Panoramic Digital Images Research Articles

Evolving Mural Defects, Dilatation, and Biomechanical Dysfunction in Angiotensin II-Induced Thoracic Aortopathies.

Thoracic aortopathy associates with extracellular matrix remodeling and altered biomechanical properties. We sought to quantify the natural history of thoracic aortopathy in a common mouse model and to correlate measures of wall remodeling such as aortic dilatation or localized mural defects with evolving microstructural composition and biomechanical properties of the wall. We combined a high-resolution multimodality imaging approach (panoramic digital image correlation and optical coherence tomography) with histopathologic examinations and biaxial mechanical testing to correlate spatially, for the first time, macroscopic mural defects and medial degeneration within the ascending aorta with local changes in aortic wall composition and mechanical properties. Findings revealed strong correlations between local decreases in elastic energy storage and increases in circumferential material stiffness with increasing proximal aortic diameter and especially mural defect size. Mural defects tended to exhibit a pronounced biomechanical dysfunction that is driven by an altered organization of collagen and elastic fibers. While aneurysmal dilatation is often observed within particular segments of the aorta, dissection and rupture initiate as highly localized mechanical failures. We show that wall composition and material properties are compromised in regions of local mural defects, which further increases the dilatation and overall structural vulnerability of the wall. Identification of therapies focused on promoting robust collagen accumulation may protect the wall from these vulnerabilities and limit the incidence of dissection and rupture.

Panoramic/Dual-Surface Digital Image Correlation Measurement Using a Single Camera.

We propose a cost-effective and simple-to-implement mirror-assisted single-camera panoramic digital image correlation (DIC) method for panoramic/dual-surface profile and deformation measurement. Specifically, two planar mirrors and a single camera attached with a four-mirror adapter are used to capture stereo images of the front and rear surfaces of a test object. These stereo images can be processed by regular stereo-DIC to retrieve shape and kinematics fields of each surface. Further, with the speckle patterns prefabricated on the mirrors, reflection transformation matrices are obtained and applied to transform all reconstructed surfaces into a common world coordinate system. As such, panoramic/dual-surface shape and deformation measurements can be realized. For validation, a high-resolution smartphone camera and an industrial camera were, respectively, used to construct mirror-assisted single-camera panoramic DIC systems. Real experiments, including panoramic shape measurement of an aluminum cylinder, dual-surface shape measurement of an aluminum plate and uniaxial tensile tests of aluminum sheet specimens, were performed, confirming the feasibility and accuracy of the method. Since only a single camera and a few auxiliary reflective mirrors are required, the proposed method provides a cost-effective and convenient way for taking panoramic/dual-surface shape and deformation measurements of regular-sized cylindrical and bar samples.

Uncertainty quantification in subject-specific estimation of local vessel mechanical properties.

Quantitative estimation of local mechanical properties remains critically important in the ongoing effort to elucidate how blood vessels establish, maintain, or lose mechanical homeostasis. Recent advances based on panoramic digital image correlation (pDIC) have made high-fidelity 3D reconstructions of small-animal (e.g., murine) vessels possible when imaged in a variety of quasi-statically loaded configurations. While we have previously developed and validated inverse modeling approaches to translate pDIC-measured surface deformations into biomechanical metrics of interest, our workflow did not heretofore include a methodology to quantify uncertainties associated with local point estimates of mechanical properties. This limitation has compromised our ability to infer biomechanical properties on a subject-specific basis, such as whether stiffness differs significantly between multiple material locations on the same vessel or whether stiffness differs significantly between multiple vessels at a corresponding material location. In the present study, we have integrated a novel uncertainty quantification and propagation pipeline within our inverse modeling approach, relying on empirical and analytic Bayesian techniques. To demonstrate the approach, we present illustrative results for the ascending thoracic aorta from three mouse models, quantifying uncertainties in constitutive model parameters as well as circumferential and axial tangent stiffness. Our extended workflow not only allows parameter uncertainties to be systematically reported, but also facilitates both subject-specific and group-level statistical analyses of the mechanics of the vessel wall.

The effect of a surgeon's position on the axial inclination of dental implants placed freehand: a single-blind study.

To examine whether a surgeons' position affects the axial angulation of dental implants placed freehand. Implants' axial angulation was assessed on digital panoramic radiographs. An occlusal line was plotted based on the neighboring teeth/crowns. The mesial angle between the long axis of the implant and the occlusal line was measured. In addition, post-hoc ideal implant-positioning planning was done on the panoramic digital image, and the angle of the intersection between the long axis of the actual and post-hoc ideal implant was measured. Student t test for unpaired observations and the Kolmogorov-Smirnov nonparametric tests were utilized to compare the ipsi- and contralateral sides and between clinicians. Seventy-seven patients (149 implants) were eligible for the study. Implants had slight mesial inclination (mean 97.7 ± 8.7 degrees) which was similar for both the ipsi- (98.2 ± 8.4 degrees) and contralateral sides (97.2 ± 9.1 degrees), P = .491. For the post-hoc planning versus actual placement comparison, the overall median (interquartile range) of implant angular deviation was minimal (-0.25 degrees [-2.98, +3.47]). This was true for both the ipsilateral (-0.5 degrees [-2.9, +2.9]) and contralateral (-0.2 [-4.2, +5.4]) sides, P = .55. For the actual versus post-hoc planning, most observations clustered around the midline (zero to minimal deviation), while for the implant to occlusal plane angle, a tendency towards slight mesial angulation was observed. Dental implants placed freehand by experienced clinicians have only slight axial deviation as measured from post-hoc optimal position. Implants placed in ipsilateral and contralateral sides and by left- and right-dominant-hand clinicians had similar angulations.

Multimodality Imaging-Based Characterization of Regional Material Properties in a Murine Model of Aortic Dissection

Chronic infusion of angiotensin-II in atheroprone (ApoE−/−) mice provides a reproducible model of dissection in the suprarenal abdominal aorta, often with a false lumen and intramural thrombus that thickens the wall. Such lesions exhibit complex morphologies, with different regions characterized by localized changes in wall composition, microstructure, and properties. We sought to quantify the multiaxial mechanical properties of murine dissecting aneurysm samples by combining in vitro extension-distension data with full-field multimodality measurements of wall strain and thickness to inform an inverse material characterization using the virtual fields method. A key advance is the use of a digital volume correlation approach that allows for characterization of properties not only along and around the lesion, but also across its wall. Specifically, deformations are measured at the adventitial surface by tracking motions of a speckle pattern using a custom panoramic digital image correlation technique while deformations throughout the wall and thrombus are inferred from optical coherence tomography. These measurements are registered and combined in 3D to reconstruct the reference geometry and compute the 3D finite strain fields in response to pressurization. Results reveal dramatic regional variations in material stiffness and strain energy, which reflect local changes in constituent area fractions obtained from histology but emphasize the complexity of lesion morphology and damage within the dissected wall. This is the first point-wise biomechanical characterization of such complex, heterogeneous arterial segments. Because matrix remodeling is critical to the formation and growth of these lesions, we submit that quantification of regional material properties will increase the understanding of pathological mechanical mechanisms underlying aortic dissection.

Local variations in material and structural properties characterize murine thoracic aortic aneurysm mechanics.

We recently developed an approach to characterize local nonlinear, anisotropic mechanical properties of murine arteries by combining biaxial extension-distension testing, panoramic digital image correlation, and an inverse method based on the principle of virtual power. This experimental-computational approach was illustrated for the normal murine abdominal aorta assuming uniform wall thickness. Here, however, we extend our prior approach by adding an optical coherence tomography (OCT) imaging system that permits local reconstructions of wall thickness. This multimodality approach is then used to characterize spatial variations of material and structural properties in ascending thoracic aortic aneurysms (aTAA) from two genetically modified mouse models (fibrillin-1 and fibulin-4 deficient) and to compare them with those from angiotensin II-infused apolipoprotein E-deficient and wild-type control ascending aortas. Local values of stored elastic energy and biaxial material stiffness, computed from spatial distributions of the best fit material parameters, varied significantly with circumferential position (inner vs. outer curvature, ventral vs. dorsal sides) across genotypes and treatments. Importantly, these data reveal an inverse relationship between material stiffness and wall thickness that underlies a general linear relationship between stiffness and wall stress across aTAAs. OCT images also revealed sites of advanced medial degeneration, which were captured by the inverse material characterization. Quantification of histological data further provided high-resolution local correlations among multiple mechanical metrics and wall microstructure. This is the first time that such structural defects and local properties have been characterized mechanically, which can better inform computational models of aortopathy that seek to predict where dissection or rupture may initiate.

Correlation of Wall Microstructure and Heterogeneous Distributions of Strain in Evolving Murine Abdominal Aortic Aneurysms.

A primary deficiency in predicting the progression and rupture-risk of abdominal aortic aneurysms (AAAs) is an inability to assign patient-specific, heterogeneous biomechanical properties to the remodelling aortic wall. Toward this end, we investigated possible correlations between three quantities having the potential for non-invasive measurement (diameter, wall thickness, and strain) and local wall microstructure within evolving experimental AAAs. AAAs were initiated in male C57BL/6J mice via in situ adventitial application of elastase and allowed to progress for 1-4weeks. Regional in vitro Green strain was assessed using custom panoramic digital image correlation and compared to local geometry and histology. Diameter correlated mildly with elastin grade and collagen, when considering all circumferential locations and remodeling times. Normalized wall thickness correlated strongly with normalized collagen area fraction, though with outliers in highly cellular regions. Circumferential Green strain correlated strongly with elastin grade when measured over the range of 20-140mmHg, though the correlation weakened across a physiologic range of 80-120mmHg. Axial strain correlated strongly between in vitro and physiologic ranges of pressures. Circumferential heterogeneities render diameter a poor predictor of underlying regional microstructure. Thickness may indicate collagen content, though corrections are needed in regions of increased cellularity. In vitro circumferential strain predicts local functional elastin over large ranges of pressure, but there is a need to extend this correlation to clinically relevant pressures. Axial strain in the aneurysmal shoulder region may reflect the elastic integrity within the apical region of the lesion and should be explored as an indicator of disease severity.

Evaluation of panoramic digital images using Panoptiq for frozen section diagnosis

Introduction: Whole slide imaging (WSI) permits intraoperative consultations (frozen sections) to be performed remotely. However, WSI files are large and can be problematic if there are tissue artifacts (e.g., tissue folds) or when slides are scanned without multiplanes (Z-stacks) to permit focusing. The Panoptiq dynamic imaging system allows users to create their own digital files that combine low power panoramic digital images with regions of interest that can be imaged using high power Z-stacks. The aim of this study was to determine the utility of the Panoptiq dynamic imaging system for frozen section telepathology. Materials and Methods: Twenty archival randomly selected genitourinary surgical pathology frozen sectional cases were evaluated using conventional light microscopy (glass slides), panoramic images, and whole slide images. To create panoramic images glass slides were digitized using a Prosilica GT camera (model GT1920C, Allied Vision Technologies) attached to an Olympus B × 45 microscope and Dell Precision Tower 810 computer (Dell). Panoptiq 3 version 3.1.2 software was used for image acquisition and Panoptiq View version 3.l.2 to view images (ViewsIQ, Richmond, BC, Canada). Image acquisition using Panoptiq software involved a pathology resident, who manually created digital maps (×4 objective) and then selected representative regions of interest to generate Z-stacks at higher magnification (×40 objective). Whole slide images were generated using an Aperio XT Scanscope (Leica) and viewed using ImageScope Software (Aperio ePathology, Leica). Three pathologists were asked to render diagnoses and rate image quality (1–10) and their diagnostic confidence (1–10) for each modality. Results: The diagnostic concordance with glass slides was 98.3% for panoramic images and 100% for WSI. Panoptiq images were comparable to the glass slide viewing experience in terms of image quality and diagnostic confidence. Complaints regarding WSI included poor focus near tissue folds and air bubbles. Panoptiq permitted fine focusing of tissue folds and air bubbles. Issues with panoramic images included difficulty interpreting low-resolution ×4 image maps and the presence of tiling artifacts. In some cases, Z-stacked areas of Panoptiq images were limited or not representative of diagnostic regions. The image file size of Panoptiq was more than 14 times smaller than that of WSI files. Conclusions: The Panoptiq imaging system is a novel tool that can be used for frozen section telepathology. Panoramic digital images were easy to generate and navigate, of relatively small file size, and offered a mechanism to overcome focusing problems commonly encountered with WSI of frozen sections. However, the acquisition of representative Panoptiq images was operator dependent with the individual creating files that may impact the final diagnosis.

Resistance of phase correlation method to disturbances at creating of panoramic digital images

Resistance of phase correlation method to disturbances at creating of panoramic digital images

Panoramic Digital Images (Panoptiq) for Cytopathology Screening and Interpretation

Panoramic Digital Images (Panoptiq) for Cytopathology Screening and Interpretation

An improved panoramic digital image correlation method for vascular strain analysis and material characterization

The full potential of computational models of arterial wall mechanics has yet to be realized primarily because of a lack of data sufficient to quantify regional mechanical properties, especially in genetic, pharmacological, and surgical mouse models that can provide significant new information on the time course of adaptive or maladaptive changes as well as disease progression. The goal of this work is twofold: first, to present modifications to a recently developed panoramic-digital image correlation (p-DIC) system that significantly increase the rate of data acquisition, overall accuracy in specimen reconstruction, and thus full-field strain analysis, and the axial measurement domain for in vitro mechanical tests on excised mouse arteries and, second, to present a new method of data analysis that similarly increases the accuracy in image reconstruction while reducing the associated computational time. The utility of these advances is illustrated by presenting the first full-field strain measurements at multiple distending pressures and axial elongations for a suprarenal mouse aorta before and after exposure to elastase. Such data promise to enable improved inverse characterization of regional material properties using established computational methods.

Regional Finite Strains in an Angiotensin-II Induced Mouse Model of Dissecting Abdominal Aortic Aneurysms

Abdominal aortic aneurysms are focal dilatations of the aorta; they typically progress to rupture, which is responsible for increasing morbidity and mortality in our aging society. It is well accepted that rupture occurs when wall stress exceeds strength, and there have been many advances over the past two decades in predicting local stresses based on patient-specific computational models. Nevertheless, two of the primary continuing limitations of such models are the assumptions of constant (i.e., non-evolving) and spatially homogeneous material properties. Mouse models of aortic aneurysms provide a means to measure evolving heterogeneous properties, but heretofore such attempts have been limited because of the complex geometries of these lesions. In this paper, we present a technical advance—panoramic digital image correlation—that can aid in the final goal of determining regional mechanical properties in mouse models of aneurysms. We show, as illustrative data, the first detailed quantification of full field surface strains for experimentally distended mouse aneurysms, data which will be fundamental to future inverse determinations of regional material properties.

Novel optical system for in vitro quantification of full surface strain fields in small arteries: I. Theory and design

Recent advances in vascular biology and pathophysiology have revealed the need to understand better the genetic basis of arterial stiffness, disease progression and responses to clinical intervention. Towards this end, in vitro experiments on arteries from genetically modified mice promise to provide significantly increased insight into both health and disease. The need to test small arteries, often of complex shape, necessitates new methods for experimental arterial mechanics, however, ones that can provide information on local changes in geometry and strain. In this paper, we present a theoretical framework for a new panoramic digital image correlation-based method sufficient to collect such information and we demonstrate the utility of this approach via validation studies on phantoms having dimensions on the order of 500–1000 μm, similar to those of large mouse arteries. In particular, we show that placing the specimen within a conical mirror and imaging the specimen via a gimbal-mounted mirror using a single camera yields stereo information sufficient to quantify the size, shape and deformation along the full length and around the entire circumference of small arteries. In a companion paper, we show further that this approach can be implemented effectively while testing arteries within a physiological solution that maintains native biomechanical properties.