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X-RAY BEAM ALIGNMENT

IP.com Disclosure Number: IPCOM000199661D
Publication Date: 2010-Sep-14
Document File: 7 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database

Abstract

A technique for deflecting an X-ray focal spot utilizing cathode control is disclosed. The technique described herein provides a means to correct misalignment of the X-ray tube of a CT system. An offset voltage or current is introduced in the electron beam depending on the cathode technology that is utilized. The offset voltage or current results in the electron beam being deflected to a non-centered position within the X-ray tube. As a result, the X-ray beam also departs from the X-ray tube in a non-centered fashion. Further, the off centered x-ray beam is adjusted in order to align precisely to a CT detector without mechanical adjustments by a field service engineer. Such a method of correcting misalignment in the electron beam saves time required for mechanical realignment of X-ray tubes of a CT system, increases resolution and reduces image artifacts.

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X-RAY BEAM ALIGNMENT

FIELD OF INVENTION

The invention generally relates to medical imaging systems and more particularly to a technique for alignment of an X-ray beam to a detector in a Computed Tomography (CT) system.

BACKGROUND OF THE INVENTION

Computed tomography (CT) is a medical imaging method employing tomography created by computer processing. Digital geometry processing is utilized to generate a three dimensional image of the inside of an object or patient from a large series of two dimensional X-ray images taken around a single axis of rotation. Generally a CT system comprises an X-ray tube, which is a vacuum tube that produces X-rays. The X-ray tube comprises an electron emitting cathode and an electron collecting anode. Flow of an electron beam is established through the X-ray tube.

Usually metal frame X-ray tubes are welded assemblies of several components. Typically, centering operations prior to weld are not perfect and the eventual X-ray tube assembly contains a large stack-up error. For example, the cathode may be misaligned to the target by as much as -1.5mm. Further, the X-ray tube must be aligned to a pre-patient collimator.

Conventionally X-ray tubes are aligned mechanically. The X-ray tube is mechanically aligned by a field engineer who uses dial indicators and very fine wrench adjustments. CT systems typically utilize mechanical alignment means such as fine thread screws. However such mechanical alignment is time consuming and typically takes many hours in the field. A typical CT system has a 107 kg X-ray tube which is aligned mechanically by a field engineer to within 27 microns in one direction and 100 microns in the other

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direction. Misalignment of the X-ray tube by any amount results in degradation of system resolution and introduction of image artifacts.

Hence there exists a need for a technique of eliminating misalignment of an X-ray beam produced by an X-ray tube of a CT system.

BRIEF DESCRIPTION OF THE INVENTION

A technique of deflecting an X-ray beam focal spot utilizing cathode control in a CT system is disclosed. The deflection of the X-ray beam compensates for misalignment of an X-ray tube of the CT system. Depending on the cathode ray technology which is utilized in the CT system, an offset current or voltage is used to deflect the electron beam within the X-ray tube.
DETAILED DESCRIPTION OF THE INVENTION

A technique of deflecting an X-ray beam focal spot in a CT system is disclosed. The deflection of X-ray beam focal spot is used to correct misalignment of an X-ray tube of the CT system. An offset voltage or current is introduced in the electron beam depending on the cathode technology that is utilized. The offset voltage or current results in the electron beam being deflected to a non-centered position within the X-ray tube. As a result, the X-ray beam also departs from the X-ray tube in a non-centered fashion. Further, the off centered X-ray beam is adjusted in order to align preci...