X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-09-30
2001-09-18
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S015000, C378S901000
Reexamination Certificate
active
06292525
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a cone beam computed tomography (CT) imaging system, and more specifically to a simplified method and apparatus for image reconstruction in such a system.
2. Description of the Prior Art
Recently a system employing cone beam geometry has been developed for three-dimensional (3D) computed tomography (CT) imaging that includes a cone beam x-ray source and a 2D area detector. An object to be imaged is scanned, preferably over a 360° angular range and along its entire length, by any one of various methods wherein the position of the area detector is fixed relative to the source, and relative rotational and translational movement between the source and object provides the scanning (irradiation of the object by radiation energy). The cone beam approach for 3D CT has the potential to achieve 3D imaging in both medical and industrial applications with improved speed, as well as improved dose utilization when compared with conventional 3D CT apparatus (i.e., a stack of slices approach obtained using parallel or fan beam x-rays).
As a result of the relative movement of the cone beam source to a plurality of source positions (i.e., “views”) along the scan path, the detector acquires a corresponding plurality of sequential sets of cone beam projection data (also referred to herein as cone beam data or projection data), each set of cone beam data being representative of x-ray attenuation caused by the object at a respective one of the source positions.
As well known, and fully described for example in the present inventor's U.S. Pat. No. 5,257,183 entitled METHOD AND APPARATUS FOR CONVERTING CONE BEAM X-RAY PROJECTION DATA TO PLANAR INTEGRAL AND RECONSTRUCTING A THREE-DIMENSIONAL COMPUTERIZED TOMOGRAPHY (CT) IMAGE OF AN OBJECT issued Oct. 26, 1993, incorporated herein by reference, image reconstruction processing generally begins by calculating Radon derivative data from the acquired cone beam data. The Radon derivative data is typically determined by calculating line integrals for a plurality of line segments L drawn in the acquired cone beam data. In the embodiment described in detail in the 5,257,183 patent, Radon space driven conversion of the derivative data is used to develop an exact image reconstruction of a region-of-interest (ROI) in the object.
A cone beam data masking technique which improves the efficiency of the calculation of the Radon derivative data in such a Radon space driven technique is described in the present inventor's U.S. Pat. No. 5,504,792 entitled METHOD AND SYSTEM FOR MASKING CONE BEAM PROJECTION DATA GENERATED FROM EITHER A REGION OF INTEREST HELICAL SCAN OR A HELICAL SCAN, issued Apr. 2, 1996, also incorporated herein by reference. The masking technique facilitates efficient 3D CT imaging when only the ROI in the object is to be imaged, as is normally the case. In the preferred embodiment described therein, a scanning trajectory is provided about the object, the trajectory including first and second scanning circles positioned proximate the top and bottom edges, respectively, of the ROI, and a spiral scanning path is connected therebetween. The scanning trajectory is then sampled at a plurality of source positions where cone beam energy is emitted toward the ROI. After passing through the ROI the residual energy at each of the source positions is acquired on an area detector as a given one of a plurality of sets of cone beam data. Each set of the cone beam data is then masked so as to remove a portion of the cone beam data that is outside a given sub-section of a projection of the ROI in the object and to retain cone beam projection data that is within the given sub-section. The shape of each mask for a given set of cone beam data is determined by a projection onto the detector of the scan path which is above and below the source position which acquired the given set of cone beam data. The masked (i.e., retained) cone beam data is then processed so as to develop reconstruction data An exact image of the ROI is developed by combining the reconstruction data from the various source positions which intersect a common integration plane. Hence, the masks are commonly referred to as “data-combination” masks.
Data-combination masks can also be used to improve the efficiency of the calculation of the derivative data in a detector data driven technique, such as the simplified ramp filter technique described in the present inventor's U.S. Pat. No. 5,881,123 entitled SIMPLIFIED CONE BEAM IMAGE RECONSTRUCTION USING 3D BACKPROJECTION, issued Mar. 9, 1999, also incorporated herein by reference. This simplified technique reconstructs the image using 2D approximation data sets formed by ramp filtering the masked cone beam data in the direction of the projection of a line drawn tangent to the scan path at the source position that acquired that set of cone beam data. Although this technique is less complex than the prior techniques, the reconstructed image is not exact.
Accordingly, U.S. patent application Ser. No. 09/162,303 entitled ADAPTIVE MASK BOUNDARY CORRECTION IN A CONE BEAM
IMAGING SYSTEM, filed Sep. 28, 1998, now U.S. Pat. No. 6,084,937 issued Jul. 4, 2000, and also incorporated herein by reference, describes a technique for computing 2D correction data which, when combined with the ramp filtered 2D approximation data sets, yields an exact image reconstruction. The 2D correction data basically comprises a point spread function representative of image reconstruction processing for each point on the detector which interesects the boundary of the data-combination mask. However, the techniques disclosed therein require circle scan paths near the top and bottom edges of the ROI when only an ROI is to be imaged. It would be desirable to provide such a simplified image reconstruction processing without the requirement of circle scan paths near the top and bottom edges of the ROI.
The present inventor's allowed U.S. patent application Ser. No. 09/343,770 entitled EXACT REGION OF INTEREST CONE BEAM IMAGING WITHOUT CIRCLE SCANS, filed Jun. 30, 1999, incorporated by reference herein, improved upon the invention described in the forenoted U.S. Pat. No. 5,504,792, by providing an exact image reconstruction of an ROI in an object without the requirement that the source scan path have top and bottom circle scan paths near the top and bottom edges of the ROI. Furthermore, the improvement is applicable to both of the Radon space and detector driven types of image reconstruction processing. As described in this U.S. patent application Ser. No. 09/343,770, and consistent with the techniques described in the above noted U.S. Pat. Nos. 5,881,123 and 5,504,792, when calculating the derivative data, the length of the line segments L formed in the acquired cone beam data (along which integral data is to be developed) are determined by the boundaries of the data-combination mask. Exact image reconstruction processing for source positions which are “internal” to the top and bottom edges of the ROI can use the simplified ramp filtering with 2D correction data technique of the forenoted U.S. patent application Ser. No. 09/162,303. However, when processing cone beam data acquired at source positions near the top or bottom edges of the ROI, the line segments L are divided into two groups, where in one of the groups the line segments L have one of their end points determined by a horizontal line of the mask (in a preferred embodiment this horizontal line is the x-axis of the mask), instead of having both of the endpoints determined by the outer boundaries of the mask. When processing along the line segments L in this one group, acquired cone beam data which resides along lines L on the other side of the horizontal axis of the mask are not used. Thereafter, integral data is calculated for the line segments L having their endpoints limited by the horizontal axis in the mask, and the data is further processed so as to develop contributions to a 3D image reconstruction of the ROI in the object
Ahmed Adel A.
Bruce David V.
Siemens Corporate Research Inc.
LandOfFree
Use of Hilbert transforms to simplify image reconstruction... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Use of Hilbert transforms to simplify image reconstruction..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Use of Hilbert transforms to simplify image reconstruction... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2549360