• Journal of Korean Neurosurgical Society
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• 제63권4호
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• pp.415-426
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• 2020

Arteriovenous malformations (AVMs) are congenital anomalies of the cerebrovascular system. AVM harbors 2.2% annual hemorrhage risk in unruptured cases and 4.5% annual hemorrhage risk of previously ruptured cases. Stereotactic radiosurgery (SRS) have been shown excellent treatment outcomes for patients with small- to moderated sized AVM which can be achieved in 80-90% complete obliteration rate with a 2-3 years latency period. The most important factors are associated with obliteration after SRS is the radiation dose to the AVM. In our institutional clinical practice, now 22 Gy (50% isodose line) dose of radiation has been used for treatment of cerebral AVM in single-session radiosurgery. However, dose-volume relationship can be unfavorable for large AVMs when treated in a single-session radiosurgery, resulting high complication rates for effective dose. Thus, various strategies should be considered to treat large AVM. The role of pre-SRS embolization is permanent volume reduction of the nidus and treat high-risk lesion such as AVM-related aneurysm and high-flow arteriovenous shunt. Various staging technique of radiosurgery including volume-staged radiosurgery, hypofractionated radiotherapy and dose-staged radiosurgery are possible option for large AVM. The incidence of post-radiosurgery complication is varied, the incidence rate of radiological post-radiosurgical complication has been reported 30-40% and symptomatic complication rate was reported from 8.1% to 11.8%. In the future, novel therapy which incorporate endovascular treatment using liquid embolic material and new radiosurgical technique such as gene or cytokine-targeted radio-sensitization should be needed.

• 한국방사선학회논문지
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• 제14권4호
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• pp.367-373
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• 2020

물체와 X선의 상호작용로 발생하는 산란선으로 야기되는 공간 산란선량은 대부분이 저에너지 영역의 전자기파로 인체에 비교적 쉽게 흡수되어 방사선 피폭정도가 증가하게 된다. 이러한 공간 산란 선량은 방사선작업 종사자 및 환자의 방사선 피폭 정도 지표로도 사용되고 있으며 간접적으로 발생하는 공간 산란 선량을 줄여 피폭을 저감화하기 위한 방안의 필요성이 마련될 필요성이 있다. 이에 본 연구에서는 공간산란 선량을 저감화 방안으로 무납 방사선 차폐 시트를 제시하였고 가슴 X선 촬영검사를 기준으로 몬테카를로(MC; Monte Carlo) 시뮬레이션을 수행하여 거리 변화에 따른 갑상샘과 생식선 위치에서 흡수되는 산란선의 흡수선량을 산출하였고 실측치와 차폐율을 비교 평가하였다.

• 대한방사선기술학회지:방사선기술과학
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• 제43권5호
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• pp.375-382
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• 2020

PET/CT is a medical equipment that detects 0.511 MeV of gamma rays. The radiation workers are inevitably exposed to ionizing radiation in the process of handling the isotope. Accordingly, PET/CT workers use syringe shields made of lead and tungsten to protect their hands. However, lead and tungsten are known to generate very high scattering particles by interacting with gamma rays. Therefore, in this study, we tried to find out the effect on the scattering particles emitted from the syringe shield. In the experiment, first, the exposure dose to the hand (Rod phantom) was evaluated according to the metal material (lead, tungsten, iron, stainless steel) using Monte Carlo simulation. The exposure dose was compared according to whether or not plastic is attached. Second, the exposure dose of scattering particles was measured using a dosimeter and lead. As a result of the experiment, the shielding rate of plastics using the Monte Carlo simulation showed the largest difference in dose of about 40 % in lead, and the lowest in iron, about 15 %. As a result of the dosimeter test, when the plastic tape was wound on lead, it was found that the reduction rate was about 15 %, 28 %, and 39 % depending on the thickness. Based on the above results, it was found that 0.511 MeV of gamma ray interacts with the shielding tool to emit scattered rays and has a very large effect on radiation exposure. However, it was considered that the scattering particles could be sufficiently removed with plastics with a low atomic number. From now on, when using high-energy radiation, the shielding tool and the skin should not be in direct contact, and should be covered with a material with a low atomic number.

• 한국발생생물학회지:발생과생식
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• 제22권1호
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• pp.19-27
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• 2018

In the present study, we employed Hershberger assay to determine possible androgenic or antiandrogenic activities of three di-2-ethylhexyl phthalate (DEHP) substitute candidates. The assay was carried out using immature castrated Sprague-Dawley male rats. After 7 days of the surgery, testosterone propionate (TP, 0.4 mg/kg/day) and test materials (low dose, 40 mg/kg/day; high dose, 400 mg/kg/day) were administered for 10 consecutive days by subcutaneous (s.c.) injection and oral gavage, respectively. Test materials were DEHP, 2-ethylhexyl oleate (IOO), 2-ethylhexyl stearate (IOS) and triethyl 2-acetylcitrate (ATEC). The rats were necropsied, and then the weights of five androgen-dependent tissues [ventral prostate, seminal vesicle, coagulating glands, levator ani-bulbocavernosus (LABC) muscle, paired Cowper's glands, and glans penis] and four androgen-insensitive tissues (kidney, adrenal glands, spleen and liver) were measured. All test materials including DEHP did not exhibit any androgenic activity in the assay. On the contrary, antiandrogen-like activities were found in all test groups, and the order of the intensity was ATEC < DEHP < ISO < IOO in the five androgen-sensitive tissues. There was no statistical difference between low dose treatment and high dose treatment of all replacement candidate groups. In DEHP groups, high dose treatment exhibited significant weight gains in LABC and Glan Penis. There was no statistical difference in androgen-insensitive tissue measurements. Since the effects of ATEC treatment on the accessory sex organs were much less or not present at all when compared to those of DEHP, ATEC could be a strong candidate to replace DEHP. IOO treatment brought most severe weight reduction in all of androgen-sensitive tissues, so this material should be excluded for further screening of DEHP substitute selection.

• 한국의학물리학회지:의학물리
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• 제29권4호
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• pp.150-156
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• 2018

This study aims to develop an improved Feldkamp-Davis-Kress (FDK) reconstruction algorithm using anisotropic total variation (ATV) minimization to enhance the image quality of low-dose cone-beam computed tomography (CBCT). The algorithm first applies a filter that integrates the Shepp-Logan filter into a cosine window function on all projections for impulse noise removal. A total variation objective function with anisotropic penalty is then minimized to enhance the difference between the real structure and noise using the steepest gradient descent optimization with adaptive step sizes. The preserving parameter to adjust the separation between the noise-free and noisy areas is determined by calculating the cumulative distribution function of the gradient magnitude of the filtered image obtained by the application of the filtering operation on each projection. With these minimized ATV projections, voxel-driven backprojection is finally performed to generate the reconstructed images. The performance of the proposed algorithm was evaluated with the catphan503 phantom dataset acquired with the use of a low-dose protocol. Qualitative and quantitative analyses showed that the proposed ATV minimization provides enhanced CBCT reconstruction images compared with those generated by the conventional FDK algorithm, with a higher contrast-to-noise ratio (CNR), lower root-mean-square-error, and higher correlation. The proposed algorithm not only leads to a potential imaging dose reduction in repeated CBCT scans via lower mA levels, but also elicits high CNR values by removing noisy corrupted areas and by avoiding the heavy penalization of striking features.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1633-1637
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• 2019

While considering the photon attenuation coefficient (${\mu}$) and its related parameters for photons shielding, it is necessary to account for its transmitted and reflected photons energy spectra and dose contribution. Monte Carlo simulation was used to study the efficiency of clay ($1.99g\;cm^{-3}$) as a shielding material below 150 keV photon. Am-241 gamma source and an X-ray of 150 kVp were calculated. The calculated value of ${\mu}$ for Am-241 is higher within 5.61% compared to theoretical value for a single-energy photon. The calculated half-value layer (HVL) is 0.9335 cm, which is lower than that of ordinary concrete for X-ray of 150 kVp. A thickness of 2 cm clay was adequate to attenuate 90% and 85% of the incident photons from Am-241 and X-ray of 150 kVp, respectively. The same thickness of 2 cm could shield the gamma source dose rate of Am-241 (1 MBq) down to $0.0528{\mu}Sv/hr$. For X-ray of 150 kVp, photons below 60 keV were significantly decreased with 2 cm clay and a dose rate reduction by ~80%. The contribution of reflected photons and dose from the clay is negligible for both sources.

• 한국방사선학회논문지
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• 제17권7호
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• pp.1041-1047
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• 2023

고 해상력 CT에 해당하는 관자뼈 CT는 높은 관전압과 얇은 단면두께 등의 적용으로 스캔 선량이 인접 부위 검사보다 높다. 이에 검사조건 중 재구성 알고리즘을 변화 적용하여 검사 선량을 줄이면서 병변에 대한 민감도가 우수한 알고리즘을 찾아 유의성과 임상 기초자료 제공 가능성을 알아보았다. 그 결과 100 kVp로 관전압을 낮추어 적용 시 선량이 약 35.6% 감소하였고, 100 kVp로 획득한 Raw data에 Definition 알고리즘 적용 시 SNR, CNR이 우수하였으며 다른 알고리즘과 비교 시 통계적으로 유의한 차이를 보였다(p<0.05). 그리고 구조적 유사도를 비교한 결과 SSIM index가 ROI 별 0.776, 0.813, 0.741로 분석되었다. 따라서 관자뼈 CT 스캔에서 알고리즘 변경적용은 CT 검사로 발생하는 선량을 일부 감소시킬 수 있고 임상 기초자료 측면에서 매우 의미가 있다고 생각한다.

• 대한방사선기술학회지:방사선기술과학
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• 제46권6호
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• pp.519-526
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• 2023

This study was intended to evaluate the shielding rate of radiation shields manufactured using 3D printers that have recently been used in various fields by comparing them with existing shields made of lead, and to find out their applicability through experiments. A 3D printer shield made of tungsten filament 1 mm, 2 mm, 4 mm shield, RNS-TX (nanotungsten) 1.1 mm, lead 0.2 mmPb, and 1mmPb were exposed to ^99mTc, ¹⁸F, and ²⁰¹TI for 15, 30, 45 minutes, and 60 minutes after measuring cumulative dose three times. Based on this, the shielding rate of each shield was calculated based on the dose in the absence of the shield. In addition, ^99mTc, ¹⁸F, and ²⁰¹TI were located 100 cm away from the phantom in which the OSLD nano Dot device was inserted, and if there was no shield for 60 minutes, the dose of thyroid was measured using 1.0 mm of lead shield, 1.1 mm of RNS-TX shield, and 2 mm of tungsten shield made by 3D printer. The use of shields during radiation shielding emitted from open radiation sources all resulted in a reduction in dose. The radiation dose emitted from the radionuclides under the experiment was all reduced when the shield was used. This study has been confirmed that tungsten is a material that can replace lead due to its excellent performance and efficiency as shield, and that it even shows the possibility of manufacturing a customized shield using 3D printer.

• Korean Journal of Radiology
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• 제23권4호
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• pp.402-412
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• 2022

Objective: To evaluate the image quality and lesion detectability of lower-dose CT (LDCT) of the abdomen and pelvis obtained using a deep learning image reconstruction (DLIR) algorithm compared with those of standard-dose CT (SDCT) images. Materials and Methods: This retrospective study included 123 patients (mean age ± standard deviation, 63 ± 11 years; male:female, 70:53) who underwent contrast-enhanced abdominopelvic LDCT between May and August 2020 and had prior SDCT obtained using the same CT scanner within a year. LDCT images were reconstructed with hybrid iterative reconstruction (h-IR) and DLIR at medium and high strengths (DLIR-M and DLIR-H), while SDCT images were reconstructed with h-IR. For quantitative image quality analysis, image noise, signal-to-noise ratio, and contrast-to-noise ratio were measured in the liver, muscle, and aorta. Among the three different LDCT reconstruction algorithms, the one showing the smallest difference in quantitative parameters from those of SDCT images was selected for qualitative image quality analysis and lesion detectability evaluation. For qualitative analysis, overall image quality, image noise, image sharpness, image texture, and lesion conspicuity were graded using a 5-point scale by two radiologists. Observer performance in focal liver lesion detection was evaluated by comparing the jackknife free-response receiver operating characteristic figures-of-merit (FOM). Results: LDCT (35.1% dose reduction compared with SDCT) images obtained using DLIR-M showed similar quantitative measures to those of SDCT with h-IR images. All qualitative parameters of LDCT with DLIR-M images but image texture were similar to or significantly better than those of SDCT with h-IR images. The lesion detectability on LDCT with DLIR-M images was not significantly different from that of SDCT with h-IR images (reader-averaged FOM, 0.887 vs. 0.874, respectively; p = 0.581). Conclusion: Overall image quality and detectability of focal liver lesions is preserved in contrast-enhanced abdominopelvic LDCT obtained with DLIR-M relative to those in SDCT with h-IR.

• 한국입자에어로졸학회지
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• 제16권4호
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• pp.73-94
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• 2020

Particulate infectious sources, including infectious viruses, can float in the air, causing airborne infections. To prevent indoor airborne infection, dilution control by ventilation and indoor air cleaners are frequently used. In this study, the risk of airborne infection by the operation of these two techniques was evaluated. In case of dilution control by ventilation, a high efficiency air filter was embedded at the inlet of supply air. In this study, infectious source reduction devices such as indoor air cleaner include all kinds of mechanical-filters, UV-photo catalysts and air ionizers through which air flow is forced by fans. Two mathematical models for influenza virus were applied in an infant care room where infants and young children are active, and the risk reduction efficiency was compared. As a result, in the case of individually operating the ventilator or the infectious source reduction device, the airborne infection risk reduction efficiencies were 55.2~61.2% and 53.8~59.9%, respectively. When both facilities were operated, it was found that the risk of airborne infection was reduced about 72.2~76.8%. Therefore, simultaneous operation of ventilation equipment and infectious source reduction device is the most effective method for safe environment that minimizes the risk of airborne infection of respiratory infectious diseases. In the case of a space where sufficient ventilation operation is difficult, it was found that the operation of an infectious source reduction device is important to prevent the spread of infectious diseases. This study is meaningful in that it provides an academic basis for strategies for preventing airborne infection of respiratory infectious diseases.