Optimization of a Photon Rejecter to Separate Electronic Noise in a Photon-counting Detector

조효민,최유나,이승완,이영진,류현주,김희중 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.11

Photon counting-based x-ray imaging technology provides the capability to count individual photons and characterize photon energies. The cadmium telluride (CdTe)-based photon-counting detector is limited in capability, however, under a high x-ray flux. A photon rejecter composed of aluminum, for example, can reduce this limitation by modulating the incident number of photons. In addition to this function, the optimal photon rejecter can separates electronic noise, which degrades image quality. The aim of this work was to optimize the photon rejecter for high quality image acquisition by removing electronic noise from the actual pulse signal. The images and spectra were acquired using a micro-focus x-ray source with a CdTe-based photon-counting detector. We acquired data with various types of photon rejecter materials composed of aluminum (Al) and iodine at three different tube voltages (50, 70 and 90 kVp). A phantom composed of high atomic number materials was imaged to evaluate the efficiency of the photon rejecter. Photon rejecters composed of 1-mm Al, 10-mm Al, and a combination of 10-mm Al and iodine provided optimum capability at 50, 70 and 90 kVp, respectively. Each optimal combination of photon rejecter material and voltage effectively separated electronic noise from the actual pulse signal and gave highest contrast-to-noise ratio for materials on the image. These optimized types of photon rejecter can effectively discriminate electronic noise and improve image quality according to the different tube voltages.

포톤 탐사법을 이용한 개선된 점진적 포톤 매핑

이상길,신병석 (사)한국컴퓨터그래픽스학회 2010 컴퓨터그래픽스학회논문지 Vol.16 No.3

Photon mapping is a traditional global illumination method using many photons emitted from the light source for photo-realistic rendering. However, this method needs a lot of resources to perform tracing of millions of photons. Progressive photon mapping solves this problem. Typical progressive photon mapping performs ray tracing at first to find the hit points on diffuse surface of objects. Next, light source repeatedly emits a small number of photons in photon tracing pass, and power of photons in each sphere that has a fixed radius with the hit points in the center is accumulated. This method requires less resources than previous photon mapping, but it spends much time for gathering enough photons since each of photons progresses through a random direction and rendering high quality image. To improve the method, we propose photon probing that calculates variance of photons in the sphere and controls radius of sphere. In addition, we apply cone filter in radiance estimation step for reducing aliasing at the edges in result image. 포톤 매핑은 대표적인 전역 조명 방법으로써 광원에서 많은 수의 포톤을 방출하여 이를 이용해 사실적인 렌더링을 수행한다. 하지만 매우 많은 수의 포톤을 추적하기 때문에 실시간 렌더링이 힘들고 많은 양의 메모리를 사용하는 문제가 있다. 이러한 문제를 개선한 방법이 점진적 포톤 매핑이다. 기존의 점진적 포톤 매핑은 먼저 광선 추적법을 통해 각 광선과 물체와의 충돌 위치를 찾는다. 다음으로 포톤 추적 단계에서는 반복적으로 적은 수의 포톤을 방출하고, 충돌 위치를 중심으로 하며 고정된 반지름을 가지는 구 안에 들어오는 포톤으로 포톤의 밝기를 누적한다. 이 방법은 포톤 매핑보다 자원을 적게 소모하지만, 방출된 포톤이 임의의 방향으로 진행하기 때문에 충분한 포톤을 확보하고 부드러운 영상을 렌더링하기 위해 많은 시간이 필요하다. 이를 보완하기 위해 본 논문에서는 포톤 탐사 단계를 추가하여 구 안에 들어오는 포톤들의 분포를 계산하고 그에 따라 구의 반지름을 조절하는 방법을 제안한다. 또한 래디언스 추정 과정에 콘 필터를 적용하여 영상을 선명히 렌더링한다.

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.

Modelling atomic relaxation and bremsstrahlung in the deterministic code STREAM

Nhan Nguyen Trong Mai,Kyeongwon Kim,Deokjung Lee Korean Nuclear Society 2024 Nuclear Engineering and Technology Vol.56 No.2

STREAM, developed by the Computational Reactor Physics and Experiment laboratory (CORE) of the Ulsan National Institute of Science and Technology (UNIST), is a deterministic neutron- and photon-transport code primarily designed for light water reactor (LWR) analysis. Initially, the photon module in STREAM did not account for fluorescence and bremsstrahlung photons. This article presents recent developments regarding the integration of atomic relaxation and bremsstrahlung models into the existing photon module, thus allowing for the transport of secondary photons. The photon flux and photon heating computed with the newly incorporated models is compared to results obtained with the Monte Carlo code MCS. The incorporation of secondary photons has substantially improved the accuracy of photon flux calculations, particularly in scenarios involving strong gamma emitters. However, it is essential to note that despite the consideration of secondary photon sources, there is no noticeable improvement in the photon heating for LWR problems when compared to the photon heating obtained with the previous version of STREAM.

Image visualization of photon counting confocal microscopy using statistical estimation

Jang, J.Y.,Cho, M. Wissenschaftliche Verlagsgesellschaft m. b. H 2016 OPTIK -STUTTGART- Vol.127 No.2

<P>In this paper, we propose image visualization method of photon counting confocal microscopy using statistical estimation. Since high power coherent light source is used to record sectional images from micro-objects in conventional confocal microscopy, it may cause damage for a structure of micro-objects. Thus, low power coherent light source may be required. However, in low light level environment, it is difficult to capture sectional images of micro-objects. On the other hand, photon counting imaging technique can detect sectional images of micro-objects in photon-starved conditions. Therefore, in this paper, we apply a photon counting imaging technique to conventional confocal microscopy for visualization of micro-objects. Photon counting detection can be modeled by statistical process. To visualize micro objects under photon-starved conditions, statistical estimation methods such as maximum likelihood estimation can be used. In addition, we present color photon counting imaging system which considers different carried photon energy with each basic color channels. To prove and evaluate our method, we show simulation results for image visualization of photon counting confocal microscopy and calculate mean square error. (C) 2015 Elsevier GmbH. All rights reserved.</P>

Colloidal Optics and Photonics: Photonic Crystals, Plasmonics, and Metamaterials

이재원,이승우 한국광학회 2023 Current Optics and Photonics Vol.7 No.6

The initial motivation in colloid science and engineering was driven by the fact that colloids can serve as excellent models to study atomic and molecular behavior at the mesoscale or microscale. The thermal behaviors of actual atoms and molecules are similar to those of colloids at the mesoscale or microscale, with the primary distinction being the slower dynamics of the latter. While atoms and molecules are challenging to observe directly in situ, colloidal motions can be easily monitored in situ using simple and versatile optical microscopic imaging. This foundational approach in colloid research persisted until the 1980s, and began to be extensively implemented in optics and photonics research in the 1990s. This shift in research direction was brought by an interplay of several factors. In 1987, Yablonovitch and John modernized the concept of photonic crystals (initially conceptualized by Lord Rayleigh in 1887). Around this time, mesoscale dielectric colloids, which were predominantly in a suspended state, began to be self-assembled into three-dimensional (3D) crystals. For photonic crystals operating at optical frequencies (visible to near-infrared), mesoscale crystal units are needed. At that time no manufacturing process could achieve this, except through colloidal self-assembly. This convergence of the thirst for advances in optics and photonics and the interest in the expanding field of colloids led to a significant shift in the research paradigm of colloids. Initially limited to polymers and ceramics, colloidal elements subsequently expanded to include semiconductors, metals, and DNA after the year 2000. As a result, the application of colloids extended beyond dielectric-based photonic crystals to encompass plasmonics, metamaterials, and metasurfaces, shaping the present field of colloidal optics and photonics. In this review we aim to introduce the research trajectory of colloidal optics and photonics over the past three decades; To elucidate the utility of colloids in photonic crystals, plasmonics, and metamaterials; And to present the challenges that must be overcome and potential research prospects for the future.

The Effect of Photon Energy on the Intensity-modulated Radiation Therapy Plan for Prostate Cancer: a Planning Study

정진범,김재성,김인아,Jeong-Woo Lee,조웅,서태석 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.1

In this study, the effect of the beam energy on the intensity modulated radiation therapy (IMRT) plan for prostate cancer was studied for competing IMRT plans optimized for delivery with either 6- or 15-MV photons. This retrospective planning study included 10 patients treated for localized prostate cancer at the Seoul National University Bundang Hospital. A dose of 66 Gy was prescribed in 33 daily fractions of 2 Gy. For inverse IMRT treatment planning, we used a 7-coplanar non-opposed beam arrangement at 0, 50, 100, 150, 210, 260, and 310 degree angles. To ensure that differences among the plans were due only to energy selection, the beam arrangement, number of beam, and dose constraints were kept constant for all plans. The dose volume histograms (DVHs) for the 6- and 15-MV plans were compared for the planning target volume (PTV) and for organs at risk (OAR), such as the rectum, bladder and both femoral heads. The conformal index was defined as the ratio of the 95% isodose volume divided by the PTV volume enclosed by the 95% isodose line, because we selected the 95% isodose line as our reference. Doses received by the 95% and 5% volume of the PTV were less than or equal to 1% for 6-MV compared to the 15-MV IMRT plan for 10 patients. Percentage of doses received by the 10% volume of the bladder and rectum were less than or equal to 1%. Percentage of doses received by the 30 and 50% volume of bladder and rectum were 1 ∼ 2% higher for 6-MV photons. Also, percentage of dose received by the 10% and 50% volume of the right and the left femur heads were 4 ∼ 5% higher for 6-MV photons. The mean homogeneity index for the 6-MV and 15-MV photon plans was 1.06. The mean conformity index of 95% was 1.04 ± 0.01 and 1.12 ± 0.02 for 6-MV and 15-MV, respectively, but this difference was not statistically significant. The mean monitor unit was 812 ± 40 and 716 ± 33 for the 6-MV and the 15-MV photon plans, respectively. The 6-MV photon plan delivers 13.4% more MU than the 15-MV plan. The-15 MV dose distributions and DVHs of the PTV generated by the clinical treatment planning calculations were as good as, or slightly better than, those generated for 6-MV photons. The organs at risk, such as the rectum, bladder, and femoral head were also similar, with the DVH curve for the 6-MV plan being slightly higher near the low-dose region, but lower near the high-dose region. Therefore, we recommend the use of 15-MV photons for IMRT of prostate cancer to achieve better in target coverage, in addition, the integrated dose can be reduce by using IMRT with 15 MV photons.

ICESat-2 고도계 자료를 활용한 여름철 북극 융빙호 탐지

한대현 ( Daehyeon Han ),김영준 ( Young Jun Kim ),정시훈 ( Sihun Jung ),심성문 ( Seongmun Sim ),김우혁 ( Woohyeok Kim ),장은나 ( Eunna Jang ),임정호 ( Jungho Im ),김현철 ( Hyun-cheol Kim ) 대한원격탐사학회 2021 大韓遠隔探査學會誌 Vol.37 No.5

북극의 융빙호(melt pond)는 해빙 면적 감소 및 북극 빙권 변화에 중요한 역할을 하기 때문에 융빙호의 정확한 관측이 필요하다. 미국 NASA의 차세대 고도계 위성인 Ice, Cloud, and Land elevation Satellite-2 (ICESat-2)는 532 nm의 녹색 레이저를 발사한 뒤 반사되는 광자(photon)의 이동 시간을 계산하여 전 지구적으로 고해상도 고도 정보를 관측한다. ICESat-2는 현재 널리 쓰이고 있는 고도계인 CryoSat-2에 비해 세밀한 관측이 가능하기 때문에, Cryosat-2에서 관측할 수 없는 작은 규모의 융빙호를 탐지할 수 있을 것으로 기대된다. ICESat-2의 기본적인 정보로는 표면 높이(surface height)와 반사되는 광자의 수(photon count)가 있다. 본 연구에서는 각 ICESat-2 지점을 중심으로 10 m 길이의 segment를 생성하여 segment 내의 높이 표준편차와 총 광자 수를 활용한 융빙호 탐지 알고리즘을 제시하였다. 융빙호는 표면이 해빙에 비해 매끄러워서 높이의 분산이 적으므로 높이의 표준편차를 활용하여 일차적으로 융빙호와 해빙을 분류하였다. 그 다음으로는 융빙호 중에서 표면이 물인 융빙호와 얼음 표면인 융빙호를 분류하였다. 표면이 물인 융빙호는 광자를 많이 흡수하기 때문에 단위 segment 내에서 반사되어 수집된 광자의 수가 적으며, 반대로 얼음으로 덮인 융빙호는 반사되는 광자의 수가 많다. 결과적으로 본 연구에서 제시하는 융빙호 탐지 방법을 통해 물과 얼음으로 덮인 융빙호를 구별하여 탐지할 수 있다. Sentinel-2 광학 영상을 활용하여 융빙호 탐지 결과의 정성적인 분석을 하였다. 그 결과 Sentinel-2 광학 영상으로 구분하기 어려운 표면이 물인 융빙호와 얼음인 융빙호를 ICESat-2를 활용해 효과적으로 분류하였다. 마지막으로 고도계 위성 및 광학 영상을 활용한 융빙호 탐지의 고찰을 서술하였다. As the Arctic melt ponds play an important role in determining the interannual variation of the sea ice extent and changes in the Arctic environment, it is crucial to monitor the Arctic melt ponds with high accuracy. Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2), which is the NASA’s latest altimeter satellite based on the green laser (532 nm), observes the global surface elevation. When compared to the CryoSat-2 altimetry satellite whose along-track resolution is 250 m, ICESat-2 is highly expected to provide much more detailed information about Arctic melt ponds thanks to its high along-track resolution of 70 cm. The basic products of ICESat-2 are the surface height and the number of reflected photons. To aggregate the neighboring information of a specific ICESat-2 photon, the segments of photons with 10 m length were used. The standard deviation of the height and the total number of photons were calculated for each segment. As the melt ponds have the smoother surface than the sea ice, the lower variation of the height over melt ponds can make the melt ponds distinguished from the sea ice. When the melt ponds were extracted, the number of photons per segment was used to classify the melt ponds covered with open-water and specular ice. As photons are much more absorbed in the water-covered melt ponds than the melt ponds with the specular ice, the number of photons per segment can distinguish the water- and ice-covered ponds. As a result, the suggested melt pond detection method was able to classify the sea ice, water-covered melt ponds, and ice-covered melt ponds. A qualitative analysis was conducted using the Sentinel-2 optical imagery. The suggested method successfully classified the water- and ice-covered ponds which were difficult to distinguish with Sentinel-2 optical images. Lastly, the pros and cons of the melt pond detection using satellite altimetry and optical images were discussed.

Doppler-free Two-photon Spectroscopy of Yb Atoms and Efficient Generation of a Cascade of Two Photons at 611.3 nm and 555.8 nm

송민수,윤태현,윤두성 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.41

We performed high-resolution Doppler-free two-photon spectroscopy of Yb atoms in an effusive atomic beam and generated a cascade of two photons at 611.3 nm (idler) and 555.8 nm (signal) with a narrow bandwidth of 37 MHz. Efficient population transfer from the ground state (6s^2 ^1S_0) to the upper state (6s7s ^1S_0), where direct transition at 291.1 nm is dipole forbidden, was achieved through a resonant two-photon excitation enhanced by the electromagnetically-induced transparency mediated by the intermediate state (6s6p ^1P_1). From the upper state, a cascade of two photons in sequence was emitted via the spin triplet state (6s2 ^3P_1). Numerical calculations of the density matrix equations taking into account the residual Doppler effect and strong driving fields explain quantitatively the experimental results for the dependences of the idler and the signal beam intensities on the various parameters of the driving fields. We report on the generation of a cascade of two photons with fluxes at the level of a few times 106 photons/s detected at a solid angle of 0.01 sr.

Selection of stimulated Raman scattering signal by entangled photons

Munkhbaatar, Purevdorj,Myung-Whun, Kim Elsevier 2017 OPTICS COMMUNICATIONS - Vol.383 No.-

<P><B>Abstract</B></P> <P>We propose an excitation-probe measurement method utilizing entangled photon pulses. The excitation-probe signal is dominated by stimulated Raman scattering as well as two-photon absorption when the time delay between the excitation pulse and the probe pulse is shorter than the pulse duration. We demonstrate that the two-photon-absorption signal can be suppressed when the photons of the pulses are entangled. The stimulated Raman scattering signal can be composed of many peaks distributed over broad photon energies owing to the transitions between numerous quantum states in complex materials. We show that the desired peaks among the many peaks can be selected by controlling the thickness of the nonlinear crystal, the pump pulse center frequency, and the polarization of the excitation pulse and probe pulse.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We propose an excitation-probe measurement method utilizing entangled photon pulses. </LI> <LI> The excitation-probe signal is dominated by nonlinear processes including stimulated Raman scattering. </LI> <LI> We demonstrate that the stimulated Raman scattering signal can be relatively enhanced by the entangled photons. </LI> <LI> The stimulated Raman scattering signal si composed of many peaks distributed over broad photon energies. </LI> <LI> Only the desired peaks among those many peaks can be selected by controlling the thickness of the nonlinear crystal. </LI> </UL> </P>