Effects of Irregular Respiratory Motion on the Positioning Accuracy of Moving Target with Free Breathing Cone-Beam Computerized Tomography

For positioning a moving target, a maximum intensity projection (MIP) or average intensity projection (AIP) image derived from 4DCT is often used as the reference image which is matched to free breathing cone-beam CT (FBCBCT) before treatment. This method can be highly accurate if the respiratory motion of the patient is stable. However, a patient’s breathing pattern is often irregular. The purpose of this study is to investigate the effects of irregular respiration on positioning accuracy for a moving target aligned with FBCBCT. Nine patients’ respiratory motion curves were selected to drive a Quasar motion phantom with one embedded cubic and two spherical targets. A 4DCT of the phantom was acquired on a CT scanner (Philips Brilliance 16) equipped with a Varian RPM system. The phase binned 4DCT images and the corresponding MIP and AIP images were transferred into Eclipse for analysis. FBCBCTs of the phantom driven by the same respiratory curves were also acquired on a Varian TrueBeam and fused such that both CBCT and MIP/AIP images share the same target zero positions. The sphere and cube volumes and centroid differences (alignment error) determined by MIP, AIP and FBCBCT images were calculated, respectively. Compared to the volume determined by MIP, the volumes of the cube, large sphere, and small sphere in AIP and FBCBCT images were smaller. The alignment errors for the cube, large sphere and small sphere with center to center matches between MIP and FBCBCT were 2.5 ± 1.8 mm, 2.4 ± 2.1 mm, and 3.8 ± 2.8 mm, and the alignment errors between AIP and FBCBCT were 0.5 ± 1.1 mm, 0.3 ± 0.8 mm, and 1.8 ± 2.0 mm, respectively. AIP images appear to be superior reference images to MIP images. However, irregular respiratory pattern could compromise the positioning accuracy, especially for smaller targets.

Image quality of cone beam CT on respiratory motion

In this study,the influence of respiratory motion on Cone Beam CT (CBCT) image quality was investigated by a motion simulating platform,an image quality phantom,and a kV X-ray CBCT.A total of 21 motion states in the superior-inferior direction and the anterior-posterior direction,separately or together,was simulated by considering different respiration amplitudes,periods and hysteresis.The influence of motion on CBCT image quality was evaluated with the quality indexes of low contrast visibility,geometric accuracy,spatial resolution and uniformity of CT values.The results showed that the quality indexes were affected by the motion more prominently in AP direction than in SI direction,and the image quality was affected by the respiration amplitude more prominently than the respiration period and the hysteresis.The CBCT image quality and its characteristics influenced by the respiration motion,and may be exploited in finding solutions.

Efficacy of Daily Cone-Beam Computed Tomography as Part of a Rescan Protocol for Large Offset to Reduce the Inter-Fractional Motion of the Prostate

Purpose: To prospectively analyze the inter-fractional motion of the prostate in patients with prostate cancer treated with intensity-modulated radiation therapy (IMRT) using image-guided radiotherapy (IGRT) with daily cone-beam computed tomography (CBCT) as part of a rescan protocol for large offset, and to evaluate the efficacy of our protocol. Materials and Methods: Eligible patients were treated with the following protocol: 1) magnesium oxide and dimethylpolysiloxane were administered to ensure that patients had regular bowel movements;2) the patients were instructed to have an appropriately distended bladder during the planning CT and daily irradiation;3) the daily CBCT image was fused with the planning CT image using the prostate outline;and 4) if large offset was recognized, a rescan CBCT image was obtained after appropriate countermeasures, such as the discharge of gas and defecation, and re-registration was performed. Three shifts for the inter-fractional motion of the prostate were analyzed, in the fractions which needed the CBCT rescan;the displacement data after the final rescan were used. Results: Sixty-one patients were eligible, and a total of 2302 fractions were available for the analysis. Rescans of the CBCT for large offset were performed in 113 (5%) of the 2302 fractions. After the first rescan, the large offset was resolved in 106 (94%) of the 113 fractions. Excessive rectal gas was the reason for the large offset in 94 (83%) of the 113 fractions. The total mean and standard deviation of the inter-fractional motion of the prostate in the AP, LR, and SI directions were 1.1 ± 2.4, -0.1 ± 2.3, and 0.7 ± 3.0 mm, respectively. Conclusion: Large offset was recognized in 5% of all fractions. Daily CBCT with our rescan protocol could resolve the large offset, which was mainly caused by excessive rectal gas, and it may therefore be promising to reduce the inter-fractional motion of the prostate.

Motion Perception of Short-Wavelength Sensitive Cones in Glaucoma Using Random Dots Moving

Purpose: To determine whether motion perception of short-wavelength sensitive(SWS)cones is capable of predicting primary open angle glaucoma (POAG) optic neuropathy.Methods: Motion perceptions of SWS cones were isolated by Blue random dot stimulusdisplayed on the Yellow background, then the detecting displacement threshold of motionperception from SWS cone in POAG was measured, and compared with the age-matchednormal group.Results: The detecting displacement thresholds of motion perception from SWS cones in8 sites of 15 degrees were all elevated in POAG compared with the normal group.Conclusion: These findings suggest that motion perception of SWS cones may revealpreclinical visual nerve damage in early POAG.

可调汽蚀文氏管调节精度影响因素的动态仿真

面向工程应用研究了可调汽蚀文氏管调节精度的影响因素,采用FLUENT中的Schnerr-Sauer混合流体空穴模型,对设计的可调汽蚀文氏管流量线性度、内部流动特性进行了动态条件下的数值模拟,并研究了偏心和反向运动对调节精度的影响。结果表明:可调汽蚀文氏管由于调节锥初始运动阶段并未进入喉部,导致汽蚀段长度增加从而降低精度;流量线性度在运动初期受节流面影响而降低,百分比流量在12%~70%范围内线性度最好,精度最高;流量变化速率对汽蚀文氏管调节精度影响在5%以内;调节锥偏心0.02 mm和0.05 mm时对汽蚀区长度调节精度影响在20%以内,而0.10 mm偏心时提高至40%,此时渐扩段汽蚀区产生偏移,压力分布不均,上侧增大而下侧降低,从而导致压力振荡;不同偏心值对喉部流量调节精度影响均在4%以内;调节锥反向运动会由于初始汽蚀段长度过短导致汽蚀特性减弱,汽蚀区变化速率减缓,流量调节精度影响在3%以内。

320 kV锥束工业CT成像系统开发

基于实验室设备自主开发了一套320 kV锥束工业CT成像系统。首先设计了基于运动控制卡的六轴机械扫描平台,并将其与320 kV射线机、平板探测器结合搭建了锥束CT成像系统的硬件。其次,利用平板探测器和运动控制卡的动态链接库开发锥束CT投影数据采集软件和重建软件,自主开发FDK算法并基于CUDA架构实现FDK算法的GPU加速。最后,采用阻尼器对锥束CT成像系统进行测试。结果表明,整个系统运行稳定,可以获得高质量的CT重建图像,且重建效果与VG STUDIO MAX 3.4软件的重建效果一致。

基于深度模糊学习的牙科CBCT运动伪影校正算法

目的 针对牙科CBCT扫描中患者不自主运动导致的重建图像运动伪影问题,提出了一种基于深度模糊学习的牙科CBCT运动伪影校正算法(DMBL),以提升牙科CBCT的成像质量。方法 首先使用模糊编码模块提取运动退化特征,从而对运动导致的退化过程进行建模,然后将得到的运动退化特征输入伪影校正模块进行运动伪影去除。其中,伪影校正模块采用了图像模糊去除和图像模糊仿真的联合学习框架,可有效处理空间变化且随机的运动模式。为验证所提方法的有效性,本文分别在仿真运动数据集和临床数据集上进行对比实验。结果 仿真数据集实验结果表明,本文方法峰值信噪比提升了2.88%,结构相似性(SSIM)提升了0.89%,均方根误差(RMSE)减少了10.58%;临床数据集实验结果表明,本文方法取得了最高的专家主观图像质量评分4.417(5分制),且与对比方法结果的评分具有显著性差异(P<0.001)。结论 本文提出的DMBL算法,通过构建深度模糊联合学习网络结构,能够有效地去除牙科CBCT图像中的运动伪影,实现高质量的图像恢复。

新型过载驾驶仪滚转弹制导系统稳定性研究

针对平台式图像导引头实际应用中的隔离度寄生回路问题,基于新型过载驾驶仪开展了滚转弹锥形运动的动态稳定性研究。根据滚转弹体的线性动力学模型,引入加速度反馈增稳的新型过载驾驶仪,构建了考虑平台图像导引头隔离度寄生回路的滚转弹体制导系统模型,推导了新型过载驾驶仪滚转弹制导系统的动态稳定性条件。分析了隔离度、舵机总延迟角等重要参数对包含隔离度寄生回路的滚转弹体动态稳定域的影响。研究表明:滚转效应、寄生效应与控制指令延迟是导致驾驶仪参数设计稳定域减小的主要因素,制导系统设计参数应远离稳定性边界从而提升锥形运动稳定性。

基于Cone Beam CT图像的呼吸运动分析

呼吸运动是有一定规律性的运动,传统呼吸运动模型用公式描述,不能准确反映不同病人的特点或同一病人不同时期的特点,无法满足实时准确分析的需要。为此,我们提出了一种通过跟踪病人自由呼吸状态下所采集的Cone Beam CT图像序列中的横隔膜的运动来建立病人呼吸运动模型的方法。该方法建立的模型与传统的呼吸运动理论模型非常相似,证明了它是可行且有效的,同时该方法更能实时准确地反映病人的呼吸运动规律,具有很高的临床实用价值。

定日镜场的输出热功率计算模型

基于全国大学生数学建模竞赛赛题的定日镜场分布数据,根据太阳视运动方法,建立太阳跟踪运动模型、阴影挡光效率理论模型、相邻定日镜遮挡选取模型与镜面反射光锥模型,得出了定日镜场的年平均光学效率、年平均输出热功率,以及单位面积的镜面年平均输出热功率,最后通过输出功率的拟合结果展现了模型的合理性。

消除或减轻CBCT常见伪影的可行化探讨与研究

随着锥形束计算机断层成像(CBCT)在医学影像领域的广泛应用,其伪影问题日益引起关注。伪影对CBCT图像的质量和诊断准确性产生不利影响,因此寻求有效的方法消除或减轻伪影对于提高CBCT影像质量具有重要意义。本文简要介绍了锥形束CT的工作原理和常见伪影类型,针对每种伪影类型,分析了其产生机制和影响因素,同时提出消除或减轻CBCT常见伪影的可行方法,提出未来的研究应致力于深入理解伪影的形成机制,开发更加精确有效的消除或减轻伪影的方法。旨在为优化CBCT图像质量,提高临床应用时的影像诊断准确性和可靠性提供参考。

Analysis on Stability of Coning Motion of Rockets Based on Nutation Theory

A nonlinear mathematic model taking the nutation and precession angles as variables for the coning motion of projectile was established according to a short period moment projection of the spining projectile. By introducing the generalized nutation angle and precession angular speed, the model that is difficult to be resolved can be transformed to a resolvable one. The interrelationship between nutation and precession was analyzed based on the linear model, and the stability condition was obtained for the spinning projectile. For the nonlinear model, the effects of the nutation and precession on the limit circle of the projectile's coning motion were investigated, and the analytical relations between the nutation angle and the precession angular speed in the steady coning motion of the spinning projectile were given.

采用弹体追踪导引律的旋转弹锥形运动稳定性

针对旋转弹采用捷联导引头和弹体追踪导引律时可能导致锥形运动失稳的问题,推导了捷联导引头在非旋转弹体坐标系下的动力学模型,建立了复数形式的弹体追踪制导控制系统数学模型;在不同弹体转速及阻尼回路增益情况下,分别考虑导引头响应延迟和陀螺标度因数误差,分析了上述制导控制系统的稳定性,并使用数值方法求得使其稳定的特征参数取值范围。研究结果表明:导引头延迟角越大,使系统稳定的制导回路增益上限越小;陀螺标度因数误差系数大于1时,使系统稳定的制导回路增益上限会变大,当陀螺标度因数误差系数小于1时,使系统稳定的制导回路增益稳定上限会变小。

The Characteristics of Interaction between Color and Motion Perception in PrimaryOpen Angle Glaucoma

Purpose: To investigate the characteristics of interaction between color and motion perception in primary open angle glaucoma (POAG) and measure motion perception of B,G and R cones, thus find a more sensitive method to diagnose the visual nerve damage in POAG. Methods : Motion perceptions of B,G and R cones were isolated by blue , green and red vertical line stimulus displayed on the yellow , purple and blue background respectively, then measured the displacement threshold and flicking threshold of motion perception from each cones in POAG, and compared it with the age-match normals.Results:The displacement threshold and flicking threshold of motion perception from B,G and R cones were all damaged in POAG compared with the normals, and the motion perception of G and B cones was deficits more obviously than the R cones.Conclusion: These findings support the suggestion that color provides an input to human motion perception. Magnocellular and parvocellular pathway may be significandy damaged in POAG,

基于DEM-FEM耦合的圆锥破碎机运动特性研究

针对圆锥破碎机工作性能研究认识的不足,构建了圆锥破碎机系统三维模型,采用离散元法(DEM)与有限元法(FEM)耦合技术,利用多面体模拟矿物颗粒,并对破碎过程中破碎腔的受力状态进行运动学仿真。分析结果表明:矿物颗粒在破碎腔破碎过程中,动锥及偏心轴承受较大力,较容易磨损;在不同转速下,动锥转速与矿物颗粒的破碎比和破碎效率呈负相关;同时分析了动锥转速和轧臼壁变形量之间的关系。为圆锥破碎机参数优化提供参考。

捷联惯导姿态算法若干问题的研究

研究了捷联系统姿态更新的等效旋动矢量算法,并以锥运动为条件,对等效旋动矢量算法进行了优化。此外还对四元数、旋动矢量及其优化算法进行了仿真比较,仿真结果表明:等效转动矢量算法的精度明显优于四元数算法,且等效转动矢量的采样频率越高,姿态更新算法的精度就越高。

椭圆锥动效应对机械抖动激光陀螺振动特性的影响

对机械抖动激光陀螺的振动特性进行了理论分析,得到了水平振动下陀螺测量敏感轴存在椭圆锥动效应,并得出了该锥动效应引起的陀螺输入角速度表达式。利用有限元分析软件ANSYS,对机械抖动激光陀螺进行了随机振动分析,仿真证实了锥动效应的存在,并采用物理方法试验验证了椭圆圆锥运动的存在及其锥动幅角的大小。通过数值仿真与分析,指出了减小锥动效应,提高陀螺振动性能的有效措施是增大抖动偏频机构的横向抗弯刚度。改进设计的试验结果表明,采用大横向抗弯刚度的新型抖动偏频机构使陀螺的抗振性能提高了4倍多。

基于章动运动理论的火箭弹锥形运动稳定性分析

基于自旋弹体短周期力矩投影的动力学方程,建立了以弹体摆动章动角和进动角为变量的弹体锥形运动的非线性数学模型,通过引入广义章动角及进动角速率,使难以用解析手段处理的非线性模型转换成可解析的一般模型。根据线性化模型分析了弹体章动及进动运动的相互关系,给出了自旋弹体章动运动稳定性条件。对非线性模型,研究了章进动运动对弹体锥形运动极限环的作用,给出了弹体锥形运动稳定时自旋弹体章动角度及进动角速度应满足的解析关系。

捷联惯导系统姿态算法比较

姿态算法是捷联惯导系统算法中的一个重要组成部分,解算姿态阵相当于建立起数学平台,其精度对捷联惯导系统的精度影响很大。该文就实际应用,对欧拉角法、方向余弦法、四元数算法、罗德利格参数法、优化旋转矢量算法及一种改进的递推旋转矢量算法做了分析,并在典型圆锥运动输入下,对后五种算法进行了仿真,为姿态算法的研究提供了参考。

捷联惯导系统中的圆锥和伪圆锥运动研究

分别对圆锥运动和伪圆锥运动的产生原因、表达形式,以及对捷联惯导系统的影响进行了分析。由于圆锥运动和伪圆锥运动并不相同,因此圆锥运动补偿算法将对两者产生不同的效果。数字仿真表明,圆锥补偿算法可以大大降低经典圆锥运动对捷联导航系统的不利影响,但同时却会增大伪圆锥运动对捷联导航系统的不利影响。因此在实际应用当中,应当结合圆锥运动和伪圆锥运动对系统的影响比重,选择合适的圆锥补偿算法。