• Investigative Magnetic Resonance Imaging
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• v.23 no.1
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• pp.38-45
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• 2019

Purpose: To demonstrate the high-resolution numerical simulation of the respiration-induced dynamic $B_0$ shift in the head using generalized susceptibility voxel convolution (gSVC). Materials and Methods: Previous dynamic $B_0$ simulation research has been limited to low-resolution numerical models due to the large computational demands of conventional Fourier-based $B_0$ calculation methods. Here, we show that a recently-proposed gSVC method can simulate dynamic $B_0$ maps from a realistic breathing human body model with high spatiotemporal resolution in a time-efficient manner. For a human body model, we used the Extended Cardiac And Torso (XCAT) phantom originally developed for computed tomography. The spatial resolution (voxel size) was kept isotropic and varied from 1 to 10 mm. We calculated $B_0$ maps in the brain of the model at 10 equally spaced points in a respiration cycle and analyzed the spatial gradients of each of them. The results were compared with experimental measurements in the literature. Results: The simulation predicted a maximum temporal variation of the $B_0$ shift in the brain of about 7 Hz at 7T. The magnitudes of the respiration-induced $B_0$ gradient in the x (right/left), y (anterior/posterior), and z (head/feet) directions determined by volumetric linear fitting, were < 0.01 Hz/cm, 0.18 Hz/cm, and 0.26 Hz/cm, respectively. These compared favorably with previous reports. We found that simulation voxel sizes greater than 5 mm can produce unreliable results. Conclusion: We have presented an efficient simulation framework for respiration-induced $B_0$ variation in the head. The method can be used to predict $B_0$ shifts with high spatiotemporal resolution under different breathing conditions and aid in the design of dynamic $B_0$ compensation strategies.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2018-2025
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• 2023

In our previous study, we proposed an integrated PG-PET-based imaging method to increase the prediction accuracy for patient dose distributions. The purpose of the present study is to experimentally validate the feasibility of the PG-PET system. Based on the detector geometry optimized in the previous study, we constructed a dual-head PG-PET system consisting of a 16 × 16 GAGG scintillator and KETEK SiPM arrays, BaSO₄ reflectors, and an 8 × 8 parallel-hole tungsten collimator. The performance of this system as equipped with a proof of principle, we measured the PG and positron emission (PE) distributions from a 3 × 6 × 10 cm³ PMMA phantom for a 45 MeV proton beam. The measured depth was about 17 mm and the expected depth was 16 mm in the computation simulation under the same conditions as the measurements. In the comparison result, we can find a 1 mm difference between computation simulation and measurement. In this study, our results show the feasibility of the PG-PET system for in-vivo range verification. However, further study should be followed with the consideration of the typical measurement conditions in the clinic application.

• Journal of radiological science and technology
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• v.47 no.1
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• pp.1-6
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• 2024

In Recent years, there has been a noticeable increase in the global incidence of breast cancer, with approximately 2.3 million cases of female breast cancer reported worldwide in 2020. Numerous studies are currently underway to enhance the accuracy of breast cancer diagnosis through the development of digital mammography detectors. This study aims to create Monte Carlo simulation-based mammographic anti-scatter grids and investigate their utility in evaluating the performance of digital mammography detector. Two types of mammographic anti-scatter grids, MAM-CP and Senographe 600T HF, were created using Monte Carlo simulation software (MCNPX 2.7.0), with grid ratios of 3.7 : 1 and 5 : 1, respectively. The grid physical characteristics (sensitivity, exposure factor, contrast improvement ratio) were calculated based on the KS C IEC60627 in the simulations using two X-ray qualities, RQA-M2 (28 kVp) and MW4 (35 kVp). As the X-ray tube voltage increased from 28 kVp to 35 kVp, sensitivity and exposure factor exhibited a decreasing trend, while contrast improvement ratio demonstrated an increasing trend. With an increase in grid ratio from 3.7 : 1 to 5 : 1, all physical characteristics showed an upward trend. Our results were consistent with a previous study that conducted measurements of physical properties using a real phantom. However, the pattern of change in the contrast improvement ratio with X-ray tube voltage differed from the previous study.

• Radiation Oncology Journal
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• v.30 no.2
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• pp.49-52
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• 2012

Purpose: To evaluate the effectiveness and safety of postoperative radiotherapy for the treatment of keloid scars administered immediately after Cesarean section. Materials and Methods: A total of 26 postpartum patients with confirmed keloids resulting from previous Cesarean sections received either 12 or 15 Gy radiotherapy. The radiotherapy was divided into three 6 MeV electron beam fractions administered during the postpartum period immediately following the final Cesarean section. To evaluate ovarian safety, designated doses of radiation were estimated at the calculated depth of the ovaries using a solid plate phantom and an ionization chamber with the same lead cutout as was used for the treatment of Cesarean section operative scars and a tissue equivalent bolus. Results: In total, the control rate was 77% (20 patients), while six (23%) developed focally elevated keloids (ranging from 0.5 to 2 cm in length) in the middle of the primary abdominal scar. Five patients experienced mild hyperpigmentation. Nonetheless, most patients (96%) were satisfied with the treatment results. The estimated percentage of the applied radiation doses that reached the calculated depth of the ovaries ranged from 0.0033% to 0.0062%. Conclusion: When administered during the immediate postpartum period, postoperative electron beam radiotherapy for repeated Cesarean section scars is generally safe and produces good cosmetic results with minimal toxicity.

• Journal of the Institute of Convergence Signal Processing
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• v.1 no.1
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• pp.49-57
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• 2000

In this study, a new algorithm for canceling a MRI artifact due to the translational motion In the image plane is described. Unlike the conventional iterative phase retrieval algorithm, in which there is no guarantee for the convergence, a direct method for estimating the motion is presented. In previous approaches, the motions in the x(read out) direction and the y(phase encoding) direction were estimated simultaneously. However, the feature of x and y directional motions are different from each other. By analyzing their features, each x and y directional motion is canceled by the different algorithms in two steps. First, it is noticed that the x directional motion corresponds to a shift of the x directional spectrum of the MRI signal, and the non-zero area of the spectrum just corresponds to the projected area of the density function on the x axis. So the motion is estimated by tracing the edges between non-zero area and zero area of the spectrum, and the x directional motion is canceled by shifting the spectrum in an reverse direction. Next, the y directional motion is canceled by using a new constraint condition, with which the motion component and the true image component can be separated. This algorithm is shown to be effective by using a phantom image with simulated motion.

• The Journal of the Acoustical Society of Korea
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• v.29 no.1E
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• pp.38-44
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• 2010

This paper is based on our comments and proposed amendments to the documents, Annex A, Phantom for determining Maximum Depth of Penetration, and Annex B, Local Dynamic Range Using Acoustical Test Objects 87/400/CDV. IEC 61391-2 Ed. 1.0 200X, prepared by IEC technical Committee 87; Ultrasonics. The documents are concerned with the influence of microstructure of reference target material on the ultrasonic backscattering. Previous works on the attenuation due to backreflection and backscattering of reference target materials are reviewed. The drawback to the use of ungraded stainless steel and metallic materials without microstructural data such as, crystal structure, basic acoustic data of sound velocity and attenuation, grain size, roughness and elastic constants has been discussed. The analysis suggested that the insightful conclusion can be made by differentiating the influence arising from target size and microstructure on the backscattering measurements. The microstructural parameters are associated with physical, geometrical, acoustical and mechanical origins of variation with frequency. Further clarification of such a diverse source mechanisms for ultrasonic backscattering would make the target material and its application for medical diagnosis and therapy simpler and more reliable.

• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3844-3853
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• 2023

Although radiation and chemotherapy methods for cancer therapy have advanced significantly, surgical resection is still recommended for most cancers. Therefore, intraoperative imaging studies have emerged as a surgical tool for identifying tumor margins. Intraoperative imaging has been examined using conventional imaging devices, such as optical near-infrared probes, gamma probes, and ultrasound devices. However, each modality has its limitations, such as depth penetration and spatial resolution. To overcome these limitations, hybrid imaging modalities and tracer studies are being developed. In a previous study, a multi-modal laparoscope with silicon photo-multiplier (SiPM)-based gamma detection acquired a 1 s interval gamma image. However, improvements in the near-infrared fluorophore (NIRF) signal intensity and gamma image central defects are needed to further evaluate the usefulness of multi-modal systems. In this study, an attempt was made to change the NIRF image acquisition method and the SiPM-based gamma detector to improve the source detection ability and reduce the image acquisition time. The performance of the multi-modal system using a complementary metal oxide semiconductor and modified SiPM gamma detector was evaluated in a phantom test. In future studies, a multi-modal system will be further optimized for pilot preclinical studies.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.9C
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• pp.861-870
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• 2002

In this paper, with targeting on the drawback of RSA of operation speed, a new 1024-bit RSA cryptosystem has been proposed and implemented in hardware to increase the operational speed and perform the variable-length encryption. The proposed cryptosystem mainly consists of the modular exponentiation part and the modular multiplication part. For the modular exponentiation, the RL-binary method, which performs squaring and modular multiplying in parallel, was improved, and then applied. And 4-stage CSA structure and radix-4 booth algorithm were applied to enhance the variable-length operation and reduce the number of partial product in modular multiplication arithmetic. The proposed RSA cryptosystem which can calculate at most 1024 bits at a tittle was mapped into the integrated circuit using the Hynix Phantom Cell Library for Hynix 0.35㎛ 2-Poly 4-Metal CMOS process. Also, the result of software implementation, which had been programmed prior to the hardware research, has been used to verify the operation of the hardware system. The size of the result from the hardware implementation was about 190k gate count and the operational clock frequency was 150㎒. By considering a variable-length of modulus number, the baud rate of the proposed scheme is one and half times faster than the previous works. Therefore, the proposed high speed variable-length RSA cryptosystem should be able to be used in various information security system which requires high speed operation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.12
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• pp.8479-8486
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• 2015

This study aim is occur in brain CT cause of beam hardening effect and reducing method, We will scan Bone opaque bead phantom on variation of image on the influence factor with equipment called 'Samatom Senation 16' with following listed herein : tube voltage, tube current, slice thickness, gantry angle, base line which affect beam-hardening effect. After that we are going to start Quantitative Analysis resulted in previous scanning and Qualitative Assessment with CT image sheet evaluation. result of quantitative analysis 140kVp $31.56{\pm}2.89HU$ on tube voltage, 150mA $-3.87{\pm}0.12HU$ on tube current, 3mm on slice thickness, and $13.31{\pm}1.03HU$ IOML on gantry angle which was the least beam-hardening effect. Like Qualitative Analysis, we went through Qualitative Assessment and most of valuers got a result of 140kVp on tube voltage, 150mA on tube current, 3mm on slice thickness. As before valuers evaluated gantry angle that scanned image from IOML or OML was the least beam-hardening effect occured. There are meaningful differences when we compare all theses factors statistically(P<0.05). therefore We consider that Minimizing artifact that caused by beam-hardening effect can provide better quality of image to deciphers and patients. if we rise tube voltage in permissible dose limit, set tube current in a limit that does not effect to image quality, use slice thickness too thin enough to harm resolution, use IOML or OML on gantry angle.

• Journal of the Korean Society of Radiology
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• v.15 no.7
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• pp.975-982
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• 2021

The purpose of this study is to evaluate the effect on the phantom for magnetic resonance imaging located nearby by partially shielding RF with a mesh made thinner than hair composed of copper, black metal, and polyester using metallic materials of titanium, which are commonly used for esophageal stents and implants in the body. Magnetic resonance images according to field of view (FOV) were analyzed in the Spin Echo T1 weighted images of TR 500 ms, TE 20 ms, NEX 1, and slice thickness 5mm using a Cardiac coil of 3T Achieva X-series. Aliasing artifact did not occur in FOV 304 mm × 304 mm, but it occurred in 250 mm × 250 mm and 170 mm × 170 mm. In FOV 170 mm × 170 mm, when a mesh was not used, the SNR was measured with 78.23, and when separated by standing a mesh in the middle, it was 215.05, and when completely shielded with a mesh, the SNR was 366.44. In addition, when completely shielded with a mesh, the aliasing artifact was also removed, and signal intensities on the left, middle and right of the image were also able to obtain homogeneous images compared to the previous two cases. In conclusion, if RF is partially shielded with a mesh, aliasing artifact can be removed, and magnetic resonance images with excellent image resolution and homogeneity can be obtained using a small FOV.