X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-12-30
2001-11-13
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S901000
Reexamination Certificate
active
06317478
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to computed tomography (CT) imaging techniques; and more particularly, to the backprojection of the attenuation data acquired during a scan to form an image.
In a computed tomography system, an x-ray source projects a cone beam that passes through an object being imaged, such as a medical patient, and impinges upon a two dimensional (2D) array of radiation detectors. The intensity of the transmitted radiation is dependent upon the attenuation of the x-ray beam by the object and each detector produces a separate electrical signal that is a measurement of the beam attenuation. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
U.S. Pat. No. 5,446,776 describes a technique employing a conventional CT system employing cone beam geometry for 3D imaging using a cone beam x-ray source and a 2D area detector. The source and detector array in the system are rotated on a gantry preferably over a 360° angular range, either by moving the cone beam x-ray source in a scanning circle about the object while keeping the 2D array detector fixed with reference to the cone beam x-ray source, or by rotating the object while the x-ray source and detector remain stationary. A group of x-ray attenuation measurements obtained from the detector array at a given angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different angular orientations during one revolution of the x-ray source and detector.
Different data processing techniques have been employed to present imaging data in manners that are helpful to the user e.g., providing tomographic information and the lie. Typically such processing, particularly for generation of 3 dimensional (3D) images, is computationally intensive, resulting in slow response due to lengthy processing time or requiring significant computational resources, with attendant cost, or both.
SUMMARY OF THE INVENTION
In an exemplary embodiment of the method of the invention, an object is imaged by applying imaging energy from a source to the object. Imaging energy that has passed through the object is detected by a detector. The object is scanned with the imaging energy such that the detector collects cone beam measurements. Direct x-ray inversion of the cone beam measurements is made, followed by backprojection and filtering. In contrast to known methods in which the filtering step precedes the backprojection step, in the present invention, the backprojection step advantageously precedes the filtering step. The inverted cone beam measurements are backprojected on the fly, thereby reducing the lag time between the end of data collection and image generation to the time required to perform a fast Fourier-based filter of the backprojected data.
An exemplary embodiment of the system of the invention includes a source for applying imaging energy to the object. A detector detects imaging energy that has passed through the object. A positioner scans the object with the imaging energy such that the detector collects cone beam measurements. An inversion calculator performs direct x-ray inversion of the cone beam measurements. A backprojection and filtering calculator calculates the backprojection and filtering of the inverted cone beam measurements. An image supplier supplies an image of the object based on the measured image data and the backprojected, filtered inverted cone beam measurements.
REFERENCES:
patent: 5446776 (1995-08-01), Tam
patent: 5465283 (1995-11-01), Tam
patent: 5901196 (1999-05-01), Sauer et al.
patent: 6233303 (2001-05-01), Tam
Bruce David V.
Cabou Christian G.
General Electric Company
Ingraham Donald S.
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