Noise Simulations For an Inverse-Geometry Volumetric CT System

This paper examines the noise performance of an inverse-geometry volumetric CT (IGCT) scanner through simulations. The IGCT system uses a large area scanned source and a smaller array of detectors to rapidly acquire volumetric data with negligible cone-beam artifacts. The first investigation compares the photon efficiency of the IGCT geometry to a 2D parallel ray system. The second investigation models the photon output of the IGCT source and calculates the expected noise. For the photon efficiency investigation. the same total number of photons was modeled in an IGCT acquisition and a comparable multi-slice 2D parallel ray acquisition. For both cases noise projections were simulated and the central axial slice reconstructed. In the second study. to investigate the noise in an IGCT system, the expected x-ray photon flux was modeled and projections simulated through ellipsoid phantoms. All simulations were compared to theoretical predictions. The results of the photon efficiency simulations verify that the IGCT geometry is as efficient in photon utilization as a 2D parallel ray geometry. For a 10 cm diameter 4 cm thick ellipsoid water phantom and for reasonable system parameters, the calculated standard deviation was approximately 15 HU at the center of the ellipsoid. For the same size phantom with maximum attenuation equivalent to 30 cm of water, the calculated noise was approximately 131 HU. The theoretical noise predictions for these objects were 15 HU and 112 HU respectively. These results predict acceptable noise levels for a system with a 0.16 second scan time and 12 lp/cm isotropic resolution

Cycling to Sustainability–The role of local public authorities in furthering the creation of sustainable Product-Service Systems to promote cycling for climate change mitigation.

This masters’s thesis studies how local public authorities can support the creation of sustainable Product-Service Systems which promote cycling to reach climate change mitigation goals in the transport sector. Transportation in general is one of the largest sources for greenhouse gas emissions in the European Union, making up about one fourth of all greenhouse gas emissions. This share is comparable in the Helsinki metropolitan area. The vast majority, about 90%, of those transport related emissions in Finland are caused by road traffic with private cars accounting for almost two thirds of those. In addition to the large amounts of greenhouse gases it produces, individual motorised traffic by cars also creates a scarcity of space in growing urban areas such as the Helsinki metropolitan area. To drastically reduce greenhouse gas emissions from transportation and to address the scarcity of space in urban areas a shift towards more sustainable modes of transportation is necessary which heavily builds on the use of public transportation as well as increasing walking and cycling. In order for this shift to happen, new solutions need to be developed. Product-Service Systems (PSS) are seen in the literature as a viable solution to decouple economic growth from increased resource consumption. However, the literature also points out that PSS needs to be designed well to unlock the full sustainability potential. Despite the seemingly big benefits PSS could offer with regards to climate change mitigation, the literature found them to not be widely implemented yet. Among the reasons for that the necessary change in business models and the resulting need for investment as well as a lack of legislation mandating more sustainable solutions were named. The role of public institutions in furthering the creation of sustainable PSS solutions is mostly only discussed from as that of legislators or procuring entities. The purpose of the thesis was therefore, to exploratively investigate whether public institutions, in particular local public authorities, could take other and more active roles in supporting the creation of sustainable PSS solutions especially with regard to those promoting cycling to enable reaching transport related climate change mitigation goals. For that six semi-structured interviews with four representatives from public institutions and two representatives from the local bike industry were conducted. The findings imply that local public authorities are already taking an active role in testing and promoting new sustainable business models through projects. Existing procurement regulations often limit supporting innovative solutions as competition might not exist. New models to, such as “market dialogue” need to be developed. Additionally the issue of financing the increased investment need for such sustainable PSS solutions needs to be addressed. This was found to be especially challenging with regard to solutions promoting cycling due the seasonality of the business

Three-Dimensional Reconstruction Algorithm for a Reverse-Geometry Volumetric CT System With a Large-Array Scanned Source

We have proposed a CT system design to rapidly produce volumetric images with negligible cone beam artifacts. The investigated system uses a large array scanned source with a smaller array of fast detectors. The x-ray source is electronically steered across a 2D target every few milliseconds as the system rotates. The proposed reconstruction algorithm for this system is a modified 3D filtered backprojection method. The data are rebinned into 2D parallel ray projections, most of which are tilted with respect to the axis of rotation. Each projection is filtered with a 2D kernel and backprojected onto the desired image matrix. To ensure adequate spatial resolution and low artifact level, we rebin the data onto an array that has sufficiently fine spatial and angular sampling. Due to finite sampling in the real system, some of the rebinned projections will be sparse, but we hypothesize that the large number of views will compensate for the data missing in a particular view. Preliminary results using simulated data with the expected discrete sampling of the source and detector arrays suggest that high resolution

Comorbidities of patients in tiotropium clinical trials : comparison with observational studies of patients with chronic obstructive pulmonary disease

Acknowledgments The authors are fully responsible for all content and editorial decisions made, were involved at all stages of manuscript development, and have approved the final version for publication. Editorial assistance, supported financially by Boehringer Ingelheim and Pfizer, was provided by Godfrey Lisk of PAREXEL International during the preparation of this manuscript. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution - Non Commercial (unported, v3.0) License. The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. Permissions beyond the scope of the License are administered by Dove Medical Press Limited.Peer reviewedPublisher PD

Geometry Analysis of an Inverse-Geometry Volumetric CT System With Multiple Detector Arrays

An inverse-geometry volumetric CT (IGCT) system for imaging in a single fast rotation without cone-beam artifacts is being developed. It employs a large scanned source array and a smaller detector array. For a single-source/single-detector implementation, the FOV is limited to a fraction of the source size. Here we explore options to increase the FOV without increasing the source size by using multiple detectors spaced apart laterally to increase the range of radial distances sampled. We also look at multiple source array systems for faster scans. To properly reconstruct the FOV, Radon space must be sufficiently covered and sampled in a uniform manner. Optimal placement of the detectors relative to the source was determined analytically given system constraints (5cm detector width, 25cm source width, 45cm source-to-isocenter distance). For a 1x3 system (three detectors per source) detector spacing (DS) was 18deg and source-to-detector distances (SDD) were 113, 100 and 113cm to provide optimum Radon sampling and a FOV of 44cm. For multiple-source systems, maximum angular spacing between sources cannot exceed 125deg since detectors corresponding to one source cannot be occluded by a second source. Therefore, for 2x3 and 3x3 systems using the above DS and SDD, optimum spacing between sources is 115deg and 61deg respectively, requiring minimum scan rotations of 115deg and 107deg. Also, a 3x3 system can be much faster for full 360deg dataset scans than a 2x3 system (120deg vs. 245deg). We found that a significantly increased FOV can be achieved while maintaining uniform radial sampling as well as a substantial reduction in scan time using several different geometries. Further multi-parameter optimization is underway