Computed tomography with increased field of view

Abstract

A volumetric computed tomography system with a large field of view has, in a forward geometry implementation, multiple x-ray point sources emitting corresponding fan beams at a single detector array. The central ray of at least one of the fan beams is radially offset from the axis of rotation of the system by an offset distance D. Consequently, the diameter of the in-plane field of view provided by the fan beams may be larger than in a conventional CT scanner. Any number of point sources may be used. Analogous systems may be implemented with an inverse geometry so that a single source array emits multiple fan beams that converge upon corresponding detectors.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of copending U.S. patent application No. Ser. 11 / 039716 filed Jan. 19, 2005, which is incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention relates generally to systems and methods for computed tomography. More specifically, it relates to improved techniques for increasing the field of view in computed tomography. BACKGROUND OF THE INVENTION [0003] In a conventional third-generation computed tomography (CT) system a single x-ray source 100 generates a fan beam 102 directed at an extended detector array 104, as shown in the cross-sectional view of FIG. 1. Fan beam 102 has a collection of rays diverging from source 100 at a divergence angle α, as shown. A system of this type, where the fan beam diverges from a single point source to a large array of detectors, is said to have a forward geometry. In an inverse geometry system, the, point source is exchanged for a small array...

AI Technical Summary

Benefits of technology

[0008] The present invention provides improved CT systems and methods that enjoy substantially increased FOV. The diameter of the in-plane FOV of CT systems according to the present invention can be larger than the in-plane extent of the detector (or source) array. Thus, the invention provides CT systems with increased FOV without the expense and complication of larger detector (or source) array sizes required in the past.

Problems solved by technology

Although the FOV of a CT system can be increased using a larger detector array, increasing the size of the array often introduces significant technical difficulty and expense.

Another drawback of this CT system design is that the source and detector must rotate through a large angle to acquire images from a sufficiently large range of angles.

If a patient moves during the rotation, the image data from different angles will not be consistent, resulting in artifacts and errors in the reconstructed three-dimensional representation.

However, the field of view 326 of this system suffers from the same problem as the conventional single source-detector system of FIG. 1.

(The same disadvantages apply to the analogous inverse geometry system.)

The FOV 414, however, while larger than FOV 416, is still substantially limited unless the detector array is quite large.

Moreover, the asymmetry of the system geometry requires a rotation of at least 360 degrees, introduces complexities to the data processing required to reconstruct a representation of the object from the data collected at various angles, and in general has non-uniform noise behavior.

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