Tomographic image quality of rotating slat versus parallel hole-collimated SPECT

Parallel and converging hole collimators are most frequently used in nuclear medicine. Less common is the use of rotating slat collimators for single photon emission computed tomography (SPECT). The higher photon collection efficiency, inherent to the geometry of rotating slat collimators, results in much lower noise in the data. However, plane integrals contain spatial information in only one direction, whereas line integrals provide two-dimensional information. It is not a trivial question whether the initial gain in efficiency will compensate for the lower information content in the plane integrals. Therefore, a comparison of the performance of parallel hole and rotating slat collimation is needed. This study compares SPECT with rotating slat and parallel hole collimation in combination with MLEM reconstruction with accurate system modeling and correction for scatter and attenuation. A contrast-to-noise study revealed an improvement of a factor 2-3 for hot lesions and more than a factor of 4 for cold lesion. Furthermore, a clinically relevant case of heart lesion detection is simulated for rotating slat and parallel hole collimators. In this case, rotating slat collimators outperform the traditional parallel hole collimators. We conclude that rotating slat collimators are a valuable alternative for parallel hole collimators

Identifying A Statistical Model For North Dakota K-12 Public School Transportation Funding By Comparing Fifteen State Transportation Funding Formulas

The purpose of this study was to review the history of North Dakota K-12 transportation funding system, identify how school districts are reimbursed for transportation expenses, and compare this information with fourteen other state transportation funding systems. North Dakota utilizes a block grant structure that has been in place since 1972 and has remained unchanged except for reimbursement factors used in the mileage and rider statistics collected at the state level. Despite the need for alternative structures that promote efficiency and actual costs, the system remains in its current block grant format. Each of the 50 states in the United States possess a K-12 transportation structure that coexists with the general state funding formula or is part of the general state budget formula. The funding formulas fall into four basic types of transportation funding. Each structure is reviewed and compared based on the strengths and weaknesses of each method. The choice of structure utilized by each state depends on initiatives regarding transportation funding created by individual state legislatures. As a result, states rely on legislative interpretation and action in designing and revising transportation funding methods. The study utilizes a multiple regression statistical analysis to generate expected costs for district transportation services provided by North Dakota school districts. The analysis displays the cost/reimbursement ratios present with the current funding system compared with the ratios found with the Expected Cost statistical model. The statistical model promotes the concept of transportation efficiency and better reflecting the actual costs consumed by the school district

New Radiocarbon Ages on Percussion-Fractured and Flaked Proboscidean Limb Bones from Yukon, Canada

Proboscidean limb bones discovered in Yukon during the 1960s and 1970s exhibit fracture patterns, notches, and bone flakes that are characteristic of percussion. Because of the unique properties of thick cortical proboscidean bone (probably woolly mammoth Mammuthus primigenius or less likely American mastodon Mammut americanum), some researchers hypothesized that these fracture patterns represent intentional hammerstone modification by humans for marrow extraction and bone tool production. As such, these fracture patterns represent evidence of early human dispersal into Eastern Beringia. Radiocarbon dating in the late 1980s indicated that the bone breakage occurred between about 25 000 and 40 000 radiocarbon years before present (14C yr BP). We report 11 new radiocarbon ages using ultra-filtration methods on a different sample of similarly fractured and flaked bones from Yukon. Only two of the radiocarbon ages fall within the expected range of 25 000 to 40 000 14C yr BP. Six other ages are non-finite, with five being more than 49 100 14C yr BP. Three finite ages range between 46 500 and 50 500 14C yr BP with large standard deviations, and these ages may also be non-finite. Two testable hypotheses to explain the observed breakage patterns were developed, the first being that humans broke the bones and the second that some presently unknown geological process broke the bones. Further research is needed to test these two hypotheses.Des ossements de membres de proboscidiens découverts au Yukon dans les années 1960 et 1970 présentent des structures de fractures, des encoches et des traces d’enlèvements d’éclats caractéristiques de la percussion. En raison des propriétés uniques de l’os cortical proboscidien (provenant probablement d’un mammouth laineux Mammuthus primigenius ou, ce qui est moins probable, d’un mastodonte américain Mammut americanum), certains chercheurs ont avancé une hypothèse selon laquelle ces structures représentent des modifications intentionnelles faites au marteau en pierre par des humains, à des fins d’extraction de la moelle et de production d’outils en os. En tant que telles, ces structures de fractures témoignent de la présence ancienne d’humains dans l’est de la Béringie. Vers la fin des années 1980, la datation au radiocarbone a permis de déterminer que les fractures auraient été faites il y a environ 25 000 à 40 000 années radiocarbones avant le présent (14C ans BP). Nous faisons état de 11 nouveaux âges au radiocarbone établis au moyen de méthodes d’ultrafiltration sur un échantillon différent d’os provenant également du Yukon et présentant de semblables fractures et traces d’enlèvements d’éclats. Seulement deux des âges au radiocarbone font partie de la gamme attendue variant entre 25 000 et 40 000 14C ans BP. Six autres âges sont non finis, dont cinq ayant plus de 49 100 14C ans BP. Trois âges finis varient entre 46 500 et 50 500 14C ans BP et ont d’importants écarts-types, et ces âges pourraient également être non finis. Deux hypothèses testables ont été émises afin d’expliquer les structures de fractures observées, la première étant que les fractures ont été causées par des humains et la seconde étant que les fractures sont le résultat d’un processus géologique inconnu à ce jour. Des recherches plus approfondies s’imposent afin de mettre ces deux hypothèses à l’épreuve

Characterizing the parallax error in multi-pinhole micro-SPECT reconstruction

The usage of pinholes is very important in preclinical micro-SPECT. Pinholes can magnify the object onto the detector, resulting in better system resolutions than the detector resolution. The loss in sensitivity is usually countered by adding more pinholes, each projecting onto a specific part of the detector. As a result, gamma rays have an oblique incidence to the detector. This causes displacement and increased uncertainty in the position of the interaction of the gamma ray in the detector, also known as parallax errors or depth-of-interaction (DOI) errors. This in turn has a large influence on image reconstruction algorithms using ray tracers as a forward projector model, as the end-point of each ray on the detector has to be accurately known. In this work, we used GATE to simulate the FLEX Triumph-I system (Gamma Medica-Ideas, Northridge, CA), a CZT-based multi-pinhole micro-SPECT system. This system uses 5 mm thick CZT pixels, with 1.5 mm pixel pitch. The simulated information was then used to enhance the image resolution by accurately modeling the DOI. Two hundred point sources were simulated and rebinned to use the DOI information. This data was then used in a GPU-based iterative reconstruction algorithm taking the simulated DOI into account. The average displacement was then determined for all point sources, and the FWHM was calculated in three dimensions, by fitting the point sources with 3D Gaussians. We show that the displacement is reduced by 83% on average. We also show a 15% resolution gain when only 5 DOI levels are used

Iterative CT reconstruction using shearlet-based regularization

In computerized tomography, it is important to reduce the image noise without increasing the acquisition dose. Extensive research has been done into total variation minimization for image denoising and sparse-view reconstruction. However, TV minimization methods show superior denoising performance for simple images (with little texture), but result in texture information loss when applied to more complex images. Since in medical imaging, we are often confronted with textured images, it might not be beneficial to use TV. Our objective is to find a regularization term outperforming TV for sparse-view reconstruction and image denoising in general. A recent efficient solver was developed for convex problems, based on a split-Bregman approach, able to incorporate regularization terms different from TV. In this work, a proof-of-concept study demonstrates the usage of the discrete shearlet transform as a sparsifying transform within this solver for CT reconstructions. In particular, the regularization term is the 1-norm of the shearlet coefficients. We compared our newly developed shearlet approach to traditional TV on both sparse-view and on low-count simulated and measured preclinical data. Shearlet-based regularization does not outperform TV-based regularization for all datasets. Reconstructed images exhibit small aliasing artifacts in sparse-view reconstruction problems, but show no staircasing effect. This results in a slightly higher resolution than with TV-based regularization

Absolute quantification in multi-pinhole micro-SPECT for different isotopes

In preclinical Single Photon Emission Tomography (SPECT), absolute quantification is interesting, expressed in percentage of injected radioactive dose per gram of tissue. This allows for accurate evaluation of disease progression and precise follow-up studies without the need for sacrificing animals. Accurate modeling of image degrading effects is currently under development for isotopes different from 99mTc. The aim of this work is to develop absolute micro-SPECT quantification for three different isotopes: 99mTc, 111In and 125I. This selection of isotopes covers a wide range of energies, is pre-clinically relevant and allows us to optimally validate the algorithms used for image reconstruction. Furthermore, we will mix these isotopes with additional iodine-based CT contrast agent, to mimic contrast-enhanced SPECT/CT protocols. For each isotope, both a calibration phantom and three 1-ml vials were scanned on the CZT-based FLEX Triumph-I scanner (GM-I). The calibration phantom allows the conversion of reconstructed voxel counts to MBq/ml. The 3-vial phantom consists of 3 different concentrations of radioactivity. Two vials contain iodine-based CT contrast agent to significantly increase the attenuation. All datasets were reconstructed using a GPU-based reconstruction algorithm, which includes resolution recovery, pinhole penetration, geometrical sensitivity correction, scatter correction and attenuation correction. We show good quantification for 99mTc and 111In. The absolute quantification of I is suboptimal, due to insufficient scatter correction. No influence can be seen when iodine-based CT contrast agent is used together with 125I