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FOCAL SPOT ADJUSTMENT SYSTEM FOR AN IMAGING TUBE

IP.com Disclosure Number: IPCOM000126276D
Publication Date: 2005-Jul-12
Document File: 7 page(s) / 38K

Publishing Venue

The IP.com Prior Art Database

Abstract

In some embodiment, this invention provides to implement a method that provides essentially the same cathode functionality with only 4 contacts that was achievable with 6 feedthroughs before. As indicated before a large array of existing X-ray tubes can be leveraged to implement electrostatic focal spot size and position control. Two contacts are used to connect two bias voltages to the two width-electrodes. Two additional contacts are for the filament supply current. A voltage divider connects left and right width-electrodes.

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FOCAL SPOT ADJUSTMENT SYSTEM FOR AN IMAGING TUBE

FIELD OF THE INVENTION

[0001]               This invention relates generally, to an imaging tube, and more particularly to a focal spot adjustment system for an imaging tube.

BACKGROUND OF THE INVENTION

[0002]               Electrostatic control of focal spot size and position has been described and implemented in the past.  One problem when implementing this technology in existing tubes is the need for electrical feedthroughs to provide the bias voltages needed at the cathode.  Typically a redesign of the cathode high voltage insulator is required.  Such a redesign is costly and time consuming.

[0003]               The present invention describes a solution to the problem that enables electrostatic control of focal spot size and position with only 4 feedthroughs.  High voltage insulators with 4 feedthroughs are commonly available in X-ray tubes that provide 2 focal spots with a large and a small filament.  Using the invention described below such high voltage insulators could be used without change when adding the additional functionality of electrostatic focal size and position control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004]                 FIG. 1 shows an example of a cathode structure.  Focal spot size and location is electrostatically controlled with 5 electrodes connected to 5 bias voltage supplies. Two additional contacts are required to energize the filament.

[0005]               FIG. 2 shows an example of a cathode arrangement for full focal spot size control (width and length) and x-deflection, having two bias voltages connect to the cathode structure.

DETAILED DESCRIPTION OF THE INVENTION

[0006]    Various embodiments of this invention provide a focal spot adjustment system for an imaging tube.  However, the embodiments are not limited and may be implemented in connection with systems such as, for example, medical and industrial X-ray imaging tubes.

[0007]   Generally, to achieve the most general focal spot size and position control five separate contacts for bias voltages are required.  Two additional feedthroughs need to be provided to energize the filament. The general concept is illustrated in FIG. 1.  We will refer to focal spot deflection as x-deflection if the focal spot is deflected normal to the length direction of the filament, and to z-deflection, when the deflection is parallel to the length direction of the filament.  The electrode pair that is symmetrical to the z-axis (x-axis) are called width-electrodes (length-electrodes).  If z-deflection is not needed but only focal spot size control in z, only one contact is then needed for both length electrodes, which reduces the total number of feedthroughs required to six.

[0008]    The purpose of the current invention is to implement a method that provides essentially the same cathode functionality with only 4 contacts that was achievable with 6 feedthroughs before. As indicated before a large array of existing X-ray tubes can be leveraged to implement electrostatic focal spot size a...