Design and Fabrication of HgI2 Sensor for Phosphor Screen based flat panel X-ray Detector

Ji Koon Park(박지군),Bong Jae Jung(정봉재),Il Hong Choi(최일홍),Si Cheol Noh(노시철) 대한전자공학회 2014 전자공학회논문지 Vol.51 No.12

X-ray Sensitivity of Hybrid-type Sensor based on CaWO₄-Selenium for Digital X-ray Imager

Park, Ji-Koon,Park, Jang-Yong,Kang, Sang-Sik,Lee, Dong-Gil,Kim, Jae-Hyung,Nam, Sang-Hee The Korean Institute of Electrical and Electronic 2004 Transactions on Electrical and Electronic Material Vol.5 No.4

The development of digital x-ray detector has been extensively progressed for the application of various medical modalities. In this study, we introduce a new hybrid-type x-ray detector to improve problems of a conventional direct or indirect digital x-ray image technology, which composed of multi-layer structure using a CaWO$_4$ phosphor and amorphous selenium (a-Se) photoconductor. The leakage current of our detector was found to be ∼180 pA/cm$^2$ at 10 V/m, which was significantly reduced than that of a single a-Se detector. The x-ray sensitivity was measured as the value of 4230 pC/cm$^2$/mR at 10 V/m. We found that the parylene thin film between a CaWO$_4$ phosphor and an a-Se layer acts as an insulator to prevent charge injection from indium thin oxide (ITO) electrode into an a-Se layer under applied bias.

Zinc Sulfide-selenium X-ray Detector for Digital Radiography

Park, Ji-Koon,Kang, Sang-Sik,Kim, Jae-Hyung,Mun, Chi-Woong,Nam, Sang-Hee The Korean Institute of Electrical and Electronic 2002 Transactions on Electrical and Electronic Material Vol.3 No.4

The high bias voltage associated with the thick layer (typically 500-1000 ㎛) of selenium required to have an acceptable x-ray absorption in radiography and fluoroscopy applications may have some practical inconvenience. A hybrid x-ray detector with zinc sulfide-amorphous selenium structure has been developed to improve the x-ray sensitivity of a a-Se based flat-panel digital imaging detector. Photoluminescence(PL) characteristic of a ZnS:Ag phosphor layer showed a light emission peak centered at about 450 nm, which matches the sensitivity spectrum of selenium. The dark current of the hybrid detector showed similar characteristics with that of a a-Se detector. The x-ray sensitivity of hybrid and a-Se x-ray detector was 345 pC/㎠/mR and 295 pC/㎠/mR at an applied voltage of 10 V/㎛, respectively. The purpose of this study was to evaluate the pertinence of a solution using a thin selenium layer, as a photosensitive converter, with a thick coating of silver doped zinc sulfide phosphor.

A Study for Effects of Image Quality due to Scatter Ray produced by Increasing of Tube Voltage

Ji-Koon Park(박지군),Je-Hoon Jun(전제훈),Sung-Woo Yang(양승우),Kyo-Tae Kim(김교태),Il-Hong Choi(최일홍),Sang-Sik Kang(강상식) 한국방사선학회 2017 한국방사선학회 논문지 Vol.11 No.7

진단목적의 방사선 의료 영상의 활용의 증가에 따라 환자의 피폭 선량 증가와 의료영상의 진단적 가치 저하에 기여하는 산란선의 관리 및 저감을 위한 연구는 필수적이라 할 수 있다. 이에 본 연구에서는 관전압 증가에 따른 산란선의 증감이 영상 화질에 미치는 영향을 분석하였다. 이를 위해 ANSI 흉부 팬텀을 이용하여, 관전압 변화에 따른 산란선 발생 비율을 측정하고, 산란선의 발생에 따른 화질 영향을 RMS(Root Mean Square) 입상성 평가, RSD(Relative Standard Deviation) 및 NPS(Noise Power Spectrum) 분석을 통해 고찰하였다. 관전압 증가에 따른 산란선 발생비율은 73 kV 관전압에서 48.8%, 93 kV 관전압 인가시 80.1%로 점차 증가하는 것으로 확인되었다. 관전압 증가에 따른 산란선 증가의 화질 영향을 분석하기 위한 RMS 분석 결과, 관전압 증가에 따른 RMS 값이 증가하는 것으로 나타나 영상의 입상성이 떨어지는 결과로 도출되었다. 공간주파수 2.5 lp/mm에서의 NPS 값 또한 관전압 73 kV 인가에 비해 93kV 관전압 증가시 20% 정도 영상의 잡음이 증가하는 것으로 나타났다. 본 연구를 통하여 관전압 변화에 따른 산란선 발생이 화질에 미치는 영향을 확인할 수 있었으며, 이러한 연구 결과는 의료영상 품질 개선을 위한 연구의 기초 자료로서 활용 가능할 것으로 판단된다. In diagnostic medical imaging, it is essential to reduce the scattered radiation for the high medical image quality and low patient dose. Therefore, in this study, the influence of the scattered radiation on medical images was analyzed as the tube voltage increases. For this purpose, ANSI chest phantom was used to measure the scattering ratio, and the scattering effect on the image quality was investigated by RMS evaluation, RSD and NPS analysis. It was found that the scattering ratio with increasing x-ray tube voltage gradually increased to 48.8% at 73 kV tube voltage and to 80.1% at 93 kV tube voltage. As a result of RMS analysis for evaluating the image quality, RMS value according to increase of tube voltage was increased, resulting in low image quality. Also, the NPS value at 2.5 lp/mm spatial frequency was increased by 20% when the tube voltage was increased by 93 kV compared to the tube voltage of 73 kV. From this study, it can be seen that the scattering radiation have a significant effect on the image quality according to the increase of x-ray tube voltage. The results of this study can be used as basic data for the improvement of medical imaging quality.

The Effects of Image Quality due to Scattering X-ray according to increasing Patient Thickness

Ji-Koon Park(박지군),Sung-Woo Yang(양승우),Jae-Hoon Jun(전제훈),Su-Yeon Cho(조수연),Kyo-Tae Kim(김교태),Ye-Ji Heo(허예지),Sang-Sik Kang(강상식) 한국방사선학회 2017 한국방사선학회 논문지 Vol.11 No.7

본 연구에서는 피사체 두께 증가에 따른 산란선 발생이 의료 영상화질에 미치는 영향을 정량적으로 분석하기 위한 연구를 수행하였다. 기존 병원에서 검사빈도가 높은 흉부를 조직등가물질로 제작한 미국표준 협회(ANSI; American National Standards Institute) 팬텀을 이용하여 피사체 두께가 증가함에 따라 발생하는 산란선 비율을 MCNPX 전산모사 하였으며, 실제 측정값과의 비교 분석을 수행하였다. 또한 피사체 두께 증가에 따라 획득된 X선 영상을 이용하여 RMS 입상성 평가, RSD 및 NPS 분석을 통해 산란선 발생 증가 에 따른 화질 영향을 평가하였다. 흉부 팬텀위에 두께 1 인치의 아크릴 팬텀을 추가적으로 증가시키면서 분석한 결과, 표준 두께인 6.1 inc h에서 산란선 비율은 48.9 %를 기준으로 1 인치 증가시마다 57.2 %, 62.4 %, 66.8 %로 증가하는 것으로 나타났으며, 이는 MCNPX 모의실험과 실제 측정한 산란선량은 유사한 결과를 보였다. 획득한 영상의 RMS 측정 결과, 피사체 두께가 증가함에 따라 표준편차가 낮아지는 값으로 도출되었다. 하지만 이를 평균 입사 선량을 고려한 RDS 분석에서는 6.1 inch에서 0.028, 7.1 inch의 경우 0.039, 8.1 inch 경우 0.051 및 9.1 inch에 서 0.062으로 증가하는 결과를 나타났다. 이는 피사체 두께 증가에 따른 산란선 발생 증가가 신호대 잡음비를 감소시킨다는 것을 알 수 있었다. 또한 검출기에 입사한 산란선 분포만 이용하여 측정한 NPS 결과에서도 피사체 두께가 증가할수록 노이즈가 증가하는 결과로 도출되었다. In this study, scattering factors affecting the quality of medical images were quantitatively analyzed and investigated. MCNPX simulation was conducted by using ANSI phantom, made of tissue equivalent materials, to calculate the scattering ratio occurred by the increase of the object thickness. Then, the result of the simulation was compared with the result of actual radiation measurement. In addition, we evaluated the image quality by the RMS evaluation, RSD and NPS analysis using X-ray images acquired with increasing object thickness. Furthermore, the scattering ratio was analyzed by increasing the thickness of acrylic phantom on chest phantom. The result showed that the scattering ratio was increased to 57.2%, 62.4%, and 66.8% from 48.9%, respectively, when the acrylic phantom thickness was increased by 1 inch from 6.1 inches. The results of MCNPX simulation and the actual measured scattering dose showed similar results. Also, as a result of RMS measurement from acquired x-ray images, the standard deviation decreased as the object thickness increased. However, in the RSD analysis considering the average incident dose, the results were increased from 0.028 to 0.039, 0.051, 0.062 as the acrylic phantom thickness was increased from 6.1 inches to 7.1 inch, 8.1 inch, and 9.1 inch, respectively. It can be seen that the increase of the scattering effect due to the increase of the object thickness reduces the SNR. Also, the NPS results obtained by measuring scattered radiation incident on the detector resulted in the increase of the noise as the object thickness increased.

Study on Electrical Properties of X-ray Sensor Based on CsI:Na-Selenium Film

Park Ji-Koon,Kang Sang-Sik,Lee Dong-Gil,Choi Jang-Yong,Kim Jae-Hyung,Nam Sang-Hee The Korean Institute of Electrical and Electronic 2003 Transactions on Electrical and Electronic Material Vol.4 No.3

In this paper, we have introduced the x-ray detector built with a CsI:Na scintillation layer deposited on amorphous selenium. To determine the thickness of the CsI:Na layer, we have estimated the transmission spectra and the absorption of continuous x-rays in diagnostic range by using computer simulation (MCNP 4C). A x-ray detector with 65 ${\mu}m$-CsI:Na/30 ${\mu}m$-Se layer has been fabricated by a thermal evaporation technique. SEM and PL measurements have been performed. The dark current and x-ray sensitivity of the fabricated detector has been compared with that of the conventional a-Se detector with 100 ${\mu}m$ thickness. Experimental results show that both detectors exhibit a similar dark current, which was of a low value below $400 pA/cm^2$ at 10 V/${\mu}m$. However, the CsI:Na-Se detector indicates high x-ray sensitivity, roughly 1.3 times that of a conventional a-Se detector. Furthermore, a CsI:Na-Se detector with an aluminium reflective layer shows a 1.8 times higher x-ray sensitivity than an a-Se detector. The hybrid type detector proposed in this work exhibits a low dark current and high x-ray sensitivity, and, in particular, excellent linearity to the x-ray exposure dose.

Fabrication of Bendable Gd2O2S:Tb Intensifying Screen and Evaluation of Fatigue Properties

Ji-Koon Park(박지군),Sung-Woo Yang(양승우),Je-Hoon Jeon(전제훈),Joo-Hee Kim(김주희),Ye-Ji Heo(허예지),Sang-Sik Kang(강상식),Kyo-Tae Kim(김교태) 한국방사선학회 2017 한국방사선학회 논문지 Vol.11 No.7

본 연구에서는 연성을 형광체 층이 가질 수 있다면 외부의 기계적 외력에 대하여 장기간 안정성을 확보할 수 있을 것으로 기대하였다. 이에 본 연구에서는 스크린 프린팅 공법을 통하여 유연한 Gd2O2S:Tb 증감지를 제작하였고 장기적인 외력에 의한 피로누적과 반복적인 외력에 의한 피로누적에 따른 영향을 고찰하고자 RMS 분석과 히스토그램을 분석을 통하여 영상 균일도를 평가하였다. 연구 결과, 지속적인 외력에 대하여는 지배적인 픽셀 영역이 일정하게 유지되면서 RSD가 10% 이내를 만족하였으나, 반복적인 외력의 경우 지배적인 픽셀 영역이 3 영역으로 분할되며 영상 균일도에 악영향을 미치며 RSD가 10% 이상으로 증가하는 것으로 나타났다. 이러한 결과를 바탕으로 기존 방사선증감지에 대비하여 기계적 안정성을 확보함으로써 곡면 검출기의 적용 가능성을 제시하였으나 아직까지 플렉시블 검출기에 적용하기 위해서는 추가적인 연구가 필요할 것으로 사료된다. 이러한 결과 유연성을 가진 방사선 증감지는 다양한 곡면에 적용이 가능하므로 향후 핵의학, 치료용, 산업 분야 등과 같은 다양한 분야에 적용할 수 있을 것으로 기대된다. In this study, it was expected that long-term stability against external mechanical external force could be secured if the phosphor layer had ductility. In this study, a bendable Gd2O2S:Tb s ensitized paper was fabricated by screen printing method and the image uniformity was evaluated through RMS analysis and histogram analysis to investigate the effect of fatigue accumulation due to long-term external force and repetitive external force. As a result, the dominant pixel area is maintained constant and the relative standard deviation is less than 10% for the long-term external force. However, for the repetitive external force, the dominant pixel area is divided into three areas and the image uniformity is adversely affected. Based on these results, it is suggested that the curved surface detector can be applied by securing the mechanical stability against the existing radiation sensitized paper. However, further studies are needed to apply it to the flexible detector. As a result, flexible radiation sensitizers can be applied to various curved surfaces, and it is expected to be applicable to various fields such as nuclear medicine, medical treatment, and industrial fields in the future.

Synthesis and Characterization of Y₂O₃:Eu Fine Particle

Park, Ji-Koon,Kang, Sang-Sik,Kwak, Min-Gi,Choi, Seung-Suk,Kim, Jae-Hyung,Nam, Sang-Hee The Korean Institute of Electrical and Electronic 2005 Transactions on Electrical and Electronic Material Vol.6 No.4

[ $Y_2O_3:Eu$ ] powder was synthesized using a solution-combustion method by dissolving $(CH_3CO_2)_3Y$ and $(CH_3CO_2)_3$ Eu in methyl-alcohol solution. Results from X-ray diffractometery (XRD), thermogravimetry (TG)-differential thermal analysis (DTA) show that $Y_2O_3:Eu$ crystallizes completely when the dry powder is sintered at $500^{\circ}C$. The investigated optical properties were the photoluminescence emission spectra, the excitation spectra and luminescence decay curve. Europium (Eu) concentration had no observable effect on the optical spectrum which depended on the emission intensity. The mean lifetime of synthesized phosphors was $2.3\~2.6 ms$.

Measurement of the Photon Fluence for the Evaluation o f Photon Detection Efficienc y of Phot on Counting Sensor

Ji-Koon Park(박지군),Ye-Ji Heo(허예지),Kyo-Tae Kim(김교태),Si-Cheol Noh(노시철),Sang-Sik Kang(강상식) 한국방사선학회 2016 한국방사선학회 논문지 Vol.10 No.1

현재 CCD 및 TFT LCD 기반의 평판형 디지털 X선 센서를 이용한 많은 디지털 X선 영상장치가 활용되고 있으며, 특히 포톤계수형 센서 기술에 대한 많은 연구가 수행되고 있다. 본 연구에서는 포톤계수형 센서의 정량적 성능 평가 항목인 포톤계수효율을 측정하기 위해 포톤계수형 센서 물질에 입사되는 X선 플루엔스 측정하였다. IEC 61223-1-2 권고안의 RQA-M2 Radiation beam quality를 이용하여 포톤 플루엔스를 측정한 결과, 10 μm 핀홀 영역에서 입사 광자 플루엔스는 4 photon/unit area․ ․ μGy, 30 μm 핀홀 영역에서 약 50 photons/unit area ․ μGy, 100 μm 핀홀 영역에서 698 photons/unit area ․ μGy의 플루엔스로 규정할 수 있었다. 셋업된 입사 플루엔스를 이용하여 포톤계수형 센서 물질에서의 X선 조사시 출력파형을 측정함으로써 실제 포톤계수효율을 측정할 수 있을 것으로 판단된다. Recently, the various digital X-ray imaging devices using CCD and TFT LCD-based flat panel digital X-ray sensor are being used. In particular, a number of studies on photon counting sensor technique have been reported. In this study, the incident X-rays fluence on the photon counting sensor material was measured to estimate photon detection efficiency which is the quantitative performance evaluation factor of photon counting sensor. The result of measuring the photon fluence by using RQA-M2 Radiation beam quality of IEC 61223-1-2 recommendations, the incident photon fluence could be defined as about 4 photons/(0.01mm) 2 ․μGy within 10 ㎛ pin-hole area, and about 50 photons/(0.03mm) 2 ․μGy within 30 ㎛ pin-hole area, and about 698 photons/(0.1mm) 2 ․μGy within 100 ㎛ pin-hole area. Consequently, with the previously setup of the incident fluence, the measuring of actual photon counting efficiency by observing the output waveform of the photon counting sensor material was considered possible.

몬테카를로 시뮬레이션을 이용한 X선 의료영상 획득 시 산란선 발생 영향 연구

박지군(Ji-Koon Park),강상식(Sang-Sik Kang),양승우(Seung-Woo Yang),허예지(Ye-Ji Heo),김교태(Kyo-Tae Kim) 한국방사선학회 2018 한국방사선학회 논문지 Vol.12 No.5

방사선 영상 기술은 피사체의 조성 및 두께에 따라 변화되는 X선의 흡수계수 차이를 기반으로 형성되는 대조도를 영상화하는 기술로서 영상 검출기에 입사하는 1차선 뿐 만 아니라 산란선이 영상 품질에 큰 영향을 미친다. 이에 본 연구에서는 피사체 두께, 조사야 변화에 따라 발생하는 산란선이 영상 품질에 미치는 영향을 고찰하고자 몬테카를로 시뮬레이션을 통하여 FSR 및 SPR 분석을 수행하였다. 연구 결과, 피사체 두께에 따른 FSR은 최대 15.3%p, SPR은 2.00 ~ 4.54로 분석되었으나, 조사야 변화에 대해서는 일정한 값을 유지하는 것으로 분석되었다. 이러한 결과를 바탕으로 피사체 두께는 영상 품질에 영향을 미치는 인자로서 고려되어야 하지만, 조사야는 영상 품질에 영향을 미치지 못하는 인자임을 검증하였다. 이러한 본 연구 결과는 영상 품질 개선을 위한 산란선에 대한 기초 자료로서 활용할 수 있을 것으로 사료된다. The medical imaging technique images the contrast formed based on the difference in absorption coefficient of X-rays which changes according to the composition and thickness of the object. At this time, not only primary rays entering the image detector but also scattered rays greatly affect the image quality. Therefore, in this paper, Forward scattering rate and Scattered to primary ratio analysis were performed through Monte Carlo simulation in order to consider influence of scattered ray generated according to object thickness and radiation exposure area change on image quality. In the study, the Forward scattering rate corresponding to the thickness of the object was analyzed at a maximum of 15.3%p and the Scattered to primary ratio was analyzed at 2.00 to 4.54, but it was analyzed as maintaining a constant value for radiation exposure area change. Based on these results, the thickness of the object should be considered as a factor influencing the quality of the image, but radiation exposure area verified that it is a factor that does not affect the image quality. We believe that the results of this research can be utilized as basic information of scattered radiation to improve image quality.