• 한국대기환경학회지
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• 제27권1호
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• pp.63-72
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• 2011

This study describes the impact of positive sampling artifact caused by a filter-based sampling in the determination of ambient organic carbon (OC). Three different sampling media combinations were employed for this investigation: (1) Quartz filter-alone (Q-alone), (2) quartz filter behind quartz-fiber filter (QBQ), and (3) quartz filter and quartz filter behind Teflon filter (Q-QBT). The measurement of ambient OC was carried out at a semi-urban site near oceanside at the end of November of 2008. It was found that Q-alone sampling configuration resulted in a higher OC than QBQ and Q-QBT by 14% and 28%, respectively due to no correction for positive artifact caused by adsorption of gas-phase OC onto the filter. A lower quantity of OC was collected from the backup quartz filter on QBQ than that from Q-QBT. A possible explanation is that the front quartz filter of QBQ was not fully saturated with gas-phase OC during the sampling period, allowing smaller amount of gas-phase OC to reach the backup quartz filter. The contribution of positive artifact to $PM_{2.5}$ mass was approximately 2.15 ${\mu}g/m^3$ which is equivalent to 6% in terms of Q-QBT sampling configuration. The positive artifact was found to be more dominated during summer than during winter, showing temperature dependence. It was concluded that Q-QBT sampling configuration offers less impact of positive artifact on ambient OC sampling than QBQ in quantification of OC.

• Asian Journal of Atmospheric Environment
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• 제11권2호
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• pp.107-113
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• 2017

This study describes (1) the impact of positive sampling artifacts caused by not only a filter-based sampling, but also a denuder-based sampling in the determination of particle-phase organic carbon (POC), (2) the effect of sample flow rate on positive artifacts, and (3) an optimum flow rate that provides a minimized negative sampling artifact for the denuder-based sampling method. To achieve the goals of this study, four different sampling media combinations were employed: (1) Quartz filter-alone (Q-alone), (2) quartz filter behind quartz-fiber filter (QBQ), (3) quartz filter and quartz filter behind Teflon filter (Q-QBT), and (4) quartz filter behind carbon-based denuder (Denuder-Q). The measurement of ambient POC was carried out in an urban area. In addition, to determine gas-phase OC (GOC) removal efficiency of the denuder, a Teflon filter and a quartz filter were deployed upstream and downstream of the denuder, respectively with varying sample flow rates: 5, 10, 20, and 30 LPM. It was found that Q-alone sampling configuration showed a higher POC than QBQ, Q-QBT, and Denuder-Q by 12%, 28%, and 23%, respectively at a sample flow rate of 20 LPM due to no correction for positive artifact caused by adsorption of GOC onto the filter. A lower quantity of GOC was collected from the backup quartz filter on QBQ than that from Q-QBT. This was because GOC was not in equilibrium with that adsorbed on the front quartz filter of QBQ during the sampling period. It is observed that the loss of particle number and mass across the denuder increases with decreasing sample flow rate. The contribution o f positive arti facts to POC decreased with increasing sample flow rate, showing 29%, 25%, and 22% for 10, 20, and 30 LPM, respectively. The 20 LPM turns out to be the optimum sample flow rate for both filter and denuder-based POC sampling.

• 핵의학기술
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• 제16권2호
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• pp.35-43
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• 2012

CT를 기반으로 감쇠 보정이 시행되는 PET/CT 검사에서는 금속 삽입물에 의한 선속 경화 현상 (Beam Hardening Artifact)으로 인공물이 발생 된다. 이는 인접한 부위의 과대 혹은 과소 평가를 유발하는 감쇠 보정으로 인해 $^{18}F$-FDG의 섭취 변화를 가져오며 영상의 질과 비뇨 생식기 질환의 진단능을 저하시킨다. 따라서 본 연구에서는 PET/CT 영상의 질 향상을 위한 금속 인공물 저감 (Metal Artifact Reduction, MAR) algorithm 재구성방법의 유용성을 평가하고자 한다. 인공 고관절 삽입물에 대한 인공물을 평가하기 위해 SPECT/PET Phantom에 고관절 삽입물을 고정 하여 PET/CT를 진행했다. W/O MAR algorithm 영상과 MAR algorithm 영상에서 CT상에 나타나는 Bright streak, Dark streak, Metal과 Background의 영역에서의 표준화 섭취 계수(Standardized Uptake Value)의 변화를 분석하였다. 또한 본원에 내원한 고관절 전치환술을 시행한 15명의 환자에게서 W/O MAR algorithm과 MAR algorithm, 비 감쇠 보정 영상을 비교 평가하였다. W/O MAR algorithm 영상에서 SUV는 Bright streak 영역에서는 $0.98{\pm}0.48$ g/ml, Dark streak 영역에서는 $0.88{\pm}0.02$ g/ml, Metal 영역에는 $0.24{\pm}0.16$ g/ml, Background 영역은 $0.91{\pm}0.18$ g/ml로 측정되었다. 하지만 MAR algorithm 영상에서는 Bright streak 영역에서는 $0.88{\pm}0.49$ g/ml, Dark streak 영역은 $0.63{\pm}0.21$ g/ml, Metal 영역에서는 $0.06{\pm}0.07$ g/ml, Background는 $0.90{\pm}0.02$ g/ml로 측정되었다. MAR algorithm 적용 시 SUV가 평균적으로 감소 하였으며, W/O MAR algorithm 영상에서는 Bright streak영역에서 Background 보다 높게 측정되어 false positive uptake로 나타났으나 MAR algorithm 영상에서는 Background와 비슷한 농도와 SUV가 나타났고, false positive uptake가 관찰되지 않았다. 따라서 MAR algorithm을 적용하여 인공 고관절 삽입물 주변 조직의 과대 혹은 과소 감쇠 보정으로 인한 섭취의 증가를 줄일 수 있었다. 하지만 Dark streak 영역에서의 SUV 저하를 줄이기 위한 방안은 더욱 많은 연구가 이뤄져야 할 것이다. 고관절 삽입 인공물로 인해 발생하는 Bright streak 영역에서의 false positive uptake를 감소시키고 이와 인접해 있는 비뇨 생식기 질환에 W/O MAR algorithm과 MAR algorithm, 비 감쇠 보정 영상이 동시에 제공된다면 더욱 진단능을 향상 시킬 수 있으리라 생각된다.

• Investigative Magnetic Resonance Imaging
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• 제23권4호
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• pp.341-350
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• 2019

Purpose: To determine the MR parameters affecting India ink artifacts on opposed-phase chemical shift magnetic resonance (MR) imaging. Materials and Methods: The use of a female Sprague-Dawley rat was approved by our Institutional Animal Care and Use Committee. Using an iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) images, which is a modified Dixon method, axial opposed-phase images of the abdominal cavity were obtained with different MR parameters: series 1, different repetition times (TRs; 400, 2000, and 4000 ms); series 2, different echo times (TEs; 10, 50, and 100 ms); series 3, different field of views (FOVs; 6, 8, 16, and 24 cm); series 4, different echo train lengths (ETLs; 2, 4, and 8); series 5, different bandwidths (25, 50, and 85); and series 6, different slice thicknesses (1, 2, 4, 8, and 16 mm). Artifacts on opposed images obtained with different parameters were compared subjectively by two radiologists. For objective analysis, the thickness of the artifact was measured. Spearman's correlation between altered MR parameters and thicknesses of India ink artifact was obtained via objective analysis. Results: India ink artifact was increasingly apparent using shorter TE, larger FOV and ETL, and thicker slices upon subjective analysis. The objective analysis revealed a strong negative correlation between the thickness of the artifact and TE (r = -0.870, P < 0.01); however, strong positive correlations were found between FOV (r = 0.854, P < 0.01) and slice thickness (r = 0.971, P < 0.01). Conclusion: India ink artifact was thicker with shorter TE, larger FOV, and larger slice thickness.

• The Korean Journal of Physiology and Pharmacology
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• 제21권5호
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• pp.555-563
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• 2017

Electrical stimulation through retinal prosthesis elicits both short and long-latency retinal ganglion cell (RGC) spikes. Because the short-latency RGC spike is usually obscured by electrical stimulus artifact, it is very important to isolate spike from stimulus artifact. Previously, we showed that topographic prominence (TP) discriminator based algorithm is valid and useful for artifact subtraction. In this study, we compared the performance of forward backward (FB) filter only vs. TP-adopted FB filter for artifact subtraction. From the extracted retinae of rd1 mice, we recorded RGC spikes with $8{\times}8$ multielectrode array (MEA). The recorded signals were classified into four groups by distances between the stimulation and recording electrodes on MEA (200-400, 400-600, 600-800, $800-1000{\mu}m$). Fifty cathodic phase-$1^{st}$ biphasic current pulses (duration $500{\mu}s$, intensity 5, 10, 20, 30, 40, 50, $60{\mu}A$) were applied at every 1 sec. We compared false positive error and false negative error in FB filter and TP-adopted FB filter. By implementing TP-adopted FB filter, short-latency spike can be detected better regarding sensitivity and specificity for detecting spikes regardless of the strength of stimulus and the distance between stimulus and recording electrodes.

• 한국방사선학회논문지
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• 제13권4호
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• pp.581-588
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• 2019

자기공명영상검사는 조직의 대조도 와 해상력이 우수하지만, 인공물이 발생 될 경우 진단에 영향을 주어 판독이 불가능한 영상을 생성하기도 한다. 치아에 삽입된 금속은 강자성체 또는 상자성체로 되어있는 경우가 대부분이며 자화율 차이로 인하여 기하학적 왜곡을 유발하여 영상진단에 저해되는 경우가 많으며 이를 저감시킬 필요가 있다. 이에 본 연구는 반자성 물질을 사용에 따른 금속 인공물 분석을 실시하고자 한다. 자성 물질로는 치아교정용 와이어와 브라켓인 스테인리스 스틸이 사용되었고 반자성 물질은 구리, 아연, 비스무트를 사용하였다. 검사장비는 1.5T, 3T가 사용되었으며 사용된 시퀀스는 SE, TSE, GE, EPI을 사용하여 측정하였다. 자체 제작된 팬텀을 물질은 균등한 신호를 위하여 아가로스 겔(10%)을 사용하였으며 인공물 유발 물질은 스테인리스 스틸은 팬텀의 정중앙에 위치시켜 검사하고 각 길이 10mm의 정 육면체 반자성 물질의 씌워 검사하였다. 인공물 측정은 Image J를 사용하여 순수한 팬텀 영상에서 자성물질을 포함한 영상을 감산하여 얻은 영상에서 Low Threshold 값을 10으로 설정 한 후 Wand tool을 사용하여 인공물 영역설정 후 면적을 구하였다. 스테인리스 스틸에서 발생한 금속 인공물은 반자성 물질 중 비스무트를 사용한 영상에서 금속 인공물이 가장 많이 감소하였으며 구리와 아연은 약간은 감소하지만, 그 정도의 차이는 크지 않다고 하겠다. 이러한 이유는 비스무트의 반자성 자화율이 가장 작아서 강자성체에서의 자화율을 가장 많이 상쇄하였기 때문이라고 생각된다. 1.5T 와 3T 모두에서 비스무트를 사용한 영상의 인공물이 가장 적게 나왔다. 시퀀스별 인공물 감소는 1.5T에서는 TSE에서 가장 많이 인공물이 감소하였으며 3T에서는 SE에서 가장 많은 인공물이 감소하였다. 따라서 반자성물질의 따른 인공물 변화의 결과는 자화율(${\chi}$)이 가장 낮은 비스무트를 사용한 영상에서 금속인공물이 기준인 Implant 인공물 보다 줄어든 양상을 보여 자화율이 낮은 물질일수록 금속 인공물이 줄어든다는 것을 알 수 있었으며, 기존 금속 인공물의 해결 방법의 단점으로 지적되어온 스캔 시간의 증가 등이 나타나지 않으면서도 인공물을 줄일 수 있는 방법으로 향후 치아 교정 물질뿐만 아니라 치아 보철물 전체에 대한 금속 인공물 저감에 관한 연구의 기초 자료로 사용될 것으로 사료된다.

• 한국콘텐츠학회논문지
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• 제17권1호
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• pp.120-128
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• 2017

요로결석증으로 인한 급성 옆구리 통증은 환자들이 응급실로 방문하는 가장 흔한 질병이다. 연구의 목적은 수신증이 동반되지 않은 환자에서 컬러 도플러를 이용하여 요관결석 검출의 유용성에 대하여 알아보고자 한다. 신장, 요관, 방광의 단순 x-ray 검사에서 요로결석 의심 소견자 또는 소변검사에서 혈뇨 양성반응을 보인 161명의 환자를 대상으로 초음파 검사를 시행하고 후향적으로 분석하였다. 초음파검사에서 진단된 요관결석은 161명 환자 중 154례 (95.6%) 이었다. 수신증이 없고 컬러 도플러 초음파검사에서 섬광인공물(TA)을 동반한 요관결석은 21명 중 18례 (85.7%)이었다(p<0.001). 초음파는 비교적 저렴하고, 보편적으로 사용하므로 옆구리 통증을 갖는 환자의 요로결석 진단에 우선적으로 이용할 수 있다. 컬러 도플러를 이용하여 구분되지 않은 결석, 비확장성 요관결석, 중간요관 결석 검출에 높은 진단 효과를 갖는다.

• Asian Pacific Journal of Cancer Prevention
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• 제13권4호
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• pp.1111-1113
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• 2012

The ER-/PR+ breast tumor may be the result of a false ER negative result. The aim of this study was to investigate whether there is a difference in patient and tumor characteristics of the ER-/PR+ phenotype in an Asian setting. A total of 2629 breast cancer patients were categorized on the basis of their age, ethnicity, tumor hormonal receptor phenotype, grade and histological type. There were 1230 (46.8%) ER+/PR+, 306 (11.6%) ER+/PR-, 122 (4.6%) ER-/PR+ and 972 (37%) ER-/PR-. ER-/PR+ tumors were 2.5 times more likely to be younger than 50 years at diagnosis (OR: 2.52; 95% CI: 1.72-3.67). Compared to ER+/PR+ tumors, the ER-/PR+ phenotype was twice more likely to be associated with grade 3 tumors (OR:2.02; 95%CI: 1.00-4.10). In contrast, compared to ER-/PR- tumors, the ER-/PR+ phenotype was 90% less likely to be associated with a grade 3 tumor (OR: 0.12; 95%CI:0.05-0.26), and more likely to have invasive lobular than invasive ductal histology (OR: 3.66; 95%CI: 1.47-9.11). These results show that the ER-/PR+ phenotype occurs in a younger age group and is associated with intermediate histopathological characteristics compared to ER+/PR+ and ER-/PR- tumors. This may imply that it is a distinct entity and not a technical artifact.

• 대한세포병리학회지
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• 제7권2호
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• pp.111-121
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• 1996

Fine needle aspiration cytology(FNAC) is preferred because of simplicity, safety, and reliability in the evaluation of patients with thyroid nodule or hyperplasia. However, there are a few limitations such as false-negative or false-positive cases and non-diagnostic material. To evaluate the usefulness of FNAC in thyroid lesions, we reviewed 704 FNAC cases of thyroid nodules from 1988 to 1994 at Soonchunhyang University Hospital. The results are as follows. 1. Among 704 FNAC cases of thyroid gland, 571(81.1%) cases were benign, 12(1.7%) were suspicious, 71(10.1%) were malignancy, and 50(7.1%) were material insufficiency. The cytologic diagnoses of the benign lesions included 168 cases of follicular neoplasm, 139 cases of adenomatous goiter, 162 cases of follicular lesion such as follicular neoplasm or adenomatous goiter, 61 cases of Hashimoto's thyroiditis, 13 cases of subacute thyroiditis, and 28 cases of colloidal nodule or benign nodule. The malignant lesions included 68 cases of papillary carcinona, two medullary carcinomas and a case of metastatic colon cancer. 2. The average number of cytologic smear slides was $4.12{\pm}1.81$ in material insufficiency and $5.63{\pm}1.79$ in diagnostic cases. This difference was statistically significant(p<0.00001). 3. Histological assessment of 150 cases revealed 2 false negative and 1 false positive cases. The false negative cases were a case of marked sclerosis in papillary carcinoma and an occult case of papillary carcinoma. The false positive case resulted from pseudo-ground glass nuclei due to marked dry artifact. 4. Comparison between the FNAC and the histologic diagnosis revealed that FNAC had a sensitivity of 93.5%, a specificity of 99.2%, a false negative rate of 6.6%, a false positive rate of 0.8%, and an overall diagnostic accuracy of 98.0%. Therefore, FNAC of thyroid gland is a very reliable diagnostic method with excellent accuracy rate.

• Nuclear Medicine and Molecular Imaging
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• 제40권1호
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• pp.51-52
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• 2006

A 39-year-old female patient who had undergone a total thyroidectomy for a papillary thyroid carcinoma underwent a whole body scan with I-131. The I-131 scan was performed 72 hours after administering 185 MBq (5 mCi) of an I-131 solution. The anterior image of the head, neck, and upper chest showed multiple areas of increased uptake in the mediastinal area considering of functional metastasis. However, radioactivity was not evident in the image taken after removing her clothes and muffler. The image obtained after placing the muffler on the pallet showed that the radioactivity was still present. It is well known that artifacts on an I-131 scan can be produced by styling hair sputum, drooling during sleep, chewing gum, and paper or a cloth handkerchief that is contaminated with the radioactive iodine from either perspiration or saliva. This activity might be mistaken for a functional metastasis. Therefore, it is essential that an image be obtained after removing the patient's clothes. In this study, artifacts due to a contaminated muffler on the I-131 scan were found. These mimicked a functional metastasis of the mediastinal area in a patient with a papillary thyroid carcinoma.