Bilateral filtering based sliding motion compensated 4D-CBCT: a simulation study / 中国辐射卫生

Objective This study reconstructed 4D-CBCT for fully automatic compensated sliding motion by incorporating the bilateral filtering into the Deformable Vector Field (DVF). Methods First, a motion compensated simultaneous algebraic reconstruction technique (Modified Simultaneous Algebra Reconstruction Technique, mSART) was used to generate a high quality reference phase by using all phase projection stogether with the initial 4D-DVFs, which were generated via Demons registration between 0% phase and each other phaseimage. The 4D-DVF was optimized by matching the forward projection of the deformed 0% phase with the measured projection of the target phase. The loss function’s DVF smoothing constrain term contained bilateral filtering kernel that contained: 1) an spatial domain Guassian kernel; 2) animage intensity domain Guassian kernel; and 3) a DVF domain Guassian kernel. By choosing suitable kernel variances, the sliding motion can be extracted. A non-linear conjugate gradient optimizer wasused. We validated the algorithm on a Non-Uniform Rotational B- spline based Cardiac-Torso (NCAT) phantom. Quantification was evaluated by: 1) the Root-Mean-Square-Error (RMSE) together with the Maximum-Error (MaxE); 2) the Dice coefficient of the extracted lung contour from the final reconstructed images and 3) the relative reconstruction error (RE) to evaluate the algorithm's performance. Results The motion trajectory's RMSE/MaxEare 0.796/1.02 mm for bilateral filtering reconstruction; and 2.704/4.08 mm for original reconstruction. Image content such a stherib position, the hearted gedefinition, the fibrous structures all had been better corrected with bilateral filtering. Conclusion We developed a bilateral filtering based fully automatic sliding motion compensated 4D-CBCT scheme. Digital phantom study confirmed the improved motion estimation and image reconstruction ability. It can be used as a 4D-CBCT image guidance tool for lung SBRTtreatment.

Periodic complex map germs and foliations

Abstract In this paper we study topological and analytical conditions on the orbits of a germ of diffeomorphism in the complex plane in order to obtain periodicity. In particular, we give a simple proof of a finiteness criteria for groups of analytic diffeomorphisms, stated in Brochero Martínez 2003. As an application, we derive some consequences about the integrability of complex vector fields in dimension three in a neighborhood of a singular point.

De Sitter symmetries and inflationary scalar-vector models / Simetrías en el espacio de De Sitter y modelos inflacionarios escalar-vector / Simetrias de De Sitter e modelos inflacionarios escalar-vetors

Abstract In this paper, we study the correspondence between a field theory in de Sitter space in D-dimensions and a dual conformal field theory in a euclidean space in (D-1)-dimensions. In particular, we investigate the form in which this correspondence is established for a system of interacting scalar and a vector fields propagating in de Sitter space. We analyze some necessary (but not sufficient) conditions for which conformal symmetry is preserved in the dual theory in (D - 1)-dimensions, making possible the establishment of the correspondence. The discussion that we address in this paper is framed on the context of inflationary cosmology. Thusly, the results obtained here pose some relevant possibilities of application to the calculation of the fields's correlation functions and of the primordial curvature perturbation Z, in inflationary models including coupled scalar and vector fields.

Resumen En este artículo se estudia la correspondencia entre una teoría de campos en el espacio de De Sitter en D-dimensiones y una teoría dual conforme en un espacio euclidiano en (D - 1)-dimensiones. En particular, se investiga la forma en la que se establece esta correspondencia para un sistema compuesto por un campo escalar y un campo vectorial acoplados propagándose en el espacio de De Sitter. Se analizan algunas condiciones necesarias (pero no suficientes) en las cuales la simetría conforme se preserva en la teoría dual en (D - 1)-dimensiones y hace posible el establecimiento de la correspondencia. La discusión presentada aquí se enmarca en el contexto de la cosmología inflacionaria, así que los resultados obtenidos plantean algunas posibilidades relevantes de aplicación en el cálculo de funciones de correlación de los campos y de la perturbación de ¡a curvatura primordial Z en modelos inflacionarios que incluyen campos escalares y vectoriales acoplados.

Resumen Neste artigo, é estudada a correspondencia entre uma teoria de campos no espaço de De Sitter em D-dimensões e uma teoria dual conforme num espaço euclidiano em (D - 1)-dimensões. Em particular, é pesquisado o caminho no qual se estabelece esta correspondência para um sistema de interação composto dum campo escalar e um vetorial, propagando-se no espaço de De Sitter. São analisadas algumas condições necessárias (mas não suficientes) para as quais a simetria conforme é preservada na teoria dual em (D-l)-dimensões, fazendo viável o estabelecimento da correspondência. A discussão apresentada aqui, está situada no contexto da cosmologia inflacionária. Portanto, os resultados obtidos representam algumas possibilidades relevantes para sua aplicacão no cálculo de funções de correlação dos campos e da perturbação da curvatura primordial Ç em modelos inflacionários incluindo campos acoplados escalares e vetoriais.