SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Tomography

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The alternating projection algorithms are easy to implement and effective for large-scale complex optimization problems, such as constrained reconstruction of X-ray computed tomography (CT). A typical method is to use projection onto convex sets (POCS) for data fidelity, nonnegative constraints combined with total variation (TV) minimization (so called TV-POCS) for sparse-view CT reconstruction. However, this type of method relies on empirically selected parameters for satisfactory reconstruction and is generally slow and lack of convergence analysis. In this work, we use a convex feasibility set approach to address the problems associated with TV-POCS and propose a framework using full sequential alternating projections or POCS (FS-POCS) to find the solution in the intersection of convex constraints of bounded TV function, bounded data fidelity error and non-negativity. The rationale behind FS-POCS is that the mathematically optimal solution of the constrained objective function may not be the physically optimal solution. The breakdown of constrained reconstruction into an intersection of several feasible sets can lead to faster convergence and better quantification of reconstruction parameters in a physical meaningful way than that in an empirical way of trial-and-error. In addition, for large-scale optimization problems, first order methods are usually used. Not only is the condition for convergence of gradient-based methods derived, but also a primal-dual hybrid gradient (PDHG) method is used for fast convergence of bounded TV. The newly proposed FS-POCS is evaluated and compared with TV-POCS and another convex feasibility projection method (CPTV) using both digital phantom and pseudo-real CT data to show its superior performance on reconstruction speed, image quality and quantification.

Concepts: Scientific method, Mathematics, Medical imaging, Tomographic reconstruction, Tomography, Optimization, Applied mathematics, Optimization problem

141

The pathophysiology underlying very late drug-eluting stent (DES) thrombosis is not sufficiently understood. Using optical coherence tomography, we investigated characteristics of very late stent thrombosis (VLST) according to different onset times.

Concepts: Optics, Tomographic reconstruction, Stent, Tomography, According to Jim

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We acquire the first experimental 3-D tomographic images with magnetic particle imaging (MPI) using projection reconstruction methodology, which is similar to algorithms employed in X-ray computed tomography. The primary advantage of projection reconstruction methods is an order of magnitude increase in signal-to-noise ratio (SNR) due to averaging. We first derive the point spread function, resolution, number of projections required, and the SNR gain in projection reconstruction MPI. We then design and construct the first scanner capable of gathering the necessary data for nonaliased projection reconstruction and experimentally verify our mathematical predictions. We demonstrate that filtered backprojection in MPI is experimentally feasible and illustrate the SNR and resolution improvements with projection reconstruction. Finally, we show that MPI is capable of producing three dimensional imaging volumes in both phantoms and postmortem mice.

Concepts: Medical imaging, Radiography, Tomographic reconstruction, Dimension, Euclidean space, Tomography, Virtopsy, Signal-to-noise ratio

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: To study the choroidal thickness profile using high-penetration optical coherence tomography in central serous chorioretinopathy (CSC).

Concepts: Optics, Ophthalmology, Tomography, Central serous retinopathy

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BACKGROUND: There are several methods that may be used to confirm the status of rib cartilage, such as physical examinations or chest radiography, for subjects with microtia. However, these methods are limited because of clinicians' inability to gain accurate information about the rib cartilage. We performed 3-dimensional chest computed tomography to preoperatively evaluate the accuracy of rib cartilage imaging. METHODS: A total of 37 patients preparing for auricular reconstruction using a rib cartilage graft underwent preoperative 3-dimensional rib cage computed tomography (3-D rib CT). The 3-D rib CT was performed in cases of secondary revisional reconstruction, those with a history of surgery using rib cartilage, in those with a history of trauma related to the rib cage, older patients with question of calcification of rib cartilage, or those with a suspected rib cartilage anomaly on physical examination. Preoperatively, the appropriateness of using the rib cartilage were evaluated. RESULTS: With the aid of the 3-D rib CT, successful autogenous auricular reconstruction was achieved in 36 patients. Framework fabrication in combination with a porous polyethylene implant and autogenous rib cartilage was performed in the remaining patient as planned preoperatively. By analyzing the 3-D rib CT image preoperatively, auricular reconstruction using a recycled rib cartilage graft with newly harvested rib cartilage was performed successfully in 13 of 14 secondary revisional cases. Based on preoperative CT images, modified surgical planning in terms of cartilage harvest and framework fabrication was needed in 8 of 11 patients who had a history of operation using rib cartilage and in 3 of 5 subjects with suspected rib cage anomalies on physical examination. Successful reconstruction was achieved using the modified surgical plan. CONCLUSIONS: A preoperative 3-D rib CT helps in surgical planning for autogenous auricular reconstruction for microtia, especially in patients with suspicious rib cartilage status.

Concepts: Hospital, Surgery, Medical imaging, Radiography, Tomographic reconstruction, Tomography, Physical examination, Human rib cage

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In this article, we demonstrate the application of a new compressed sensing three-dimensional reconstruction algorithm for electron tomography that increases the accuracy of morphological characterization of nanostructured materials such as nanocrystalline iron oxide particles. A powerful feature of the algorithm is an anisotropic total variation norm for the L1 minimization during algebraic reconstruction that effectively reduces the elongation artifacts caused by limited angle sampling during electron tomography. The algorithm provides faithful morphologies that have not been feasible with existing techniques.

Concepts: Medical imaging, Nanomaterials, Tomography, Reconstruction algorithm, Discrete tomography, American Civil War, Total variation

28

This work aims to improve the process of speckle noise reduction while preserving edges and other relevant features through filter expansion from 2-D to 3-D. Despeckling is very important for data visual inspection and as a preprocessing step for other algorithms, as they are usually notably influenced by speckle noise. To that intent, a 3-D approach is proposed for the adaptive complex-diffusion filter. This 3-D iterative filter was applied to spectral-domain optical coherence tomography medical imaging volumes of the human retina and a quantitative evaluation of the results was performed to allow a demonstration of the better performance of the 3-D over the 2-D filtering and to choose the best total diffusion time. In addition, we propose a fast graphical processing unit parallel implementation so that the filter can be used in a clinical setting.

Concepts: Medicine, Optics, Medical imaging, Retina, Optical coherence tomography, Tomography, Real number, Image processing

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To study the choroidal thickness in eyes with inferior posterior staphyloma (IPS) and to elucidate its role in the development of macular complications.

Concepts: Optics, Medical imaging, Eye, Ophthalmology, Tomography, Staphyloma

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Objective: The purpose of this study was to describe computed tomography (CT) features of the ununited anconeal process and relate them with the following elbow dysplasia signs: medial coronoid disease, medial humeral condyle changes, osteoarthritis (OA), and radioulnar incongruence. Methods: Computed tomographic images of dogs older than six months with an ununited anconeal process were evaluated (n = 13). Ununited anconeal process features were described as being complete or incomplete, and the degree of displacement, volume, and presence of cysts and sclerosis were also evaluated. Medial coronoid disease was defined as an irregular medial coronoid process shape, presence of sclerosis and fragmentation. Medial humeral condyle changes were defined as subchondral bone flattening, lucencies, and sclerosis. Osteoarthritis was graded depending on the osteophytes size. Radioulnar incongruence was measured on a sagittal view at the base of the medial coronoid process. Results: Eleven elbows had a complete and two had an incomplete ununited anconeal process. All ununited anconeal processes had cystic and sclerotic lesions. Seven ununited anconeal processes were displaced and six were non-displaced. Mean ununited anconeal process volume was 1.35 cm3 (0.61 cm³ - 2.08 cm³). Twelve elbows had signs of medial coronoid disease (4 of them with a fragmented medial coronoid process), and one elbow did not show any evidence of medial coronoid disease. Ten elbows had medial humeral condyle changes. One elbow had grade 1 OA, seven elbows had grade 2, and five elbows grade 3. All elbows had radioulnar incongruence: three elbows had a negative and 10 elbows had a positive radioulnar incongruence. Mean radioulnar incongruence was 1.49 mm (0.63 mm - 2.61 mm). Computed tomographic findings were similar in the majority of the elbows studied: complete ununited anconeal processes with signs of medial coronoid disease, positive radioulnar incongruence, high grade of OA, sclerotic medial humeral condyle changes, and large ununited anconeal process volumes. Clinical significance: Incomplete small ununited anconeal process volumes could be associated with a lower incidence of medial coronoid disease or medial humeral condyle changes. We recommend performing preoperative CT of elbows with an ununited anconeal process to evaluate concurrent lesions.

Concepts: Tomographic reconstruction, Humerus, Elbow, Tomography, Second grade, Brachialis muscle, Brachioradialis, Coronoid process of the ulna