• The Korean Journal of Nuclear Medicine Technology
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• v.18 no.2
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• pp.33-38
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• 2014

Purpose Auto exposure control (AEC) in SPECT/CT automatically controls the exposure dose (mA) according to patient's shape and size. The aim of this study was to evaluate the effect of AEC in SPECT/CT on exposure dose reduction and image quality. Materials and Methods The model of SPECT/CT used in this study was Discovery 670 (GE, USA), Smart mA for AEC; and $^{99m}Tc$ as a radioisotope. To compare SPECT and CT images by CT exposure dose variation, we used a standard technique set at 80, 100, 120, 140 kVp, 10, 30, 50, 100, 150, 200, 250 mA, and AEC at 80, 100, 120, 140 kVp, 10-250 mA. To evaluate resolution and contrast of SPECT images, triple line phantom and flangeless Esser PET phantom were used. For CT images, noise and uniformity were checked by anthropomrphic chest phantom. For dose evaluation to find DLP value, anthropomorphic chest phantom was used and the CT protocol of torso was applied by standard technique (120 kVp, 100 mA) and AEC (120 kVp, 10-250 mA). Results When standard and AEC were applied, the resolutions at SPECT images with attenuation correction (AC) were the same as FWHM by center 3.65 mm, left 3.48 mm, right 3.61 mm. Contrasts of standard and AEC showed no significant difference: standard 53.5, 29.8, 22.5, 15.8, 6.0, AEC 53.5, 29.6, 22.4, 15.7, 6.1 In CT images, noise values at standard and AEC were 15.4 and 18.5 respectively. The application of AEC increases noise but the value of coefficient variation were 33.8, 24.9 respectively, obtaining uniform noise image. The values of DLP at standard and AEC were 426.78 and 352.09 each, which shows that the application of AEC decreases exposure dose more than standard by approximately 18%. Conclusion The results of our study show that there was no difference of AC in SPECT images based on the CT exposure dose variation at SPECT/CT images. It was found that the increased CT exposure dose leads to the improvement of CT image quality but also increases the exposure dose. Thus, the use of AEC in SPECT/CT contributes to obtaining equal AC SPECT images, and uniform noise in CT images while reducing exposure dose.

• Nuclear Engineering and Technology
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• v.38 no.4
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• pp.383-390
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• 2006

Having its roots in medical applications, industrial gamma ray CT has opened up new roads far investigating and modeling industrial processes. Using a line of research related to industrial gamma ray CT, the authors set up a system of single source and detector gamma transmission tomography for wood timber and a packed bed phantom. The hardware of the CT system consists of two servo motors, a data logger, a computer, a radiation source and a radiation detector. One motor simultaneously moves the source and the detector for a parallel beam scanning, whereas the other motor rotates the scan table at a preset projection angle. The image is reconstructed from the measured projections by the filtered back projection method. The phantom was designed to simulate a cross section of a packed bed with a void. The radiation source was 20mCi of Cs-137 and the detector was a 1 inch $\times$ 1 inch NaI (TI) scintillator shielded by a lead collimator. The experimental gamma ray CT image has sufficient resolution to reveal air holes and the density distribution inside the phantom. The system could possibly be applied to a packed bed column or a pipe flow in a petrochemical plant.

• Current Optics and Photonics
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• v.1 no.1
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• pp.17-22
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• 2017

Mechanical property of tissue is closely related to diseases such as breast cancer, prostate cancer, cirrhosis of the liver, and atherosclerosis. Therefore measurement of tissue mechanical property is important for a better diagnosis. Ultrasound elastography has been developed as a diagnostic modality for a number of diseases that maps mechanical property of tissue. Optical coherence elastography (OCE) has a higher spatial resolution than ultrasound elastography. OCE, therefore, could be a great help for early diagnosis. In this study, we made tissue phantoms and measured their compressive moduli with a rheometer measuring the response to applied force. Uniaxial strain of the tissue phantom was also measured with OCE by using cross-correlation of speckles and compared with the results from the rheometer. In order to compare stiffness of tissue phantoms by OCE, the applied force should be measured in addition to the strain. We, however, did not use a load cell that directly measures the applied force for each sample. Instead, we utilized one silicone film (called as reference phantom) for all OCE measurements that indirectly indicated the amount of the applied force by deformation. Therefore, all measurements were based on displacement, which was natural and effective for image-based elastography such as OCE.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.228-230
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• 2002

The relative electron density resolution was discussed by the noise power spectrum (NPS) in the heavy ion CT image. The heavy ion beam $\^$12/C accelerated up to 400MeV/u by RIMAC was used in this study. The two-dimensional (2-D) NPS in the CT image was obtained from the one-dimensional (1-D) NPS of the measured residual range distribution of water phantom for single projection, and the noise variance in the CT image was calculated from 2-D NPS. The technique used in the reconstruction was the filtered back-projection method with Shepp-Logan filter. The calculated value suggests the result of our previous works using the density resolution phantom, assuming that the relative electron density resolution is twice the standard deviation. Therefore, the estimation of the noise in CT images by 2-D NPS obtained the measured residual range distribution is the useful method.

• Progress in Medical Physics
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• v.13 no.4
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• pp.229-233
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• 2002

We have tested a combined CT/SPECT system with a single CZT detector for x-ray and gamma-ray medical imaging. The size of detector is 10$\times$10$\times$5 ㎣, and the anodes are pixellated as a 4$\times$4 array with a pixel dimension of $1.5\times$1.5 $\textrm{mm}^2$. The cathode was coated with a continuous Au-plated. We have characterized the system performance by scanning a radiographic resolution phantom and the Hoffman Brain phantom. Pulse counting electronics with very short shaping time (50 ㎱) are used to satisfy high photon rates in x-ray imaging, and response linearity up to 3$\times$10$^{5}$ counts per second per detector element is achieved. Energy resolution of 10.4% and 5.3% FWHM at Tc-99m 140 keV peak are obtained for the 50 ㎱ and 2 $mutextrm{s}$ shaping times, respectively. The spatial resolutions of CT and SPECT are about 1mm and 9mm, respectively. Photopeak efficiency of detector systems are 41.0% for 50㎱ and 72.5% for 2 $mutextrm{s}$ shaping time.

• Progress in Medical Physics
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• v.23 no.3
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• pp.199-208
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• 2012

The computational human phantom including major radiation sensitive organs at risk (OARs) can be used in the field of radiotherapy, such as the variation of secondary cancer risks caused by the radiation therapy and the effective dose evaluation in diagnostic radiology. The present study developed a Korean adult female voxel phantom, VKH-Woman, based on serially sectioned color slice images of Korean female cadaver. The height and weight of the developed female voxel phantom are 160 cm and 52.72 kg, respectively that are virtually close to those of reference Korean female (161 cm and 54 kg). The female phantom consists of a total of 39 organs, including 27 organs recommended in the ICRP 103 publication for the effective dose calculations. The female phantom composes of $261{\times}109{\times}825$ voxels (=23,470,425 voxels) and the voxel resolution is $1.976{\times}1.976{\times}2.0619mm^3$ in the x, y, and z directions. The VHK-Woman is provided as both ASCII and Binary data formats to be conveniently implemented in Monte Carlo codes.

• Investigative Magnetic Resonance Imaging
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• v.10 no.2
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• pp.89-97
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• 2006

Purpose : To evaluate MR image qualities we developed a new MRI phantom with the fixation structures necessary to position it into coil firmly. Materials and methods : We designed MRI phantom for eight evaluation items such as slice thickness accuracy, high contrast spatial resolution, low contrast object detectability, geometry accuracy, slice position accuracy, image intensity uniformity, percent signal ghosting and signal to noise ratio. For the positioning of phantom at coils, the fixation structures were set up on the surface of phantom. Six different MRI units were used for test the possibility for the clinical application and their image qualities were evaluated. Results : We acquired appropriate MR image qualities enough for the evaluation on all used MR units and confirmed that their evaluations were within reliable values compared to real ones for some items. The positioning of our phantom into head coils with fixation structures worked well for proper imaging. Conclusion : We found that our prototype of MRI phantom had the possibility of clinical application for MR image quality assessment.

• The Korean Journal of Nuclear Medicine Technology
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• v.13 no.1
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• pp.63-66
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• 2009

Purpose: ACR (American College of Radiology) offers variable parameters to PET/CT quality control by using ACR Phantom. ACR Phantom was made to evaluate parameters which are uniformity, attenuation, scatter, contrast and resolution. Manual analysis method wasn't good for the use of QC because values of parameter were changed as it may user and it takes long time to analysis. Ki-Chun Lim, a nuclear scientist in AMC, developed program that automatically analysis values of parameter by using ACR Phantom to overcome above problems. In this study, we evaluated automatic analysis program's usability, through the comparing SUV of each method, reproducibility of SUV when repeated analysis and the time required. Materials and Methods: Using Flangeless Esser PET Phantom, the ideal ratio of 4 : 1 hot cylinder and BKG but it actually showed a ratio of 3.89 to 1 hot cylinder and BKG. SIEMENS Biograph True Point 40 was used in this study. We obtained images using ACR phantom at Fusion WB PET Scan condition (2 min/bed) and 120 kV, 100 mAs CT condition. Using True X method, 3 iterations, 14 subsets, Gaussian filter, FWHM 4 mm and Zoom Factor 1.0, $168{\times}168$ image size. We obtained Max. & Min. SUV and SUV Mean values at Cylinder (8, 12, 16, 25 mm, Air, Bone, Water, BKG) by automatic program and obtained SUV by manual method. After that, we compared manual and automatic method. we estimate the time required from opened the image data to final work sheet was completed. Results: Automatic program always showed same result and same the time required. At 8, 12, 16 and 25 m cylinder, manual method showed 6.69, 3.46, 2.59, 1.24 CV values. The larger cylinder size became, the smaller CV became. In manual method, bone, air, water's CV were over 9.9 except BKG (2.32). Obtained CV of Mean SUV showed BKG was low (0.85) and bone was high (7.52). The time required was 45 second, 882 second respectably. Conclusions: As a result of difference automatic method and manual method, automatic method showed always same result, manual method showed that the smaller hot cylinders became, the lager CV became. Hot cylinders mean region size, the smaller hot cylinder size becomes we had some trouble in doing ROI poison setting. And it means increase in variation of SUV. The Study showed the time required of automatic method was shorten then manual method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.6
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• pp.879-884
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• 2012

Photoacoustic Tomography (PAT) is a promising medical imaging modality by reason of its particularity. It combines optical imaging contrast of optical imaging with the spatial resolution of ultrasound imaging and can demonstrate change of biological feature in an image. For that reason, many studies are in progress to apply this technic for diagnosis. But, real-time PAT system is necessary to confirm a biological reaction induced by external stimulation immediately. Thus, we developed a real-time PAT system using linear array transducer and self-developed Data acquisition board (DAQ) resources, To evaluate the feasibility and performance of our proposed system, two type of phantom test were also performed. As a result of those experiments, the proposed system shows enough performance and confirm its usefulness.

• The Journal of Korean Society for Radiation Therapy
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• v.20 no.1
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• pp.17-23
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• 2008

Purpose: Cone-beam CT using linear accelerator attached to on-board imager is a image guided therapy equipment. Because it is to check the patient's set-up error, correction, organ and target movement. but imaging dose should be cause of the secondary cancer when taking a image. The aim of this study is investigation of appropriate cone beam CT scan mode to compare and estimate the image quality and skin dose. Materials and Methods: Measurement by Thermoluminescence dosimeter (TLD-100, Harshaw) with using the Rando phantom are placed on each eight sites in seperately H&N, thoracic, abdominal section. each 4 methods of scan modes of are measured the for skin dose in three time. Subsequently, obtained average value. Following image quality QA protocol of equipment manufacturers using the catphan 504 phantom, image quality of each scan mode is compared and analyzed. Results: The results of the measured skin dose are described in here. The skin dose of Head & Neck are measured mode A: 8.96 cGy, mode B: 4.59 cGy, mode C: 3.46 cGy mode D: 1.76 cGy and thoracic mode A: 9.42 cGy, mode B: 4.58 cGy, mode C: 3.65 cGy, mode D: 1.85 cGy, and abdominal mode A: 9.97 cGy, mode B: 5.12 cGy, mode C: 4.03 cGy, mode D: 2.21 cGy. Approximately, dose of mode B are reduced 50%, mode C are reduced 60%, mode D are reduced 80% a point of reference dose of mode A. the results of analyzed HU reproducibility, low contrast resolution, spatial resolution (high contrast resolution), HU uniformity in evaluation item of image quality are within the tolerance value by recommended equipment manufacturer in all scan mode. Conclusion: Maintaining the image quality as well as reducing the image dose are very important in cone beam CT. In the result of this study, we are considered when to take mode A when interested in soft tissue. And we are considered to take mode D when interested in bone scan and we are considered to take mode B, C when standard scan. Increasing secondary cancer risk due to cone beam CT scan should be reduced by low mAs technique.