Transversely isotropic elasticity imaging of cancellous bone

To measure spatial variations in mechanical properties of biological materials, prior studies have typically performed mechanical tests on excised specimens of tissue. Less invasive measurements, however, are preferable in many applications, such as patient-specific modeling, disease diagnosis, and tracking of age- or damage-related degradation of mechanical properties. Elasticity imaging (elastography) is a nondestructive imaging method in which the distribution of elastic properties throughout a specimen can be reconstructed from measured strain or displacement fields. To date, most work in elasticity imaging has concerned incompressible, isotropic materials. This study presents an extension of elasticity imaging to three-dimensional, compressible, transversely isotropic materials. The formulation and solution of an inverse problem for an anisotropic tissue subjected to a combination of quasi-static loads is described, and an optimization and regularization strategy that indirectly obtains the solution to the inverse problem is presented. Several applications of transversely isotropic elasticity imaging to cancellous bone from the human vertebra are then considered. The feasibility of using isotropic elasticity imaging to obtain meaningful reconstructions of the distribution of material properties for vertebral cancellous bone from experiment is established. However, using simulation, it is shown that an isotropic reconstruction is not appropriate for anisotropic materials. It is further shown that the transversely isotropic method identifies a solution that predicts the measured displacements, reveals regions of low stiffness, and recovers all five elastic parameters with approximately 10% error. The recovery of a given elastic parameter is found to require the presence of its corresponding strain (e.g., a deformation that generates ??? is necessary to reconstruct C????), and the application of regularization is shown to improve accuracy. Finally, the effects of noise on reconstruction quality is demonstrated and a signal-to-noise ratio (SNR) of 40 dB is identified as a reasonable threshold for obtaining accurate reconstructions from experimental data. This study demonstrates that given an appropriate set of displacement fields, level of regularization, and signal strength, the transversely isotropic method can recover the relative magnitudes of all five elastic parameters without an independent measurement of stress. The quality of the reconstructions improves with increasing contrast, magnitude of deformation, and asymmetry in the distributions of material properties, indicating that elasticity imaging of cancellous bone could be a useful tool in laboratory studies to monitor the progression of damage and disease in this tissue.     

染色体三维结构重建方法研究

染色体三维结构重构问题是近年生物领域中基因组学的热点研究问题,是以二维交互频率数据为基础来预测其三维空间结构。最新相关实验表明染色质的三维空间结构对于基因表达、调控等方面都具有重要意义。而Hi-c数据能利用染色质交互信息形成二维接触矩阵重构出染色体三维结构。本综述以染色体三维结构重建方法为研究对象,通过对染色体三维结构重建方法进行比较分析,综述了目前基于Hi-c数据在染色体三维结构重建中的经典方法,系统介绍了染色体三维结构重建技术的发展脉络,以促进染色体三维结构重建的进一步研究。     

Transform-based backprojection for volume reconstruction of large format electron microscope tilt series

Alignment of the individual images of a tilt series is a critical step in obtaining high-quality electron microscope reconstructions. We report on general methods for producing good alignments, and utilizing the alignment data in subsequent reconstruction steps. Our alignment techniques utilize bundle adjustment. Bundle adjustment is the simultaneous calculation of the position of distinguished markers in the object space and the transforms of these markers to their positions in the observed images, along the bundle of particle trajectories along which the object is projected to each EM image. Bundle adjustment techniques are general enough to encompass the computation of linear, projective or nonlinear transforms for backprojection, and can compensate for curvilinear trajectories through the object, sample warping, and optical aberration. We will also report on new reconstruction codes and describe our results using these codes.     

Evaluation of viscoelastic property inhomogeneities in soft tissues exposed to low frequency perturbations

This work presents the methods of recognition of inhomogeneities of tissue shear viscoelastic properties using partial data on the internal displacements in an object exposed to low-frequency perturbation. An approach to detect tissue inhomogeneities using the single displacement component is presented.     

Application of Numerical Methods to Elasticity Imaging

Elasticity imaging can be understood as the intersection of the study of biomechanical properties, imaging sciences, and physics. It was mainly motivated by the fact that pathological tissue presents an increased stiffness when compared to surrounding normal tissue. In the last two decades, research on elasticity imaging has been an international and interdisciplinary pursuit aiming to map the viscoelastic properties of tissue in order to provide clinically useful information. As a result, several modalities of elasticity imaging, mostly based on ultrasound but also on magnetic resonance imaging and optical coherence tomography, have been proposed and applied to a number of clinical applications: cancer diagnosis (prostate, breast, liver), hepatic cirrhosis, renal disease, thyroiditis, arterial plaque evaluation, wall stiffness in arteries, evaluation of thrombosis in veins, and many others. In this context, numerical methods are applied to solve forward and inverse problems implicit in the algorithms in order to estimate viscoelastic linear and nonlinear parameters, especially for quantitative elasticity imaging modalities. In this work, an introduction to elasticity imaging modalities is presented. The working principle of qualitative modalities (sonoelasticity, strain elastography, acoustic radiation force impulse) and quantitative modalities (Crawling Waves Sonoelastography, Spatially Modulated Ultrasound Radiation Force (SMURF), Supersonic Imaging) will be explained. Subsequently, the areas in which numerical methods can be applied to elasticity imaging are highlighted and discussed. Finally, we present a detailed example of applying total variation and AM-FM techniques to the estimation of elasticity.     

生物组织弹性成像方法及其新技术进展

弹性是一种描述物质物理意义的重要参数,在描述物质在热力学和动力学的变化过程中有着重要的意义。在医学上,弹性的变化往往和病变联系在一起。然而,绝大多数生物组织在他们的力学特性上所表现出的复杂性并不是弹性模量一项参数就可以完全表述的,在对于他们的粘弹性表征和流变学行为的描述中,粘滞性往往和弹性一样的重要。现在被广泛用来对生物组织机械特性表征的成像技术是弹性成像,其基本原理是给组织施加一个激励,组织会产生一个响应,而该响应的分布结合技术的处理方法,可以反映出其弹性模量等力学属性的差异。本文介绍了生物组织常见的弹性成像方法:超声弹性成像,磁共振弹性成像以及光学相干弹性成像;详细阐述了新发展起来的技术-光声弹性成像和光声粘弹成像,并讨论分析其应用前景。     

Breast reconstruction by superior gluteal microvascular free flaps without silicone implants

The author's experience with 10 gluteus maximus myodermal free flap breast reconstructions is reviewed against the current methods of reconstruction using silicone implants, latissimus dorsi flaps, regional skin flaps, and rectus abdominis myodermal flaps. The superior gluteal free flap can achieve a reliable, permanent, and aesthetic reconstruction of the breast without silicone implants. The softness, projection, natural appearance, and patient satisfaction are excellent compared with other methods. It is particularly useful in patients who object to the use of artificial implants, are not suitable for regional flaps, or have disappointing results from previous reconstructions. Technical modifications of the flap design and selection of the recipient vessels are important.     

A microcomputer based system for three-dimensional reconstructions from tomographic or histologic sections

The reconstructions of three-dimensional (3-D) objects from serial two-dimensional (2-D) images can contribute to the understanding of many biologic structures, from organelles to organs and tissues. The 3-D reconstruction of sections can be divided into several major tasks: image acquisition, alignment of slices, internal object definition, object reconstruction and rotation of the completed image. A fast, versatile, interactive system was devised for the reconstruction of 3-D objects from serial 2-D images using a low-cost microcomputer, original programs and commercial software. The system allows reconstruction from any serial images, e.g., electron micrographs, histologic sections or computed tomograms. A photographic image or a microscopic field is acquired into the computer memory using a video digitizer. Slices are superimposed and aligned to each other using an operator-interactive program. A contour-(edge-) finding algorithm isolates an object of interest from the background image by "subtraction" of the image from an overlaid, slightly shifted identical image. Contours for each slice are input to a reconstruction procedure, which calculates the x, y and z coordinates of every point in a slice and the thickness and number of slices. It then calculates the illumination for every point using a given point source of light and an intensity-fading coefficient. Finally, the points are represented by cubes to provide dimension and reflective surfaces. A cube of appropriate shade and color represents in 2-D the equivalent of a 3-D object; this results in a very effective 3-D image. The reconstruction is rotated by recalculating the positions of every point defining the object and rebuilding the image.(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal changes in tissue elasticity in chaparral shrubs

An important physiological feature of chaparral shrubs is the development of low water potentials during periods of drought characteristic of southern Californian summers. Changes in tissue elasticity may be an important characteristic allowing these low water potentials to be reached and maintained without the development of detrimental water deficits. To examine this possibility, seasonal changes in tissue elasticity were measured in 3 species of chaparral shrubs, Arctostaphylos glandulosa Eastw., Quercus dumosa Nutt. and Ceanothus greggii Gray., by the pressure-volume method. Tissue elasticity was characterized using graphs of the modulus of elasticity plotted as a function of turgor pressure, and maximum values of the elastic modulus. The moduli of elasticity of the shrubs increased following leaf emergence in the spring, were highest during periods of low soil water potential, and tended to decrease following the summer-fall drought period. Increases in tissue elasticity facilitate water uptake from drying soils, but result in greater turgor loss during tissue dehydration.     

Scanning probe recognition microscopy investigation of tissue scaffold properties

Scanning probe recognition microscopy is a new scanning probe microscopy technique which enables selective scanning along individual nanofibers within a tissue scaffold. Statistically significant data for multiple properties can be collected by repetitively fine-scanning an identical region of interest. The results of a scanning probe recognition microscopy investigation of the surface roughness and elasticity of a series of tissue scaffolds are presented. Deconvolution and statistical methods were developed and used for data accuracy along curved nanofiber surfaces. Nanofiber features were also independently analyzed using transmission electron microscopy, with results that supported the scanning probe recognition microscopy-based analysis.     

Adaptive Geometric Tessellation for 3D Reconstruction of Anisotropically Developing Cells in Multilayer Tissues from Sparse Volumetric Microscopy Images

The need for quantification of cell growth patterns in a multilayer, multi-cellular tissue necessitates the development of a 3D reconstruction technique that can estimate 3D shapes and sizes of individual cells from Confocal Microscopy (CLSM) image slices. However, the current methods of 3D reconstruction using CLSM imaging require large number of image slices per cell. But, in case of Live Cell Imaging of an actively developing tissue, large depth resolution is not feasible in order to avoid damage to cells from prolonged exposure to laser radiation. In the present work, we have proposed an anisotropic Voronoi tessellation based 3D reconstruction framework for a tightly packed multilayer tissue with extreme z-sparsity (2–4 slices/cell) and wide range of cell shapes and sizes. The proposed method, named as the ‘Adaptive Quadratic Voronoi Tessellation’ (AQVT), is capable of handling both the sparsity problem and the non-uniformity in cell shapes by estimating the tessellation parameters for each cell from the sparse data-points on its boundaries. We have tested the proposed 3D reconstruction method on time-lapse CLSM image stacks of the Arabidopsis Shoot Apical Meristem (SAM) and have shown that the AQVT based reconstruction method can correctly estimate the 3D shapes of a large number of SAM cells.     

Investigation and comparative characteristic of factors determining human skin elasticity

The results of examining the variation in skin elasticity at its expansion are presented for different skin thickness, different content of collagen and intercellular and intracellular fluids, different venous pressure, and for tension and relaxation of the smooth muscle of skin vessels (vasomotion). Elasticity was determined using the acoustic method by the velocity of the surface shear acoustic wave, the self-resonance method by the frequency of mechanic skin resonance, and the vacuum method by the volume of the skin segment pulled into the aperture of a thin tube by air rarefaction. It is shown that the main factors determining the skin elasticity are its stretching, thickness, and collagen and fluid content. The influence of venous pressure and contractile activity of the vasculature on elasticity is insignificant. This gives grounds for using skin elasticity factors as indicators of systemic and local lesion of connective tissue.     

The Use of Electron Tomography for Structural Analysis of Disordered Protein Arrays

A method based on Fourier transforms is described for obtaining a 3-D reconstruction from a paracrystalline object with static disorder. The method is derived from the standard methods used in 3-D reconstruction of 2-D crystals except that all of the Fourier coefficients are used and not just the sampled data from the periodic lattice. Thus, not only is the spatially ordered part of the structure visualized in 3-D, but also the spatially disordered part. Application of the method to 3-D reconstructions of insect flight muscle is described as well as prospects for extension of the method to radiation-sensitive specimens.     

The restoration of flattened fossils

Neither collapse, due to decay in a soft-bodied organism, nor compaction, due to overburden pressure, normally lead to significant lateral expansion in flattened fossils except in the case of some with rigidly mineralized skeletons. The fossils are thus analogous to a variety of two-dimensional views of a three-dimensional object. This realization provides a foundation for drawing and testing a reconstruction using either computer or manual graphic restoration methods. A complementary approach based on the photography of simple models, which is particularly useful where a complex three-dimensional morphology is under study, is described and illustrated by two examples, the Middle Cambrian arthropod Odaraia and the Upper Ordovician graptolite Direllograptus .     

Volumic patient-specific reconstruction of muscular system based on a reduced dataset of medical images

Three-dimensional mechanical modelling of muscles is essential for various biomechanical applications and clinical evaluation, but it requires a tedious manual processing of numerous images. A muscle reconstruction method is presented based on a reduced set of images to generate an approximate parametric object from basic dimensions of muscle contours. A regular volumic mesh is constructed based on this parametric object. The approximate object and the corresponding mesh are deformed to fit the exact muscles contours yielding patient-specific geometry. Evaluation was performed by comparison of geometry to that obtained by contouring all computed tomography (CT) slices, and by quantification of the mesh quality criteria. Muscle fatty infiltration was estimated using a threshold between fat and muscle. Volumic fat index (VFI) of a muscle was computed using first all the complete CT scan slices containing the muscle (VFI(ref)) and a second time only the slices used for reconstruction (VFI(recons)). Mean volume error estimation was 2.6% and hexahedron meshes fulfilled quality criteria. VFI(recons) respect the individual variation of fat content.     

Eyelids and eye socket reconstruction using the expanded forehead flap and scapha composite grafting.

After trauma or excision of malignant tumor, it is difficult to achieve satisfactory results when reconstructing deformed eyelids and the socket for an ocular prosthesis. The authors demonstrate examples of successful reconstruction for a prosthetic eye that provided adequate and aesthetic soft-tissue support achieved by applying a three-step surgical procedure of reconstruction of the eye socket, the eyelids, and the tarsus and eyelid margin. Because it is highly vascularized and its distal end can be divided into two or three portions for easy three-dimensional reconstruction, the expanded forehead flap alone, with a galea flap, or with a free rectus abdominis muscle perforator flap was used. The expanded forehead flap also provides excellent thin upper lid contour and good color-matching with a recipient site. For the eye socket, sufficient volume of tissue was provided from the expanded forehead flap with or without a galea or a free rectus abdominis muscle perforator flap, and a deep and convex fornix was formed. This resulted in a good fit and in stability of the ocular prosthesis. The surface and the inner lining of the eyelids were reconstructed using portions of the expanded forehead flap. For the tarsus and eyelid margin, conventional reconstruction techniques use cartilage of the concha, which has limitations of length and which does not fit the shape of the tarsal margin. The authors used the scapha composite graft, and a natural shape and good elasticity resulted.     

超声弹性成像技术在前列腺癌诊断中的应用

超声弹性成像技术是一项新兴的超声成像方法,可通过分析不同组织间机械组织差异区分组织软硬度,早期主要应用于乳腺、甲状腺结节的区分和定性。随着科技的进步和医疗水平的提高,目前弹性成像技术可在二维声像图的基础上,对感兴趣区域进行定性诊断和定量分析,已逐步应用于医学各领域相关研究和临床疾病的鉴别诊断。本文介绍了弹性成像的基本原理和目前弹性成像技术在医学领域中的相关应用,叙述了前列腺癌的发展趋势和目前常用的筛查、诊断方法,详细阐述了弹性成像技术在前列腺癌诊断中的应用方法和现状,分析总结了弹性成像技术在前列腺癌诊断中的应用价值。运用弹性成像技术无创、经济便捷、实时动态、可重复性好等优点,联合前列腺癌相关筛查、诊断检查,可有效帮助早期诊断前列腺癌,减少前列腺穿刺术的针数,提高前列腺癌的检出率。     

Cryoelectron-microscopy image reconstruction of symmetry mismatches in bacteriophage phi29

A method has been developed for three-dimensional image reconstruction of symmetry-mismatched components in tailed phages. Although the method described here addresses the specific case where differing symmetry axes are coincident, the method is more generally applicable, for instance, to the reconstruction of images of viral particles that deviate from icosahedral symmetry. Particles are initially oriented according to their dominant symmetry, thus reducing the search space for determining the orientation of the less dominant, symmetry-mismatched component. This procedure produced an improved reconstruction of the sixfold-symmetric tail assembly that is attached to the fivefold-symmetric prolate head of phi29, demonstrating that this method is capable of detecting and reconstructing an object that included a symmetry mismatch. A reconstruction of phi29 prohead particles using the methods described here establishes that the pRNA molecule has fivefold symmetry when attached to the prohead, consistent with its proposed role as a component of the stator in the phi29 DNA packaging motor.     

去细胞方法及其在组织工程中的应用

去细胞基质在组织工程及再生医学的大量应用为解决组织器官的修复和重建等难题带来了希望。去细胞方法大致可以分为三类：化学处理法、物理处理法及酶学处理法,且已经应用于组织工程及再生医学的各个方面。本文总结并分类目前常用的去细胞方法及其在组织工程各方面的应用,对目前国内外常用的去细胞方法及其在组织工程及再生医学中的应用进行回顾总结与分析。     

Bilateral vermilion flaps for lower lip repair

A more natural reconstructive procedure of the lower lip using bilateral vermilion flaps was applied in five patients with excellent results. The vermilion defects were about two-fifths to three-fifths. In three patients, the vermilion defect was repaired using bilateral vermilion flaps alone. In the remaining two patients, a narrow horizontal lip defect was repaired by bilateral vermilion flaps and a subcutaneous V-Y advancement flap of the lower lip. A single vermilion flap or bilateral vermilion flaps are considered to be of great value for vermilion reconstruction because of the inherent elasticity and common anatomic unit. The postoperative scars are not remarkable at all. A long and narrow horizontal lip defect (perhaps within 1.5 cm downward from the vermilion border) may be effectively repaired by the combination of vermilion flap(s) and a V-Y advancement flap without sacrificing any additional healthy tissue.