The future demands of computed tomography imaging regarding the x-ray source can be summarized with higher scan power, shorter rotation times, shorter cool down times and smaller focal spots. We report on a new tube technology satisfying all these demands by making use of a novel cooling principle on one hand and of a novel beam control system on the other hand. Nowadays tubes use a rotating anode disk mainly cooled via radiation. The Straton x-ray tube is the first tube available for clinical routine utilizing convective cooling exclusively. It is demonstrated that this cooling principle makes large heat storage capacities of the anode disk obsolete. The unprecedented cooling rate of 4.8 MHU/min eliminates the need for waiting times due to anode cooling in clinical workflow. Moreover, an electronic beam deflection system for focal spot position and size control opens the door to advanced applications. The physical backgrounds are discussed and the technical realization is presented. From this discussion the superior suitability of this tube to withstand g-forces well above 20 g created by fast rotating gantries will become evident. Experience from a large clinical trial is reported and possible ways for future developments are discussed.
The Vienna rectifier (VR) is used in applications that require unidirectional, non-isolated, three-phase AC to DC conversion with constant output voltage and sinusoidal input currents. However, because of the unidirectional topology, the input currents become discontinuous at small output power values. As a consequence, the relationship between rectifier input voltage and duty cycle changes compared to continuous conduction mode. Therefore, if no additional measures are taken, the rectifier input currents will be distorted. This work describes a new control scheme that allows operation of the VR with sinusoidal input currents in discontinuous conduction mode (DCM). The limits of operation are described, concerning maximum mains voltage, maximum midpoint current and minimum resistance to the mains in DCM. Further, the noise emission in DCM is compared to continuous conduction mode (CCM) operation. Finally, the proposed scheme is experimentally verified on a hardware prototype.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.