• The Korean Journal of Nuclear Medicine Technology
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• v.17 no.1
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• pp.71-75
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• 2013

Purpose: Currently, decrement revision using LDCT is used in PET/CT. But cold artifacts are often found in decrement revision image by mismatch between LDCT image and Emission image near diaphragm due to patient's respiration. This research studied reduction of cold artifact by patient's respiration using CTAC Shift among revision methods. Materials and Methods: From March to September in 2012, 30 patients who had cold artifacts by respiration were targeted using PET/CT Discovery 600 (GE Healthcare, MI, USA) equipment. Patients with cold artifacts were additionally scan in diaphragm area, and the image shown cold artifacts at whole body test were revised using CTAC Shift. Cold artifacts including image, additional scan image and CTAC Shift revision image were evaluated as 1~5 points with naked eye by one nuclear medicine expert, 4 radiotechnologists with over 5 year experience. Also, standard uptake value of 3 images was compared using paired t-test. Results: Additional scan image and CTAC Shift revision image received relatively higher score in naked eye evaluation than cold artifacts including image. The additional scan image and CTAC Shift revision image had high correlation as the results of ANOVA test of standard uptake value and did not show significant difference. Conclusion: When cold artifacts are appeared by patient's respiration at PET/CT, it causes not only patient inconvenience but troubles in test schedule due to extra radiation exposure and time consumption by additional scan. But if CTAC Shift revision image can be acquired with out additional scan, it is considered to be helped in exact diagnosis without unnecessary extra radiation exposure and additional scan.

• 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.

• Journal of Radiation Protection and Research
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• v.35 no.4
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• pp.135-141
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• 2010

Purpose : The patients who visited this department for pulmonary disease and need CT scans for Follow-up to observe change of CT value, evaluation of image quality and decrease of radiation dose as change of kVp. Subjects and Methods : Subjects were the patients of 20 persons visited this department for pulmonary disease and Somatom Sensation 16(Semens, Enlarge, Germany) was used. Measurement of CT value as change of kVp was done by setting up ROI diameter of 1cm at the height of thyroid, aortic arch, right pulmonary artery in arterial phase image using 100 kVp, measuring 3 times, and recorded the average. CT value of phantom was measured by scanning phantoms which means contrast media diluted by normal saline by various ratio with tube voltage of 80 kVp, 100 kVp, 120 kVp, 140 kVp and recorded the average of 3 CT values of center of phantom image. In analysing radiation dose, CTDIVOL values of the latest arterial phase image of 120 kVp and as this research set that of 100 kVp were analyzed comparatively. 2 observers graded quality of chest images by 5 degrees (Unacceptable, Suboptimal, Adequate, Good, Excellent). Results : CT value of chest image increased at 100 kVp by 14.06%~27.26% in each ROI than 120 kVp. CT value of phantom increased as tube voltage lowered at various concentration of contrast media. CTDIVOL decreased at 100 kVp(5.00 mGy) by 36% than 120 kVp(7.80 mGy) in radiation dose analysis. here were 0 Unacceptable, 1 Suboptimal, 3 Adequate, 10 Good, 6 Excellent in totally 20 persons. Conclusion : Chest CT scanning with low kilo-voltage for patients who need CT scan repeatedly can bring images valuable for diagnose, and decrease radiation dose against patients.

• Progress in Medical Physics
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• v.19 no.2
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• pp.120-124
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• 2008

In this study, we developed the protopype of QA phantom for image QA including an additional component for image based radiation treatment system. The new phantom considered two main parts: Image quality and fusion accuracy. Image quality part included for daily CT number linearity and spatial resolution, and fusion accuracy part designed to simulate a simple translation-rotation setting. The CT scans of the phantom obtained from conventional CT, MVCT of Tomotherapy unit, and both image sets were satisfied the recommendation of spatial resolution. This phantom was simple and efficient for daily imaging QA, and it is important to provide a new concept of verification of image registration.

• Journal of the Korean Society of Radiology
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• v.12 no.1
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• pp.85-91
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• 2018

Computed tomography, which obtains section images from reconstruction process using projection images, has been applied to various fields. The spatial resolution of the reconstructed image depends on the device used in CT system, the object, and the reconstruction process. In this paper, we investigates the effect of the number of projection images and the pixel size of the detector on the spatial resolution of the reconstructed image under the parallel beam geometry. The reconstruction program was written in Visual C++, and the matrix size of the reconstructed image was $512{\times}512$. The numerical bar phantom was constructed and the Min-Max method was introduced to evaluate the spatial resolution on the reconstructed image. When the number of projections used in reconstruction process was small, artifact like streak appeared and Min-Max was also low. The Min-Max showed upper saturation when the number of projections is increased. If the pixel size of the detector is reduced to 50% of the pixel size of the reconstructed image, the reconstructed image was perfectly recovered as the original phantom and the Min-Max decreased as increasing the detector pixel size. This study will be useful in determining the detector and the accuracy of rotation stage needed to achieve the spatial resolution required in the CT system.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.1
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• pp.146-151
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• 2000

The importance of shape reconstruction is increasing in many areas such as RPD(Rapid Product Development) and reverse engineering. Typical data in these areas are mainly classified as the shape data measured by a laser scanner and the data extracted from the CT image. The goal of this research is to realize three-dimensional shape construction by showing a possible way to analyze input image data and reconstruct the original shape. Two main steps of the reconstructing process are obtaining cross-section data from image processing and linking loops between one slice and the next. Objects reconstructed in this way are compared with other objects using a laser scanner and modelled by commercially available software. The technique is expected to be used in reverse engineering applications and the object modeling with automated process.

• Korean Journal of Digital Imaging in Medicine
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• v.12 no.2
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• pp.113-117
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• 2010

This research attempts to qualitatively evaluate the intensity change by radiopharmaceuticals and obtain computed tomography using phantom injected with various nuclide. Cylindrical phantom is used for comparing and analysing the effect on diagnosis image during radiopharmaceuticals inspection. Inside of the phantom, water is injected and computed tomography image is scanned. During nuclear medicine invitro, frequently used radiopharmaceuticals, $^{99m}TcO_4$ 20 mCi and $^{18}F$ 14 mCi, is diluted in the water phantom and scanned in the same method. Traverse image obtained by CT scan is divided into six traverse image in the same slice of each scanned image. CT-number(HU) value of 10 measuring point is measured in 2 cm interval based on the center of the phantom. Measured HU value, based on the water phantom, is compared with the image after injecting $^{99m}TcO_4$ and $^{18}F$. Average scale of water is 2.8~1.6 HU, $^{99m}TcO_4$ is 3.0~1.6 HU and $^{18}F$ is 1.2~0 HU. Average of water is $2.3{\pm}0.17$ HU, $^{99m}TcO_4$ is $2.2{\pm}0.85$ HU and F-18 is $0.7{\pm}0.95$ HU. Based on water, reduced value of about 0.1 HU and about 0.5 HU is acquired from $^{99m}TcO_4$ and F-18. Radionuclide used in nuclear medicine inspection utilizes 100~200 KeV energy and obtains image through scintillation camera and PET-CT utilizes 511 KeV positron annihilation energy to obtain image. What we learned from this research is that gamma rays from these energies used in CT scan for diagnosis purpose or radioactive therapy plan can change the intensity of the image. The nuclear medicine inspection for reducing the effect of emitted gamma ray diagnosis image should be obtained after a period of time considering half-life which would be reduced distortion or changed in image.

• Journal of the Korean Society of Radiology
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• v.11 no.6
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• pp.453-458
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• 2017

Computed Tomography (CT) provides information on the Diagnostic Reference Level Computed Tomography Dose Index (CTDI) and Dose Length Product (DLP) for accurate diagnosis of patients. However, it does not provide a dose change according to the table height for the diagnostic reference level provided by the CT equipment. The purpose of this study was to evaluate the image and dose according to the table height change using phantom (PMMA: Polymethyl Methacrylate) in order to find the optimal image and the minimum dose during computed tomography examination. When examining using a 32 cm PMMA phantom with the same thickness as the abdomen of an adult, there was little change in dose with table height. However, the noise evaluation of the image caused a high fluctuation of noise depending on the table height. and in the case of the 16 cm PMMA phantom, the change of the noise was small, but the dose change was about 30%. In conclusion, the location of the patient and the center of the detector are important during computed tomography (CT) examinations. In addition, table height setting is considered to be important for examinations with optimized image and minimum dose.

• Journal of radiological science and technology
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• v.40 no.4
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• pp.595-603
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• 2017

The study is to produced a brain phantom simulating corpus striatum, which can evaluate the progression of parkinson's disease, to investigate possibility of reducing the brain exposure dose to CT while maintaining optimal image quality during PET-CT examinations. CT scans were performed by varying tube voltage (100, 120 kVp) and tube current (80, 140, 200 mAs) with $^{18}F$ FP-CIT injected into the phantom's hot sphere and background (radioactivity ratio 3:1)(reference condition; 120 kVp, 140 mAs). Estimated effective dose was calculated by using conversion factor according to each condition, and image quality was evaluated by setting SNR and CRChot image evaluation factors. Experimental results showed that the predicted effective dose below the CT imaging reference condition was reduced by at least 10% and by up to 60%, and the predicted effective dose beyond the reference condition was increased by 40%. In addition, there was no significant difference between SNR and CRChot of PET images, and it was confirmed that brain dose decreased with decrease of tube voltage and tube current. At the same time, there was no significant change in the quality of the image in terms of SNR and CRChot despite the change in scan conditions. This fact suggests that the quality of the images acquired under the existing dose conditions can be obtained even at low dose conditions and it is expected that it will be possible to use the brain PET-CT scan as a basic data for the research on reduction of dose and improvement of image quality.

• Journal of KIISE:Software and Applications
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• v.32 no.7
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• pp.612-624
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• 2005

In this paper, we propose a surface-based registration using a gaussian weighted distance map for PET-CT brain image fusion. Our method is composed of three main steps: the extraction of feature points, the generation of gaussian weighted distance map, and the measure of similarities based on weight. First, we segment head using the inverse region growing and remove noise segmented with head using region growing-based labeling in PET and CT images, respectively. And then, we extract the feature points of the head using sharpening filter. Second, a gaussian weighted distance map is generated from the feature points in CT images. Thus it leads feature points to robustly converge on the optimal location in a large geometrical displacement. Third, weight-based cross-correlation searches for the optimal location using a gaussian weighted distance map of CT images corresponding to the feature points extracted from PET images. In our experiment, we generate software phantom dataset for evaluating accuracy and robustness of our method, and use clinical dataset for computation time and visual inspection. The accuracy test is performed by evaluating root-mean-square-error using arbitrary transformed software phantom dataset. The robustness test is evaluated whether weight-based cross-correlation achieves maximum at optimal location in software phantom dataset with a large geometrical displacement and noise. Experimental results showed that our method gives more accuracy and robust convergence than the conventional surface-based registration.