Automatic recognition of vertebral landmarks in fluoroscopic sequences for analysis of intervertebral kinematics

Intervertebral kinematics closely relates to the functionality of the spinal segments. Direct measurement of the intervertebral kinematics in vivo is very problematic. The use of a fluoroscopic device can provide continuous screening of the lumbar tract during patient spontaneous motion, with an acceptable, low X-ray dose. The kinematic analysis is intended to be limited to planar motion. Kinematic parameters are computed from vertebral landmarks on each frame of the image sequence. Landmarks are normally selected manually in spite of the fact that this is subjective, tedious to perform and regarded as one of the major contributors to errors in the computed kinematic parameters. The aim of this work is to present an innovative method for the automatic recognition of vertebral landmarks throughout a fluoroscopic image sequence to provide an objective and more precise quantification of intervertebral kinematics. The recognition procedure is based upon comparing vertebral features in two adjacent frames by means of a cross-correlation index, which is also robust despite the low signal-to-noise ratio of the lumbar fluoroscopic images. To provide a quantitative assessment of this method a calibration model was used which consisted of two lumbar vertebrae linked by a universal joint. The reliability and accuracy of the kinematic measurements have been investigated. The errors are of the order of a millimetre for the localisation of the intervertebral centre of rotation and tenths of a degree for the intervertebral angle. Error analysis suggests that this method improves the accuracy of the intervertebral kinematic calculations and has the potential to automate the selection of anatomical landmarks.     

Radiographic and Magnetic Resonance Imaging Identification of Thoracolumbar Spine Variants with Implications for the Positioning of the Conus Medullaris in Rhesus Macaques

The anatomy of the vertebral column in mammals may differ between species and between subjects of the same species, especially with regards to the composition of the thoracolumbar spine. We investigated, using several noninvasive imaging techniques, the thoracolumbar spine of a total of 44 adult rhesus macaques of both genders. Radiographic examination of the vertebral column showed a predominant spine phenotype with 12 rib‐bearing thoracic vertebrae and 7 lumbar vertebrae without ribs in 82% of subjects, whereas a subset of subjects demonstrated 13 rib‐bearing thoracic vertebrae and 6 lumbar vertebrae without ribs. Computer tomography studies of the thoraco‐lumbar spine in two cases with a pair of supernumerary ribs showed facet joints between the most caudal pair of ribs and the associated vertebra, supporting a thoracic phenotype. Magnetic resonance imaging (MRI) studies were used to determine the relationship between the lumbosacral spinal cord and the vertebral column. The length of the conus medullaris portion of the spinal cord was 1.5 ± 0.3 vertebral units, and its rostral and caudal positions in the spinal canal were at 2.0 ± 0.3 and 3.6 ± 0.4 vertebral units below the thoracolumbar junction, respectively (n = 44). The presence of a set of supernumerary ribs did not affect the length or craniocaudal position of the conus medullaris, and subjects with13 rib‐bearing vertebrae may from a functional or spine surgical perspective be considered as exhibiting12 thoracic vertebrae and an L1 vertebra with ribs. Anat Rec, 300:300–308, 2017. © 2016 Wiley Periodicals, Inc.     

Geometry of the Intervertebral Volume and Vertebral Endplates of the Human Spine

Replacement of a degenerated vertebral disc with an artificial intervertebral disc (AID) is currently possible, but poses problems, mainly in the force distribution through the vertebral column. Data on the intervertebral disc space geometry will provide a better fit of the prosthesis to the vertebrae, but current literature on vertebral disc geometry is very scarce or not suitable. In this study, existing CT-scans of 77 patients were analyzed to measure the intervertebral disc and vertebral endplate geometry of the lumbar spine. Ten adjacent points on both sides of the vertebrae (S1-superior to T12-inferior) and sagittal and transverse diameters were measured to describe the shape of the caudal and cranial vertebral planes of the vertebrae. It was found that the largest endplate depth is located in the middle or posterior regions of the vertebra, that there is a linear relationship between all inferior endplate depths and the endplate location (p < 0.0001) within the spinal column, and that the superior endplate depth increases with age by about 0.01 mm per year (p < 0.02). The wedge angle increases from T12-L1 to L5-S1. The results allow for improvement of the fit of intervertebral disc-prostheses to the vertebrae and optimized force transmission through the vertebral column.     

Automatic lumbar vertebral identification using surface-based registration

This work proposes the use of surface-based registration to automatically select a particular vertebra of interest during surgery. Manual selection of the correct vertebra can be a challenging task, especially for closed-back, minimally invasive procedures. Our method uses shape variations that exist among lumbar vertebrae to automatically determine the portion of the spinal column surface that correctly matches a set of physical vertebral points. In our experiments, we register vertebral points representing posterior elements of a single vertebra in physical space to spinal column surfaces extracted from computed tomography images of multiple vertebrae. After registering the set of physical points to each vertebral surface that is a potential match, we then compute the standard deviation of the surface error for each registration trial. The registration that corresponds to the lowest standard deviation designates the correct match. We have performed our current experiments on two plastic spine phantoms and two patients.     

基于 OpenSim 的轻度青少年特发性脊柱侧凸个性化建模与分析

目的 建立青少年特发性脊柱侧凸患者的个性化脊柱运动学和动力学建模方法并验证其准确性,为脊柱侧凸的非手术矫形治疗提供治疗机制分析与效果评估的工具。 方法 基于患者影像学数据计算并调整 Schmid 开发的 OpenSim 青少年脊柱模型的骨骼与肌肉参数,使模型与特定患者相匹配;基于文献数据添加椎间刚度并在侧凸 段进行修正,使模型符合脊柱侧凸患者椎关节力学特征,进而建立患者侧凸脊柱的个性化运动学和动力学仿真分析模型;基于运动捕捉数据计算逆运动学,并使用静态优化计算肌肉激活度,将计算结果与影像学及肌电(electromyogram,EMG)数据进行对比验证。 结果 站立状态逆运动学计算得到的各椎骨冠状面角度平均误差为0. 164°,符合运动学误差要求;站立状态胸椎段与腰椎段竖脊肌凸侧与凹侧肌肉激活度比值分别为 0. 489 与0. 631,与 EMG 数据吻合;侧屈运动中对椎间刚度进行修正后的模型与未修正模型相比,肌肉激活更接近 EMG 数据。 结论 本文方法建立的模型满足运动学与肌肉力的准确性要求。     

A new method for determining lumbar spine motion using Bayesian belief network

A Bayesian network dynamic model was developed to determine the kinematics of the intervertebral joints of the lumbar spine. Radiographic images in flexion and extension postures were used as input data for modeling, together with movement information from the skin surface using an electromagnetic motion tracking system. Intervertebral joint movements were then estimated by the graphic network. The validity of the model was tested by comparing the predicted position of the vertebrae in the neutral position with those obtained from the radiographic image in the neutral posture. The correlation between the measured and predicted movements was 0.99 (p < 0.01) with a mean error of less than 1.5°. The movement sequence of the various vertebrae was examined based on the model output, and wide variations in the kinematic patterns were observed. The technique is non-invasive and has potential to be used clinically to measure the kinematics of lumbar intervertebral movement. This work was supported by the Hong Kong Research Grant Council (Competitive Earmarked Research Grant CERG CUHK5251/04E).     

脊柱跟随载荷在离体生物力学应用研究中的进展

阐述跟随载荷在维持脊柱生物力学中的重要性,归纳近年来人离体脊柱标本跟随载荷模拟的各种方法及手段。通过与人体脊柱各椎体活动度、椎间盘内压等真实数据对比,从力学角度分析各类模拟手段的可行性,总结人体颈椎、胸椎、腰椎离体生物力学实验中最适合的加载载荷及扭矩,并探讨常规脊柱内固定术式对脊柱生物力学特性的影响。     

Parametric characterization of spinal motions in osteoporotic vertebral fracture at level T12 with fluoroscopy

Vertebral fractures due to osteoporosis are a common skeletal disorder affecting the mobility of the patients, although little is known about the relationship between spinal kinematics and osteoporotic fracture. The purpose of this study was to characterize the motions of the thoracolumbar spine affected by osteoporotic vertebral fracture at level T12 and compare the results with those of non-fracture osteoporosis subjects. We examined the continuous segmental kinematics of the vertebrae, and describe the segmental motion of the spine when a fracture at T12 is present. Fluoroscopy sequences of the thoracolumbar spines during sagittal and lateral flexion were collected from 16 subjects with osteoporosis of their spine (6 with vertebral fractures at T12, 10 without a fracture). Vertebrae T10-L2 in each frame of the sequences were landmarked. Kinematic parameters were calculated based on the landmarks and motion graphs were constructed. Compared to the control subjects who did not have a fracture, fracture subjects had a more asymmetric lateral range of motion (RoM) and required a longer time to complete certain phases of the motion cycle which are parameterized as lateral flexion ratio and percentage of motion cycle, respectively. Prolonged deflection was more frequently found from the fracture group. Characterizing the motions of the fractured vertebra together with its neighboring vertebrae with these kinematic parameters is useful in quantifying the dysfunction and may be a valuable aid to tracking progress of treatment.     

Automatic Estimation of Orientation and Position of Spine in Digitized X-rays using Mathematical Morphology

In this paper, we propose a method for automatic determination of position and orientation of spine in digitized spine X-rays using mathematical morphology. As the X-ray images are usually highly smeared, vertebrae segmentation is a complex process. The image is first coarsely segmented to obtain the location and orientation information of the spine. The state-of-the-art technique is based on the deformation model of a template, and as the vertebrae shape usually shows variation from case to case, accurate representation using a template is a difficult process. The proposed method makes use of the vertebrae morphometry and gray-scale profile of the spine. The top-hat transformation-based method is proposed to enhance the ridge points in the posterior boundary of the spine. For cases containing external objects such as ornaments, H-Maxima transform is used for segmentation and removal of these objects. The Radon transform is then used to estimate the location and orientation of the line joining the ridge point clusters appearing on the boundary of the vertebra body. The method was validated for 100 cervical spine X-ray images, and in all cases, the error in orientation was within the accepted tolerable limit of 15°. The average error was found to be 4.6°. A point on the posterior boundary was located with an accuracy of ±5.2 mm. The accurate information about location and orientation of thespine is necessary for fine-grained segmentation of the vertebrae using techniques such as active shape modeling. Accurate vertebrae segmentation is needed in successful feature extraction for applications such as content-based image retrieval of biomedical images.     

The vertebral level of origin of spinal nerves in the rat

Several dissections were performed to determine the level of spinal cord termination and the vertebral level at which the dorsal and ventral roots of spinal nerves C1-S4 emerged from the spinal cord in the rat. These levels of emergence were then compared to the level of exit from the vertebral canal. The dissections demonstrated that the effect of differential growth between spinal cord and vertebral column begins in the lower cervical region and becomes progressively more pronounced throughout thoracic and lumbar levels. The disparity between the vertebral level of emergence of spinal roots from the spinal cord and their level of exit via intervertebral foramina was found to be considerably larger than was previously reported by Greene ('68). It was further noted that the spinal cord terminated at the level of the intervertebral disc between the third and fourth lumbar vertebrae, not between the fourth and fifth lumbar vertebrae as reported by Greene ('68).     

Estimation of out-of-plane vertebra rotations on radiographic projections using CT data: a simulation study

This study extends previous research concerning in vivo intervertebral motion by means of single-plane fluoroscopy in an attempt to overcome 2D analysis limitations. Knowledge of out-of-plane vertebra rotations will extend the results provided by planar kinematic studies, which is particularly important for lateral bending investigation where axial rotation accompanies side bending, but is also valuable in sagittal analysis (e.g. indicating an absence of coupled axial rotation). Combining a fluoroscopic projection of a vertebra with volumetric information provided by CT data, vertebra 3D position can be estimated. Out-of-plane vertebral rotations are estimated by comparing Digitally Reconstructed Radiographs (DRRs) in different orientations with a reference fluoroscopic projection, maximising the image cross-correlation index. DRRs have been computed from CT-data using a ray-casting algorithm. In this work a feasibility study of the method was performed by means of a computer simulation. To this end the CT volume (vertebra L4, segmented) provided by the Visible Human Project was utilised and reference fluoroscopic projections were simulated in different orientations adding various levels of noise. Accuracy and precision of the proposed method was determined. Error analysis reveals that an accuracy of less than 1 degree can be achieved in computation of out-of-plane vertebral angles.     

The diameter of the vertebral canal in dogs in cases of lumbosacral transitional vertebrae or numerical vertebral variations

From Th1 to L7 midsagittal and interpedicular vertebral canal diameters were measured in macerated spines of 162 dogs to determine, whether the presence of lumbosacral transitional vertebrae or numerical vertebral variations are associated with dislocation of the maximal enlargement of the lumbar vertebral canal. Relative to dogs with a regular number of 27 presacral vertebrae (C7/Th13/L7), the maximal enlargement of the lumbar vertebral canal was more frequently ( P < 0.05) located at vertebra 24 in dogs with 26 presacral vertebrae (C7/Th13/L6), and more frequently at vertebra 25 in dogs with 28 presacral vertebrae (C7/Th13/L8). However, in dogs with 26 presacral vertebrae, maximal agreement in the spinal position of maximal lumbar vertebral canal diameters was achieved relative to dogs with 28 presacral vertebrae by adding one additional thoracic (Th6, 7, or 8) segment. Therefore, the present findings strongly suggest that relative to the regular (C7/Th13/L7) condition, decrease in the number of presacral vertebrae (C7/Th13/L6) is associated with incorporation of a midthoracic segment, whereas increase in the number of presacral vertebrae (C7/Th13/L8) is not related to the presence of an additional vertebral segment. When using Th1 as landmark, the difference in the position of the maximal enlargement of the lumbar vertebral canal between dogs with 26 and dogs with 28 presacral vertebrae in average was only one segment. It is known from previous reports that the maximal enlargement of the lumbar vertebral canal corresponds with the maximal enlargement of the lumbar spinal cord. When using S1 or the transitional vertebra as the landmark for determination of the appropriate site for subarachnoid cannulation, this site is expected to range within the same limits regardless of the vertebral formula.     

从生物力学角度看腰椎手术发展

外科手术作为腰椎退行性疾病(lumbar degenerative diseases,LDDs)的重要治疗手段,其进展依赖于人们对脊柱生物力学理念的理解与革新.充分认识腰椎衰老退变过程中生物力学改变是理解LDDs发病过程、改革LDDs手术策略,进而采用针对性更强、更微创治疗方法的重要基础.本文阐述LDDs与椎体、椎间盘...     

Spine Localization in X-ray Images Using Interest Point Detection

This study was conducted to evaluate a new method used to calculate vertebra orientation in medical x-ray images. The goal of this work is to develop an x-ray image segmentation approach used to identify the location and the orientation of the cervical vertebrae in medical images. We propose a method for localization of vertebrae by extracting the anterior—left—faces of vertebra contours. This approach is based on automatic corner points of interest detection. For this task, we use the Harris corner detector. The final goal is to determine vertebral motion induced by their movement between two or several positions. The proposed system proceeds in several phases as follows: (a) image acquisition, (b) corner detection, (c) extracting of the corners belonging to vertebra left sides, (d) global estimation of the spine curvature, and (e) anterior face vertebra detection.     

脊柱腰段断面解剖观测及临床意义

目的旨在为脊柱腰段病变的影像诊断和手术治疗提供形态学依据。方法 30例横断面标本,观测椎体、椎弓根、椎孔、椎弓板等结构。结果椎体横、矢径,以及椎孔横径存在性别差异(男性女性,P0.0001),但椎孔矢径无性差(P=0.6441),而不同椎体间椎孔矢径存在差异(P=0.0349),不同椎体的横、矢径存在显著差异(P0.0001);脊椎指数均1:4.5,且存在性别差异(P0.0001),不同腰椎间有显著性差异(P=0.0018);腰椎椎板夹角变化较大(70°～90°),同椎骨A、B两个断面该角的大小具有显著性差异(P0.0001),但无性差、各椎体间也无显著性差异;椎弓根横径、OE径存在性别差异(男性女性,P0.0001),不同椎体的该两径存在显著差异(P0.0001),但该两径值的侧差无显著性差异(P0.6070);Z角在不同腰椎间存在显著性差异(P0.0001),但无性差、侧差(性别P=0.4153,侧差P=0.7579)。结论⑴不同性别、不同腰椎间的形态数据存在显著差异;⑵椎体横、矢径,椎孔横、矢径,脊柱指数,椎弓板夹角均可作为诊断腰椎孔狭窄的参考指标;⑶椎弓根螺钉选择需结合术前影像测量。     

Automatic Cobb Measurement of Scoliosis Based on Fuzzy Hough Transform with Vertebral Shape Prior

To reduce variability of Cobb angle measurement for scoliosis assessment, a computerized method was developed. This method automatically measured the Cobb angle on spinal posteroanterior radiographs after the brightness and the contrast of the image were adjusted, and the top and bottom of the vertebrae were selected. The automated process started with the edge detection of the vertebra by Canny edge detector. After that, the fuzzy Hough transform was used to find line structures in the vertebral edge images. The lines that fitted to the endplates of vertebrae were identified by selecting peaks in Hough space under the vertebral shape constraints. The Cobb angle was then calculated according to the directions of these lines. A total of 76 radiographs were respectively analyzed by an experienced surgeon using the manual measurement method and by two examiners using the proposed method twice. Intraclass correlation coefficients (ICC) showed high agreement between automatic and manual measurements (ICCs > 0.95). The mean absolute differences between automatic and manual measurements were less than 5°. In the interobserver analyses, ICCs were higher than 0.95, and mean absolute differences were less than 5°. In the intraobserver analyses, ICCs were 0.985 and 0.978, respectively, for each examiner, and mean absolute differences were less than 3°. These results demonstrated the validity and reliability of the proposed method.Key words: Cobb angle, scoliosis, fuzzy Hough transform (FHT), shape prior, radiograph     

平行光三维运动测量系统的研制及其在人体完整腰椎上的应用

为了进行人体完整腰椎的运动学研究，设计和制造平行光三维运动测量和分析系统。改进加载装置，以减少实验设备对腰椎运动的干扰。随着载荷的改变，人体新鲜腰椎标本产生不同的运动。通过测量系统，设立在每个椎体上的三个标志点的运动分别投影到光屏，摄像机动态记录，输入计算机图像处理系统。利用刚体运动的原理进行计算，获得各标志点的三维运动量的完整腰椎的运动学特点。     

Vertebral body shape variation in the thoracic and lumbar spine: characterization of its asymmetry and wedging

This study was designed to characterize the vertebral body (VB) shape, focusing on vertebral wedging, along the thoracic and lumbar spine, and to look for shape variations with relation to gender, age, and ethnicity. All thoracic and lumbar (T1-L5) dissected vertebrae of 240 individuals were measured and analyzed by age, gender, and ethnicity. A 3D digitizer was used to measure all VB lengths, heights, and widths, and their ratios were calculated. This study showed that the VB size was independent of age or ethnicity. VB left lateral wedging was found in most vertebrae of most individuals, yet systematically was absent in six vertebrae (T4, T8-T9, T11, L3-L4) with a greater tendency in females than males ( approximately 92% vs. 86%). The VB was anteriorly wedged from T1 through L2 (peak at T7), nonwedged at L3, and posteriorly wedged at L4-L5 (peak at L5). VB width decreased from T1 to T4 and then increased toward L4-L5, so that the spinal configuration in the coronal plane resembled two pyramids of opposite directions, sharing an apex at T4. The inferior VB width was significantly greater than the superior width of both the same vertebra and the adjacent lower vertebra, indicating a trapezoidal shape of the VB and an inverted trapezoidal shape of the intervertebral space. In conclusion, these findings indicate that the human vertebra, in its normal condition, maintains its external dimensions with age, independent of gender or ethnic origin. Clinical and surgical implications of the unique thoracolumbar architecture are discussed.     

颈椎人工椎间盘置换有限元分析

目的　建立C4~5节段PrestigeTM-LP颈椎人工椎间盘植入后的三维有限元模型,进行手术节段的运动分析。 方法 采用对成年男性的新鲜尸体的颈椎标本进行CT三维扫描方法建立C4~5节段和PrestigeTM-LP人工间盘有限元,模拟完成C4~5人工椎间盘置换手术。测量生理加载下手术节段前屈/后伸、侧弯及轴向旋转运动角度。结果 有限元模型对颈椎的结构,包括椎体间韧带、颈椎关节突关节、钩椎关节等均进行了精确的重建,并较好地模拟手术操作进行PrestigeTM-LP人工间盘植入。运动加载后运动角度,前屈5.7°,后伸3.5°,侧弯5.0°,旋转11.3°,与文献报道结果较为接近。 结论　有限元模型具有精确度高,手术模拟真实的特点,可作为颈椎人工椎间盘生物力学研究的一种较好途径。PrestigeTM-LP颈椎人工椎间盘置换可较好地保留手术节段的运动功能。