Improvements In computed tomography perfusion output using complex singular value decomposition and the maximum slope algorithm

OBJECTIVE: Determine if complex singular value decomposition (cSVD) used as preprocessing in the maximum slope algorithm reduces image noise of resultant physiologic parametric images. Noise will be decreased in the parametric maps of cerebral blood flow (CBF), cerebral blood volume (CBV) as compared to the same algorithm and data set with no cSVD applied. MATERIALS AND METHODS: A set of 10 patients (n=15) underwent a total combined 15 CT perfusion studies upon presenting with stroke symptoms. It was determined these patients suffered from occlusions resulting in a prolonged arrival time of blood to the brain. DICOM data files of these patients scans were selected based on this increased arrival delay. We compared the output of estimation calculations for cerebral blood flow (CBF), and cerebral blood volume (CBV), using preprocessing cSVD against the same scan data with no preprocessing cSVD. Image noise was assessed through the calculation of the standard deviation within specific regions of interest copied to specific areas of grey and white matter as well as CSF space. A decrease in the standard deviation values will indicate improvement in the noise level of the resultant images.. Results for the mean value within the regions of interest are expected to be similar between the groups calculated using cSVD and those calculated under the standard method. This will indicate the presence of minimal bias. RESULTS: Between groups of the standard processing method and the cSVD method standard deviation (SD) reductions were seen in both CBF and CBV values across all three ROIs. In grey matter measures of CBV, SD was reduced an average of 0.0034 mL/100g while measures of CBF saw SD reduced by an average of 0.073 mL/100g/min. In samples of white matter, standard deviations of CBV values were reduced on average by 0.0041mL/100g while CBF SD's were reduced by 0.073 mL/100g/min. CSF ROIs in CBV calculations saw SD reductions averaging 0.0047 mL/100g and reductions of 0.074 mL/100g/min in measures of CBF. Bias within CBV calculations was at most minimal as determined by no significant changes in mean calculated values. Calculations of CBF saw large downward bias in the mean values. CONCLUSIONS: The application of the cSVD method to preprocessing of CT perfusion imaging studies produces an effective method of noise reduction. In calculations of CBV, cSVD noise reduction results in overall improvement. In calculations of CBF, cSVD, while effective in noise reduction, caused mean values to be statistically lower than the standard method. It should be noted that there is currently no evaluation of which values can be considered more accurate physiologically. Simulations of the effect of noise on CBF showed a positive correlation suggesting that the CBF algorithm itself is sensitive to the level of noise

Vol. 49 No. 2 - Whole No. 355

Mythprint is the monthly bulletin of the Mythopoeic Society, a nonprofit educational organization devoted to the study, discussion, and enjoyment of myth and fantasy literature, especially the works of J.R.R. Tolkien, C.S. Lewis, and Charles Williams. To promote these interests, the Society publishes three magazines, maintains a World Wide Web site, and sponsors the annual Mythopoeic Conference and awards for fiction and scholarship, as well as local and written discussion groups

Vol. 47 No. 7 - Whole No. 336

Mythprint is the monthly bulletin of the Mythopoeic Society, a nonprofit educational organization devoted to the study, discussion, and enjoyment of myth and fantasy literature, especially the works of J.R.R. Tolkien, C.S. Lewis, and Charles Williams. To promote these interests, the Society publishes three magazines, maintains a World Wide Web site, and sponsors the annual Mythopoeic Conference and awards for fiction and scholarship, as well as local and written discussion groups

Vol. 48 No. 4 - Whole No. 345

Mythprint is the monthly bulletin of the Mythopoeic Society, a nonprofit educational organization devoted to the study, discussion, and enjoyment of myth and fantasy literature, especially the works of J.R.R. Tolkien, C.S. Lewis, and Charles Williams. To promote these interests, the Society publishes three magazines, maintains a World Wide Web site, and sponsors the annual Mythopoeic Conference and awards for fiction and scholarship, as well as local and written discussion groups

Critical spin liquid at 1/3 magnetization in a spin-1/2 triangular antiferromagnet

Although magnetically ordered at low temperatures, the spin-1/2 triangular antiferromagnet Cs_2CuCl_4 exhibits remarkable spin dynamics that strongly suggest proximity to a spin liquid phase. Here we address the question of whether a proximate spin liquid may also occur in an applied magnetic field, leaving a similar imprint on the dynamical spin correlations of this material. Specifically, we explore a spatially anisotropic Heisenberg spin-1/2 triangular antiferromagnet at 1/3 magnetization from a dual vortex perspective, and indeed find a new ``critical'' spin liquid phase described by QED3 with an emergent SU(6) symmetry. A number of nontrivial predictions are given for the dynamical spin structure factor in this ``algebraic vortex liquid'' phase, which can be tested experimentally via inelastic neutron scattering. We also discuss how the well-studied ``up-up-down'' magnetization plateaus can be captured within our approach, and further predict the existence of a stable gapless solid phase in a weakly ordered up-up-down state. Finally, we predict several anomalous ``roton'' minima in the excitation spectrum in the regime of lattice anisotropy where the canted Neel state appears.Comment: 5 pages, 2 figures; expanded intro & discussion of theory; minor correction to structure facto

Vol. 48 No. 10 - Whole No. 351

Mythprint is the monthly bulletin of the Mythopoeic Society, a nonprofit educational organization devoted to the study, discussion, and enjoyment of myth and fantasy literature, especially the works of J.R.R. Tolkien, C.S. Lewis, and Charles Williams. To promote these interests, the Society publishes three magazines, maintains a World Wide Web site, and sponsors the annual Mythopoeic Conference and awards for fiction and scholarship, as well as local and written discussion groups

Vol. 49 No. 4/5 - Whole No. 357/358

Mythprint is the monthly bulletin of the Mythopoeic Society, a nonprofit educational organization devoted to the study, discussion, and enjoyment of myth and fantasy literature, especially the works of J.R.R. Tolkien, C.S. Lewis, and Charles Williams. To promote these interests, the Society publishes three magazines, maintains a World Wide Web site, and sponsors the annual Mythopoeic Conference and awards for fiction and scholarship, as well as local and written discussion groups

Vol. 49 No. 10 - Whole No. 363

Mythprint is the monthly bulletin of the Mythopoeic Society, a nonprofit educational organization devoted to the study, discussion, and enjoyment of myth and fantasy literature, especially the works of J.R.R. Tolkien, C.S. Lewis, and Charles Williams. To promote these interests, the Society publishes three magazines, maintains a World Wide Web site, and sponsors the annual Mythopoeic Conference and awards for fiction and scholarship, as well as local and written discussion groups