum CT number difference observed between CT body and head electron density phantom was 15%.

Age-dependent Difference in the Computed Tomography Numbers of the Normal Parotid Gland of Koreans (나이에 따른 한국인 정상 이하선의 전산화단층촬영값의 차이)

  • Jeong Ho-Gul;Lee Eun-Sook;Kim Kee-Deog;Park Chang-Seo
    • Journal of Korean Academy of Oral and Maxillofacial Radiology
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    • v.29 no.2
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    • pp.451-458
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    • 1999
  • Purpose : To determine normal CT number range of parotid gland by analyzing the change by age increase and the difference among individuals and between both sexes in CT number of normal parotid gland. Materials & Methods : 134 subjects who took the CT scan between the period of Jan. 1996 and Dec. 1997 at Yonsei University, Dental Hospital were selected. Criteria for selection were that the patients must be within the normal range clinically and radiologically, and the entire parotid gland on the axial view must be shown. Among the axial views. the one showing the greatest parotid gland size was selected and its CT number was recorded. Also. CT numbers from both masseter muscle were recorded as its control. Results : There was statistically significant correlation between CT number of right and left of parotid glands and masseter muscles. With the increase of age. there is a significant decrease in the CT number of parotid gland(p<0.05). There was no statistically significant difference in CT number between sexes except the 7th decade and beyond age group of parotid gland(p>0.05). Conclusion : As age increases, CT number of parotid gland has a tendency to decrease, and there is no significant difference in the CT numbers between left and right parotid gland. Therefore in the CT scan of patients suspected of having a salivary gland disease of the parotid gland. to consider normal range of the age-dependent CT numbers of parotid gland and compare the CT numbers of the right and left parotid gland might be useful in diagnosing the disease.

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Evaluation of using Gantry Tilt Scan to Head & Neck of Patients during Radiation Therapy for Reduction of Metal Artifact (Head & Neck 환자의 방사선 치료시 Metal Artifact의 감소를 위한 Gantry Tilt Scan의 유용성 평가)

  • Lee, Chung-Hwan;Yun, In-Ha;Hong, Dong-Gi;Back, Geum-Mun;Kwon, Gyeong-Tae
    • The Journal of Korean Society for Radiation Therapy
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    • v.22 no.2
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    • pp.85-95
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    • 2010
  • Purpose: The degradation of an image quality and error of the beam dose calculation can be caused because the metal artifact is generated during the CT simulation of head and neck patient. The usability of the gantry tilt scan for reducing the metal artifact tries to be appraised. Materials and Methods: The inferior $20^{\circ}$ gantry tilt scan was made in order to reduce the metal artifact and $0^{\circ}$ reconstruction image was acquired. The AAPM CT performance Phantom was used in order to compare the CT number of the reconstructed image and Original image. the difference of volume was compared by using the acrylic phantom. The homogeneity of the CT number was evaluated the Intensity volume Histogram (IVH) as in order to evaluate an influence by the metal artifact. A dose was evaluated as the Dose Volume Histogram (DVH). Results: in the comparison of the CT number and volume, the difference showed up less than 0.5%. As to the comparison of IVH, in the gantry tilt scan, influence by an artifact was reduced and the homogeneity of the CT number was improved. The comparison of DVH result reduced the mean dose error of the both sides parotid 0.2~6%. Conclusion: In the Head & Neck radiation therapy, It is difficult and to distinguish tumor and normal tissue and the error of dose is generated by the metal artifact. The delineation of the exact organization was possible if the Gantry tilt scan was used. The CT number homogeneity was improved and the error of dose could be reduced. The Gantry tilt scan confirmed in the Head & Neck radiation therapy to be very useful in the exact radiation therapy.

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Effect of the slice thickness and the size of region of interest on CT number (상층두께와 관심영역의 크기 변화가 CT 번호에 미치는 영향)

  • Lee Ji-Youn;Kim Kee-Deog;Park Chang-Seo
    • Imaging Science in Dentistry
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    • v.31 no.2
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    • pp.85-91
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    • 2001
  • Purpose: To evaluate the effect of the slice thickness and the size of region of interest (ROI) on CT number using quantitative CT phantom Materials and Methods: The phantom containing 150 mg/cc, 75 mg/cc and 0 mg/cc calcium hydroxyapatite was scanned with 1, 3, 5 and 10 mm slice thicknesses by single energy quantitative computed tomography (QCT). CT numbers were measured on center position of the phantom. Shape of ROI was circular and sizes were 1, 3, 5, 11, 16, 21, 26 and 33 mm². ANOVA and Tukey's multiple comparison method were performed for statistical comparison of CT numbers according to different slice thicknesses. Coefficient of variation of CT number measured in each size of ROI was evaluated in same slice thickness. Results : CT numbers had statistically significant difference according to slice thicknesses (p<0.05). As the slice thickness increased, CT number also increased. As the density of phantom became lower and the size of ROI became smaller, the coefficient of variation of CT number increased. When the size of ROI was more than 11 mm² in 1 mm slice thickness, 5 mm² in 3 mm slice thickness and 3 mm² in 5 mm slice thickness, the coefficient of variation became consistent. In 10 mm slice thickness, the size of ROI had little effect on the coefficient of variation. Conclusion: CT number had variation according to the slice thickness and the size of ROI although the object was homogeneous. The slice thickness and the size of ROI are critical factors in precision of the CT number measurements.

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A Study on Usefulness of Clinical Application of Metal Artifact Reduction Algorithm in Radiotherapy (방사선치료 시 Metal artifact reduction Algorithm의 임상적용 유용성평가)

  • Park, Ja Ram;Kim, Min Su;Kim, Jeong Mi;Chung, Hyeon Suk;Lee, Chung Hwan;Back, Geum Mun
    • The Journal of Korean Society for Radiation Therapy
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    • v.29 no.2
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    • pp.9-17
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    • 2017
  • Purpose: The tissue description and electron density indicated by the Computed Tomography(CT) number (also known as Hounsfield Unit) in radiotherapy are important in ensuring the accuracy of CT-based computerized radiotherapy planning. The internal metal implants, however, not only reduce the accuracy of CT number but also introduce uncertainty into tissue description, leading to development of many clinical algorithms for reducing metal artifacts. The purpose of this study was, therefore, to investigate the accuracy and the clinical applicability by analyzing date from SMART MAR (GE) used in our institution. Methode: and material: For assessment of images, the original images were obtained after forming ROIs with identical volumes by using CIRS ED phantom and inserting rods of six tissues and then non-SMART MAR and SMART MAR images were obtained and compared in terms of CT number and SD value. For determination of the difference in dose by the changes in CT number due to metal artifacts, the original images were obtained by forming PTV at two sites of CIRS ED phantom CT images with Computerized Treatment Planning (CTP system), the identical treatment plans were established for non-SMART MAR and SMART MAR images by obtaining unilateral and bilateral titanium insertion images, and mean doses, Homogeneity Index(HI), and Conformity Index(CI) for both PTVs were compared. The absorbed doses at both sites were measured by calculating the dose conversion constant (cCy/nC) from ylinder acrylic phantom, 0.125cc ionchamber, and electrometer and obtaining non-SMART MAR and SMART MAR images from images resulting from insertions of unilateral and bilateral titanium rods, and compared with point doses from CTP. Result: The results of image assessment showed that the CT number of SMART MAR images compared to those of non-SMART MAR images were more close to those of original images, and the SD decreased more in SMART compared to non-SMART ones. The results of dose determinations showed that the mean doses, HI and CI of non-SMART MAR images compared to those of SMART MAR images were more close to those of original images, however the differences did not reach statistical significance. The results of absorbed dose measurement showed that the difference between actual absorbed dose and point dose on CTP in absorbed dose were 2.69 and 3.63 % in non-SMRT MAR images, however decreased to 0.56 and 0.68 %, respectively in SMART MAR images. Conclusion: The application of SMART MAR in CT images from patients with metal implants improved quality of images, being demonstrated by improvement in accuracy of CT number and decrease in SD, therefore it is considered that this method is useful in dose calculation and forming contour between tumor and normal tissues.

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The Comparison of Computerized Tomography Utilization between before and after Coverage of Medical Insurance (전산화 단층촬영의 의료보험 급여전후 촬영건수 비교)

  • Suh, Shin-Il;Kim, Han-Joong;Park, Eun-Cheol;Sohn, Myong-Sei;Kim, Dong-Kee
    • Korea Journal of Hospital Management
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    • v.3 no.1
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    • pp.121-133
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    • 1998
  • We analyzed volume changes in the computerized tomography(CT) and the magnetic resonance imaging(MRI) utilizations. These two volumes are comparative because CT has been covered by the Medical Insurance from the beginning of 1996, however, MRI has not been covered up to now. We investigated 80 hospitals which afforded a facility of CT by the end of 1994. For the comparison of CT utilization, we selected two periods. The first period was from January to June of 1995, in which CT had not been covered by the Medical Insurance and the second period was from January to June of 1966, in which CT had been covered. The information we obtained were characteristics of hospitals, patients numbers per month, monthly uses of CT and MRI, and payments of CT claims, etc. After the Medical Insurance coverage, the number of CT uses per 1,000 patients were increased from January to March, however, was decreased from April to June in 1996 compared to the same periods of 1995. the number of CT uses in clinics were large than those in tertiary hospitals. The number of CT uses in small cities were larger than those in big cities. On the other hand, the number of MRI uses per 1,000 patients did not changed from January to May and was increased from June in 1996 compared to the same periods of 1995. These results showed the substitutional relationship of CT and MRI uses. After the insurance coverage for CT, the utilization of CT was increased because patients payed less than before. However, insurers restricted the payments to the CT claims. This impact might explain the substitutional relationship between CT and MRI.

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Changes in CT Number and Noise Level according to Pitch in Spiral Image Acquisition (나선형영상획득에서 Pitch에 따른 CT 감약계수와 잡음의 변화)

  • Kang, SungJin
    • Journal of the Korean Society of Radiology
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    • v.14 no.7
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    • pp.981-989
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    • 2020
  • In this study, a self-made customized phantom was used to quantitatively measure the change in CT number and noise according to the change of pitch. In order to acquire an image using the phantom, the inside of the phantom was filled with sterile distilled water. Inside the glass tube, a solution obtained by diluting the ratio of normal saline and contrast medium to 100%(NS), 400:1, 200:1, 100:1, 50:1, respectively, was placed and imaged. At this time, the pitch was divided into steps of 0, 0.35, 0.7, 1.05, and 1.4 for each dilution ratio of the solution and imaged, respectively. One-way ANOVA analysis were performed to verify whether the mean of the CT number and noise values measured in all ROIs by dilution ratio showed a significant difference according to the change in pitch. As a result of the experiment, there was no statistically significant difference in the change of the CT number according to the change in the pitch for each dilution ratio, but the noise value tended to increase with the increase of the pitch, and showed a statistically significant difference. In the spiral image acquisition of CT, noise can be changed to a significant level depending on the pitch. Therefore, it will be necessary to set the quality evaluation items and criteria for CT images using the spiral image acquisition method.