• 대한의용생체공학회:의공학회지
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• 제37권2호
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• pp.68-74
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• 2016

In this study, we investigated the rotational characteristics which were comprised of directionality and linearity of target registration error (TRE) as a study in advance to enhance the accuracy of contour-based registration in neuronavigation. For the experiment, two rigid head phantoms that have different faces with specially designed target frame fixed inside of the phantoms were used. Three-dimensional coordinates of facial surface point cloud and target point of the phantoms were acquired using computed tomography (CT) and 3D scanner. Iterative closest point (ICP) method was used for registration of two different point cloud and the directionality and linearity of TRE in overall head were calculated by using 3D position of targets after registration. As a result, it was represented that TRE had consistent direction in overall head region and was increased in linear fashion as distance from facial surface, but did not show high linearity. These results indicated that it is possible for decrease TRE by controlling orientation of facial surface point cloud acquired from scanner, and the prediction of TRE from surface registration error can decrease the registration accuracy in lesion. In the further studies, we have to develop the contour-based registration method for improvement of accuracy by considering rotational characteristics of TRE.

• 대한방사선기술학회지:방사선기술과학
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• 제39권4호
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• pp.631-636
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• 2016

공간 분해능을 평가하기 위해서 이제까지는 일정하게 두 물체의 간격(이중 표적)을 근접한 것부터 점점 떨어진 간격으로 만들어진 테스트 패턴이나 팬텀을 이용하였다. 이러한 방법으로 공간분해능을 평가하면 분해능은 테스트용으로 제작된 팬텀에 있는 표적 간격으로 제한된다. 본 연구는 이러한 문제를 극복하고자 1개의 단일 표적으로 공간 분해능을 간편하게 측정할 수 있는 새로운 방법을 제안하고 검증한 것이다. 이를 위해 PSF 및 JND를 이용하여 공간 분해능을 추정하는 개념을 제시하였다. 이렇게 유도된 공간 분해능 추정 이론을 검증하기 위해, 상용 팬텀을 이용하여 실험하였다. 실험으로 얻어진 디지털 영상에서 라인 픽셀 프로파일을 구하기 위해 만든 LabVIEW 프로그램을 이용하여 분석한 결과, 본 연구에서 유도한 단일 표적을 이용한 공간 분해능 추정 이론과 실험적으로 일치하는 것을 알 수 있었다. 실험 결과로 디지털 영상에서 공간분해능의 상대적 평가는 단일 표적을 가지고도 충분하다는 것을 증명할 수 있었다. 따라서 단일 표적 공간분해능 평가법을 이용하면 이제까지 사용되어 왔던 이중 표적을 이용한 공간분해능 평가의 한계를 극복할 수 있다.

• Imaging Science in Dentistry
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• 제47권3호
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• pp.199-207
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• 2017

Purpose: Evaluation of alveolar bone is important in the diagnosis of dental diseases. The periodontal ligament space is difficult to clearly depict in cone-beam computed tomography images because the reconstruction filter conditions during image processing cause image blurring, resulting in decreased spatial resolution. We examined different reconstruction filters to assess their ability to improve spatial resolution and allow for a clearer visualization of the periodontal ligament space. Materials and Methods: Cone-beam computed tomography projections of 2 skull phantoms were reconstructed using 6 reconstruction conditions and then compared using the Thurstone paired comparison method. Physical evaluations, including the modulation transfer function and the Wiener spectrum, as well as an assessment of space visibility, were undertaken using experimental phantoms. Results: Image reconstruction using a modified Shepp-Logan filter resulted in better sensory, physical, and quantitative evaluations. The reconstruction conditions substantially improved the spatial resolution and visualization of the periodontal ligament space. The difference in sensitivity was obtained by altering the reconstruction filter. Conclusion: Modifying the characteristics of a reconstruction filter can generate significant improvement in assessments of the periodontal ligament space. A high-frequency enhancement filter improves the visualization of thin structures and will be useful when accurate assessment of the periodontal ligament space is necessary.

• Nuclear Engineering and Technology
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• 제53권12호
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• pp.4158-4165
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• 2021

In this study, tissue equivalency (TE) of a newly developed epoxy-based phantom to 3-5 years child's tissue was investigated in paediatric energy range. Epoxy-based TE-phantoms were produced at different glandular/adipose (G/A) ratios of 17/83%, 31/69%, 36/64% and 10/90%. A procedure was developed in which specific amounts of boron, calcium, magnesium, sulphur compounds are mixed with epoxy resin, together with other minor substitutes. In paediatric energy range of 40-60 kV_p half-value layer (HVL) values were measured and then Hounsfield Units (HU) were determined from Computed Tomography(CT) scans taken in the X-ray energy range of 80-120kV_p. It is found that radiation absorption properties of these phantoms in terms of the measured HVL values related to linear attenuation coefficients (µ) are very well mimicking a 3 years child's soft tissue in case a ratio of 10/90%G/A. Additionally, the HU values of phantoms were determined from the CT scans. The HU = 47.8 ± 4.8 value was found for the epoxy-based phantom produced at a ratio of 10/90%G/A. The obtained HVL and HU values also support the suitability of the new epoxy based-phantom produced at a ratio of 10/90%G/A for a satisfactory mimicking a 3 years child's soft tissue by 5%. Thus they can have a potential use to perform the quality controls of medical X-ray systems and dose optimization studies.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4698-4707
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• 2022

As part of the ICRP Task Group 103 project, we developed ten thyroid models for the pediatric mesh-type reference computational phantoms (MRCPs). The thyroid is not only a radiosensitive target organ needed for effective dose calculation but an important source region particularly for radioactive iodines. The thyroid models for the pediatric MRCPs were constructed by converting those of the pediatric voxel-type reference computational phantoms (VRCPs) in ICRP Publication 143 to a high-quality mesh format, faithfully maintaining their original topology. At the same time, we improved several anatomical parameters of the thyroid models for the pediatric MRCPs, including the mass, overlying tissue thickness, location, and isthmus dimensions. Absorbed doses to the thyroid for the pediatric MRCPs for photon external exposures were calculated and compared with those of the pediatric VRCPs, finding that the differences between the MRCPs and VRCPs were not significant except for very low energies (<0.03 MeV). Specific absorbed fractions (target ⟵ thyroid) for photon internal exposures were also compared, where significant differences were frequently observed especially for the target organs/tissues close to the thyroid (e.g., a factor of ~1.2-~327 for the thymus as a target) due mainly to anatomical improvement of the MRCP thyroid models.

• Nuclear Engineering and Technology
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• 제55권1호
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• pp.295-303
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• 2023

Whole-body counters are widely used to assess internal contamination after a nuclear accident. However, it is difficult to determine radioiodine activity due to limitations in conventional calibration phantoms. Inhaled or ingested radioiodine is heterogeneously distributed in the human body, necessitating time-dependent biodistribution for the assessment of the internal contamination caused by the radioiodine intake. This study aims at calculating counting efficiencies considering the biodistribution of ¹³¹I in whole-body counting measurement. Monte Carlo simulations with computational human phantoms were performed to calculate the whole-body counting efficiency for a realistic radioiodine distribution after its intake. The biodistributions of ¹³¹I for different age groups were computed based on biokinetic models and applied to age- and gender-specific computational phantoms to estimate counting efficiency. After calculating the whole-body counting efficiencies, the efficiency correction factors were derived as the ratio of the counting efficiencies obtained by considering a heterogeneous biodistribution of ¹³¹I over time to those obtained using the BOMAB phantom assuming a homogeneous distribution. Based on the correction factors, the internal contamination caused by ¹³¹I can be assessed using whole-body counters. These correction factors can minimize the influence of the biodistribution of ¹³¹I in whole-body counting measurement and improve the accuracy of internal dose assessment.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.1949-1958
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• 2023

The International Commission on Radiological Protection (ICRP) Publication 116 was released to provide a comprehensive dataset of the dose coefficients (DCs) for external exposures produced with the adult reference voxel phantoms of ICRP Publication 110. Although an advanced skeletal dosimetry method for photons and neutrons using fluence-to-dose response functions (DRFs) was introduced in ICRP Publication 116, the ICRP-116 skeletal DCs were calculated by using the simple method conventionally used (i.e., doses to red bone marrow and endosteum approximated by doses to spongiosa and/or medullary cavities). In the present study, the photon and neutron DRFs were used to produce skeletal DCs of the ICRP-110 reference phantoms, which were then compared with the ICRP-116 DCs. For photons, there were significant differences by up to ~2.8 times especially at energies <0.3 MeV. For neutrons, the differences were generally small over the entire energy region (mostly <20%). The general impact of the DRF-based skeletal DCs on the effective dose calculations was negligibly small, supporting the validity of the ICRP-116 effective DCs despite their skeletal DCs derived from the simple method. Meanwhile, we believe that the DRF-based skeletal DCs could be beneficial in better estimates of skeletal doses of individuals for risk assessments.

• 한국의학물리학회지:의학물리
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• 제34권2호
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• pp.15-22
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• 2023

This study compared the dose calculated using the electron Monte Carlo (eMC) dose calculation algorithm employing the old version (eMC V13.7) of the Varian Eclipse treatment-planning system (TPS) and its newer version (eMC V16.1). The eMC V16.1 was configured using the same beam data as the eMC V13.7. Beam data measured using the VitalBeam linear accelerator were implemented. A box-shaped water phantom (30×30×30 cm³) was generated in the TPS. Consequently, the TPS with eMC V13.7 and eMC V16.1 calculated the dose to the water phantom delivered by electron beams of various energies with a field size of 10×10 cm². The calculations were repeated while changing the dose-smoothing levels and normalization method. Subsequently, the percentage depth dose and lateral profile of the dose distributions acquired by eMC V13.7 and eMC V16.1 were analyzed. In addition, the dose-volume histogram (DVH) differences between the two versions for the heterogeneous phantom with bone and lung inserted were compared. The doses calculated using eMC V16.1 were similar to those calculated using eMC V13.7 for the homogenous phantoms. However, a DVH difference was observed in the heterogeneous phantom, particularly in the bone material. The dose distribution calculated using eMC V16.1 was comparable to that of eMC V13.7 in the case of homogenous phantoms. The version changes resulted in a different DVH for the heterogeneous phantoms. However, further investigations to assess the DVH differences in patients and experimental validations for eMC V16.1, particularly for heterogeneous geometry, are required.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2004년도 제29회 추계학술대회 발표논문집
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• pp.96-99
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• 2004

본 연구는 전신 GSO PET 스캐너를 사용하여 Cs-137 투과 선원을 이용한 감쇠보정기법들을 평가하는 것이다. 이를 위하여, 4개의 모양이 다른 팬텀들을 사용하여 감쇠보정기법들을 검사하였다. 뇌영상을 위하여 256 mm의 시야가 사용되었고, 약 110MBq의 F-18 선원이 팬텀실험을 위해 사용되었다. 감쇠를 보정하기위해서, 방출선원이 팬텀에 주입된 후, Cs-137점선원의 투과 스캔 데이터가 획득되었다. 방출선원 데이터는 산란보정을 하였고, 4가지 종류의 감쇠보정기법을 이용하여 감쇠보정을 하였다. 재구성된 팬텀 영상들이 비교평가되었고, 임상 뇌영상은 핵의학 의사들이 평가를 하였다. 결과적으로 균일성 평가를 위한 원형팬텀의 영상에서, 측정감쇠보정기법을 이용시 가운데 부분이 떨어져 보였으나, 나머지 감쇠보정 기법들에서는 균일하게 보였다. 임상 뇌 데이터의 경우, 두개골에 대한 감쇠 효과를 볼 수 있었고, 두개골에 대한 감쇠보정이 적용되지 않은 영상에서는 인공산물이 발생하는 것을 보여주었다. 결론적으로, 정량적 뇌영상에 대한 정확도를 높이기 위해서, 두개골에 대한 감쇠보정이 적용된 개선된 감쇠보정 방법이 요구되어진다. 본 연구는 앞으로 Cs-137 점선원을 이용한 감쇠보정기법이 포함된 뇌 PET 영상 장치를 개선하는데 유용할 것으로 사료된다.

• 한국전자파학회논문지
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• 제23권1호
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• pp.101-107
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• 2012

MICS 및 ISM 대역의 무선기기 설계 시에 인체 팬텀을 이용한 성능검증이 필수적으로 요구되고 있으나, 인체팬텀에 관한 연구 대부분이 휴대폰에 의한 생체 영향에 국한되어 있는 실정이다. 본 논문에서는 FCC에서 제안하고 있는 MICS 대역과 ISM 대역의 인체 팬텀에 대한 전기적 상수를 이용하여 준고체형 팬텀들을 제작하였다. 제작된 준 고체형 팬텀들은 각 대역에서 FCC에서 제시한 전기적 상수(MICS 대역에서 $\varepsilon_r=56.7$, $\sigma=0.94$, ISM 대역에서 $\varepsilon_r=52.7$, $\sigma=1.95$)들을 만족하였다. 또한, 제작된 준 고체형 팬텀의 재료들은 쉽게 구매 가능한 재료들로 구성되었으며, 팬텀 재료의 다양성을 위해서 각 대역에서 polyethylene과 TX-151을 이용한 방법과 글리세린을 이용한 두 가지 방법을 제시하였다. 제작된 준 고체형 팬텀은 평탄한 형태이며, 유전율 측정기로 제작후 1일 (24 시간)이 경과한 후 팬텀의 전기적 특성을 측정하였다.