Automatic lumen segmentation in IVOCT images using binary morphological reconstruction

Abstract\ud \ud \ud \ud Background\ud Atherosclerosis causes millions of deaths, annually yielding billions in expenses round the world. Intravascular Optical Coherence Tomography (IVOCT) is a medical imaging modality, which displays high resolution images of coronary cross-section. Nonetheless, quantitative information can only be obtained with segmentation; consequently, more adequate diagnostics, therapies and interventions can be provided. Since it is a relatively new modality, many different segmentation methods, available in the literature for other modalities, could be successfully applied to IVOCT images, improving accuracies and uses.\ud \ud \ud \ud Method\ud An automatic lumen segmentation approach, based on Wavelet Transform and Mathematical Morphology, is presented. The methodology is divided into three main parts. First, the preprocessing stage attenuates and enhances undesirable and important information, respectively. Second, in the feature extraction block, wavelet is associated with an adapted version of Otsu threshold; hence, tissue information is discriminated and binarized. Finally, binary morphological reconstruction improves the binary information and constructs the binary lumen object.\ud \ud \ud \ud Results\ud The evaluation was carried out by segmenting 290 challenging images from human and pig coronaries, and rabbit iliac arteries; the outcomes were compared with the gold standards made by experts. The resultant accuracy was obtained: True Positive (%) = 99.29 ± 2.96, False Positive (%) = 3.69 ± 2.88, False Negative (%) = 0.71 ± 2.96, Max False Positive Distance (mm) = 0.1 ± 0.07, Max False Negative Distance (mm) = 0.06 ± 0.1.\ud \ud \ud \ud Conclusions\ud In conclusion, by segmenting a number of IVOCT images with various features, the proposed technique showed to be robust and more accurate than published studies; in addition, the method is completely automatic, providing a new tool for IVOCT segmentation.São Paulo Research Foundation – Brazil ( FAPESP – Process Number: 2012/157212), National Council of Scientific and Technological Development, Brazil (CNPq), Heart Institute of São Paulo, Brazil (InCor), Biomedical Engineering Laboratory of the University of São Paulo, Brazil (LEBUSP). The unknown reviewers, who have made important contributions to this work.São Paulo Research Foundation – Brazil ( FAPESP – Process Number: 2012/15721-2), National Council of Scientific and Technological Development, Brazil (CNPq), Heart Institute of São Paulo, Brazil (InCor), Biomedical Engineering Laboratory of the University of São Paulo, Brazil (LEB-USP). The unknown reviewers, who have made important contributions to this work

Computer Vision Techniques for Transcatheter Intervention

Minimally invasive transcatheter technologies have demonstrated substantial promise for the diagnosis and treatment of cardiovascular diseases. For example, TAVI is an alternative to AVR for the treatment of severe aortic stenosis and TAFA is widely used for the treatment and cure of atrial fibrillation. In addition, catheter-based IVUS and OCT imaging of coronary arteries provides important information about the coronary lumen, wall and plaque characteristics. Qualitative and quantitative analysis of these cross-sectional image data will be beneficial for the evaluation and treatment of coronary artery diseases such as atherosclerosis. In all the phases (preoperative, intraoperative, and postoperative) during the transcatheter intervention procedure, computer vision techniques (e.g., image segmentation, motion tracking) have been largely applied in the field to accomplish tasks like annulus measurement, valve selection, catheter placement control, and vessel centerline extraction. This provides beneficial guidance for the clinicians in surgical planning, disease diagnosis, and treatment assessment. In this paper, we present a systematical review on these state-of-the-art methods.We aim to give a comprehensive overview for researchers in the area of computer vision on the subject of transcatheter intervention. Research in medical computing is multi-disciplinary due to its nature, and hence it is important to understand the application domain, clinical background, and imaging modality so that methods and quantitative measurements derived from analyzing the imaging data are appropriate and meaningful. We thus provide an overview on background information of transcatheter intervention procedures, as well as a review of the computer vision techniques and methodologies applied in this area

Effects of Catheterization on Artery Function and Health: When Should Patients Start Exercising Following Their Coronary Intervention?

Coronary artery disease (CAD) is a leading cause of death worldwide, and percutaneous transluminal coronary angiography (PTCA) and/or percutaneous coronary intervention (PCI; angioplasty) are commonly used to diagnose and/or treat the obstructed coronaries. Exercise-based rehabilitation is recommended for all CAD patients; however, most guidelines do not specify when exercise training should commence following PTCA and/or PCI. Catheterization can result in arterial dysfunction and acute injury, and given the fact that exercise, particularly at higher intensities, is associated with elevated inflammatory and oxidative stress, endothelial dysfunction and a pro-thrombotic milieu, performing exercise post-PTCA/PCI may transiently elevate the risk of cardiac events. This review aims to summarize extant literature relating to the impacts of coronary interventions on arterial function, including the time-course of recovery and the potential deleterious and/or beneficial impacts of acute versus long-term exercise. The current literature suggests that arterial dysfunction induced by catheterization recovers 4-12 weeks following catheterization. This review proposes that a period of relative arterial vulnerability may exist and exercise during this period may contribute to elevated event susceptibility. We therefore suggest that CAD patients start an exercise training programme between 2 and 4 weeks post-PCI, recognizing that the literature suggest there is a 'grey area' for functional recovery between 2 and 12 weeks post-catheterization. The timing of exercise onset should take into consideration the individual characteristics of patients (age, severity of disease, comorbidities) and the intensity, frequency and duration of the exercise prescription

Automatic segmentation of cross-sectional coronary arterial images

We present a novel approach to segment coronary cross-sectional images acquired using catheterization imaging techniques, i.e. intra-vascular ultrasound (IVUS) and optical coherence tomography (OCT). The proposed approach combines cross-sectional segmentation with longitudinal tracking in order to tackle various forms of imaging artifacts and to achieve consistent segmentation. A node-weighted directed graph is constructed on two consecutive cross-sectional frames with embedded shape constraints within individual cross-sections or frames and between consecutive frames. The intra-frame constraints are derived from a set of training samples and are embedded in both graph construction and its cost function. The inter-frame constraints are imposed by tracking the borders of interest across multiple frames. The coronary images are transformed from Cartesian coordinates to polar coordinates. Graph partition can then be formulated as searching an optimal interface in the node-weighted directed graph without user initialization. It also allows efficient parametrization of the border using radial basis function (RBF) and thus reduces the tracking of a large number of border points to a very few RBF centers. Moreover, we carry out supervised column-wise tissue classification in order to automatically optimize the feature selection. Instead of empirically assigning weights to different feature detectors, we dynamically and automatically adapt those weighting depending on the tissue compositions in each individual column of pixels

Evaluating an Alternative Endothelial Cell Source to Vascularize Engineered Tissue Constructs

A major translational challenge in the fields of therapeutic angiogenesis and regenerative medicine is the need to create functional microvasculature. Cell-based strategies to promote neovascularization have been widely explored, but cell sourcing remains a significant limitation. Induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) are a promising, autologous, alternative cell source. The purpose of this study was to assess whether a potentially autologous endothelial cell (EC) source derived from iPSC-ECs can form the same robust, stable microvasculature as previously documented for other sources of ECs. The endothelial lineage of iPSC-ECs was first characterized as through endothelial marker expression and compared to human umbilical vein endothelial cells (HUVECs). Similarities in endothelial markers were demonstrated and genetic expression profile analysis revealed significant genotypic similarities between the iPSC-ECs and HUVECs. A well-established in vitro assay was utilized, in which endothelial cell-coated (iPSC-ECs or HUVECs) beads were co-embedded with fibroblasts in a 3D fibrin matrix, to assess the iPSC-ECs’ ability to form stable microvessels. iPSC-ECs exhibited a five-fold reduction in capillary network formation compared to HUVECs in this assay. Variation of cell sourcing, lot, cell density, and media formulation demonstrated no differences in iPSC-EC sprouting, eliminating these variables as the underlying cause. Despite quantitative differences, iPSC-ECs demonstrated some characteristics of mature vasculature including hollow lumen formation, pericyte recruitment and association, and deposition of basement membrane components. To determine a cause of the in vitro sprouting attenuation, iPSC-ECs’ capillary morphogenetic mechanisms were identified through chemical inhibition of sprouting and analysis of the expression levels of key proteases. Increasing matrix density reduced sprouting, although this effect was attenuated by distributing the normal human lung fibroblasts (NHLFs) within the 3D matrix. Inhibition of both MMP- and plasmin-mediated fibrinolysis was required to completely block sprouting of both HUVECs and iPSC-ECs. Further analysis revealed MMP-9 expression and activity were significantly lower in iPSC-EC/NHLF co-cultures than in HUVEC/NHLF co-cultures, which may account for the observed deficiencies in angiogenic sprouting of the iPSC-ECs. To investigate if the in vitro attenuation was also an in vivo phenomenon, iPSC-ECs were evaluated for their ability to form functional microvasculature in a well-established in vivo model, in which endothelial cells (iPSC-ECs or HUVECs) were co-injected with fibroblasts and a fibrin matrix into the dorsal flank of severe combined immunodeficiency (SCID) mice. Qualitatively, iPSC-ECs were capable of forming perfused vessels that inosculated with mouse vessels and demonstrated similar vessel morphologies to HUVECs. However, quantitatively, iPSC-ECs exhibited a two-fold reduction in vessel density and a three-fold reduction in the number of perfused vessels compared to HUVECs. Further analysis revealed that the presence of the basement membrane component, type IV collagen, and the mural cell marker, alpha-smooth muscle actin, were significantly lower, roughly 25% and 33% respectively, around iPSC-EC/NHLF vasculature relative to that observed in HUVEC/NHLF implants, suggesting reduced vessel maturity. Collectively, these findings demonstrate that a potentially autologous EC with an unlimited source, specifically iPSC-ECs, has the ability to revascularize tissue and argues for a deeper understanding of iPSC-ECs and their differences to enable the promise and potential of iPSC-ECs for clinical translation.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147627/1/bezenahj_1.pd