Papers by Author: Bong Soo Lee

Abstract: We developed a fiber-optic beta/gamma imaging detector that can obtain the scintillating images for beta-or gamma-ray emitted from the radioisotope. To evaluate spatial resolution of proposed imaging detector, we obtained the optical images using USAF 1951 resolution target. And then, a modulation transfer function curve of the optical image was calculated. Also, we measured the scintillating images of Tl-204 and Cs-137 with information respecting the beta-and gamma-rays distribution. Finally, the intensities of scintillating light as a function of radioactivity were analyzed from the region of interest in the scintillating image.

Abstract: To estimate Cerenkov radiation generated in various dielectric materials, in this study, we calculated therapeutic photon beams induced electron fluxes in a CaF₂, PMMA, SiO₂ and Al₂O₃ by using the Monte Carlo N-particle Extended transport code (MCNPX). Also, we clarified the relationship between electron fluxes produced in various dielectrics and energy depositions in water by irradiation of therapeutic photon beams. The electron fluxes and the energy depositions were calculated as a function of water depth.

Abstract: In this study, we have fabricated a fiber-optic dosimeter using an organic scintillator and a plastic optical fiber for measuring percentage depth doses with radiotherapeutic high energy photon beams. The scintillating light generated in an organic dosimeter probe embedded in a solid water phantom is guided by a plastic optical fiber to the light-measuring device. Using this fiber-optic dosimeter, percentage depth doses are measured with 6 and 15 MV energies of photon beams whose field sizes are 2 x 2 and 10 x 10 cm2, and the results are compared with those measured using conventional dosimeters such as an ionization chamber and EBT films used in radiotherapy dosimetry.

Abstract: The purpose of the present study is to develop a magnetic resonance (MR)-compatible electrocardiogram (ECG) amplifier. If ECG signals are measured simultaneously with the acquisition of MR images, there can be a mutual interference effect. The present system was designed to block noises caused by the main magnetic field, gradient magnetic field and radiofrequency (RF) pulse when MR images are acquired. It uses analogue elements in order to remove any possible effect on MR images. In addition, a radio-frequency-interference (RFI)-free optical data link using the pulse-width modulation (PWM) technique is adopted in order to transmit ECG signals measured inside the MR room.

Abstract: In this study, we designed a flat-panel digital X-ray imaging module based upon the amorphous silicon (a-Si) technology and tested potential for medical imaging and nondestructive testing. The module employs a commercially available a-Si photosensor array of a 143 μm x 143 μm pixel size and a 42.9 cm x 42.9 cm active area, coupled with a CsI(Tl) scintillator of a 550 μm thickness, and a readout IC board which can be accessed through our home made GUI software. The experimental test was performed to evaluate the system response with exposure, modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE).

Abstract: This study aimed to investigate the hypothesis that administration of the air with 30% oxygen compared with normal air (21% oxygen) enhances verbal cognitive functioning through increased activation in the brain. Nine male college students participated in the study. The experiment consisted of two runs, one for verbal cognition task with normal air (21% oxygen) and the other for verbal cognition task with hyperoxic air (30% oxygen). Functional brain images were taken with a 3T MRI using the single-shot EPI method. From the results of the verbal behavioral analysis, the accuracy rate was enhanced with 30% oxygen administration when compared to 21% oxygen. The activities were observed at the occipital, parietal, temporal and frontal lobes during both 21% and 30% oxygen administration. There were more activations observed at the right middle frontal gyrus, right inferior frontal gyrus, right superior frontal gyrus, cingulate gyrus, left middle temporal gyrus, and left fusiform gyrus with 30% oxygen administration. These results suggest that a higher concentration of breathed oxygen increases saturation of blood oxygen in the brain, and facilitates verbal performance.

Abstract: The aim of this study is to develop a new method to measure one-dimensional dose distribution of high-energy electron using a miniature fiber-optic radiation sensor. The measurements are made by a thin plastic optical fiber with an organic scintillating sensor tip. The scintillating light in the visible wavelength range is guided to a silicon photodiode by plastic optical fiber in order to convert light output to electrical signal. The one-dimensional spatial dependence of elctron beam is measured by moving the sensor tip with uniform speed. It is shown that this fiber-optic radiation sensor has better spatial resolution than conventional ion chamber and it needs much less time to measure one-dimensional dose distribution in the high radiation fields.

Abstract: The gas electron multiplier (GEM), placed in the drift volume of a conventional gas detector, is a conceptually simple device for producing a large gas gain by concentrating the drift electric field over a very short distance to the point that electron avalanching occurs. This device consists of a thin insulating foil of several tens of μm in thickness, covered on each side with a thin metal layer, with tiny holes, usually 100 μm or less in diameter, and with a spacing of 100-200 μm through the entire foil, perforated by using chemical etching or high-powered laser beam technique. In this study, we have investigated its operating properties with various experimental conditions and demonstrated the possibility of using this device as a digital X-ray imaging sensor, by acquiring X-ray images based upon the scintillation lights of the GEM with a standard CCD camera.