Objective We developed a novel method using the anatomical markers along the thoracic aorta to accurately quantify both longitudinal and circumferential cyclic strain in the thoracic aorta. We have applied this method to quantify circumferential and longitudinal cyclic strain in non-diseased thoracic aortas over the cardiac cycle and to compute age-related changes of the human thoracic aorta. Methods Changes in thoracic aorta cyclic strains were quantified using the 4D cardiac-gated CT image data of fourteen patients; aged 35-80, with no visible aortic pathology (aneurysms or dissection). We measured the diameter and circumferential cyclic strain in the arch and descending thoracic aorta (DTA), the longitudinal cyclic strain along the DTA, and changes in arch length and motion of the ascending aorta relative to the DTA. Diameters were computed distal to the left coronary artery, proximal and distal to the brachiocephalic trunk, and distal to the left common carotid, left subclavian, and the first and seventh intercostal arteries (ICoA). Cyclic strains were computed using the Green-Lagrange strain tensor. Arch length was defined along the vessel centerline from the left coronary artery to the first ICoA. The length of the DTA was defined along the vessel centerline from the first to seventh ICoA. Longitudinal cyclic strain was quantified as the difference between the systolic and diastolic DTA lengths divided by the diastolic DTA length Comparisons were made between seven young (age 41±7 yrs, 6M, 3F) and seven older (age 68±6 yrs, 6M, 3F) patients. Results For the seven locations analyzed, the diameters of the thoracic aorta increased, on average, by 14% with age from the young (mean age 41 years) to the older (mean age 68 years) group. The circumferential cyclic strain of the thoracic aorta decreased, on average, by 55% with age from the young to the older group. The longitudinal cyclic strain decreased with age by 50% from the young to older group (2.0 ± 0.4% versus 1.0 ± 1%, p=0.03). The arch length increased by 14% with age from the young to the older group (134 ± 17mm versus 152 ± 10mm, p=0.03). Conclusions The thoracic aorta enlarges circumferentially and axially and deforms significantly less in the circumferential and longitudinal directions with increasing age. This represents the first quantitative description of in vivo longitudinal cyclic strain and length changes for the human thoracic aorta, creating a foundation for standards in reporting data related to in vivo deformation, and may have significant implications in endo-aortic device design, testing and stability.

Kirigami tessellations, regular planar patterns formed by cutting flat, thin sheets, have attracted recent scientific interest for their rich geometries, surprising material properties and promise for technologies. Here we pose and solve the inverse problem of designing the number, size, and orientation of cuts that allows us to convert a closed, compact regular kirigami tessellation of the plane into a deployment that conforms approximately to any prescribed target shape in two and three dimensions. We do this by first identifying the constraints on the lengths and angles of generalized kirigami tessellations which guarantee that their reconfigured face geometries can be contracted from a non-trivial deployed shape to a novel planar cut pattern. We encode these conditions in a flexible constrained optimization framework which allows us to deform the geometry of periodic kirigami tesselations with three, four, and sixfold symmetry, among others, into generalized kirigami patterns that deploy to a wide variety of prescribed boundary target shapes. Physically fabricated models verify our inverse design approach and allow us to determine the tunable material response of the resulting structures. We then extend our 1 arXiv:1812.08644v1 [cond-mat.soft] 20 Dec 2018 framework to create generalized kirigami patterns that deploy to approximate curved surfaces in R 3 . Altogether, this work illustrates a novel framework for designing complex, shape-changing sheets from simple cuts showing the power of kirigami tessellations as flexible mechanical metamaterials.Kirigami is the creative art of paper cutting and folding that originated in Japan. Kirigami tessellations, which are regular planar patterns formed by cuts, have recently emerged as paradigms of mechanical metamaterials. Various studies have focused on their geometry and kinematics (1-3), the mechanics of their deployment (4-9), the mathematics of their constructions (10), and as materials with a range of unusual properties such as topological insulators (11, 12), aux-

Surface registration between cortical surfaces is crucial in medical imaging for performing systematic comparisons between brains. Landmark-matching registration that matches anatomical features, called the sulcal landmarks, is often required to obtain a meaningful 1-1 correspondence between brain surfaces. This is commonly done by parameterizing the surface onto a simple parameter domain, such as the unit sphere, in which the sulcal landmarks are consistently aligned. Landmarkmatching surface registration can then be obtained from the landmark aligned parameterizations. For genus-0 closed brain surfaces, the optimized spherical harmonic parameterization, which aligns landmarks to consistent locations on the sphere, has been widely used. This approach is limited by the loss of bijectivity under large deformations and the slow computation. In this paper, we propose FLASH, a fast algorithm to compute the optimized spherical harmonic parameterization with consistent landmark alignment. This is achieved by formulating the optimization problem to C and thereby linearizing the problem. Errors introduced near the pole are corrected using quasiconformal theories. Also, by adjusting the Beltrami differential of the mapping, a diffeomorphic (1-1, onto) spherical parameterization can be effectively obtained. The proposed algorithm has been tested on 38 human brain surfaces. Experimental results demonstrate that the computation of the landmark aligned spherical harmonic parameterization is significantly accelerated using the proposed algorithm.

Noninvasive hemodynamic assessment enhanced the identification of high-risk plaques that subsequently caused ACS. The integration of noninvasive hemodynamic assessments may improve the identification of culprit lesions for future ACS. (Exploring the Mechanism of Plaque Rupture in Acute Coronary Syndrome Using Coronary CT Angiography and Computational Fluid Dynamic [EMERALD]; NCT02374775).

No abstract

The knowledge of dynamic changes in the vascular system has become increasingly important in ensuring the safety and efficacy of endovascular devices. We developed new methods for quantifying in vivo three-dimensional (3D) arterial deformation due to pulsatile and nonpulsatile forces. A two-dimensional threshold segmentation technique combined with a level set method enabled calculation of the consistent centroid of the cross-sectional vessel lumen, whereas an optimal Fourier smoothing technique was developed to eliminate spurious irregularities of the centerline connecting the centroids. Longitudinal strain and novel metrics for axial twist and curvature change were utilized to characterize 3D deformations of the abdominal aorta, common iliac artery, and superficial femoral artery (SFA) due to musculoskeletal motion and deformations of the coronary artery due to cardiac pulsatile motion. These illustrative applications show the significance of each deformation metric, revealing significant longitudinal strain and axial twist in the SFA and coronary artery, and pronounced changes in vessel curvature in the coronary artery and in the inferior region of the SFA. The proposed methods may aid in designing preclinical tests aimed at replicating dynamic in vivo conditions in the arterial tree for the purpose of developing more durable endovascular devices including stents and stent grafts.

Figure 1: 3DPeople Dataset. We present a synthetic dataset with 2.5 Million frames of 80 subjects (40 female/40 male) performing 70 different actions. The dataset contains a large range of distinct body shapes, skin tones and clothing outfits, and provides 640 × 480 RGB images under different viewpoints, 3D geometry of the body and clothing, 3D skeletons, depth maps, optical flow and semantic information (body parts and cloth labels). In this paper we use the 3DPeople dataset to model the geometry of dressed humans. AbstractRecent advances in 3D human shape estimation build upon parametric representations that model very well the shape of the naked body, but are not appropriate to represent the clothing geometry. In this paper, we present an approach to model dressed humans and predict their geometry from single images. We contribute in three fundamental aspects of the problem, namely, a new dataset, a novel shape parameterization algorithm and an end-to-end deep generative network for predicting shape.First, we present 3DPeople, a large-scale synthetic dataset with 2.5 Million photo-realistic images of 80 subjects performing 70 activities and wearing diverse outfits. Besides providing textured 3D meshes for clothes and body, we annotate the dataset with segmentation masks, skeletons, depth, normal maps and optical flow. All this together makes 3DPeople suitable for a plethora of tasks.We then represent the 3D shapes using 2D geometry im-ages. To build these images we propose a novel spherical area-preserving parameterization algorithm based on the optimal mass transportation method. We show this approach to improve existing spherical maps which tend to shrink the elongated parts of the full body models such as the arms and legs, making the geometry images incomplete.Finally, we design a multi-resolution deep generative network that, given an input image of a dressed human, predicts his/her geometry image (and thus the clothed body shape) in an end-to-end manner. We obtain very promising results in jointly capturing body pose and clothing shape, both for synthetic validation and on the wild images.

Purpose Vessel deformations have been implicated in endoluminal device fractures, and thus better understanding of these deformations could be valuable for device regulation, evaluation, and design. The purpose of this study is to describe geometric changes of the superficial femoral artery (SFA) resulting from hip and knee flexion in older subjects. Material and Methods The SFAs of seven healthy subjects aged 50–70 years were imaged using magnetic resonance angiography with legs straight and with hip and knee flexion. From geometric models constructed from these images, axial, twisting, and bending deformations were quantified. Results There was greater shortening in the bottom third of the SFA than the top two thirds (mean±standard deviation) (Top=5.9±3.0%, Middle=6.7±2.1%, Bottom=8.1±2.0%) (P<0.05), significant twist in all sections (Top=1.3±0.8°/cm, Middle=1.8±1.1°/cm, Bottom=2.1±1.3°/cm), and greater curvature increase in the bottom third than the top two thirds (Top=0.15±0.06cm−1, Middle=0.09±0.07cm−1, Bottom=0.41±0.22cm−1) (P<0.001). Conclusions The SFA tends to deform more in the bottom third than the other sections, likely due to less musculoskeletal constraint distal to the adductor canal and vicinity to knee flexion. The SFAs of these older subjects curve off-axis with normal joint flexion, probably resulting from known loss of arterial elasticity with age. This slackening of the vessel enables a method for non-invasive quantification of in vivo SFA strain, which may be valuable for treatment planning and device design. In addition, the spatially-resolved arterial deformations quantified in this study may be useful for commercial and regulatory device evaluation.