Focal Spot Coincidence Improvement in X-ray Tubes
Publication Date: 2003-Apr-15
The IP.com Prior Art Database
Third Generation CT Scanners routinely use the quarter ray offset in order to improve resolution. In this method, the x-ray tube focal spot is placed ¼ of the detector spacing away from the central ray. One of the important paramters in this method is the spacing between the two focal spots. This is maintained by developing fixtures that control the spacing between the anode and the cathode during construction of the insert. The position of the cathode along the anode cathode axis can be controlled during operation of the system by servos that control the pressure on that portion of the tube acting as a spring. The desired position of the cathode can be established by using the z-position detectors on the CT systems. Another possibility of controlling coincidence during manufacture is to replace the springy section of the insert with one that can yield and maintain its spacing.
FIELD OF TECHNOLOGY:
Curved Surface Field Emission Arrays for Electron GunFocal Spot Coincidence Improvement in X-ray Tubes
Third Generation Computed Tomography (CT) Scanners routinely use the quarter ray offset in order to improve resolution.� In this method, the x-ray tube focal spot is not placed on the central ray.� Instead, it is placed ¼ of the detector spacing away from the central ray.� Since most systems now have two focal spots, one of the important paramters is the spacing between the two focal spots.� This is now kept under control in production by developing fixtures that control the spacing between the anode and the cathode during construction of the insert.
The spacing control is not always perfect.� As the tube heats and cools, the position of each of the two focal spots moves.� It is possible to design a tube where the position does not move with heating and cooling for one filament.� However, tubes with more than one filament are now the common practice in CT systems, and such a design would amplify the motion of spot(s) produced by the second filament.
The invention works by using pressure (or tension) on the exterior of the insert.� If a metal center section x-ray tube is designed properly, a compliant joint will act as a spring under the pressure, and the position of the cathode can change as desired.� Alternatively, one can design the spring to work on the anode end.� This alternate approach is less natural in a tube that is anode grounded and uses a pancake connector on the cathode, but it has the advantage of also allowing for compensation of motion of the focal spot along the anode cathode axis during heating and cooling of the x-ray tube since the major compon...