X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-04-20
2001-01-16
Bruce, David V. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S155000
Reexamination Certificate
active
06175609
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention was made with Government support under Government Contract No. 70NANB5H1148 awarded by NIST. The Government has certain rights in this invention.
This invention relates generally to computed tomography (CT) imaging and, more particularly, to scanning an object of interest with a CT scanner.
In at least one CT system configuration, and during a scanning process, an x-ray source projects an x-ray beam towards a detector and the x-ray beam passes through the object being imaged. In known industrial CT systems, for example, the object being imaged is positioned on a manipulator which rotates the object during the scanning process. The beam, after being attenuated by the object, impinges upon the detector. The detector includes an array of generally rectangular detector cells, and the intensity of the attenuated beam radiation received at each detector cell is dependent upon the attenuation of the x-ray beam by the object. Each detector cell, or element, of the array produces a separate electrical signal that is a measurement of the beam intensity at the detector cell location. The attenuation measurements from all the detector cells are acquired separately to produce a transmission profile.
The x-ray beam received at the detector array typically includes two components, namely, a primary signal and a scatter signal. The scatter signal typically reduces resolution and contrast in reconstructed images, which is undesirable. To reduce the impact of scatter signals, a collimator can be placed over the detector. The collimator is configured to substantially prevent scatter beams from impinging upon the detector cells.
While stationary collimators generally are satisfactory for reducing the affects of scatter signals in one-dimensional, or linear, detector arrays, such collimators may not provide optimum results when used in connection with multi-dimensional, or area, detector arrays. Particularly, the pitch of the detector elements in area arrays may be orders of magnitude less than the pitch of the detector elements in linear arrays, and stationary collimators may not be as effective when used in connection with such small pitch detector elements.
To reduce the contribution of the scatter signal received at area detector arrays, a CT system can be configured to directly measure either the scatter signal or the primary signal. The component of the measured signal due to scatter can be determined and then subtracted from the total signal to generate substantially uncorrupted projection data. Directly measuring either the scatter signal or the primary signal, however, is complex and time consuming.
It would be desirable to reduce the contribution of scatter to an image reconstructed from data collected by an area detector in a CT system. It also would be desirable to reduce the contribution of scatter without directly measuring the primary or scatter signal.
SUMMARY OF THE INVENTION
A computed tomography system, in one embodiment, includes a movable collimator and the system is adapted to implement a scatter correction algorithm to estimate a primary signal and a scatter signal without requiring direct measurement of such signals. During a scan, the collimator is moved from a first position to a second position. When the collimator is in the first or second position, the collimator is not located over the detector and does not collimate the beam impinging upon the detector. As the collimator moves between the first and second positions, however, the collimator at least partially collimates the x-ray beam impinging upon the detector array. A first signal intensity at the detector array is obtained when the collimator is in the first or second position, and a second signal intensity at the detector array is obtained after the collimator is moved between the first and second positions. These signal intensities are then utilized to estimate the scatter signal. The estimated scatter signal is then used to generate substantially uncorrupted projection data.
REFERENCES:
patent: 4101768 (1978-07-01), Lill
patent: 4707608 (1987-11-01), DiBianca
patent: 5144141 (1992-09-01), Rougeot et al.
patent: 5231654 (1993-07-01), Kwasnick et al.
patent: 5231655 (1993-07-01), Wei et al.
patent: 5293417 (1994-03-01), Wei et al.
patent: 5303282 (1994-04-01), Kwasnick et al.
patent: 5430298 (1995-07-01), Possin et al.
Edic Peter Michael
Pfoh Armin Horst
Bruce David V.
General Electric Company
Ingraham Donald S.
Stoner Douglas E.
LandOfFree
Methods and apparatus for scanning an object in a computed... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods and apparatus for scanning an object in a computed..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods and apparatus for scanning an object in a computed... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2479080