전산화 단층촬영 번역(한국어 원본)Atherosclerosis는 여러 가지 biochemistrical, physical 자극에 의해 시작되는 inflammation response가 만성적으로 진행되어 발생하는 artery disease로 알려져 있다 (1). Hemodynamics는 artery disease을 진단하고 평가하는 방법 중 하나인 hematology의 한 분과로 cardiac cycle, blood pressure, heart beat, electrocardiography 등의 heart나 blood vessel 내에서의 blood의 운동, blood pressure, blood flow 등을 연구 대상으로 한다 (2). 최근 computer와 computerized technique의 발전으로 인해 Computational Fluid Dynamics(CFD)나 Fluid-Structure Interaction(FSI) 등의 numerical analysis를 이용한 hemodynamic approach가 가능하게 되었고, 이를 활용한 연구가 활발히 진행되고 있다 (3-9).
Medical imaging을 numerical model에 활용할 경우, irregular blood vessel geometry를 모사하거나 clinical research를 포함한 patient-specific 정보를 활용할 수 있다는 점에서 큰 장점을 지닌다. 일반적으로 이를 위해, Computed Tomography(CT)나 Magnetic Resonance Imaging (MRI)의 단층사진을 적층 하거나 (10-14), IntraVascular UltraSound (IVUS)를 이용하여 3-dimensional vessel geomety를 생성하는 방법이 활발히 진행되고 있다 (15, 16). 그러나 대부분의 medical imaging은 lesion이 진행된 vessel, 즉, stenosis가 많이 진행되거나 시술이 필요한 상태의 vessel을 대상으로 얻어진다. 이는 vessel disease의 특성상 오랜 시간에 걸쳐 lesion이 진행되고, lesion이 상당히 진행된 상태에서 통증이나 자각이 느껴지며, medical imaging을 얻기 위해 행해지는 angiography는 다수의 첨단 장비와 전문가를 필요로 하기에 검사의 대상이 한정되기 때문이다. 따라서 대부분의 medical imaging을 이용한 numerical model은 lesion이 진행된 상태를 모사하고 있다. 이러한 연구는 lesion 부위 및 상태진단이나 차후 처방을 판단하는데 합리적이나 lesion의 원인이나 발생부위 예측, lesion의 진행과정을 이해하기에는 한계를 가진다.
Lesion이 진행되는 과정을 hemodynamic index로 설명하기 위하여, 기존에는 virtual vessel이나 ideal shape을 가진 vessel의 stenosis rate이나 eccentricity of stenosis를 고려한 연구들이 진행되었다 (17-20). Clinical demonstration이나 numerical analysis를 병행한 연구로, Stone et al. (21) 은 stent transplant operation을 경험한 환자들과 vessel이 50%이하로 막힌 환자들을 대상으로 초기의 IVUS profile과 6개월 후의 profile을 이용하였으며, Yiannis et al. (22) 는 streptozotocin 처방을 받은 24마리 돼지를 30주 동안 관찰하여 low WSS와 atherosclerosis 진행의 상관관계를 연구하였다. Diseased artery를 토대로 healthy artery를 생성하기 위한 연구로 Olgac et al. (23) 과 Knight et al. (24) 은 lesion을 지닌 CT에서 plaque components, lumen region, remodeling이 나타난 영역에서 contrast가 존재한다고 언급하였으며 이를 구분하여 healthy state vessel을 생성하였다. 또한 healthy state artery에서의 wall shear parameter(WSS, OSI, RRT)등과 plaque 진행의 상관관계를 도출하였다. 그러나 선행 연구들은 cylinder와 같은 exact geometry로 blood vessel을 모사하고 임상실험의 어려움으로 인해 동물을 이용하거나 서로 다른 환자들을 비교하였다. 또한 실제 diseased artery를 토대로 healthy artery를 생성하는 연구는 diseased artery 연구에 비해 초기단계이며 특히, CT와 VH-IVUS를 함께 이용한 연구는 전무한 실정이다. 앞서 언급하였듯이 lesion 발생부위 예측, 발생 원인 규명, 진전과정 등을 이해하기 위해서는 diseased artery의 blood flow characteristic만으로는 한계를 가지며 healthy artery에서의 blood flow에 대한 검토가 반드시 이뤄져야 한다.
본 연구에서는 diseased artery 정보를 토대로 healthy artery를 재구성 하기 위하여, coronary artery의 angiography가 행해진 실제 3명 patients(Case 1, Case 2, Case 3)의 CT 뿐만 아니라 VH-IVUS에서 계산된 lumen의 area와 plaque components의 area를 이용하여 healthy artery의 area를 산정하였다. 즉, lumen의 area와 plaque 구성성분이 더해진 단면적을 각각 diseased artery와 healthy artery의 lumen 단면적 기준으로 간주하고, diseased artery의 plaque을 가상적으로 제거하여 healthy artery를 재구성하였다. 또한 이를 적용하여 diseased artery model과 healthy artery model을 생성하였다. 마지막으로 생성된 healthy artery을 활용하여 diseased artery과의 geometric 비교 및 CFD simulation을 통해 lesion이 발생할 부위에서의 flow characteristic을 분석하였다 |
전산화 단층촬영 번역(영어 번역본)Atherosclerosis is known as an artery disease caused by chronic progression of inflammation response that is started by various biochemistrical and physical stimuli (1). Hemodynamics is a branch of hematology, which is a method for diagnosing and evaluating artery disease, and it targets motion of blood within heart or blood vessel such as cardiac cycle, blood pressure, heart beat, and electrocardiography (2). Recent development in computers and computerized techniques enabled hemodynamic approach using numerical analysis such as computational fluid dynamics (CFD) and fluid-structure interaction (FSI), and studies utilizing these techniques are active in progress (3-9).
Application of medical imaging in a numerical model is advantageous as it allows simulation of irregular blood vessel geometry and allows utilization of patient-specific information. In general, stacking of computed tomography (CT) or magnetic resonance imaging (MRI) images or generation of 3-dimensional vessel geometry using intravascular ultrasound (IVUS) is actively used to achieve this goal (15, 16). However, most medical imaging is obtained from vessels with progressed lesion, that is, vessels with late-stage stenosis or vessels requiring surgery. This is because lesion progresses over a long time and pain and awareness occurs after lesion has significantly progressed due to properties of vessel disease, and target of angiography is limited as it requires numerous advanced equipments and experts. Therefore, most numerical models using medical imaging simulates state of lesion progression. Such research is reasonable for diagnosis of lesion site and state and for evaluating subsequent treatment, but it is limited in understanding of cause of lesion, prediction of forming site, and progression of lesion.
In order to explain progression of lesion using hemodynamic index, studies in the past have accounted for rate and eccentricity of stenosis in virtual vessels or vessels with ideal shape (17-20). Two studies that performed clinical demonstration and numerical analysis in parallel are by Stone et al. (21), who have used initial IVUS profile and profile obtained after 6 months for patients who have experienced stent transplant operation or have vessels with blockage ratio below 50%, and by Yiannis et al. (22), who have observed 24 pigs with streptozotocin prescription for 30 weeks to study correlation between low WSS and atherosclerosis progression. As a study that constructed healthy artery based on diseased artery, Olgac et al. (23) and Knight et al. (24) have mentioned that contrast exists in regions with plaque components, lumen region, and remodeling on CT of lesion, and classified these to construct healthy state vessel. They also derived correlation between wall shear parameter (WSS, OSI, RRT, etc.) and plaque progression in healthy state artery. But these previous studies have simulated blood vessel as an exact geometry such as cylinder, and used animals or different patients due to difficulty in clinical experiments. Also, research on construction of healthy artery based on actual diseased artery is in early stage compared to research on diseased artery, and there is no study that uses CT and VH-IVUS in conjunction. As mentioned earlier, blood flow characterization of diseased artery by itself is insufficient for understanding of prediction of lesion formation site, identification of cause of lesion, lesion progression, etc., and review of blood flow in healthy artery must be accomplished.
In this study, in order to reconstruct healthy artery based on information from diseased artery, area of healthy artery was calculated by using areas of lumen and plaque components calculated from CT and VH-IVUS of three patients (Case 1, Case 2, Case 3) who have completed angiography of coronary artery. That is, area of lumen and cross-sectional area of plaque components were assumed as the standard for lumen of diseased artery and lumen of healthy artery, respectively. And plaque of diseased artery was virtually removed to reconstruct healthy artery. This was applied to generate diseased artery and healthy artery models. Finally, the constructed healthy artery was used for geometric comparison with diseased artery and analysis of flow characteristics at the site where lesion will form using CFD simulation. |
