Clinical evaluation of respiratory motion compensation for anatomical roadmap guided cardiac electrophysiology procedures

X-ray fluoroscopically guided cardiac electrophysiological procedures are routinely carried out for diagnosis and treatment of cardiac arrhythmias. X-ray images have poor soft tissue contrast and, for this reason, overlay of static 3-D roadmaps derived from preprocedural volumetric data can be used to add anatomical information. However, the registration between the 3-D roadmap and the 2-D X-ray image can be compromised by patient respiratory motion. Three methods were designed and evaluated to correct for respiratory motion using features in the 2-D X-ray images. The first method is based on tracking either the diaphragm or the heart border using the image intensity in a region of interest. The second method detects the tracheal bifurcation using the generalized Hough transform and a 3-D model derived from 3-D preoperative volumetric data. The third method is based on tracking the coronary sinus (CS) catheter. This method uses blob detection to find all possible catheter electrodes in the X-ray image. A cost function is applied to select one CS catheter from all catheter-like objects. All three methods were applied to X-ray images from 18 patients undergoing radiofrequency ablation for the treatment of atrial fibrillation. The 2-D target registration errors (TRE) at the pulmonary veins were calculated to validate the methods. A TRE of 1.6 mm ± 0.8 mm was achieved for the diaphragm tracking; 1.7 mm ± 0.9 mm for heart border tracking, 1.9 mm ± 1.0 mm for trachea tracking, and 1.8 mm ± 0.9 mm for CS catheter tracking. We present a comprehensive comparison between the techniques in terms of robustness, as computed by tracking errors, and accuracy, as computed by TRE using two independent approaches.     

Markerless real-time 3-D target region tracking by motion backprojection from projection images

Accurate and fast localization of a predefined target region inside the patient is an important component of many image-guided therapy procedures. This problem is commonly solved by registration of intraoperative 2-D projection images to 3-D preoperative images. If the patient is not fixed during the intervention, the 2-D image acquisition is repeated several times during the procedure, and the registration problem can be cast instead as a 3-D tracking problem. To solve the 3-D problem, we propose in this paper to apply 2-D region tracking to first recover the components of the transformation that are in-plane to the projections. The 2-D motion estimates of all projections are backprojected into 3-D space, where they are then combined into a consistent estimate of the 3-D motion. We compare this method to intensity-based 2-D to 3-D registration and a combination of 2-D motion backprojection followed by a 2-D to 3-D registration stage. Using clinical data with a fiducial marker-based gold-standard transformation, we show that our method is capable of accurately tracking vertebral targets in 3-D from 2-D motion measured in X-ray projection images. Using a standard tracking algorithm (hyperplane tracking), tracking is achieved at video frame rates but fails relatively often (32% of all frames tracked with target registration error (TRE) better than 1.2 mm, 82% of all frames tracked with TRE better than 2.4 mm). With intensity-based 2-D to 2-D image registration using normalized mutual information (NMI) and pattern intensity (PI), accuracy and robustness are substantially improved. NMI tracked 82% of all frames in our data with TRE better than 1.2 mm and 96% of all frames with TRE better than 2.4 mm. This comes at the cost of a reduced frame rate, 1.7 s average processing time per frame and projection device. Results using PI were slightly more accurate, but required on average 5.4 s time per frame. These results are still substantially faster than 2-D to 3-D registration. We conclude that motion backprojection from 2-D motion tracking is an accurate and efficient method for tracking 3-D target motion, but tracking 2-D motion accurately and robustly remains a challenge.     

Multiple-object 2-D-3-D registration for noninvasive pose identification of fracture fragments

This paper presents a multiple-object 2-D-3-D registration technique for noninvasively identifying the poses of fracture fragments in the space of a preoperative treatment plan. The plan is made by manipulating and aligning computer models of individual fracture fragments that are segmented from a diagnostic computed tomography. The registration technique iteratively updates the treatment plan and matches its digitally reconstructed radiographs to a small number of intraoperative fluoroscopic images. The proposed approach combines an image similarity metric that integrates edge information with mutual information, and a global-local optimization scheme, to deal with challenges associated with the registration of multiple small fragments and limited imaging orientations in the operating room. The method is easy to use as minimum user interaction is required. Experiments on simulated fractures and two distal radius fracture phantoms demonstrate clinically acceptable target registration errors with capture range as large as 10 mm.     

Three-dimensional diffraction by infinite conducting and dielectric wedges using a generalized total-field/scattered-field FDTD formulation

We extend the generalized total-field/scattered-field formulation of the finite-difference time-domain method to permit efficient computational modeling of three-dimensional (3-D) diffraction by infinite conducting and dielectric wedges. This new method allows: 1) sourcing a numerical plane wave having an arbitrary incident angle traveling into, or originating from, a perfectly matched layer absorbing boundary and 2) terminating the infinite wedge inside the perfectly matched layer with negligible reflection. We validate the new method by comparing its results with the analytical diffraction coefficients for an infinite 3-D right-angle perfect electric conductor wedge obtained using the uniform theory of diffraction. Then, we apply the new method to calculate numerical diffraction coefficients for a 3-D infinite right-angle dielectric wedge, covering a wide range of incident and scattering angles. Finally, we show means to compactly store the calculated diffraction coefficients in a manner which permits easy interpolation of the results for arbitrary incidence and observation angles.     

正交视觉与倾角仪组合空间位姿测量方法研究

为了解决跨尺度微小型零件在精密装配中宏尺度与微特征的测量分辨问题，提出了一种基于正交双目视觉与倾角仪组合的空间位姿高精测量系统。该系统建立了成像单元、倾角仪辅助测量单元、零部件夹持单元之间的坐标转换关系，并结合倾角仪提供的角度信息，提出了针对微小型零件的空间位姿高精测量解析算法。同时，以光纤阵列及连接头为研究对象，搭建了两零件的空间位姿实时测量及自动化装配测试平台。结果表明，在3mm×2mm×2mm的空间范围内，组合测量系统测得的位置与姿态偏差分别小于(±2μm, ±2μm, ±3μm)和(±0.005°, ±0.004°, ±0.005°)。相对于传统的测量方法，该组合测量系统显著提高了微器件的测量精度，可进一步满足微小型零件的空间位姿精密测量及自动化装配需求。     

Guide wire reconstruction and visualization in 3DRA using monoplane fluoroscopic imaging

A method has been developed that, based on the guide wire position in monoplane fluoroscopic images, visualizes the approximate guide wire position in the three-dimensional (3-D) vasculature, that is obtained prior to the intervention with 3-D rotational X-ray angiography (3DRA). The method assumes the position of the guide wire in the fluoroscopic images is known. A two-dimensional feature image is determined from the 3DRA data. In this feature image, the guide wire position is determined in a two-step approach: a mincost algorithm is used to determine a suitable position for the guide wire, and subsequently a snake optimization technique is applied to move the guide wire to a better position. The resulting guide wire can then be visualized in 3-D in combination with the 3DRA dataset. The reconstruction accuracy of the method has been evaluated using a 3DRA image of a vascular phantom filled with contrast, and monoplane fluoroscopic images of the same phantom without contrast and with a guide wire inserted. The evaluation has been performed for different projection angles, and with different parameters for the method. The final result does not appear to be very sensitive to the parameters of the method. The average mean error of the estimated 3-D guide wire position is 1.5 mm, and the average tip distance is 2.3 mm. The effect of inaccurate C-arm geometry information is also investigated. Small errors in geometry information (up to 1 degrees) will slightly decrease the 3-D reconstruction accuracies, with an error of at most 1 mm. The feasibility of this approach on clinical data is demonstrated.     

BaGa4Se7与KTiOAsO4光参量振荡产生中红外激光性能对比

BaGa₄Se₇(硒镓钡,简称BGSe)与KTiOAsO₄(砷酸氧钛钾,简称KTA)均可在1.06 μm激光泵浦下产生中红外激光。首先仿真计算出两种非线性晶体的相位匹配曲线,结果显示:切割角为(56.3°, 0°)的BGSe晶体在I类相位匹配条件下和切割角为(90°, 0°)的KTA在II-A类相位匹配条件下均可产生~3.5 μm的闲频光。然后理论计算出BGSe (56.3°, 0°, I类)的有效非线性系数为?11.9 pm/V,KTA(90°, 0°,II-A类)的有效非线性系数为?3.2 pm/V;在其他条件相同的情况下,15 mm长BGSe (56.3°, 0°, I类) 的OPO振荡阈值是20 mm长KTA (90°, 0°, II-A类) OPO振荡阈值的35.11%。最后通过实验验证BGSe (56.3°, 0°, I类, 15 mm) 的振荡阈值小于KTA(90°, 0°, II-A类, 20 mm),输出的中红外激光能量大于KTA。因此,BGSe是一种极具应用前景的中红外非线性晶体。     

A global scattering center representation of complex targets usingthe shooting and bouncing ray technique

We present a methodology to extract a global scattering center model a complex target. Using the shooting and bouncing ray technique, we first extract the three-dimensional (3-D) scattering center representations of the target at various aspect angles. Next the correspondence between scattering centers across angles are established by utilizing 3-D location information. The data are grouped based on 3-D scattering center locations and are organized in the form of angular visibility maps. Such data organization gives good insights into target physics and feature stability. Furthermore, we define a stability measure to quantitatively rank order the scattering centers based on their angular stability. Finally, we demonstrate the usefulness of such stable features by carrying out a five-target template-based matching experiment to estimate the angular pose of an unknown target     

激光大尺度3维动态聚焦扫描加工系统研究

为了满足激光3维微加工不断提高的精度要求、不断增大的加工尺寸范围,以及加工效率的上升需求,采用理论分析和计算结合的方法,研制出由动态聚焦镜和2维扫描振镜组合的动态聚焦系统,与高精度X-Y-Z 3维高精度工作台集成为一台激光大尺度3维动态聚焦扫描加工设备。设计了焦距为100mm、视场角15、光阑口径7mm、后工作距137mm、相对畸变小于0.5%的远心f-镜和入光口径8mm、光学杠杆比1:8、后工作距800mm40mm的动态聚焦镜系统,并使用ZEMAX软件对系统关键光学部件动态聚焦镜和远心f-镜进行光学设计及系统性能评价。结果表明,通过工艺控制软件分层拼接,实现了460mm310mm50mm大尺度3维动态聚焦的高精度紫外激光微加工功能,在该3维扫描范围内,激光聚焦光斑直径始终保持小于10m,从而满足大尺度激光3维精密微加工需求。     

平板玻璃微小楔角的散斑法测量

本文提出了一种检验平板玻璃微小楔角的新实验方法。它利用激光散斑技术,记录了由于微小楔角引起的散斑位移量的散斑图,由此导出被测试件的微小楔角。这种方法具有光路简单、非接触、精度高等特点。到目前为止,尚未见有这方面的具体报导。     

3维函数光子晶体的特性研究

为了研究3维函数光子晶体的光子禁带特性,采用平面波展开法计算得到色散曲线,推导了平面波展开法的相关计算公式以及介质球介电常数的函数关系式,探讨了可调参量函数系数I和介质球半径R₁对光子禁带特性的影响。结果表明,3维函数光子晶体呈立方体晶格分布,由介质球填充空气背景;与常规3维介质光子晶体相比,3维函数光子晶体不仅能得到可调谐的光子禁带,而且可以拓展禁带带宽,并增加光子禁带的数量;改变函数系数I的大小可以实现对光子禁带数量、位置和带宽的调谐;改变介质球半径R₁可以对光子禁带带宽实现展宽,并改变光子禁带的位置。该研究对设计新型可调谐器件是有帮助的。     

System for analyzing high-resolution three-dimensional coronary angiograms

Three-dimensional (3-D) high-resolution coronary angiograms offer a means for visualizing the entire coronary arterial tree from any orientation and for detecting and quantitating coronary arterial stenoses. Previously, a skilled operator had to perform several hours of tedious manual analysis using an interactive graphical user-interface (GUI) system (Tree Trace) to analyze a 3-D angiogram. The authors have devised an improved GUI system, consisting of three tools for analyzing 3-D angiograms. The Artery Extractor first performs automatic image-analysis operations to extract the central axes of the arterial tree. Next, using the Artery Display tool and results from the Artery Extractor, the operator can visualize structures in the angiogram and compute various measurements. Finally, the aforementioned Tree Trace tool can be used to manually correct irregularities in the automatically generated results of the Artery Extractor. The system greatly reduces operator analysis time, gives exactly reproducible results, uses true 3-D image-processing operations, and provides a comprehensive interface for visualizing and quantifying features of the 3-D coronary arteries.     

Registration and tracking to integrate X-ray and MR images in an XMR facility

We describe a registration and tracking technique to integrate cardiac X-ray images and cardiac magnetic resonance (MR) images acquired from a combined X-ray and MR interventional suite (XMR). Optical tracking is used to determine the transformation matrices relating MR image coordinates and X-ray image coordinates. Calibration of X-ray projection geometry and tracking of the X-ray C-arm and table enable three-dimensional (3-D) reconstruction of vessel centerlines and catheters from bi-plane X-ray views. We can, therefore, combine single X-ray projection images with registered projection MR images from a volume acquisition, and we can also display 3-D reconstructions of catheters within a 3-D or multi-slice MR volume. Registration errors were assessed using phantom experiments. Errors in the combined projection images (two-dimensional target registration error--TRE) were found to be 2.4 to 4.2 mm, and the errors in the integrated volume representation (3-D TRE) were found to be 4.6 to 5.1 mm. These errors are clinically acceptable for alignment of images of the great vessels and the chambers of the heart. Results are shown for two patients. The first involves overlay of a catheter used for invasive pressure measurements on an MR volume that provides anatomical context. The second involves overlay of invasive electrode catheters (including a basket catheter) on a tagged MR volume in order to relate electrophysiology to myocardial motion in a patient with an arrhythmia. Visual assessment of these results suggests the errors were of a similar magnitude to those obtained in the phantom measurements.     

Electrostatic “fractional” image methods for perfectlyconducting wedges and cones

Engheta (1996) introduced a definition for the electric charge “fractional-order” multipoles using the concept of fractional derivatives and integrals. Here, we utilize that definition to introduce a detailed image theory for the two-dimensional (2-D) electrostatic potential distributions in front of a perfectly conducting wedge with arbitrary wedge angles, and for the three-dimensional potential in front of a perfectly conducting cone with arbitrary cone angles. We show that the potentials in the presence of these structures can be described equivalently as the electrostatic potentials of sets of equivalent “image” charge distributions that effectively behave as “fractional-order” multipoles; hence, the name “fractional” image methods. The fractional orders of these so-called fractional images depend on the wedge angle (for the wedge problem) and on the cone angle (for the cone problem). Special cases where these fractional images behave like the discrete images are discussed, and physical justification and insights into these results are given     

3-D/2-D registration by integrating 2-D information in 3-D

In image-guided therapy, high-quality preoperative images serve for planning and simulation, and intraoperatively as "background", onto which models of surgical instruments or radiation beams are projected. The link between a preoperative image and intraoperative physical space of the patient is established by image-to-patient registration. In this paper, we present a novel 3-D/2-D registration method. First, a 3-D image is reconstructed from a few 2-D X-ray images and next, the preoperative 3-D image is brought into the best possible spatial correspondence with the reconstructed image by optimizing a similarity measure (SM). Because the quality of the reconstructed image is generally low, we introduce a novel SM, which is able to cope with low image quality as well as with different imaging modalities. The novel 3-D/2-D registration method has been evaluated and compared to the gradient-based method (GBM) using standardized evaluation methodology and publicly available 3-D computed tomography (CT), 3-D rotational X-ray (3DRX), and magnetic resonance (MR) and 2-D X-ray images of two spine phantoms, for which gold standard registrations were known. For each of the 3DRX, CT, or MR images and each set of X-ray images, 1600 registrations were performed from starting positions, defined as the mean target registration error (mTRE), randomly generated and uniformly distributed in the interval of 0-20 mm around the gold standard. The capture range was defined as the distance from gold standard for which the final TRE was less than 2 mm in at least 95% of all cases. In terms of success rate, as the function of initial misalignment and capture range the proposed method outperformed the GBM. TREs of the novel method and the GBM were approximately the same. For the registration of 3DRX and CT images to X-ray images as few as 2-3 X-ray views were sufficient to obtain approximately 0.4 mm TREs, 7-9 mm capture range, and 80%-90% of successful registrations. To obtain similar results for MR to X-ray registrations, an image, reconstructed from at least 11 X-ray images was required. Reconstructions from more than 11 images had no effect on the registration results.     

一种激光搜跟器的光学设计

为提高激光搜跟器对地目标的搜索范围和成像分辨率,提出了一种机载平台下的共孔径激光搜跟器扫搜和跟踪目标的方法,并进行了光学系统的设计。激光搜跟器采用捷联的方式固定于飞行器上,提高了其稳定性;激光的出射和回波的接收,采用共孔径的R-C式反射望远系统实现,缩小了其整体尺寸,并提高了成像分辨率;扫描搜索目标采用双光楔组件实现,并提高了搜索频率和扩大了搜索视场;给出了双光楔旋转角和出射光偏转角之间的关系。设计结果表明,当系统通光孔径为φ300 mm,焦距为2 100 mm时,总体尺寸为685 mm,可扫描搜索视场为±5°,成像视场为±0.08°,成像点弥散斑最大为2.417 μm,系统MTF值在50 lp/mm时大于0.4,满足成像要求;当目标距离为3 km时,可搜索范围达到526 m,可实现对4 m大小目标的成像,成像分辨率为2″。     

US-fluoroscopy registration for transcatheter aortic valve implantation

Transcatheter aortic valve implantation is a minimally invasive alternative to open-heart surgery for aortic stenosis in which a stent-based bioprosthetic valve is delivered into the heart on a catheter. Limited visualization during this procedure can lead to severe complications. Improved visualization can be provided by live registration of transesophageal echo (TEE) and fluoroscopy images intraoperatively. Since the TEE probe is always visible in the fluoroscopy image, it is possible to track it using fiducial-based single-perspective pose estimation. In this study, inherent probe tracking performance was assessed, and TEE to fluoroscopy registration accuracy and robustness were evaluated. Results demonstrated probe tracking errors of below 0.6 mm and 0.2°, a 2-D RMS registration error of 1.5 mm, and a tracking failure rate of below 1%. In addition to providing live registration and better accuracy and robustness compared to existing TEE probe tracking methods, this system is designed to be suitable for clinical use. It is fully automatic, requires no additional operating room hardware, does not require intraoperative calibration, maintains existing procedure and imaging workflow without modification, and can be implemented in all cardiac centers at extremely low cost.     

光子禁带型遮阳品的设计

为了屏蔽紫外线,提出光子禁带型遮阳品,分别用传输矩阵、时域有限差分法计算紫外线在1维、2维光子禁带型遮阳品中的透射率。结果表明,选取合适的参量,可以设计紫外线的1维、2维光子禁带遮阳品;入射角对1维、2维遮阳品的禁带波长下限都有较大影响。     

Cylindrical FDTD Analysis of LWD Tools Through Anisotropic Dipping-Layered Earth Media

Electrical logging-while-drilling (LWD) tools are commonly used in oil and gas exploration to estimate the conductivity (resistivity) of adjacent Earth media. In general, Earth media exhibit anisotropic conductivities. This implies that when LWD tools are used for deviated and horizontal drilling, the resulting borehole problem may include dipping-layered media with dipping beds having full 3 times 3 conductivity tensors. To model this problem, we describe a 3-D cylindrical finite-difference time-domain (FDTD) algorithm extended to fully anisotropic conductive media and implemented with cylindrical perfectly matched layers to mimic open-domain problems. The 3-D FDTD algorithm is validated against analytical results in simple formations, showing good agreement, and used to simulate the response of LWD tools through anisotropic dipping beds for various values of anisotropic conductivities and dipping angles     

后路经椎弓根椎体楔形截骨矫形治疗胸腰椎陈旧性骨折伴后凸畸形

目的：探讨后路经椎弓根椎体楔形截骨矫形治疗胸腰椎陈旧性骨折伴后凸畸形的临床疗效。方法：回顾性分析我科于2006年1月至2010年10月收治的胸腰椎陈旧性骨折伴后凸畸形患者23例,男15例,女8例;年龄23岁至88岁;胸113例,胸127例,腰19例,腰24例;胸腰段（胸10~腰2）后凸畸形Cobb角为32°至66°,平均为46°±2.4°;伤椎后凸Cobb角为16°至42°,平均30°±1.8°。术前神经损伤程度按照ASIA分级：C级3例,D级11例,E级9例;腰背痛VAS评分平均7.84±0.28。23例患者均采用经椎弓根椎体楔形截骨矫形、减压、椎弓根钉系统内固定植骨融合手术治疗。结果：术后胸腰段后凸Cobb角平均12°±1.7°,矫正率74%;伤椎Cobb角为0°至4°,平均2.8°,矫正率91%;术后随访X片,胸腰段Cobb角矫正丢失角度不明显（2°至5°）。术后神经功能ASIA分级：3例C级2例改善至E级,1例为D级;11例D级均改善至E级;腰背痛VAS评分平均为2.9±0.13;内固定物无松动或断裂,无假关节形成等并发症。结论：后路经椎弓根椎体楔形截骨矫形治疗胸腰椎陈旧性骨折伴后凸畸形可重建胸腰段矢状面生理曲度,改善临床症状。