Review of Failed CT Phantom Image Evaluations in 2005 and 2006 by the CT Accreditation Program of the Korean Institute for Accreditation of Medical Image

박혜정,정승은,이영준,조우일,도경현,김성훈,나동규 대한영상의학회 2008 Korean Journal of Radiology Vol.9 No.4

Objective: The CT accreditation program was established in 2004 by the Korean Institute for Accreditation of Medical Image (KIAMI) to confirm that there was proper quality assurance of computed tomography (CT) images. We reviewed all the failed CT phantom image evaluations performed in 2005 and 2006. Materials and Methods: We analyzed 604 failed CT phantom image evaluations according to the type of evaluation, the size of the medical institution, the parameters of the phantom image testing and the manufacturing date of the CT scanners. Results: The failure rates were 10.5% and 21.6% in 2005 and 2006, respectively. Spatial resolution was the most frequently failed parameter for the CT phantom image evaluations in both years (50.5% and 49%, respectively). The proportion of cases with artifacts increased in 2006 (from 4.5% to 37.8%). The failed cases in terms of image uniformity and the CT number of water decreased in 2006. The failure rate in general hospitals was lower than at other sites. In 2006, the proportion of CT scanners manufactured before 1995 decreased (from 12.9% to 9.3%). Conclusion: The continued progress in the CT accreditation program may achieve improved image quality and thereby improve the national health of Korea. Objective: The CT accreditation program was established in 2004 by the Korean Institute for Accreditation of Medical Image (KIAMI) to confirm that there was proper quality assurance of computed tomography (CT) images. We reviewed all the failed CT phantom image evaluations performed in 2005 and 2006. Materials and Methods: We analyzed 604 failed CT phantom image evaluations according to the type of evaluation, the size of the medical institution, the parameters of the phantom image testing and the manufacturing date of the CT scanners. Results: The failure rates were 10.5% and 21.6% in 2005 and 2006, respectively. Spatial resolution was the most frequently failed parameter for the CT phantom image evaluations in both years (50.5% and 49%, respectively). The proportion of cases with artifacts increased in 2006 (from 4.5% to 37.8%). The failed cases in terms of image uniformity and the CT number of water decreased in 2006. The failure rate in general hospitals was lower than at other sites. In 2006, the proportion of CT scanners manufactured before 1995 decreased (from 12.9% to 9.3%). Conclusion: The continued progress in the CT accreditation program may achieve improved image quality and thereby improve the national health of Korea.

Particle Swarm Optimization을 이용한 PET/CT와 CT영상의 정합

이학재(Hak-Jae Lee),김용권(Yong-Kwon Kim),이기성(Ki-Sung Lee),문국현(Guk-Hyun Moon),주성관(Sung-Kwan Joo),김경민(Kyeong-Min Kim),천기정(Gi-Jeong Cheon),최종학(Jong-Hak Choi),김창균(Chang-Kyun Kim) 대한방사선과학회(구 대한방사선기술학회) 2009 방사선기술과학 Vol.32 No.2

영상정합 기술은 두 개 이상의 영상을 서로 맞추어, 각각의 영상이 가지고 있는 단점을 보완하여, 새로운 정보를 획득하게 하는 기술이다. 본 논문은 의료 영상간의 2D 영상 정합을 통해 환자의 점진적 병세파악에 도움을 주는 것을 목적으로 하고 있다. 서로 다른 시점과 장비로부터 얻어진 CT와 PET/CT영상을 정합하기 위하여 정확한 해부학적 정보를 제공하는 CT영상간의 정합을 먼저 수행하고 이를 통하여 얻어진 기하학적 정합파라미터들을 PET 영상에 적용하여, 독립 CT영상 위에 PET영상을 중첩하였다. 정합작업을 위해 먼저 각각의 CT영상에 대해 전처리 작업을 실시하였고, 영상의 변형은 affine 좌표변환을 이용하였다. 정합할 영상간의 유사도 평가를 위해 mutual information을 이용하였으며, 빠르고 정확한 정합을 위하여 최적화 알고 리듬인 particle swarm optimization 방법을 이용하였다. 이를 통해 실제 환자의 독립 CT와 PET/CT영상을 이용하여 실험하였고, PET/CT의 영상에서 확인할 수 있었던 병소에 대한 해부학적 위치 정보가 영상정합 과정을 통해 독립 CT 영상에서도 동일한 위치에 표시됨을 확인하였다. 제안된 알고리듬은 PET/CT 뿐만 아니라 향후 도입될 SPECT/CT, MRI/PET 등 다중영상기기와 기존의 독립 CT 영상기기와의 정합에도 폭넓게 사용될 것으로 기대된다. Image registration is a fundamental task in image processing used to match two or more images. It gives new information to the radiologists by matching images from different modalities. The objective of this study is to develop 2D image registration algorithm for PET/CT and CT images acquired by different systems at different times. We matched two CT images first (one from standalone CT and the other from PET/CT) that contain affluent anatomical information. Then, we geometrically transformed PET image according to the results of transformation parameters calculated by the previous step. We have used Affine transform to match the target and reference images. For the similarity measure, mutual information was explored. Use of particle swarm algorithm optimized the performance by finding the best matched parameter set within a reasonable amount of time. The results show good agreements of the images between PET/CT and CT. We expect the proposed algorithm can be used not only for PET/CT and CT image registration but also for different multi-modality imaging systems such as SPECT/CT, MRI/PET and so on.

Advanced intelligent Clear-IQ Engine (AiCE) of Coronary CT Angiography in 640 MSCT: Effect on Image Quality Compared with Deep Learning Reconstruction and Iterative Reconstruction

전상현(Sang-Hyun Jeon),안기용(Gi-Yong An),심학준(Hak Joon Shim),고성민(Sung Min Ko),전필현(Pil Hyeon Jeon) 대한CT영상기술학회 2021 대한CT영상기술학회지 Vol.23 No.1

목적: 최근에는 인공지능의 출현과 함께 CT를 위한 인공지능 기반 영상 재구성 기법의 개발로 환자가 받는 피폭선량을 감소시키고 영상의 노이즈를 줄이며, 동일 선량일 때 분해능을 증가시키는 등 다양한 장점이 있다. 본 연구에서는 최초의 상용화 된 인공지능 기반 재구성 기법(이하 AiCE)의 이미지 품질이 CCTA에서 필터보정 역투영법 및 반복적 재구성 기법과 비교하여 임상적 유용성에 대해서 평가해 보고자 하였다. 대상 및 방법: 이 연구는 환자 연구와 팬텀 연구로 구분하였고, 체질량지수에 따라 3개의 군으로 분류하였다. 동일 환자에게서 필터보정 역투영법, 반복적 재구성 기법, AiCE로 영상을 재구성하였다. 팬텀 연구는 인체모형 흉부팬텀 내 대동맥 기부 및 좌주관상동맥을 표현할 수 있도록 무침 주사기를 설치하였고, 3개의 재구성 기법을 사용하여 영상을 획득 하였다. 이미지 품질을 객관적으로 평가하기 위해 각 데이터에 대해 4가지 매개 변수인 영상잡음, CT 밀도, 신호 대 잡음비, 대조도 대 잡음비를 분석 하였다. 결과: AiCE는 필터보정 역투영법에 비해 노이즈가 51.46 % 감소되었고, 반복적 재구성 기법에 비해 30.13 % 감소한 것을 알 수 있었다. 또한 체질량지수 분포에 상관없이 AiCE는 반복적 재구성 기법에 비해 노이즈 개선 효과가 상당히 뚜렷하게 나타났다. AiCE는 필터보정 역투영법, 반복적 재구성 기법에 비해 큰 체질량지수 범주에서 노이즈가 크게 감소하고 더 나은 이미지 품질을 보여주었다. 결론: 필터보정 역투영법, 반복적 재구성 기법의 이미지와 비교하여 AiCE는 이미지 노이즈를 줄이고 신호 대 잡음비 및 대조도 대 잡음비와 같은 이미지의 매개변수를 개선하는데 매우 효과적인 것을 알 수 있었다. AiCE의 개선 효과는 체질량지수가 클수록 증가함을 알 수 있었다. Purpose: The development of Deep Learinig Reconstruction(DLR) technology for CT has various advantages, including reducing exposure dose received by patients, reducing noise in images, and increasing resolution at the same dose. In this work, we wanted to evaluate the image quality of Advanced Intelligent Clear-IQ Engine(AiCE) on clinical utility compared to Filtered Back Projection(FBP) and Iterative Reconstruction(Adaptive Iterative Dose Reduction 3D; AIDR3D) in Coronary CT Angiography. Material and method: This study was divided into three groups according to BMI, and the subject study was divided into two groups: patient study and phantom study. We reconstruct the images using three algorithms: FBP, AIDR3D, and AiCE in the same patient. Phantom study was designed to represent Aortic root and Left main coronary arty in Lungman Phantom, and reconstructed images using three algorithms. To objectively evaluate image quality, we analyze four parameters: Image noise, CT density, Signal-to-noise ratio(SNR) and Contrast-to-noise ratio(CNR) for each data. Result: AiCE reduced noise by 51.46 % compared to FBP. It was found that it was reduced by 30.13 % compared to AIDR3D. In addition, regardless of the BMI category, AiCE has a significant noise improvement effect compared to AIDR3D. AiCE showed significantly reduced noise and better image quality in the larger BMI category compared to FBP and AIDR3D. Conclusion: Compared to FBP, AIDR3D images, we find that AiCE is very effective in reducing image noise and improving parameters of images such as SNR and CNR. It was shown that the improvement effect of AiCE increased with a larger BMI.

SPECT/CT에서 감쇠 보정 및 위치 정보의 유용성 평가

최종숙,정우영,신상기,조시만,Choi, Jong-Sook,Jung, Woo-Young,Shin, Sang-Ki,Cho, Shee-Man 대한핵의학기술학회 2008 핵의학 기술 Vol.12 No.2

목적 : 융합 SPECT/CT가 기존 SPECT에 비해 병소의 해부학적 위치를 정확히 판단할 수 있는지 정성 평가하고, CT 감쇠 보정이 SPECT 영상에 미치는 효과를 알아보아 SPECT/CT의 유용성을 제시하고자 한다. 실험재료 및 방법 : 1. 융합 영상의 평가 : 2008년 1월(月)부터 8월(月)까지 Precedence 16 혹은 Symbia T2에서 $^{131}I$-MIBG, Bone, $^{111}In$-Octreotide, Meckel 게실, Parathyroid MIBI 등을 SPECT/CT 시행한 환자를 대상으로 하였고, SPECT/CT영상을 융합한 것과 하지 않은 것을 비교하여 정성 평가하였다. 2. 감쇠보정의 평가 : Symbia T2로 2008년 6월에서 8월까지 $^{201}Tl$ 심근 검사를 한 환자 38명을 대상으로 Cedars-Sinai의 QPS를 이용하여 산출하였다. Ant, Inf, Lat, Septum, Apex로 5개부분으로 분류하고, 각 부분에 대한 관류의 상태를 백분율로 산출했다. CT AC와 Non AC를 평균${\pm}$표준편차로 각 부분에 대한 관류 상태를 비교하고 차이를 분석하였다. 결과 : 1. 융합 영상의 평가 : 에너지가 높은 $^{131}I$ SPECT의 경우 병소와 주위 조직 간의 섭취율 차이로 인해 (주위 조직이 saturation 됨) 병소의 위치 파악이 어려웠으나 CT로 융합한 결과 해부학적 위치를 정확히 평가할 수 있었다. 또한 멕켈게실이나 $^{111}In$과 같이 장이나 장기쪽에 질환을 찾는 경우에는 그 우수성이 더욱 뛰어 났다. Bone SPECT/CT는 척추간의 구별을 확실히 할 수 있어 임상의가 정확한 결과를 제시하는데 도움을 준다. 2. 감쇠 보정의 평가 : 감쇠 보정 전후의 관류 백분율의 차이가 Ant, Lat에서는 통계적으로 유의한 차이가 없었으나(p>0.05), Inferior, Apex, Septum에서는 유의한 차이가 있었다(p<0.05). 차이를 보이는 값 중 Inferior Wall에서 CT AC perfusion : $76.84{\pm}6.52%$, Non AC perfusion : $68.58{\pm}7.55%$로 CT 보정에 의한 차이가 $8.26{\pm}4.95%$로 가장 크게 측정되었다(t=10.29, p<0.01). 결론 : SPECT에 CT가 부착되면서 병변의 기능적 활성도를 나타내는 분자학적 영상은 물론 병변의 해부학적 위치 정보를 보다 정확하게 확인할 수 있게 되었다. 이것은 비정상적 부위를 찾아내는 것에 그치지 않고 복잡한 인체 부위에서 정상군과 비정상군을 분리하는데 많은 도움을 주게 되었다. 따라서 임상의는 하나의 검사 영상으로 진단과 치료계획을 동시에 시행할 수 있을 것이다. 또한 감쇠가 잘 되는 흉곽 부위 안에 있는 심근 검사에는, CT로 보다 정확한 감쇠 보정을 할 수 있기 때문에 SPECT 검사 시 관심부위의 관류 상태를 더욱 신뢰할 수 있어 치료 예후의 정당성을 입증할 수 있을 것으로 판단된다. Purpose: We make a qualitative analysis of whether Fusion SPECT/CT can find lesion's anatomical sites better than existing SPECT or not, and we want to show the usefulness of SPECT/CT through finding out effects of CT attenuation correction on SPECT images. Materials and Method: 1. The evaluation of fusion images: This study comprised patients who was tested $^{131}I$-MIBG, Bone, $^{111}In$-Octreotide, Meckel's diverticulum, Parathyroid MIBI with Precedence 16 or Symbia T2 from 2008 Jan to Aug. We compared SPECT/CT image with non fusion image and make a qualitative analysis. 2. The evaluation of attenuation correction: We classified 38 patients who was tested 201Tl myocardial exam with Symbia T2 into 5 sections by using Cedars Sinai' QPS program - Ant, Inf, Lat, Septum, Apex. And we showed each section's perfusion states by percentage. We compared the each section's perfusion-states differences between CT AC and Non AC by average${\pm}$standard deviation. Results: 1. The evaluation of fusion images : In high energy $^{131}I$ cases, it was hard to grasp exact anatomical lesions due to difference between regions and surrounding lesions' uptake level. After combining with CT, we could grabs anatomical lesion more exactly. And in meckel's diverticulum case or to find lesions around bowels or organs with $^{111}In$ cases, it demonstrates its superiority. Bone SPECT/CT images help to distinguish between disk spaces certainly and give correct results. 2. The evaluation of attenuation correction: There is no significant difference statistically in Ant and Lat (p>0.05), but there is a meaningful difference in Inferior, Apex and Septum (p<0.05). AC perfusion at inferior wall in the 5 sections of myocardium: The perfusion difference between Non AC perfusion image ($68.58{\pm}7.55$) and CT corrected perfusion image ($76.84{\pm}6.52$) was the largest by $8.26{\pm}4.95$ (p<0.01, t=10.29). Conclusion: Nuclear medicine physicians can identify not only molecular image which shows functional activity of lesions but also anatomical location information of lesions with more accuracy using the combination of SPECT and CT systems. Of course this combination helps nuclear medicine physician find out the abnormal parts. Moreover combined data sets help separate between normal group and abnormal group in complicated body part. So clinicians can carry out diagnosis and treatment planning at the same time with a single test image. In addition, when we examine a myocardium in thorax where attenuation can occur easily, we can trust perfusion more in a certain region in SPECT test because CT provides the capability for accurate attenuation correction. In these reasons, we think we can prove the justice after treatment fusion image.

복부 CT에서 Adaptive Statistical Iterative Reconstruction과 Model-Based Iterative Reconstruction의 사용에 따른 선량 감소 및 화질 평가

손은영(Eun young Son),홍선숙(Sun suk Hong) 대한CT영상기술학회 2013 대한CT영상기술학회지 Vol.15 No.1

목적 본 연구는 복부 CT 검사에서 adaptive statistical iterative reconstruction 기법과 model based iterative reconstruction 기법으로 획득한 이미지를 토대로 복부 장기의 effective dose 변화 및 화질의 정량적인 분석을 통하여 최적의 영상 정보를 제공할 수 있는 iterative reconstruction을 알아보고자 한다. 대상 및 방법 본 연구를 위해 CT 장비는 GE사의 64-slice multidetector-row CT Discovery 750 HD를 사용하였고, 인체 모형 Rando phantom을 사용하였으며, 복부 장기 effective dose 측정을 위하여 유리 선량계를 사용하였다. 장비의 성능 평가를 하기 위하여 ACR phantom을 사용하였고, Image J와 Matlab program을 사용하여 noise, SNR, distortion 및 resolution 측정을 통해 화질을 정량적으로 평가, 분석하였다. 결과 DLP 및 effective dose는 인위적으로 선량을 감소하여 ASIR와 MBIR로 재구성함에 따라 그 비율대로 유사하게 선량이 감소하였다. Noise는 120 mAs-ASIR(ASIR 40%)에서 최소, 100 mAs-ASIR(ASIR 50%)부터 증가하는 것으로 나타났으며, MBIR은 dose를 감소하지 않고 reconstruction하였을 경우 최소로 측정되어 dose가 감소함에 따라 noise는 증가하는 것으로 나타났다. SNR의 경우 180 mAs-ASIR(ASIR 10%)와 140 mAs-MBIR에서 가장 높게 나타났다. 현재 복부 CT에 사용되는 조건의 영상을 기준으로 image의 distortion을 평가했을 때 80 mAs-ASIR(ASIR 70%)까지 PSNR이 30 dB을 넘게 측정되었으며, MBIR은 모두 30 dB 이하로 측정되었다. 해상력과 선예도 측정 결과에서는 100 mAs-MBIR이 100 mAs-ASIR(ASIR 50%)에 비해 sharpness는 20.58%, resolution은 33.19% 높게 측정되었다. ACR phantom을 통한 장비의 성능 평가는 모두 적합한 것으로 나타났다. 결론 본 연구는 복부 CT 검사에서 200 mAs부터 60 mAs까지 10%씩 선량을 감소하여 ASIR와 MBIR로 재구성한 이미지를 토대로 복부 장기의 effective dose 변화 및 화질을 평가하기 위하여 진행하였다. 결과 모두 환자의 선량을 감소시켜 ASIR와 MBIR로 재구성하여도 진단 가치가 있는 것을 확인할 수 있었으며, 이러한 기법을 복부 CT protocol에 적용한 결과 180 mAs-ASIR(ASIR 10%)에서 최적화된 정보를 얻을 수 있었다. MBIR의 경우 ASIR에 비하여 같은 선량에서 약 67%의 많은 noise를 감소하며, 해상력이 높은 것으로 나타났으나 현재 실용화하기 위해서는 고성능의 컴퓨터와 많은 재구성 시간을 요구하는 단점을 가지고 있다. Ⅰ. Purpose The purpose of this study was to assess iterative reconstruction methods that provide optimal image information in abdominal CT exams. It was based on the acquired images by adaptive statistical iterative reconstruction (ASIR) and model- based iterative reconstruction (MBIR). We analyzed the change of effective dose in abdominal organs and image quality quantitatively. Ⅱ. Meterial and Methods CT scans were performed with a 64-slice multidetector-row CT Discovery 750HD and Rando phantom. Glass dosimeters were used to measure effective dose of organs. ACR phantom was used for performance evaluation of the equipment. We quantitatively evaluated and analyzed image quality by measurement of noise, SNR, distortion, and resolution by using Image J and Matlab program. Ⅲ. Result As we gradually lowered radiation dose and reconstructed with ASIR and MBIR, the value of DLP and effective dose also decreased similarly. Noise value was the lowest at 120 mAs-ASIR (ASIR 40%), and got increased from 100 mAs-ASIR (ASIR 50%). SNR value was the highest at 180 mAs-ASIR (ASIR 10%) and 140 mAs-MBIR. In evaluation of distortion of image quality based on abdominal CT protocol, PSNR showed over 30 dB up to 80 mAs-ASIR (ASIR 60%), and below 30 dB at all MBIRs. In measurement of resolution, sharpness and resolving power at 100 mAs-MBIR were respectively 20.58% and 33.19% higher than those at 180 mAs-ASIR (ASIR 10%). All performance evaluation of the equipment through ACR phantom was found to be acceptable. Ⅳ. Conclusions There’s diagnostic value with both iterative reconstruction methods, ASIR and MBIR, while reducing patient dose. In abdominal CT protocol, we can get optimal information at 180 mAs-ASIR (ASIR 10%). MBIR can provide 67% less noise and higher resolution compared to ASIR in the same dose, however, it requires high performance computer and considerable time to reconstruct.

Preliminary Application of Synthetic Computed Tomography Image Generation from Magnetic Resonance Image Using Deep-Learning in Breast Cancer Patients

Jeon, Wan,An, Hyun Joon,Kim, Jung-in,Park, Jong Min,Kim, Hyoungnyoun,Shin, Kyung Hwan,Chie, Eui Kyu The Korean Association for Radiation Protection 2019 방사선방어학회지 Vol.44 No.4

Background: Magnetic resonance (MR) image guided radiation therapy system, enables real time MR guided radiotherapy (RT) without additional radiation exposure to patients during treatment. However, MR image lacks electron density information required for dose calculation. Image fusion algorithm with deformable registration between MR and computed tomography (CT) was developed to solve this issue. However, delivered dose may be different due to volumetric changes during image registration process. In this respect, synthetic CT generated from the MR image would provide more accurate information required for the real time RT. Materials and Methods: We analyzed 1,209 MR images from 16 patients who underwent MR guided RT. Structures were divided into five tissue types, air, lung, fat, soft tissue and bone, according to the Hounsfield unit of deformed CT. Using the deep learning model (U-NET model), synthetic CT images were generated from the MR images acquired during RT. This synthetic CT images were compared to deformed CT generated using the deformable registration. Pixel-to-pixel match was conducted to compare the synthetic and deformed CT images. Results and Discussion: In two test image sets, average pixel match rate per section was more than 70% (67.9 to 80.3% and 60.1 to 79%; synthetic CT pixel/deformed planning CT pixel) and the average pixel match rate in the entire patient image set was 69.8%. Conclusion: The synthetic CT generated from the MR images were comparable to deformed CT, suggesting possible use for real time RT. Deep learning model may further improve match rate of synthetic CT with larger MR imaging data.

Usefulness of Dual Energy CT to Improve Image Quality Degradation due to Lens Shielding

윤준(Joon Yoon),김현주(Hyeonju Kim) 한국방사선학회 2019 한국방사선학회 논문지 Vol.13 No.7

방사선 피폭감소를 위해 사용하는 비스무스 차폐체를 적용하여 CT스캔 시 차폐체에 의한 선속경화현상으로 화질이 감소되는 경우가 있다. 이에 G사의 듀얼 에너지 CT의 GSI모드 적용을 통해 화질저하 현상을 줄일 수 있는 에너지 영역대를 찾아보고, 가능성을 실험을 통해 알아보고자 하였다. 그 결과 비스무스 차폐 후 듀얼 에너지 CT 스캔 시 50 keV에서 118±10.6 HU, 50.1±14.6 HU로 화질저하 전 CT value와 가장 유사하였고(p>0.05), Image J의 Multi-point기능을 적용한 Pixel value에서도 50 keV에서 176.6±7.1, 138.3±1.1로 측정 되었다(p>0.05). CT검사 시 차폐체의 사용은 불가항력적으로 화질저하를 유발하지만 듀얼 에너지 CT 의 GSI기능 적용으로 차폐체를 사용하고도 화질을 유지할 수 있다는 것을 실험을 통해 알 수 있었다. 향후 다양한 차폐체를 듀얼 에너지 CT를 이용, 평가 후 보안 한다면 CT검사의 최대 단점인 피폭 감소를 위한 방사선 차폐체 사용으로 발생한 화질저하라 단점을 극복할 수 있을 것으로 기대된다. Applying the bismuth shield used to reduce the radiation exposure, image quality may be reduced due to beam hardening caused by the shield during CT scan. Therefore, we tried to find out the energy range that can reduce image degradation by applying GSI mode of G company s dual energy CT and examine the possibility through experiment. As a result, after bismuth shielding, 118 ± 10.6 HU and 50.1 ± 14.6 HU at 50 keV after dual-energy CT scan were the most similar to the CT value before image deterioration(p> 0.05). It was measured 176.6 ± 7.1 and 138.3 ± 1.1 at 50 keV(p> 0.05). Experiments showed that the use of the shield during CT inspection inevitably degrades the image quality, but experiments show that the GSI function of the dual energy CT can maintain the image quality even when the shield is used. If the various shields are secured after the evaluation using the dual energy CT, it is expected to overcome the disadvantages of poor image quality caused by the use of the radiation shield for reducing the exposure, which is the biggest disadvantage of the CT scan.

수정체 차페로 기인한 화질저하 개선을 위한 듀얼 에너지 CT의 유용성

윤준,김현주 한국방사선학회 2019 한국방사선학회 논문지 Vol.13 No.7

Applying the bismuth shield used to reduce the radiation exposure, image quality may be reduced due to beam hardening caused by the shield during CT scan. Therefore, we tried to find out the energy range that can reduce image degradation by applying GSI mode of G company's dual energy CT and examine the possibility through experiment. As a result, after bismuth shielding, 118 ± 10.6 HU and 50.1 ± 14.6 HU at 50 keV after dual-energy CT scan were the most similar to the CT value before image deterioration(p> 0.05). It was measured 176.6 ± 7.1 and 138.3 ± 1.1 at 50 keV(p> 0.05). Experiments showed that the use of the shield during CT inspection inevitably degrades the image quality, but experiments show that the GSI function of the dual energy CT can maintain the image quality even when the shield is used. If the various shields are secured after the evaluation using the dual energy CT, it is expected to overcome the disadvantages of poor image quality caused by the use of the radiation shield for reducing the exposure, which is the biggest disadvantage of the CT scan. 방사선 피폭감소를 위해 사용하는 비스무스 차폐체를 적용하여 CT스캔 시 차폐체에 의한 선속경화현상으로 화질이 감소되는 경우가 있다. 이에 G사의 듀얼 에너지 CT의 GSI모드 적용을 통해 화질저하 현상을 줄일 수 있는 에너지 영역대를 찾아보고, 가능성을 실험을 통해 알아보고자 하였다. 그 결과 비스무스 차폐 후 듀얼 에너지 CT 스캔 시 50 keV에서 118±10.6 HU, 50.1±14.6 HU로 화질저하 전 CT value와 가장 유사하였고(p>0.05), Image J의 Multi-point기능을 적용한 Pixel value에서도 50 keV에서 176.6±7.1, 138.3±1.1로 측정 되었다(p>0.05). CT검사 시 차폐체의 사용은 불가항력적으로 화질저하를 유발하지만 듀얼 에너지 CT의 GSI기능 적용으로 차폐체를 사용하고도 화질을 유지할 수 있다는 것을 실험을 통해 알 수 있었다. 향 후 다양한 차폐체를 듀얼 에너지 CT를 이용, 평가 후 보안 한다면 CT검사의 최대 단점인 피폭 감소를 위한 방사선 차폐체 사용으로 발생한 화질저하라 단점을 극복할 수 있을 것으로 기대된다.

Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part I: Studies on Image Quality Using Dual Source CT

황혜전,서준범,이진성,송재우,김성수,이현주,임채훈 대한영상의학회 2012 Korean Journal of Radiology Vol.13 No.6

Objective: To determine whether the image quality (IQ) is improved with iterative reconstruction in image space (IRIS), and whether IRIS can be used for radiation reduction in chest CT. Materials and Methods: Standard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying a dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from a single tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Objective noise was measured. The subjective IQ was evaluated by radiologists for the followings: noise, contrast and sharpness of mediastinum and lung. Results: Objective noise was significantly lower in H-IRIS than in F-FBP (p < 0.01). In both SDCT and LDCT, the IQ scores were highest in F-IRIS, followed by F-FBP, H-IRIS and H-FBP, except those for sharpness of mediastinum, which tended to be higher in FBP. When comparing CT images between the same dose and different reconstruction (F-IRIS/F-FBP and H-IRIS/H-FBP) algorithms, scores tended to be higher in IRIS than in FBP, being more distinct in half-dose images. However, despite the use of IRIS, the scores were lower in H-IRIS than in F-FBP. Conclusion: IRIS generally helps improve the IQ, being more distinct at the reduced radiation. However, reduced radiation by half results in IQ decrease even when using IRIS in chest CT. Objective: To determine whether the image quality (IQ) is improved with iterative reconstruction in image space (IRIS), and whether IRIS can be used for radiation reduction in chest CT. Materials and Methods: Standard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying a dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from a single tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Objective noise was measured. The subjective IQ was evaluated by radiologists for the followings: noise, contrast and sharpness of mediastinum and lung. Results: Objective noise was significantly lower in H-IRIS than in F-FBP (p < 0.01). In both SDCT and LDCT, the IQ scores were highest in F-IRIS, followed by F-FBP, H-IRIS and H-FBP, except those for sharpness of mediastinum, which tended to be higher in FBP. When comparing CT images between the same dose and different reconstruction (F-IRIS/F-FBP and H-IRIS/H-FBP) algorithms, scores tended to be higher in IRIS than in FBP, being more distinct in half-dose images. However, despite the use of IRIS, the scores were lower in H-IRIS than in F-FBP. Conclusion: IRIS generally helps improve the IQ, being more distinct at the reduced radiation. However, reduced radiation by half results in IQ decrease even when using IRIS in chest CT.

C-Spine CT 검사 시 bend를 이용한 Image Quality 향상의 유용성

고창영(Ko Chang Yeong),김성규(Kim Seong Gyoo),김성현(Kim Seong Hyeon),맹철수(Meang Cheol Soo),박시래(Park Si Rae),이경용(Lee Kyeong Yong),장길수(Jang Gil Soo) 대한CT영상기술학회 2011 대한CT영상기술학회지 Vol.13 No.1

목 적 C-Spine CT 검사 시 경추 5번에서 흉추 1번은 해부학적 구조상 shoulder와 overlap이 되기 때문에 beam hardening artifact를 유발하여 image quality가 저하되는 경우가 많이 있다. 이에 bend를 이용한 position의 변화를 통해 beam hardening artifact를 최소화 하여 image quality를 향상시키는 방법을 연구해 보았다. 대상 및 방법 병원을 방문한 환자 중 C-Spine CT가 처방된 외래 환자 20명을 대상으로 bend를 이용하였을 때와 이용하지 않았을 때를 비교 검사하였다. 그 후 검사결과를 영상의학과 의사 2명이 평가표를 기준으로 비교, 평가하였다. 결 과 본 연구 방법으로 검사하여 나온 영상을 토대로 bend를 이용하였을 때와 이용하지 않았을 때를 비교한 결과는 다음과 같다. - 100점 만점을 기준으로 1) 근육과 지방의 상태와 명확성에서는 bend 미사용 시 75점, bend 사용 시 91점 2) 척수강의 상태와 명확성에서는 bend 미사용 시 42.5점, bend 사용 시 69.5점 3) ROI내 Artifact 유무 or Artifact의 정도는 bend 미사용 시 45점, bend 사용 시 83.5점 4) 갑상선 실질은 균일한가?에서는 bend 미사용 시 81점, bend 사용 시 94점 - Bend를 이용하였을 때가 이용하지 않았을 때 보다 평균 23.625점 더 높았다. 결 론 Bend를 이용했을 때가 이용하지 않았을 때 보다 C-Spine과 shoulder의 overlap을 최소화시켜 beam hardening artifact를 줄일 수 있었으며, 이로 인해 C-Spine CT 검사 시 경추 5번에서 흉추 1번 사이의 image quality를 향상시킬 수 있었다. Ⅰ. Purpose In taking a C-spine CT, we can often find the image quality reduction between C5-T1, because beam hardening artifact is caused by overlap of both shoulders and C-spine. So we investigated the solution to improve image quality by changing position using bend in order to make beam hardening artifact minimized. Ⅱ. Materials and Methods Twenty outpatients were participated in this study, who were examined with/without band and compared to each other. Two radiologists analyzed them and made test results according evaluation table. Ⅲ. Results In the results, we compared both the evaluated scores obtained from band use case and non-use case respectively. - Followings are the standard 100 score 1) For clarity of the fat and muscle state, the score with the band is 91 and 75 without the band. 2) For the clarity and the state of spinal cannel, the score with the band is 69.5 and 42.5 without the band. 3) For checking existence of Artifact and the degree of artifact in ROI, the score with the band is 83.5 and 45.0 without the band. 4) For confirming the uniformity of thyroid parenchyma, the score with the band is 94 and 81 without the band. - The average score with the band is 23.625 higher than that without the band. Ⅳ. Conclusion The band use cases showed more improved image quality than non-use cases, because using band could minimize the shoulder and C-spine overlap, resulting in reduction of beam hardening artifact.