基于可视中国人高分辨人体结构数据集的辐射剂量模拟研究进展

中国数字化辐射虚拟人研究是以中国数字人高分辨三维结构数据集为基础,构建可用于蒙特卡洛辐射模拟的三维计算模型,并实现X射线、中子、质子等多粒子多能级的仿真计算。论著中讨论了基于高分辨人体结构数据集的辐射模型构建过程和特点,以及蒙特卡洛模拟软件,并将剂量测定结果与现有的国外人体模型模拟数据进行了比较。中国数字化辐射虚拟人模型是具备中国人体特征的辐射模型。计算结果很大程度上补充或校正了现有放射学计量数据集,为临床放疗规划、核医药、核辐射防护设计提供精确量化参考。     

三维辐射传输模型在森林生态系统研究中的应用与展望

太阳辐射是森林生态系统功能与服务得以维持并发展的基础, 对森林中的辐射传输过程进行建模对于理解森林生态系统过程具有重要意义。近年来, 三维辐射传输模型的迅速发展使得冠层辐射能量分布格局与动态的准确模拟成为可能。为更好地理解三维辐射传输模型以使其更有效地服务于森林生态系统研究, 该文从模型的原理、应用及发展趋势3个角度展开论述。首先简要介绍了辐射度方法、光线追踪法等森林三维辐射传输模型常用的原理及目前代表性的模型, 然后总结了三维辐射传输模型在森林生态系统研究中的应用, 最后对模型未来如何通过提高易用性、增加多模型耦合等方式更好地应用于森林生态系统研究进行了展望。随着森林生态系统大数据的积累与过程模型的不断完善, 三维辐射传输模型将在未来森林生态理论研究与实践中发挥更加重要的作用。     

64层螺旋CT脑血管造影在颅内动脉瘤诊断中的应用

目的:探讨64层螺旋CT血管造影(CTA)对颅内动脉瘤的诊断价值。方法:回顾性分析54例临床怀疑为颅内动脉瘤,并同时行64层CTA和DSA检查的病例,其中47例疑诊动脉瘤患者行动脉瘤夹闭手术,将MSCTA,DSA与手术结果对照。结果:54患者中经MSCTA检出57个动脉瘤,DSA检出55个动脉瘤,另7例MSCTA和DSA均未检出动脉瘤,余47例接受手术并检出58个动脉瘤。64层CTA发现动脉瘤的敏感性为96.6%,特异性为87.5%,准确性为96.5%,阳性预测值为98.2,阴性预测值为77.7。MIP和VR技术对动脉瘤的形态、分支血管、血栓和钙化方面的显示优于DSA。结论:64层CTA诊断颅内动脉瘤具有较好的异性、敏感性及三维显示能力,具有较高的临床应用价值。。     

用有限元法比较上颌总义齿塑料基托中不同材料的网状加强

上颌总义齿基托纵折者临床常见,即使采用“不碎塑料基托”,仍有出现纵折现象。临床上对一些反复纵折病例,采用网状加强后效果显著。为了进一步探讨其不同网状加强的效果,本文对四种不同材料的网状加强,用三维有限元法进行分析比较,并与未加强的塑料基托进行对照。材料与方法一、建立有限元模型以张少锋等所建立的上颌全口义齿及其支持组织的三维有限元模型为基础加以改进,即用90个壳单元模拟义齿基托,用103个杆单元模拟粘     

颈动脉瘤个体化模型血流数值分析

动脉瘤日益受到广泛关注,介入术成为动脉瘤的理想化治疗方法,但现实临床实践缺少理论支撑,所以数值模拟成为研究动脉瘤血流动力学参数的关键技术。为了研究动脉瘤的血液动力特性,进而探讨不同参数对动脉瘤的血液动力学特性影响因素,本研究基于1例个体化动脉瘤的影像数据,通过影像提取的方法建立了个体化动脉瘤模型,并根据双向流固耦合的方法进行血流场分析(流线,壁面变形分布,壁面剪切力分布)。通过数值分析结果表明,在一个心动周期的不同时刻动脉瘤瘤腔内的涡流强度先增强再减弱并在0.1 s达到最强。动脉瘤壁面的壁面切应力(wall shear stress, WSS)的分布也随着时间的变化,同样在0.1 s时刻壁面WSS分布梯度较大,到0.22 s时刻以及后各个时刻达到均匀无梯度分布。而从壁面变形来看,一个心动周期前0.3 s时刻动脉瘤壁的最大变形位置均为瘤顶处并呈现由小到大再到小的变化(0.1 s时刻达到最大变形量),0.3 s时刻的最大变形量位置发生改变,为瘤颈中间部位,但变形量很小为0.01 mm。     

三维细胞培养技术应用于肿瘤细胞的研究进展

三维细胞培养是一种模拟细胞在体内微环境生长的新兴培养技术。在三维支架中细胞能以三维空间的方式生长,并以三维方式与周围的微环境交互作用,能充分体现肿瘤细胞的黏附、侵袭及远端转移过程,可作为动物模型和二维培养模型之间的桥梁。三维细胞培养技术广泛应用于肿瘤模型构建、肿瘤细胞生理学研究以及肿瘤耐药机制分析等的研究。     

犬囊状动脉瘤模型的制作

本文报道用“静脉囊镶嵌技术·制成犬的囊状动脉瘤模型。18个模型(6个单侧型,6个分叉型,6个末梢型)造型后2周经IA DSA检查。本模型在分型、血流动力学改变方面与人类囊状脑动脉瘤类似。不同类型的动脉瘤模型既有相同的血流动力学特征,又有各自的特点,这与动脉瘤与载瘤动脉的角度有关。我们认为该模型可应用于研究动脉瘤的血流动力学与血管内栓塞治疗。     

三维细胞培养技术的发展及其在干细胞和肿瘤细胞中的应用

三维细胞培养技术是在二维细胞培养和动物实验模型的基础上发展起来的简单、有效的细胞培养方式。利用三维细胞培养技术可以更好的模拟体内微环境,为相关研究领域提供新的手段。目前,三维细胞培养技术在组织工程、肿瘤学、再生医学和干细胞生物学等研究领域均有应用。该文就近年来三维细胞培养技术的发展及其在干细胞和肿瘤细胞中的应用进行综述。     

腹主动脉瘤的流固耦合分析方法研究

目的:将流固耦合分析方法运用于血流动力学的研究,可以获得更加准确的结果,为临床诊断和治疗提供有效的指导.方法:本文运用ANSYS和CFX对腹主动脉瘤(Abdominal Aortic Aneurysm,AAA)进行流固耦合模拟分析,以便获得动脉瘤的血流速度和瘤壁的应力分布,判断易破裂危险区域.结果:实验结果表明,本例的腹部主动脉瘤应力峰值位于瘤体颈部.结论:流动和壁面切应力分布揭示动脉瘤颈部为破裂的危险区域.     

构建和评估猪氨基酰化酶I的三维结构

运用同源模建的方法构建了pACY1三维结构模型,并在能量最小化后对模型进行分子动力学模拟和结构合理性评估。同源模建生成了50个原始模型,经过PROCHECK评测后,筛选出模型A、B进行能量最小化,并得到模型A1、B1。分子动力学模拟结果表明模型B1二聚体结构较稳定。PROCHECK、ProSa以及WHATIF检测结果验证了模型B1属于合理性结构。得到的猪氨基酰化酶Ⅰ(pACY1)的三维结构,为研究其结构与功能关系打下基础。     

Correlation Between the Rupture Risk and 3D Geometric Parameters of Saccular Intracranial Aneurysms

The purpose of this study is to evaluate the association of the location and geometric parameters of intracranial aneurysm with the risk of rupture. A retrospective study consisted of 284 patients diagnosed with saccular intracranial aneurysm between January 2009 and May 2013 at Wuxi Third People’s Hospital was conducted. 3D digital subtraction angiography images from all patients (240 ruptured, 44 unruptured) were obtained and analyzed. The location of the aneurysms and the 3D geometric parameters including the aneurysm depth, the neck size, diameter of the parent artery, aneurysm angle, aspect radio, size ratio, and the neck-to-parent-artery ratio (NPR) were compared between ruptured and unruptured groups. Results: In ruptured group, anterior communicating artery, posterior communicating artery (PCoA), and the bifurcation of internal carotid artery (ICA) were the top three locations for aneurysm occurrence, accounting for 40.00, 30.42, and 12.08 % respectively. While in the unruptured group, top three locations were PCoA (36.36 %), posterior cerebral circulation (18.18 %), and the bifurcation of the ICA (15.91 %). Distribution of aneurysm location is significantly different (p < 0.05) between ruptured and unruptured aneurysms. For the 3D geometric parameters characterizing aneurysm, aneurysm depth (p < 0.05), parent artery diameter (p < 0.05), aneurysm angle (p < 0.01), aspect ratio (p < 0.01), and size ratio (p < 0.01) all showed a significant difference between ruptured and unruptured group. No difference was found in the neck size and the NPR ratio between the two groups. 3D geometric parameters such as aneurysm depth, parent artery diameter, aneurysm angle, aspect ratio, and size ratio can be helpful in evaluating the rupture risk of saccular intracranial aneurysm for a better prevention and prognosis.     

High-resolution computational fluid dynamics detects flow instabilities in the carotid siphon: Implications for aneurysm initiation and rupture?

The carotid siphon is by nature a tortuous vessel segment with sharp bends and large area variations, and of relevance to the study of intracranial aneurysm initiation and rupture. The aim of this paper was to determine whether the siphon might harbor flow instabilities, if care is taken to resolve them. This study focused on five consecutive internal carotid artery (ICA) aneurysm cases from the open-source Aneurisk dataset. The aneurysm, always downstream of the siphon, was digitally removed using previously developed and verified tools. Computational fluid dynamic (CFD) models included long cervical segments upstream, and middle and anterior cerebral arteries downstream. High-resolution pulsatile simulations were performed using the equivalent of ~24$~24$ million linear tetrahedra on average (range 16-32 M) and 30,000 time-steps/cycle. Two of the five cases were laminar with mild flow instabilities right after peak systole. One of the cases experienced strong periodic vortex shedding at a frequency of around 100 Hz. The remaining two cases harbored higher frequency flow instabilities and complex 3D vortical structures, extending to the cerebral arteries downstream. Our findings suggest that the carotid siphon, a conduit to the majority of anterior intracranial aneurysms, may experience flow instabilities, consistent with in vitro reports, but seemingly at odds with the majority of CFD studies, which have been done at lower resolutions. This has obvious implications for elucidating the forces involved in aneurysm initiation; and propagation of flow instabilities into ICA or downstream aneurysms could also impact understanding of the forces involved in aneurysm rupture.     

Direct numerical simulation of transitional flow in a patient-specific intracranial aneurysm

In experiments turbulence has previously been shown to occur in intracranial aneurysms. The effects of turbulence induced oscillatory wall stresses could be of great importance in understanding aneurysm rupture. To investigate the effects of turbulence on blood flow in an intracranial aneurysm, we performed a high resolution computational fluid dynamics (CFD) simulation in a patient specific middle cerebral artery (MCA) aneurysm using a realistic, pulsatile inflow velocity. The flow showed transition to turbulence just after peak systole, before relaminarization occurred during diastole. The turbulent structures greatly affected both the frequency of change of wall shear stress (WSS) direction and WSS magnitude, which reached a maximum value of 41.5Pa. The recorded frequencies were predominantly in the range of 1-500Hz. The current study confirms, through properly resolved CFD simulations that turbulence can occur in intracranial aneurysms.     

Analysis of Morphological Parameters to Differentiate Rupture Status in Anterior Communicating Artery Aneurysms

In contrast to size, the association of morphological characteristics of intracranial aneurysms with rupture has not been established in a systematic manner. We present an analysis of the morphological variables that are associated with rupture in anterior communicating artery aneurysms to determine site-specific risk variables. One hundred and twenty-four anterior communicating artery aneurysms were treated in a single institution from 2005 to 2010, and CT angiograms (CTAs) or rotational angiography from 79 patients (42 ruptured, 37 unruptured) were analyzed. Vascular imaging was evaluated with 3D Slicer© to generate models of the aneurysms and surrounding vasculature. Morphological parameters were examined using univariate and multivariate analysis and included aneurysm volume, aspect ratio, size ratio, distance to bifurcation, aneurysm angle, vessel angle, flow angle, and parent-daughter angle. Multivariate logistic regression revealed that size ratio, flow angle, and parent-daughter angle were associated with aneurysm rupture after adjustment for age, sex, smoking history, and other clinical risk factors. Simple morphological parameters such as size ratio, flow angle, and parent-daughter angle may thus aid in the evaluation of rupture risk of anterior communicating artery aneurysms.     

In vitro evaluation of flow divertors in an elastase-induced saccular aneurysm model in rabbit

Endovascular coiling is an acceptable treatment of intracranial aneurysms, yet long term follow-ups suggest that endovascular coiling fails to achieve complete aneurysm occlusions particularly in wide-neck and giant aneurysms. Placing of a stentlike device across the aneurysm neck may be sufficient to occlude the aneurysm by promoting intra-aneurysmal thrombosis; however, conclusive evidence of its efficacy is still lacking. In this study, we investigate in vitro the efficacy of custom designed flow divertors that will be subsequently implanted in a large cohort of animals. The aim of this study is to provide a detailed database against which in vivo results can be analyzed. Six custom designed flow divertors were fabricated and tested in vitro. The design matrix included three different porosities (75%, 70%, and 65%). For each porosity, there were two divertors with one having a nominal pore density double than that of the other. To quantify efficacy, the divertors were implanted in a compliant elastomeric model of an elastase-induced aneurysm model in rabbit and intra-aneurysmal flow changes were evaluated by particle image velocimetry (PIV). PIV results indicate a marked reduction in intra-aneurysmal flow activity after divertor implantation in the innominate artery across the aneurysm neck. The mean hydrodynamic circulation after divertor implantation was reduced to 14% or less of the mean circulation in the control and the mean intra-aneurysmal kinetic energy was reduced to 29% or less of its value in the control. The intra-aneurysmal wall shear rate in this model is low and implantation of the flow divertor did not change the wall shear rate magnitude appreciably. This in vitro experiment evaluates the characteristics of local flow phenomena such as hydrodynamic circulation, kinetic energy, wall shear rate, perforator flow, and changes of these parameters as a result of implantation of stentlike flow divertors in an elastomeric replica of elastase-induced saccular aneurysm model in rabbit. These initial findings offer a database for evaluation of in vivo implantations of such devices in the animal model and help in further development of cerebral aneurysm bypass devices.     

A Patient-Specific Computational Fluid Dynamic Model of Middle Cerebral Artery Aneurysm Before and One Year After Surgery

Computational fluid dynamics (CFD) has been widely used for studying intracranial aneurysm hemodynamics, while its use for guiding clinical strategy is still in development. In this study, CFD simulations helped inform treatment decision for a middle cerebral artery (MCA) aneurysm case was investigated. A patient with a 10.4 × 9.8 mm aneurysm attached with a small aneurysm at the edge of the trifurcation in the left MCA was included in this study. For removing the MCA aneurysm, two scenarios were considered: Plan-A involved clipping the small aneurysm and Plan-B involved clipping the whole aneurysm. A suitable treatment plan was decided by comparing the clinical measurements and CFD analysis between these two plans. One-year after the surgery, the CFD analysis was conducted again on the post-operative aneurysm model to verify the selected surgical plan in terms of morphometric and hemodynamic properties changes in the aneurysm. Based on the CFD simulation and clinical experience, surgical Plan-A was adopted. One-year after the surgery, both the hemodynamic and morphological properties improved in the post-operative aneurysm model, indicating the recovery of the patient. The patient-specific aneurysm CFD analysis can help to determine a better surgical plan for patients with special cerebral aneurysms. This study showed how CFD analysis can be used to aid clinical diagnosis and treatment.     

Posterior Cerebral Artery Angle and the Rupture of Basilar Tip Aneurysms

Since the initial publication of the International Study of Unruptured Intracranial Aneurysms (ISUIA), management of unruptured intracranial aneurysms has been mainly based on the size of the aneurysm. The contribution of morphological characteristics to treatment decisions of unruptured aneurysms has not been well studied in a systematic and location specific manner. We present a large sample of basilar artery tip aneurysms (BTA) that were assessed using a diverse array of morphological variables to determine the parameters associated with ruptured aneurysms. Demographic and clinical risk factors of aneurysm rupture were obtained from chart review. CT angiograms (CTA) were evaluated with Slicer, an open source visualization and image analysis software, to generate 3-D models of the aneurysms and surrounding vascular architecture. Morphological parameters examined in each model included aneurysm volume, aspect ratio, size ratio, aneurysm angle, basilar vessel angle, basilar flow angle, and vessel to vessel angles. Univariate and multivariate analyses were performed to determine statistical significance. From 2008–2013, 54 patients with BTA aneurysms were evaluated in a single institution, and CTAs from 33 patients (15 ruptured, 18 unruptured) were available and analyzed. Aneurysms that underwent reoperation, that were associated with arteriovenous malformations, or that lacked preoperative CTA were excluded. Multivariate logistic regression revealed that a larger angle between the posterior cerebral arteries (P1-P1 angle, p = 0.037) was most strongly associated with aneurysm rupture after adjusting for other morphological variables. In this location specific study of BTA aneurysms, the larger the angle formed between posterior cerebral arteries was found to be a new morphological parameter significantly associated with ruptured BTA aneurysms. This is a physically intuitive parameter that can be measured easily and readily applied in the clinical setting.     

An approach to quantitative assessment of hemodynamic differences between unruptured and ruptured ophthalmic artery aneurysms

Background and purpose: Hemodynamic parameters are important in the pathogenesis, evolution and rupture of intracranial aneurysm. Energy loss (EL) has been applied for the rupture risk prediction of artery aneurysms recently. We proposed a new EL and further investigate its effects on the rupture of aneurysms. Materials and methods: Sixty-four patient-specific ophthalmic aneurysm datasets were divided into ruptured and unruptured groups based on their clinical history. Based on patient-specific 3D-DSA data, realistic models were retrospectively reconstructed and then analyzed by using computational fluid dynamic method. Results: The flow field feature EL in ruptured cases was significantly higher than that in unruptured cases. The average wall shear stress (WSS) and the maximum WSS in ruptured cases were higher than those in unruptured cases. Modified pressure loss coefficient (PLC_M) in ruptured cases was slight higher than that in unruptured cases but the difference has no statistical significance. Multivariate logistic regression analysis demonstrated flow field feature EL (p < 0.05) and the maximum WSS (p < 0.05) were the only independently significant variables to predict rupture of ophthalmic aneurysm. There were no differences in PLC_M, the maximum oscillatory shear index (OSI), the average OSI and AR between the two groups. Conclusion: Flow field feature EL may be a reliable factor to predict the rupture risk of aneurysms.