Hyosung Cho

Measurements of X-ray Imaging Performance of Granular Phosphors With Direct-Coupled CMOS Sensors

For Gd2O2S:Tb granular phosphor screens having a wide range of mass thicknesses, we have investigated the fundamental imaging performance in terms of modulation-transfer function (MTF), noise-power spectrum (NPS) and detective quantum efficiency (DQE). As an optical photon readout device, a CMOS photodiode array with a pitch of 48 mum was used. Under the representative radiation quality, RQA 5, recommended by the IEC (International Electrotechnical Commission, Report 1267), the MTF was measured using a slanted-slit method to avoid aliasing and the NPS was determined by two-dimensional (2D) Fourier analysis of white images. The DQE was assessed from the measured MTF, NPS and the estimated photon fluence. Figure-of-merit (FOM) curves are presented to describe the tradeoff between the X-ray sensitivity and spatial resolution of screens as a function of mass thickness. This study will be useful for the selection guidance of Gd2O2S:Tb phosphors for the relevant imaging tasks of digital radiography.

Measurement of Two-Dimensional Photon Beam Distributions Using a Fiber-Optic Radiation Sensor for Small Field Radiation Therapy

In this study, a fiber-optic radiation sensor with an organic scintillator is fabricated to measure high-energy photon beam from a clinical linear accelerator (CLINAC) and a fiberoptic sensor array is also fabricated to measure two-dimensional, high-resolution and real-time dose distributions for small field radiotherapy dosimetry. The scintillating lights generated from each organic sensor probe embedded and arrayed in a water phantom are guided by 10 m plastic optical fibers to the light- measuring device. The two-dimensional photon beam distributions in a water phantom are measured with different energies and field sizes of photon beams. Also, percent depth dose curves for 6 and 15 MV photon beams are obtained.

Measurements and Characterization of Cerenkov Light in Fiber-Optic Radiation Sensor Irradiated by High-Energy Electron Beam

In general, Cerenkov light can cause a problem in detecting a real light signal that is generated in a fiber-optic radiation sensor using an organic scintillator for dose measurements of high-energy electron beams. In this study, the intensity of Cerenkov light is measured and characterized as functions of incident angles, energy, and field size of the electron beam from a LINAC (linear accelerator). To remove or minimize Cerenkov light, a subtraction method using a background optical fiber is investigated.

Characterization of One-Dimensional Fiber-Optic Scintillating Detectors for Electron-Beam Therapy Dosimetry

In this study, a one-dimensional fiber-optic scintillating detector was developed for electron-beam therapy dosimetry. Each fiber-optic detector contains an organic scintillator as a sensitive volume and it is embedded and arrayed in a plastic phantom to measure one-dimensional high-energy electron-beam profiles of clinical linear accelerators. Plastic optical fibers guide the scintillating light which each detector probe generates to a photodiode array. The one-dimensional electron-beam profiles in the plastic phantom were measured in two different field sizes and for two electron-beam energies. Also, isodose and two-dimensional dose distributions in the plastic phantom were obtained using the one-dimensional scintillating detector array with two different electron beam energies.

Performance of a Digital Gamma-Imaging System Based Upon CdTe-CMOS Sensor and

As a continuation of our digital radiographic sensor R&D, we have developed a digital gamma-imaging system based upon the commercially-available CdTe-CMOS sensor (AJAT, SCAN1000) and the 75Se gamma source (MDS, Gamma Mat@ SE) for our ongoing application of nondestructive testing. Here the sensor has a 750-mum-thick CdTe photoconductor as an efficient radiation converter and a CMOS pixel array having 100times100 mum2 pixel size and 5.41times51.0 mm2 active area, bump-bonded to the photoconductor for signal readout. The source has about 62.8 Ci activity and a physical size of 3.0 mm in diameter. For the first time in this project, we have succeeded in obtaining useful gamma images from the imaging system and evaluated the imaging performance in terms of the resolving power, the line spread function (LSF), the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE). For comparison, we also evaluated the image quality by using a microfocus X-ray source (Hamamatsu, L9121-01) having a focal spot size of about 5 mum.

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In this study, we fabricated a fiber-optic radiation sensor with an organic scintillator to measure the high-energy photon beam from a clinical linear accelerator, and a two-dimensional fiber-optic sensor array to measure high-resolution and real-time dose distributions for small field radiotherapy dosimetry. The scintillating lights generated from each organic sensor probe embedded and arrayed in a water phantom are guided by 10 m plastic optical fibers to the light-measuring device. Two-dimensional photon beam distributions in a water phantom were measured for photon beams with different energies and field sizes. Also, percent depth dose curves for 6 and 15 MV photon beams were obtained.

Se Source for Nondestructive Testing

In this study, one-dimensional fiber-optic radiation sensor with an organic scintillator tip is fabricated to measure high energy X-ray beam profile of CLINAC. According to the energy and field size of X-ray, scintillating light signal from one-dimensional fiber-optic sensor is measured using a photodiode-amplifier system. This sensor has many advantages such as high resolution, real-time measurement and ease calibration over conventional ion chamber and film.

Measurement of two-dimensional photon beam distributions using a fiber-optic radiation sensor for small field radiation therapy

In this study, we have fabricated one-dimensional fiber-optic radiation sensor array for high energy electron beam therapy dosimetry. Fiber-optic radiation sensor comprises an organic scintillator as a sensing volume, optical fiber as a light guider and photo-detector as a light measuring device. Usually, photomultiplier tube or photodiode is used as a photo-detector however we have tried to use a charge-coupled device as a scintillating light measuring system for one-dimensional fiber-optic radiation sensor array. This system can take an image of the proximal ends of one-dimensional fiber-optic sensor array and can measure light intensities of individual image of optical fibers simultaneously using simple imaging software. Charge-coupled device as a light measuring detector has many advantages which are easy in multi-dimensional measurements, high spatial resolution and relatively low cost. We have measured one-dimensional electron beam distributions in a PMMA phantom with different energies and field sizes of electron beam using a fiber-optic sensor and a charge-coupled device. Also, the percentage depth dose curves for high energy electron beams are obtained.

Fabrication and performance evaluation of one-dimensional fiber-optic radiation sensor for X-ray profile irradiated by clinical linear accelerator

In this study, a one-dimensional fiber-optic scintillating detector is developed for electron beam therapy dosimetry. Each fiber-optic detector has an organic scintillator as a sensitive volume and it is embedded and arrayed in the plastic phantom to measure one-dimensional high energy electron beam profile of clinical linear accelerator (CLINAC). The scintillating lights generated from each detector probe are guided by plastic optical fibers to the photodiode array. The one-dimensional electron beam profiles in a plastic phantom are measured with different field sizes and energies of electron beam and the intensity of Cerenkov light which is generated from optical fiber is measured as a function of the incident angle of electron beam. Also, isodose and three-dimensional percent depth dose curves in a plastic phantom are obtained using a one-dimensional scintillating detector array with different electron beam energies.

Performance Evaluation of One-dimensional Fiber-optic Radiation Sensor for Measuring High Energy Electron Beam Using a Charge-coupled Device

In this study, we have fabricated multi-dimensional fiber-optic radiation detectors with organic scintillators, plastic optical fibers and photo-detectors such as photodiode array and a charge-coupled device. To measure the X-ray dose distributions of the clinical linear accelerator in the tissue-equivalent medium, we have fabricated polymethylmethacrylate phantoms which have one-dimensional and two-dimensional fiber-optic detector arrays inside. The one-dimensional and two-dimensional detector arrays can be used to measure percent depth doses and surface dose distributions of high energy X-ray in the phantom respectively.